13
MUCH OF THIS CHAPTER is devoted to the defence of the ship, not only from the enemy but also from corrosion and marine life forms. The defence of a ship against enemy attack forms a multi-layered system. It begins with pre-emptive strikes against enemy bases, followed by destruction of launching vehicles (aircraft, submarines) before they can launch, and then either destruction of incoming weapons or decoying them away from the target. It is impossible to make a ship invisible to the wide range of sensors available but reducing signatures makes the enemy’s task more difficult and enhances the effectiveness of decoys. Some missiles will always get through, calling for passive defence measures. In the RN Survivability is divided into:
Susceptibility – The avoidance of weapons using stealth, decoys and hard kill.
Vulnerability – Resistance to damage and damage control.1
Stealth2
The introduction of the acoustic mine and, later, of the acoustic torpedo by the US in 1943, placed a new emphasis on making ships quieter, further emphasised as passive sonars were developed. The main noise sources are:
Machinery Noise
Machinery noise will usually occur at discrete frequencies, corresponding to rotational speed or reciprocating rate, and this makes it easy to identify ship types and classes. The first step is to balance rotating machines so that noise at the rate of shaft rotation is much reduced, and the machine is then clad with absorbent material or placed in an insulating box. The machine and its box are further supported on flexible mounts to isolate them from the hull and hence the sea. It may prove easier to mount several machines on a ‘raft’ which is then itself flexibly mounted. Great care is needed to ensure that there are no ‘shorts’ conducting sound direct to the sea, as for example through cooling water pipes (not forgetting the cooling water itself). Inspection forms a major element in the cost of noise reduction.
The machinery spaces can also be screened by a cloud of air bubbles emitted from ducts round the hull (‘Masker’). Successful trials of bubble screening were carried out in 1917, but were not followed up in the mistaken view that noise reduction was unnecessary in ships using active sonar (asdic).
Propeller Cavitation
The boiling point of water falls as pressure is reduced and at very low pressures water will boil at normal sea water temperatures. A propeller blade generates thrust from pressure on the face (rear side) and from suction on the back (forward side), and this suction can cause the water to boil or ‘cavitate’ – a word coined by Sir Charles Parsons when the phenomenon proved troublesome in Turbinia. In Second World War destroyers cavitation would lead to a loss of thrust and efficiency from the mid-20kts upward with a reduction in top speed of about 1kt. The bubbles of water vapour so formed would collapse with violence (up to 100 tons/in2) and dig deep pits in the hard bronze propeller – up to 0.5in deep in a few hours at full speed. It came as a surprise to find that cavitation led to noise at speeds as low as 8kts from a wartime propeller in good condition and lower still if damaged. However, around 1950 scientists at Portland put glass windows in the bottom of the frigate Helmsdale and there was cavitation clear to see. At the tip of the blade water will spill over from the pressure side to the suction side, causing a vortex that has very low pressure at the centre, also causing cavitation and hence noise.3
At first it was thought that reducing the rotational speed (rpm) and increasing the blade area would increase the speed at which cavitation started. Nine sets of model propellers for the Diamond were tested at AEW Haslar of which two were tried full scale on the ship, while seven models and six full scale tests were tried for Savage.4 No improvement was obtained.
The next step was to build on the theoretical work of Dr Lerbs at Haslar. The radial distribution of thrust over the propeller was reduced towards the tip to decrease the strength of the vortex. Each section was pitched to allow the water to flow onto the blade at very small angles of incidence and the thin blade sections were curved (cambered) to generate thrust. There were many problems, not the least of them being the 3 weeks of tiresome arithmetic to carry out the design (and 5 months for a skilled craftsman to make the model). The theory was incomplete and empirical corrections (‘fudge factors’) had to be devised. The strength of these complex, thin blades was uncertain until John Conolly devised a new approach, and proved it with full-scale strain measurements on a propeller working in the sea – very difficult with the equipment of the day.5
Eventually, a Lerbs propeller was made and tried (Set J). It was very promising with a 0.75kt improvement in quiet speed, but the thrust produced was not what was intended and it was about 5 per cent down in efficiency. It had a blade area 1.1 times the area of a circle of the same diameter, the blades overlapping considerably.6 Fourteen models were tested, making variations on pitch, camber and blade area, and five were tried full-size on Savage. By the time the author joined, the team were fairly confident of how to deal with cavitation on the back and face of the blade. Theory suggested that the problem of tip vortex cavitation could be reduced by increasing the number of blades, so five-, seven-, nine- and eleven-bladed models were tried. The law of diminishing returns set in with eleven blades but five blades gave considerable benefit over three on the model. This gain was not fully repeated at full scale, but the reduction in vibration with five blades made it worthwhile, and most surface warships since have had five blades.,7(In single-screw ships the flow pattern is usually better suited to four blades.)
By 1957 some fourteen models designed by Arthur Honnor were tested, leading to a five-bladed propeller for Whitby. Trials were very successful: quiet speed was nearly double that of wartime propellers, efficiency was at least as good and vibration was negligible.8 This became the first production design, but the same approach was used for other classes and soon all the RN surface fleet had quiet propellers – 10 years ahead of any other navy. There were teething troubles but these were overcome. Viewing trials became part of the ‘first of class programme’ for each new class.
Once there was confidence in reading across from model to ship the designers started making ad hoc changes to the model – ‘Joe, file a bit off where the bubbles start’ – and transfer the optimum shape to full scale. In the author’s view, this was real engineering, taking the best available theory as far as it would go, building on this from scientific testing, then empirical corrections based on tests and trials, file a bit off and another successful design is complete.
In a viewing trial the propeller was observed through glass windows in the bottom of the ship. These were usually under the steering gear, and the position was cramped and very uncomfortable, particularly if the ship was pitching. The propeller was made to appear stationary by using stroboscopic lighting.
(D K Brown collection)
The Type 14 Hardy burning after an Exocet hit during weapon trials. She was also hit by a Sea Skua ASM, a Mark VIII torpedo, and numerous shells, before being sunk by AS mortar projectiles. The amount of damage she withstood before sinking was remarkable, but she was out of action after the first hit. (D K Brown collection)
Much of this development read across to submarines even though the problem was different (Scotsman was the main trials ship in the early days). At depth, the sea pressure is too great for cavitation, but the changes in flow as each propeller blade passes through wake shadows behind fins, etc generate low frequency pressure pulses at ‘blade rate’ (rpm × number of blades), which can be heard at long distances. The understanding of design theory from the Savage series has enabled this, too, to be moderated, usually with a larger number of blades, heavily skewed (see Chapter 9for the pump jet).
Air bubble screening was originally seen as an alternative to quiet propellers. The first attempt was called ‘Nightshirt’ and consisted of a spider’s web of small pipes ahead of the propeller from which air could be blown. It caused a considerable drop in efficiency, about 1.5kts loss of speed, and usually vibrated itself apart very quickly. The second version, ‘Agouti’, was far more successful. Air was passed down the propeller shaft and out through ducts cut in the leading edge of the blades into the sea through a series of small holes. This had no effect on efficiency and was effective in reducing noise, particularly at higher speeds when cavitation could not be prevented. The mechanical complexity, particularly with controllable-pitch propellers was considerable!
For some time ‘Agouti’ and quiet propellers were seen as rivals, but the trials in Penelope in 1970 showed they were complementary and both were needed. A modern noise-reduced propeller (Type 23 ‘Duke’ class) is displayed in the National Maritime Museum.
A selection of propeller models tested during the early development of quiet propellers. The three-bladed model in the centre is Savage Set R, the first success. The five-bladed model, centre left, is typical of surface ship designs for many years.
(D K Brown collection)
The larger, No 2 cavitation tunnel at Haslar enabled more realistic tests to be carried out. This destroyer model, seen from below, has a typical wartime propeller on the port (lower) shaft and a more modern ‘quiet’ design on the starboard shaft. The newer design has only very faint traces of cavitation compared with the older model.
(D K Brown collection)
Flow Noise and the Penelope Trial
At speeds above about 20kts the main noise source is turbulence in the water flow over the hull itself. To investigate this noise source the frigate Penelope was towed behind the Scylla at speeds of up to 22.9kts during 1970.9 Penelopes machinery was shut down (with the exception of one small generator, elaborately mounted, on the quarterdeck to work the steering) and her propellers were removed. The towrope was 6000ft long, but stretched a further 25 per cent under load, so that Scylla’s noise and flow would not interfere.10
The noise levels recorded from Penelope represent the lowest-possible level for a conventional surface ship and the most recent ships are nearly there. Resistance measurements were also taken in confirmation of William Froude’s trials with Greyhound in 1872. Finally, a very detailed survey was made of the flow through the propeller position, measuring both velocity and direction of the flow at each point.
Top right: Savage Set J.
(D K Brown collection)
A conventional cavitation test on a five-bladed propeller driven from behind. The flow is from right to left along the shaft axis and uniform over the propeller swept disk. Though not entirely realistic, such tests are fairly quick to set up, enabling development to advance rapidly.
(D K Brown collection)
Above Water Signatures
Much can be done to reduce the radar signature of a ship by shaping the above water parts. Re-entrant corners must be avoided11 and the hull sides sloped. If the sides are sloped outwards to the deck edge (flare), as in the Type 23 class, stability will be improved if the ship sinks deeper in the water. Sloping the other way (tum-blehome) has a very bad effect on stability.12 Further reduction can be obtained by using radar absorbent material.
Penelope was used for a number of propeller trials and, as shown here, was towed at 23kts by Scylla to measure the noise generated by the flow over the hull.
(D K Brown collection)
Much was learnt from post-war ship target trials, particularly with respect to underwater explosions breaking the back of the ship, as seen here with Scorpion.
(D K Brown collection)
Infra-red signatures can be reduced by cooling the hot exhaust gases and by the use of low-emissivity paint. Neither of these measures will make 4000 tons of hot steel invisible but the reduction of the signatures makes decoys much more effective. (See ‘Hunt’ class, in Chapter 10, for magnetic and pressure signatures.)
Battleworthiness13
‘To float, to move, to fight.’14
Admiral of the Fleet Lord Chatfield said that ‘Ships are built to fight, and must be able to take blows as well as to deliver them’. In each of the opening years of the Second World War there were almost as many incidents of damage to destroyers as there were such ships in commission, while in the Falklands War 60 per cent of frigates were damaged.15 Even in peacetime warships are more prone to accidental damage than are merchant ships.
The first line is active defence, ie pre-emptive strikes on enemy bases, destroying the attacking vehicle before it can launch or killing the missile in flight. It has often been argued that the consequence of a hit from a modern weapon is so serious that all funds should go to active defence. However, some weapons will always get through, and attention must be paid to passive defence, minimising the effect of a hit; but the balance between active and passive defence is not easy to draw and nor is the balance between defence and other functions.16
The threat can be divided into three headings – accident, terrorism and enemy attack. Accident covers fire and explosion (98 major incidents), collision (125) and groundings (50) – figures in brackets are RN incidents from 1945 to 1984.17 Terrorist attacks have been few, but the potential threat remains, as shown by the attack on the uss Cole in Yemen in 2000. There is a bewildering array of weapons which can be used against warships, but their effects can be considered under six headings: – Fire, Flood, Structural collapse, Shock, Blast, Impact (splinters etc).
Non-contact underwater explosions such as those from ground mines and torpedoes cause violent and rapid flexing of the hull, which leads to buckling and collapse of the hull girder, the most common cause of loss amongst Second World War destroyers. There is no certain protection but some things can help. Discontinuities in primary structure, such as a break of forecastle, must be avoided. Overall design stresses should be kept low, mainly by increasing the depth, keel to deck. Shaft glands at bulkheads should be flexible, allowing considerable relative movement between shaft and structure. The lethal radius of these weapons is fairly small and the measures outlined make the enemy’s task more difficult. Contact torpedoes and mines still pose a threat (as in the 1991 Gulf War) – a Second World War torpedo will, typically,18 make a hole 30ft long by 15ft high, rendering structure non-watertight over double that distance.19
The shock from such explosions will cause violent movements of equipment, which may break. Cast iron should be avoided, as should overhanging (cantilevered) weights. Flexible mounts have been devised which attenuate the shock considerably. These have been very successful and shock damage has been rare – this immunity leads to proposals to abolish shock protection, the very factor that made such damage rare! One ship of each new class is subjected to high shock loads to confirm the effectiveness of the treatment.
Underwater weapons will almost certainly cause flooding which can sink the ship (usually by capsize) or immobilise it by flooding machinery spaces. A typical RN frigate should survive with any three compartments flooded, four with a little luck (in the Falklands War Coventry had five compartments flooded and stood no chance). The machinery spaces can also be attacked by air-flight weapons and a good defence is provided by the so-called unit system, introduced to the RN in the ‘E’ class cruisers of the First World War. The simplest style for a steam ship is alternating spaces – boiler-room, engine-room, boiler-room, engine-room – arranged so that either boiler-room can work either engine-room, so if one space of each kind survives the ship can move. COGOG ships can be given similar capability. An early computer study gave the following results.
|
Arrangement |
% probability of loss of mobility from one hit |
|
One unit, 2 spaces (boiler-room, engine-room) |
50 |
|
Two adjacent compartments each with a complete power plant (COGOG) |
25 |
|
Two widely-spaced units |
10 |
Great care is needed to ensure that units are truly independent and do not rely on a common auxiliary system. The next generation of all-electric ships should be even better, with multiple generators, widely spaced, driving separated motors, perhaps podded outside the hull.
The unit system has been extended to the philosophy of ‘zones’, up to five in a frigate, each independent for power, ventilation (preventing the spread of smoke), chilled water, cooking, toilets, etc. Complete implementation is very difficult as, in the limit, each equipment should be duplicated within a zone to allow for maintenance, but even partial implementation is a big step forward. Ideally, the crew should live in the zone in which they fight, obviating the need to open doors and hatches when going to Action Stations.
Blast and splinters from air-flight missiles can destroy large areas of topside structure and the vital equipment within. Protection by armour is not possible – a Falklands-type Exocet (a small missile) could probably penetrate 12in of armour.20 One can limit the effects, but the main protection is to concentrate components of a system, duplicate them and separate the alternates. Some protection to main cable runs maybe worth while. If this is incorporated with the structure it need not cost too much and could reduce the number of splinters hitting the cables by 99 per cent.
At the end of the Second World War flooding was the only one of these effects for which calculation was possible, and even this, without a computer, was very approximate. Damaged stability calculations are now available at the click of a mouse, and far more accurate. Other effects were considered subjectively in the light of full-scale trials with obsolete ships, often modified to try new ideas. Trials had to be abandoned when the dangers of asbestos were recognised. A very few were held, but they had to be at least 200 miles from shore and access was only possible in full air-fed suits. A trial known as HULVUL was possible using the first asbestos-free frigate in 1988.21 There were over 100 separate trials, starting with a burning helicopter on the flight deck. A later trial had half the boiler room structure replaced with a replica of the Type 23 structure for a big underwater explosion. Lessons from the Falklands War are discussed in the next section.
In the meantime, computer simulation advanced rapidly. By the mid-1980s the effects of blast and splinters could be reproduced fairly accurately and it was possible to study whipping and shock. Fire was still not properly represented but progress was being made. The aim is to be able to write a specification somewhat on the lines of – after one hit anywhere with a 500kg warhead the ship is to have x% chance of retaining y% of her fighting capability.22
The outstanding problem is that ships are lost from quite simple faults, so computer assessments must go into very great detail. By the time that level of detail is available for a new ship it is probably too late to make changes. The approach would seem to be a two-stage one. The first stage would be a very crude analysis of major features, such as bulkhead spacing. This would be followed when the design is complete by a very detailed study. Few alterations would be possible in the current design but lessons could be read for the next generation.
The real problem in damage limitation is to decide what the object is. It cannot be to build an ‘unsinkable ship’.23 The author has suggested that the aim is to make the enemy’s task as difficult as possible and ships must not be disabled by a trivial attack. Ultimately, the responsibility lies with the designer – can he sleep at night when his creation is sunk, knowing he has done his best?
Lessons of the Falklands War
It is tempting to say, and nearly true, that there were no new lessons. Many old lessons were re-learnt and minor improvements in procedures (both ashore and afloat) and in equipment were made. The official Action Grid had over 180 entries but most of these were either trivial, or in some cases pious aspirations, unlikely to lead anywhere. Contemporary accounts in the press were usually wrong.24 Constructor Commander Rod Puddock was with the Task Force both to advise on emergency repairs and to record damage and other lessons.25 (Note that this author does not always agree with the official lesson. It is hoped that personal views will be kept clearly separate.)
Submarine threat. Following the sinking of the cruiser General Belgrano by HMS Conqueror no major Argentine surface warship left harbour. The SSN acted as the ‘Grand Fleet’, ruling the sea; the uncertainty of their whereabouts formed an important part of the deterrent. The one operational Argentine diesel-electric submarine caused much AS activity but was not located.
AEW. The lack of airborne early-warning was the most serious deficiency, eventually reduced by fitting Search-water radar to eight Sea King helicopters. The lack of AEW caused much wasteful patrolling by Sea Harriers.
Gunfire support. Destroyers and frigates fired some 8000 rounds of 4.5in ammunition during the whole war in support of ground troops and, additionally, some elderly Sea Slug missiles were fired at coast defence batteries – a frightening thought. It is claimed that these bombardments played an important part in the collapse of Argentine morale. Certainly the range and accuracy were most impressive. For example, on D-Day, Ardent fired on Goose Green airfield at a range of 22,000 yards, destroying a Pucara with her first 20 rounds and going on to fire another 130 rounds during the day. On the other hand, in 1916 during preparation for the Somme battle, British guns were firing 10,000 rounds per hour on a very small area.
Close-range AA guns. Only one Argentine aircraft was shot down by light AA guns, though Argentine AA on shore was more effective. The official lesson was that the fleet needed more and better light AA, and much has been done to implement this approach by fitting CIWS such as Phalanx and Goalkeeper. On the other hand, it seems valid to argue that light AA was ineffective against mostly obsolescent Argentine aircraft and would be useless against modern aircraft and missiles.
Fire. In the Second World War fire following bomb attack was quite uncommon but in the Falklands serious fires were all too frequent. Almost all serious fires involved oil fuel – ‘dieso’ – which had a flash point only slightly lower than that of wartime oil (dieso 56°C, FFO 66°). Stowage was probably safer and firefighting certainly better.
Aluminium in structural form does not burn but does soften at about 550°C (when life is extinct and all equipments ruined) and melts at 650°. By way of comparison, steel melts at about 1500°, and ship fires typically reach 900°. Aluminium is a very much better conductor of heat than is steel. Foam mattresses could have burnt, but there is little evidence that they were involved in most fires. Following major furnishing fires at the Manchester Wool-worth’s and at Summerland (Isle of Man) in the mid-1960s, replacement materials had been sought. These had only been found with great difficulty – at that time industry was not interested in fire-resistant foam – and the first order was about to be placed. There was a small amount of PVC-covered electric cable in older ships which could give off toxic fumes in a fire. Newer insulating materials were not absolutely free of fumes but the risk was small. Transmission of fire through a bulkhead gland was virtually impossible and there is no evidence that it occurred. Direct transmission through the steel bulkhead was possible if cooling by hose was not used.
Sheffields fire was started by burning fuel from an Exocet in a ready-use fuel tank. The tank was high in the ship so that fuel would be available in the event of loss of electric power, while its shape helped to settle out any impurities. These were worthy objects, but fuel must be, stowed low down both for protection and because it is easier to blanket a low tank with foam if a fire does start.
The biggest problem was smoke: in wartime fore and aft access for small ships had been on the open upper deck, but the new ships had covered access on 2 deck and not all the bulkhead openings were smoke-tight. None were tight on the Type 21 frigates, which had a single ventilation system for the whole ship. Improved firefighting arrangements are covered later.
Linings obstructed access to the ship’s side for leak stopping, and a considerable reduction in their extent was made at the expense of increased housekeeping work. There was a prolonged and rational debate over the extent of linings in the Type 23, which led to a much lesser extent than in earlier ships. Some materials (unbacked Formica) fractured into sharp fragments on impact.26
Exocet. The effect of Exocet was no surprise. The RN had seen film and results of French tests before it purchased this missile. Two of the RN’s earliest Exocets were fired into the frigate Undaunted in 1978, making the missile’s potential very clear.
Shock tests were carried out against one ship of each new class, usually just before the first refit so that any defects could be made good. This trial is with invincible (not an Argentinian propaganda picture!).
(D K Brown collection)
Sheffield burning. As with almost all Falklands War fires, fuel was the major material burning.
(D K Brown collection)
Machinery. The Defence Committee particularly praised the reliability of warship machinery, dismissing unofficial reports that said there were few engines functioning fully on return. Invincible carried out a routine engine change at sea in sheltered waters after fighting stopped. Time between routine changes of Olympus had increased from the original figure of 3000 hours to 4500 hours. Six frigates had engine changes on return, of which four were routine. Two steam frigates were unable to develop full power due to action damage.
Committees. There were a number of effective committees covering different aspects of vulnerability before the war but they lacked cohesion. In particular, naval committees concentrated on training and technical committees on material. While there is no evidence that this lack of co-ordination caused any serious problems, improvement was clearly possible and desirable. A joint Vulnerability Policy Committee was set up (the author was its first chairman with a naval deputy) co-ordinating the work of several working parties.
Miscellaneous. There were many minor points: for example, there was a perceived need for many more welding sets and operators skilled in their use.
Self Protection. Everyone got used to carrying anti-flash gear, gas mask case,27 life jacket, immersion suit helmet, etc.28 Heating was turned down to encourage men to wear warm clothing, a protection against flash and of value if they had to swim. Hermes was able to operate in the war zone almost fully closed down,29 but this was not possible with the much smaller complement of Invincible.
Contaminated fuel. Some problems were caused by biological contamination in the fuel tanks when fuel was purchased from untried refineries.
Perhaps the biggest lesson to be re-learnt was that serious damage is almost inevitable in war. Sixteen of the twenty-one destroyers and frigates that reached the Falklands were hit; those that were not were late arrivals.30 During the early years of the Second World War there were almost as many incidents of damage to destroyers each year as ships in commission. An earlier Defence Committee report (1983) said: ‘Fire precautions and damage control are not appropriate matters on which to cut corners; the resulting economies are false if they contribute to loss of lives or ships.’ In response, the MoD pointed out that in a cost limited ship some compromise was inevitable.
Fire
The major fires during the Falklands War excited considerable attention from the media, though the accounts were almost always wrong.31 With one exception the fires were associated with oil fuel and, though foam-filled furniture may have been involved, it was not the origin of the fires. There was an interesting exchange of views with the Home Office a little later over the fire hazards of domestic furniture. Their concern was to adopt materials which would not be ignited by a dropped cigarette; the ship designers’ was to choose materials which would not give off toxic or corrosive fumes when in a fire. This led to very different choices, but it would seem that both were right. A frigate carries some 700 tonnes of fuel (dieso), 45 tonnes of ammunition, and about 100 tonnes of other combustible material (personal effects, furnishings, paper, etc), this last category being very widely distributed and with a big superficial area, increasing smoke generation. The first step is to keep the fuel low down, as this not only provides some protection but also if a fire starts it is easier to put a foam blanket over it.
Personal effects such as uniforms and civilian clothes present a problem. The best solution seems to be fire-resistant stowage. Private additions need not be forbidden but they do need control, particularly sleeping bags. An inspection team visiting a frigate found a highly-flammable bean-bag in the wardroom! Office paper should be reduced with computer recording. There is no insulation for cables (30 tonnes) which is completely fire-resistant but current ships have the best available – and the older ships were not bad.
Fires will always start, even by accident, and the first step is rapid action by a well-trained crew, a topic outside the scope of this book. The next step is to confine the fire and smoke to a limited area. Modern frigates are divided into five zones each with their own firefighting system. It is essential that the zone boundaries (bulkheads) prevent the spread of flames and smoke. Proper testing both on completion and in service is necessary but expensive.
Materials should be selected that give off the smallest amount of fumes when in a fire.32 Speed is of the essence in firefighting and automatic systems have been developed which extinguish the initial flame in fractions of a second. The ban on fluorocarbons was a setback, as these were used in all machinery spaces for firefighting, but recent work with water mist (not sprinklers) has shown great promise. Good access for firefighters is needed and escape routes should have luminous markers that can be seen in smoke. Small breathing apparatus sets (ELSA) are now available which provide air during escape.
The frigate complex at Devonport where frigates can be refitted under cover. This has obvious advantages in terms of speed and efficiency. (D K Brown collection)
Firefighting needs good communications and visibility requires thermal imaging cameras. More recent accidental fires give confidence that the fire hazard has been greatly reduced since the Falklands War.
Materials
Surface Ship Steels
By the early 1950s development was complete of two steels for the main structure of surface warships. ‘A’ quality had a yield strength and ultimate tensile strength (UTS) very similar to commercial mild steel but it was made to higher standards, in particular, it retained toughness to −30°C.33It has been used extensively in post-war RN ships, but by 1980s commercial steels were available meeting the same standards. ‘B’ quality had higher yield and UTS replacing D, DW and S quality steels. It has been used to a limited extent in warship structures where tensile stresses are high. More often the likely failure mode is buckling, where high tensile strength is of little value. In general, high tensile strength steels have a fatigue life at best no better than mild steel and often worse.
A ‘Castle’ class OPV in dock. The underwater paint is an early self-polishing co-polymer with a very long life. It was blue – a marked contrast to the usual red. Note the large bilge keels and the knuckle. (D K Brown collection)
|
A |
B |
|
|
Yield Stress (tons/in2) |
16 |
20 |
|
UTS (tons/in2) |
28–3 |
31–38 |
|
Elongation (%) |
22 |
17 |
In earlier welded ships it was usual to use a number of riveted seams intended to stop any cracks which might start in the plates. Both A and B quality were ‘tough’, even at low temperatures, which means they will not allow a crack to extend, and where ordinary mild steel was used it was common to run occasional strakes of A quality to stop cracks without the need for riveting.34
Submarine Steels, etc35
Starting with Explorer and Excalibur, a new carbon manganese molybdenum steel, UXW, was introduced. A very similar steel was used for the Porpoise class, but thicker plating was needed and the composition was altered, which led to welding problems. To alleviate this difficulty, the steel was used in the normalised and tempered condition with a drop in yield strength.
The later Porpoises and the Oberons had QT28 with a minimum proof stress of 28 tons/in2, which was used in the quenched and tempered state.36 For Dreadnought and early SSNs a stronger steel, QT35, was introduced. Despite lengthy development testing and care in manufacture this steel was prone to cracking, as manufacturing methods were not up to the standard of cleanliness required. The USN had similar problems with early HY80 but were quicker to find a solution, and US-made improved HY80 was used for the SSBN and a few SSN. A British equivalent, Q1(N), was developed and introduced in Superb; with a yield strength of 25.6 tons/in2, it was used up to and including the Trafalgars. Q2(N) with a yield strength of 45 tons/in2 has been developed. Care is needed to ensure that the weld strength matches the plate strength – in general, diving depth will increase in direct proportion to yield strength.
Typical Yield Strength (or Proof Strength)
|
tons/in2 |
|
|
Mild steel |
15.8 |
|
S |
18.4 |
|
UXW |
25 |
|
QT28 |
27.8 |
|
QT35 |
35.9 |
|
HY80 |
35.6 |
|
QKN) |
35.6 |
|
Q2(N) |
44.6 |
There are many materials which are stronger than Q2(N) but, so far, fabrication problems and the difficulty in working penetrations for hatches and torpedo tubes have prevented their use. The table below compares theoretical collapse depths for a mythical submarine in different materials.
|
Metres |
|
|
HY80 |
1000 |
|
HY130 |
1600 |
|
Titanium |
3000 |
|
GRP |
3500 |
|
Carbon RP |
6000 |
Seawater Systems
There are numerous cooling water systems in a nuclear submarine containing seawater at the pressure corresponding to depth, the largest being the main turbine condensers. Failure of any of these systems could lead to the loss of the submarine; indeed, such a failure is believed to have caused the loss of uss Thresher. Materials used must be corrosion resistant, erosion resistant and strong enough to resist diving pressure. Such materials were – are – not easy to come by, and there were worrying problems for a time. At the end of the war, the few piping systems were of mild steel or gunmetal. Later diesel boats tried copper-nickel-iron and then cupro-nickel. Early nuclear boats used 70/30 cupro-nickel. Castings were aluminium bronze and later nickel-aluminium-bronze. This latter material has a very complicated micro-structure and great care was needed in manufacture and in welding to get a satisfactory and lasting result. It did have the virtue of the socalled ‘leak before break’ effect, giving warning of impending failure.
This brief note on submarine materials is only illustrative: there were many other materials, each with its own problems. Building and running a submarine fleet is demanding.
Painting and Preparation
Developments in paint and in preparation for painting have made an enormous, and largely unrecognised, contribution to reducing the cost of running a navy. Paint can do many things whose relative importance will vary from one part of the ship to another; paint will always play a major part in preventing corrosion and, when appropriate, will provide a non-slip surface, easy to clean and easy to maintain with an attractive appearance. Under water, paint should prevent the growth of biological fouling and, above water, it can help to reduce radar and infrared signatures.
These benefits do not come cheap: it has been estimated that the cost of preparation and painting may amount to 2–3 per cent of the building cost – upwards of £3 million – but well worth it. Much of the cost is due to interference with other work that must be stopped when the nastier paints are being sprayed.
In the Beginning
At the end of the Second World War most paints were simple, oil-based types, cheap and easy to apply but offering poor protection. Under water, the hull was coated with an anti-fouling paint called Pocoptic, based on an American formulation and good for its day. Even so, factional resistance went up by 0.25 per cent per day out of dock (double that in tropical waters – 90 per cent in 6 months). This was soon replaced by 161P, developed by the Central Dockyard Laboratory (CDL) and made in Portsmouth Dockyard; this roughly halved the rate of fouling. The significance of this improvement is made clear in a paper dealing with a proposed modernisation of Majestic.37 The extra displacement would reduce her speed by 0.5kt with a clean bottom but, 6 months out of dock, the modernised ship would be a whole knot faster due to improved anti-fouling paint.
Preparation
It is much easier to prevent rust forming than to remove it afterwards. From about 1960 plate was grit-blasted as soon as it arrived in the yard and given a very thin coat of tough primer that would not interfere with welding. When this coat was damaged it would be touched up at once. Some of the more advanced coatings required a further blast to shiny bare metal immediately before application. Proper preparation has made an enormous difference to the life of a ship. Hermes was the only ship in the Falklands task force painted to Second World War standards, and the only one noticeably rusty on her return.38
Topsides
An old-fashioned First Lieutenant would paint ship at every opportunity, and long life was not seen as important – after 10 years up to 80 coats of paint were found on the exterior of Leanders, weighing 45 tons.39 It was found that the mismatch of ‘touch-up’ patches was due more to differences in gloss than to shades. Considerable improvements have been made.
Decks
The dominating requirements for decks are that they should be non-slip and easy to clean, and these are contradictory. For much of the period the helicopter deck had a very rough finish on which the tyres would grip. This was hard to clean and the rest of the upper deck was grit blasted, covered with a zinc metal spray that was then covered in a glossy epoxy paint. Abrasive tread strips were then stuck to give grip. This complicated system protected the metal of the deck and was generally safe but the tread strips soon came to look untidy. This system was developed in Australia and came to the RN via the Inter-Naval Corrosion Conference, a most useful group of five navies who met every 3 years to pool their experience.40 Latterly, an epoxy paint has been introduced which is suitable for both the upper deck and helicopter deck. It took some time to persuade shipyards and Dockyards that a fully weatherproof tent was needed for the application.
Illustrious arriving off the Falklands in 1982 to relieve the Invincible (background). Such was the hurry to dispatch the new carrier that she was sent out without anti-fouling, allowing a valuable quantification of the effects of fouling.
(D K Brown collection)
Machinery Space Bilges
This was, and perhaps still is, the most difficult area of all. In the older steam ships, the machinery spaces were warm and moist, with much of the bilge area almost inaccessible. Corrosion was rapid: Rothesay was found to have fourteen longitudinals on one side and nine on the other so badly corroded as to be virtually useless – it was lucky she did not break in half. Initially, a paint based on chlorinated rubber was used, the best available, but not up to the severe conditions. The introduction of the gas turbine made matters worse, for the synthetic lubricating oil they used proved to be the world’s best paint-stripper. From about 1960, the bilges were zinc-metal sprayed, but it was some time before application problems were solved and the sprayed surface was often damaged during machinery installation.
Eventually, Central Dockyard Laboratory (CDL) developed a very hard epoxy to cover the zinc and this proved excellent, though it is so hard that touching-up damaged areas is almost impossible.
Outer Bottom
The first line of defence is ‘Impressed Current Cathodic Protection’ (ICCP), in which a carefully monitored electrical potential is applied to the hull, preventing electrical action between the hull and the seawater. The current requirements would be enormous if the hull were bare metal so it is coated with coal tar epoxy paint chosen because it is resistant to the high current density round the electrodes. Early Leanders did not have ICPP and after 6 years there would be extensive pitting up to 8mm deep. The later ships were protected and after the same time in service showed no more than occasional 0.5mm pits.
The earlier anti-fouling paints used copper oxide as the toxin. As this leached out it left a rough surface. If it dried out, as when the ship docked, a new coat had to be applied. Each coat added roughness due to ripples in application and dirt inclusions. During the 1970s International Paints introduced a ‘Self Polishing Anti-Fouling’ which was very long lasting, did not suffer from drying out, and actually got smoother in service. Trials supported these claims, but worries over health took a long while to resolve. It seems that the original coat may last half the life of the ship, while the increase of resistance is negligible.41 The saving in fuel and reduction of dockings has saved very large sums of money. The toxin used in the original version is harmful to marine life and was phased out in 2002, being replaced by a less effective copper compound. The long-term solution probably lies in a ‘non-stick’ paint.
Each coat of painting adds to roughness, as there will be paint ripples and overspray; dirt inclusions while docking adds 25 micron on average. A rule of thumb is that 10 microns of roughness adds 1 per cent to frictional resistance, which allowing for wave making, etc means 0.5 per cent on the fuel bill. R L Townsin details roughness measurements on a Type 42 destroyer: after blast cleaning and priming average roughness was 55 microns,42 with three coats of anti-corrosive 135 microns, and as completed 180 microns.43 Roughness and fouling add about £80,000 to the annual fuel bill of a frigate – £4 million for the Navy as a whole. Early in the post-war years a typical warship would complete with an average roughness of some 300 microns and deteriorate in service. More recently, greater care and improved equipment has brought this down to about 100 microns and self-polishing paints really do get smoother in service.
Fouling
The underwater form of a ship offers a happy home to many marine organisms, loosely grouped as ‘fouling’. The main components are: diatom slime, slippery to the touch but with an equivalent roughness of some 600 microns, due in part to the grit which it picks up; then there are vegetable growths – grass – and zoological growth such as barnacles.
At the end of the Falklands War, Illustrious was sent out without any anti-fouling paint. After 5 months afloat in the River Tyne (then lethal to most living organisms) and a further 9 months in the South Atlantic the frictional resistance was about 2½ times that of a clean ship, corresponding to a 3kt loss of speed.44 After the bottom was cleaned, shaft power was reduced by 80 per cent at lower speeds and 56 per cent at full speed, restoring the design performance.
Submarine Paints
Until the 1960s the external, anti-corrosion paint was an oil-based paint, ACC 655, with a high lead content, which was then replaced by coal tar epoxy with a life of 10 years. There was a problem in finding a satisfactory anti-fouling that would retain a black colour. Until the 1970s pocoptic black was used, which had cuprous oxide as the toxin but heavily diluted with carbon black. The later 317E had black cuprous sulphate and oxide and was also used as the boot topping in surface ships.45 Self-polishing anti-fouling paints were treated with caution, as there were fears that submarines could be tracked using residue from the paint.
Conclusions
The reduction of serious corrosion has largely obviated the need for plating to be replaced during the life of the ship, resulting in a great reduction in docking time and cost. The fuel saving from anti-fouling has also been very considerable, and these savings have made possible a considerable reduction in the size and number of Dockyards. Day-to-day maintenance has been eased. Many of these savings are due to the work of the chemists at the Central Dockyard Laboratory at Portsmouth, both in developing special paints and in producing a ‘consumers’ guide’ to commercial materials. The closure of CDL46 may well be a false economy. This is all too brief an account omitting many lesser but difficult problems.47
A junior rates bunk space in a Type 22 frigate – a far cry from the hammocks of the Second World War era. (D K Brown collection)
Lifesaving Gear
Very soon after the Second World War the Admiralty set up a committee under Admiral Talbot to review the causes of death of RN personnel during the conflict. They concluded that well over half the deaths occurred after men had left the ship, either in the water or on unprotected life rafts.48A standing RN Lifesaving Committee was set up, with membership from seamen, constructors and doctors. Initially there was some debate as to whether to go for inflatable gear or something akin to the old cork jackets with inherent buoyancy, but the decision came down for inflatables. The RAF had considerable experience of inflatable gear and their advice was freely given.
Survivors must be able to board a life raft easily; once inside they must be protected from cold wind and spray or hot sun, and insulated by a double skin from the cold seawater. The ‘passenger’ space should be virtually airtight so as to preserve a high humidity, preventing evaporation from wet clothing, and conserving body warmth (or keeping cool in the tropics). The raft should carry food and water for several days, be difficult to capsize and easy to right if it does, and be conspicuous. The buoyancy should be subdivided to reduce the effect of a puncture and there should be a repair kit. Regular checks are essential but the effort needed should be as small as possible. None of these requirements is as easy as it sounds.49
By about 1950 a 20-man raft had been designed, tested and some had been issued.50 It was oval in shape and had double buoyancy tubes made from three-ply rubberised cotton.51 It had inflatable hoops that supported the tent and helped in righting a capsized raft. It had entry in the form of a sleeve, which could be closed by frozen hands. The stowage had a hydraulic release that would ensure that they floated clear of a sinking ship. There was also a survival pack with food and water. By the early 1970s better, artificial materials were available and a new circular 24-man raft was introduced.
A large section of the Type 23 Lancaster ready for assembly in Yarrow’s module hall. Note the original pendant number, later changed because ‘Form 232’ was used to report groundings, collisions and similar embarrassing accidents. (Yarrow)
The problem with the wartime lifebelt was that it would not keep the head of an unconscious man out of water – rather the opposite. A new jacket was designed using two-ply cotton; it proved able to keep an unconscious man’s head out of water, on a target price of £5. It was thought that a man jumping off a high place might break his neck – leaping into the sea from a carrier flight deck disproved this.52 Special jackets were developed which would keep a heavily-armed Marine afloat and another for those on hazardous duties who might be unconscious when they hit the water.
An immersion suit was developed by 1950 but was not generally issued until the late 1970s. Space on the upper deck for all this gear was hard to find, and it had to be dispersed so that a single hit would not destroy it all.53 During the Falklands War it was found that manholes were too small for a well-fed sailor carrying full survival gear.54 On the other hand, the relatively light casualties on the warships that sank suggest that the lifesaving gear was effective. Since that war ELSA, a shortlife breathing apparatus, has been issued to make possible escape from toxic fumes. Careful maintenance and regular inspection are essential – yachtsmen beware.55
Habitability56
When the war ended in 1945 the ratings’ mess decks aboard RN ships would have seemed quite familiar to Nelson’s men. A ‘mess’ consisted of a bare wooden table with long benches either side; in the deckhead over there were hooks from which hammocks could be slung. The design standard for most ships was 20ft2 per man for junior rates and 25ft2 for senior rates. Wartime additions of equipment like radar had reduced the space available while at the same time increasing the complement; actual space per man was about 15–17ft2 for juniors and 17–19ft2 for seniors – this for all purposes. Food was cooked centrally and carried a considerable distance to the ill-ventilated messes. Drastic changes were needed, particularly when conscription ended and volunteers had to be attracted and retained.
Trials in the early 1950s of cafeteria eating,57 close to the galley and separate from living spaces, showed real advantages without dramatic increase in space requirements,58 while at the same time food quality was improved and wastage much reduced. Parallel trials of bunks were also successful. In the mid-1950s the Leanders, ‘Tribals’ and ‘Counties’ were designed with cafeterias, bunks, seating for all,59 and some increase in overall space per man – 21ft2 for juniors and 25 for senior rates, of which 4ft2 was allocated to the dining hall. Older ships in refit were, as far as was possible, brought up to these standards. Experience showed that, though these standards were a big step forward, there was need for more. There was too little distinction between Chief Petty Officers and POs, the use of ‘my’ bunk as a settee was very unpopular, and storage spaces were inadequate when civilian clothes were allowed. Messing areas were generally unattractive in appearance. There was an interim improvement in 1966, mainly affecting the Leanders.
These problems were fully tackled in the ‘1970 Standards’ for accommodation; it helped when experience showed that space in the dining hall could be slightly reduced. Space per man was increased to 24ft2 for junior rates, 29ft2 for POs and 35ft2 for CPOs, while seats were provided for all, clear of the sleeping area. Fleet Chiefs (52ft2) were to have single cabins, Chiefs 2-, 4- or 6-berth and POs 6-berth. A new range of furniture was designed, and a firm of consultants produced a range of decor schemes. Washplaces were replaced by bathrooms with showers and stainless steel basins, and were completely lined. Laundries and drying rooms were added.60 All these improvements took up space and added to the ‘hotel’ electrical load, but they were essential if young men were to be attracted and retained in the navy. Officers’ accommodation had been fairly spacious but unattractive and junior officers usually shared. By 1970 all (except those under training) had single-berth cabins with new-design furniture. Galleys were now all-electric, and great attention was paid to convenience and to hygiene.61 Simple air flow had given place to full air-conditioning, working well in later ships.
A Sandown class GRP minehunter under construction by Vosper Thornycroft. (Vosper Thornycroft)
There were many who thought these standards were too luxurious for a fighting ship (even a few ratings thought this and would have preferred more pay and austere living). This view came to the fore after the Falklands War when some blamed accommodation standards for contributing to fire and making damage control difficult. This was argued out in the final design of the Type 23 frigates and only a few changes were made. British ships are very similar in space per man to the average for NATO (slightly below) and the standard is broadly similar. During the 1980s there were few complaints.
The length and hence overall size of a frigate is governed by the upper deck length that is required for weapons and sensors, with allowance for physical and electronic clearances. Typically, this will leave space for about 100 men at current standards. Additional men are expensive – £80,000 per man to build, much more than the capital cost of a London hotel room. Big increases might mean larger engines, as well as a general increase in ship size. There is keen pressure to reduce complement but damage control is very dependent on skilled manpower and compromise is needed, though it is a difficult balance to get right.
Ventilation
There were at least two major investigations into ventilation between the wars, which showed the need for considerable improvement, but at the time of the first money was too short for much to be done and the later one was too close to the outbreak of war. During the war things could only get worse: many heat-generating equipments were installed, with more men in less space, while the ships were closed down for long periods. Operations took place in extreme conditions in the Arctic and in the Tropics. It was clear that something had to be done.62
Before the war most manned spaces had a fan supply of fresh air and natural exhaust, whilst smelly compartments had forced extraction and natural supply, usually from neighbouring compartments. If properly designed, installed and maintained, this system could work quite well in moderate climates, but all too often these conditions were not met. During the war air-conditioning was introduced for operations spaces, and for submarines.63
It was clear that electronic devices would increase in number and power which, with thermionic valves, meant a very great generation of heat. The threat of nuclear war and fall out meant that ships would have to close down very quickly and remain closed down for long periods in conditions from the Arctic to the Tropics.
Design Parameters.64
In the mid-1950s the decision was made to install full airconditioning in the ‘Tribal’ class frigates.65 There were teething troubles but the scheme was generally successful and has been adopted in all later ships. One lesson was the need for standby units. It was also found that air-conditioning machinery takes up space and weight, and consumes a considerable amount of electric power, much of which appears as waste heat. Warships have a particular problem in that passageways are very congested and hence designers are driven to small trunks with air at high velocity, which can be noisy.66
The units supply a mixture of fresh and recirculated air that is filtered and either heated or cooled before being distributed. There are two main conditions: Cruise, in which fresh air is drawn directly, while in the Action state air is drawn through NBC filters.
The ‘heat load’ within a compartment is made up of heat from men, machinery (including the air conditioning machinery), boundaries – sun and sea – and the fresh air. Air conditioning has made a great difference to life at sea and, though expensive, must be seen as essential.67
Welding and Modular Construction
In 1945 it was generally accepted that future warships should be welded and that this should be associated with pre-fabrication of units under cover in the shop. The units should be as large as possible within the limits of the yard’s craneage. Serious cracking in welded structures68 led to the introduction of riveted ‘crack-arresters’, usually at the upper deck edge and at the turn of bilge. These crack-arresters were gradually omitted as better steel and improved procedures became available. During the war there had been extensive use of lap welds but, in future, all welds would be butted, which implied more accurate cutting to shape. Cutting was by flame cutters controlled at first by optical scanning of drawings and later by direct computer input. This had an important side benefit: the smoother hull had less resistance and endurance went up by some 5 per cent.
The first post-war frigates were designed so that radar offices and similar spaces could be built separately, fitted out and tested ashore before being inserted into the ship, but this feature was not used as far as is known. Steady development followed; wider plates meant fewer welds, as did a reduction in the number of longitudinals. Design and planning meant more welds could be made in the ‘down-hand’ position with the welder above his work. There was increasing use of machine welding, which produced welds more quickly and of better quality. Modernisation of shipyards enabled bigger units to be handled, though they were still quite small, at between 10 and 30 tons.
By the late 1970s it was realised that outfit work was very expensive, particularly on the slip. Easton quotes the following cost ratios (about 1980):69
|
Prefabrication shop (structure) |
1 |
|
Unit Assembly |
5 |
|
Work on berth |
10 |
|
Afloat |
20 |
The idea grew of fabricating very much larger sections that could be fitted out through their open ends or with the deck off70 before being joined to form the ship.71 Construction would begin of structural units weighing 40–60 tons. Some limited outfitting would take place before they were joined into modules of up to 400 tons that were fitted out prior to being moved to the slip.
Slightly earlier, there had been an alternative approach, also referred to as ‘Modular Construction’. The idea here was that weapon systems could be installed in a box or boxes, tested ashore and dropped into the ship where there would be power supplies, chilled water, etc arranged to connect. There were at least three schemes: the USN went for very large boxes in their SSES system, which would hold a complete system; Germany developed and used the MEKO system, with boxes of about normal container size; the British scheme, ‘Cellularity’, used much smaller boxes grouped in ‘cells’ that could be enlarged. A full-scale mock up of a large cell was built at Portsmouth and showed great promise.72
A modern warship-builder: Yarrow’s shipyard on the Clyde, where many frigates have been built. (Yarrow)
It was claimed that these modular schemes made mid-life modernisation simple and cheap.73 However, power supplies and so forth were very different for different weapon fits and changes were still difficult. It was eventually decided that mid-life modernisation was uneconomic and only limited updates would be undertaken. This was probably the right decision for the wrong reasons. The Type 42 modernisation was said to cost more than a new ship, but examination of the figures showed that one of the biggest items was Dockyard overheads charged on weapon systems which they did not touch!
Yarrows alone invested some £3 million in computer aided design but, as the managing director pointed out, investment in people is even more important. At all levels a better-educated workforce was needed – and achieved. Computer design reaches into production; pipe and cable systems can be planned. Some 12,000 cables in a Type 23 can be cut to length before installation. There are also about 12,000 key drawings defining a Type 23.
Also, round about 1980 new cutting and welding methods were introduced. The plates and frames were cut very accurately, saving a great deal of time on rectification and setting up. Plasma welding, under water, virtually eliminated weld distortion (the so-called Starved Horse effect leading to corrugated side plating). Computer controlled planning ensured that each item required in the assembly area arrived just before it was needed. The importance of this cannot be overemphasised: a Type 23 has some 6 million ‘parts’, all of which must be in the right place at the right time.74 All these measures reduced building cost very considerably75 – also making mid-life modernisation almost impossible.
Vosper Thornycroft were able to adapt much of this modular approach for GRP construction in the Sandown class. Some 10,000 drawings were produced using CAD, which ensure that every part fits. Much of the GRP lay-up uses preimpregnated glass cloth fed into the mould by machine, with hand press down. Units weighed up to 20 tons and were fitted out before being inserted into the hull.76
Conclusions
Many of the topics here may seem remote from the usual image of warship design, but they all matter. It is the duty of the naval architect to get them all right or, where they conflict, to reach the best compromise. His ship must have the best hull form, itself a compromise, the right steel, in a structure which will withstand the pressure of the sea and the attack of the enemy over a long life and protected from corrosion. The naval architect must also remember that men live in the ship and as well as good food and reasonable comfort they should be proud of the appearance of their ship. A warship is the representative of its country and, as such, should have an awesome beauty, frightening to the wrongdoer. Get it all right and the designer too may be proud of ‘his’ ship.
1 I prefer the term ‘battleworthy’, parallel to ‘seaworthy’, and also a term used by the RAF of aircraft. More recently, a third sub-title has been added: ‘recoverability’ – the ability to repair damage.
2 E P Lover, ‘Cavitation Tunnel Testing for the RN’, Newcastle University Conference 1979; and D K Brown, ‘Stealth and Savage’, Warship 32 (1984).
3 This is similar to the wingtip vortices from aircraft, and to the vortex formed when bath water is running away.
4 More detail is given on these tests and the way in which trials were carried out using windows in the bottom in D K Brown, ‘Stealth and Savage’, Warship? 32 (1984).
5 Theory predicted failure of one very thin design, so it was made and tried, and it did break!
6 Some people thought its success was solely due to its area and a conventional propeller of the same area was made, tried and failed.
7 As far as I know, the different effect of number of blades in model and ship has not been explained, but I devised a large empirical correction to allow for it which is still in use.
8 I was trials officer and was taken down for a cup of cocoa in the stokers’ mess – it was the first time that a cup would stand on a mess table without vibrating off!
9 H J S Canham, ‘Resistance, propulsion and wake tests with Penelope’, Trans RINA (1975).
10 Those most involved were given a 1 ft length of the rope – mine is still in use as a doorstop as I write.
11 It is said that one specification read that ‘all right angles must be more than 93° or less than 87°’.
12 P Sims and J S Webster, ‘Tumblehome Warships’, Trans SNAME 1977.
13 D K Brown, ‘The Battleworthy Frigate’. NECI, Newcastle 1990. This paper was used as lecture notes for naval constructors at University College, London until 2000.
14 Old damage control school motto.
15 Most of those that were not damaged had only just arrived when the fighting stopped.
16 It has been said that a point defence missile system is intended to defend a point that would not need defending if the system were not there.
17 G A Ransome, ‘RN accidents and losses since 1945’, Warship Supplement 91,92 and 93 (1987–88), World Ship Society.
18 There was very considerable scatter in examples considered; figures quoted are 50 per cent probability.
19 Damage extent varies roughly with the square root of the charge size.
20 The use of ceramic or composite armour is often proposed. For the same level of protection Kevlar would weigh about a quarter that of steel, but cost 15–20 times as much.
21 There was a lot of opposition from sailors at that time to having ‘their’ ship blown up. I could not understand this, as I would far prefer ‘my’ ship to go in a useful trial than be scrapped. However, we took great care to keep the real name secret but Navy News revealed it was Naiad.
22 ‘Procuring for Survivability’ RINA Conference. D Manley, Warship 2001. This approach has been further developed in recent years.
23 At least two ‘unsinkable’ ships lie on the bottom – Titanic, Bismarck.
24 For an excellent account of the war at sea see J D Brown, The Royal Navy and the Falklands War (London 1987). This book is particularly good on the assembly of the force and operational aspects not covered here. Technical aspects are covered in the Defence Committee report Implementing the Lessons of the Falklands Campaign, HMSO May 1987. The principal Ship Dept witness was the Chief Naval Architect, Keith Foulger, whose clear and comprehensive evidence comes through in the report.
25 He received the OBE for his services to the Task Force. A summary of his report appeared in JNE.
26 They had been tested but against high-velocity bullets which did not cause fragmentation.
27 Beards were shaved off to ensure the mask fitted.
28 Some larger men had difficulty in getting through manholes wearing full kit, suggesting that damage control exercises had not been fully realistic.
29 Hatches and doors had to be opened for the crew to move to action stations, which took 8 minutes. Perhaps one of the major lessons is the need for the crew to live close to their action station, obviating the need to open up the ship just as attack is imminent. Sleeping below the waterline was prohibited.
30 In the last Arab-Israeli war both sides lost about one third of their tanks and aircraft.
31 Aluminium in bulk does not burn.
32 Small quantities of ordinary wood are acceptable, but ‘fire-resistant’ wood is not, because of the fumes given off when in a fire.
33 Yield strength is the maximum stress at which elongation is directly proportional to load. UTS (Ultimate Tensile Strength) is the stress at failure in tension.
34 Tests showed that B quality could stop a fast running crack at – 40°C at a stress of 12 tons/in2. A quality was similar.
35 K Hall et al, ‘Materials For RN Submarines’, RINA Symposium (1993).
36 Proof stress is that corresponding to 0.2 per cent extension equivalent to yield strength in metals where the yield point is not well defined.
37 ADM 167/133 (PRO).
38 The author worked on her as an apprentice in the 1940s.
39 The hydrofoil Speedy was weight-critical and could not take off at over 117 tons. On commissioning, the builders gave the captain a 1-pint tin of touch-up paint and told him it was to last at least one commission.
40 The social life was splendid.
41 A token 1/16 per cent per day is allowed for mechanical damage to the paint.
42 One millionth of a metre.
43 R L Townsin et al, ‘Speed, Power and Roughness’, Trans RINA (1980).
44 M Barret, ‘Illustrious – Effects of no anti-Fouling paint’, Naval Architect (March 1985).
45 94MM was used briefly on SSNs but was soon abandoned because of its high mercuric chloride content.
46 Founded about 1840.
47 The author was responsible for painting for many years.
48 One of the most horrifying documents I have read. No department was responsible for lifesaving equipment; the inflatable lifebelt had been condemned as unsafe on trials in August 1939 but remained in production throughout the war. In Arctic waters a survivor on a Carley float would live for about an hour, and in temperate waters for several hours.
49 This author was on the Lifesaving Committee in the mid-1970s.
50 Overload capacity 27. There was also an 8-man raft for small craft.
51 For some reason supporters of round versus oval rafts waged war with religious fervour.
52 Dr John Coates RCNC, who has contributed to this and other sections, received the OBE for his work in testing lifesaving gear.
53 When the Indian frigate Khukri was sunk during the Indo-Pakistan war of 1971, most of her lifesaving gear was destroyed. I was told this by one of the few survivors, who had an Olympic medal for swimming.
54 This suggests that damage exercises had not been realistic.
55 There can be problems from subcontractors. The gas release on one unit proved unreliable. The actual manufacturer was horrified to learn that his unit was used in lifesaving. It was intended for pub soda siphons where if it failed first time a thump would ensure it worked next time.
56 H D Ware, ‘Habitability of Surface Warships’, Trans RINA (1986). This was written when Harry Ware was on my staff. He liked to be referred to as the last Chief Draughtsman, a historic title later changed to PTO(l).
57 The Majestics were intended to have cafeteria messing at the end of the war, and there was plenty of experience in US-built ships such as escort carriers.
58 There was a near-mutiny in Vanguard when she introduced a cafeteria, but this seem to have been due to teething troubles.
59 This involved using lower bunks as seats.
60 Warrior (1860) had a laundry!
61 Galley floors were among the very few areas of complaint in the 1980s.
62 A J Sims, ‘The Habitability of Naval Ships under Wartime Conditions’, Trans INA (1945); N G Holt and F E Clemitson, ‘Notes on the Behaviour of HM Ships during the War’, Trans INA (1949). The discussions of these two papers are particularly valuable.
63 One submarine, without air conditioning, made a routine report of air temperature and humidity in the boat – the reply said that the conditions reported would not support human life.
64 H D Ware, ‘Habitability of Surface Warships’, Trans RINA (1986).
65 The design owes a great debt to Reg White, then a leading draughtsman (retired as chief).
66 Typical early installations are described in R N Newton, Practical Construction of Warships (3rd edition, London 1960).
67 H D Ware, ‘Habitability of Surface Warships’, Trans RINA (1986).
68 An example was the carrier Vengeance during Operation ‘Rusty’ in December 1948, an exercise in the Arctic to test the effects of extreme cold weather, in which a crack ran right across the flight deck and down the sides.
69 R W S Easton [Managing Director, Yarrows], ‘Modern Warships, Design and Construction’, Council of Engineering Institute, Glasgow 1983.
70 Fabricating the deck separately had other major advantages. With it upside down, all the pipe and cable runs could be installed easily.
71 Bath Iron Works (Maine) were the pioneers in this approach.
72 P J Gates, ‘Cellularity: An Advanced Weapon Electronics Integration Technique’, Trans RINA (1985).
73 Many of the claims in technical journals were greatly exaggerated. It was implied that an AS frigate could become an AA ship in a few days.
74 D K Brown, ‘The Duke Class Frigates examined’, Warship Technology, Part 1 in No 8, Part 2 in No 9 (1989).
75 A substantial amount of the savings attributed to competition in the 1980–90 era was actually due to improved building methods.
76 D K Brown, ‘Sandown’, Warship Technology, Part 8 (1989).