Appendix 5

Comparisons

It is always difficult to compare one design with another, particularly when they use different codes of practice and have different roles. During 1987–8 British and US forward design groups produced frigate studies to the same requirements and these studies were made public.¹⁴

In the first phase both teams worked to the same armament (127mm gun, anti-ship missiles, CIWS and a helicopter). They both had a sustained speed of 27kts and an endurance of 5000 miles at 19kts. The UK ship came out at 4548 tons, the US at 5832 tons (full load). The major differences lay in protection, complement¹⁵ and machinery. In order to study difference in ‘ship’ design, the US vessel was redesigned to UK standards in these three aspects.

The revised ships compare:

One of the bigger differences was in structure. The US came out at 1174 tons and the UK 926 tons, a difference of 247 tons.¹⁶ Some of this was due to the US concept of ‘vital spaces’ thought so important that they should be able to operate even if the rest of the zone (see Chapter 13) is disabled. The UK view is that major damage in a zone would inevitably disable the vital space. The US ship has a much larger double bottom.

USN rules on damaged stability are much more explicit regarding the treatment of heel and trim, though the author believes this difference is reduced in interpretation. USN rules would forbid the low quarterdeck adopted in many RN ships (good!). The medium-speed diesel generators used in the USN are 141 tons heavier than the high speed units used in the UK. There are many other differences, including the compound effect by which the bigger ship needs more fuel and attracts bigger margins and grows even more. Finally, this author noted that the Limeys are thirsty, requiring 6 tons of beer and 13 tons more fresh water.

The study’s authors also attempt to estimate cost differences. Taking the UK ship built in UK as a base line 100, they suggest the same ship built in the USA would cost 108, while the US variant would cost 124 (the original US ship would cost 122 due to simpler machinery). It is a fascinating paper.

¹⁴ L D Ferreiro (US) & M H Stonehouse (UK), ‘A Comparative Study of US and UK Frigate Design’, Trans SNAME Vol 99 (1991) and Trans RINA (1994). (Note only the RINA version has the discussion at both venues.)

¹⁵ US 24 officers, 190 PO & CPO, 76 JR; RN 25 officers, 69 PO & CPO, 110 JR.

¹⁶ Some discussers (including this author) thought that the figure given was not typical of US practice. See p29 of ref 1, RINA.