[Sailor Steve]

There are several problems involved in ship design. One of them is speed. Drag increase is more severe than in other types of vehicles due to the non-compressibility of water, and the way this forces the ship to create its own waves, which in turn build up so the ship is trying to climb a hill of its own making. One of the solutions is the fineness ratio - if two ships have the same beam (width), but one is longer than the other, the longer one will be inherently faster. The other problem is power - the ship must be longer to house the machinery necessary to provide all that energy.

Torplexed mentioned the Iowa class battleships. The previous class, the North Carolinas, were nominally rated at 35,000 tons, were 729 feet long, had a 108 foot beam, and made 27 knots on 121,000 horsepower. The Iowas were nominally 45,000 tons, 887 feet long, and had the same 108-foot beam. That extra 158 feet gave them a much better fineness ration and room for a lot of extra machinery, but even with almost double the horsepower at 212,000 shp, they only went from 27 to 32 knots maximum speed.

So the Queen Elizabeth class were 641 feet long, had a beam of 90 feet and a nominal displacement of 34,000 tons, and made 24 knots on 75,000 horsepower. Hood, at 45,000 design tons, had to be 860 feet long on a 104-foot beam to carry the machinery to make the 150,000 horsepower (double that of QE) required to push her to the desired 32 knot speed.

It's a pain in the fantail, but that's why it had to be that way.




And a pain to go through all that and not really say anything more than Torplexed did.