[gurps] Ultra-Ships according to Vehicles

[David Scheidt]

On Thu, Feb 5, 2009 at 2:21 PM, Onno Meyer <Onno.Meyer at gmx.de> wrote:
> Take a 375-ton catamaran, powered by 30 MW of hydrojets. The
> engines give 300 tons of motive thrust.
>
> With no hydrodynamics, the drag is 6,879 and the speed is
> 26.6 * 2 (planing) * 1.1 (streamlining) = 58.5 mph.
> With mediocre lines, the drag is 1376 and the speed is
> 45.5 * 2 (planing) * 1.1 (streamlining) = 100 mph.
> With average lines, the drag is 688 and the speed is
> 57.3 * 2 (planing) * 1.1 (streamlining) = 126 mph.
> With fine lines, the drag is 457 and the speed is
> 67.7 * 1.1 (streamlining) = 72.3 mph.
> With very fine lines, the drag is 344 and the speed is
> 72.2 * 1.1 (streamlining) = 79.4 mph.
>
> So in order of efficiency the lines are average, mediocre,
> very fine, fine and none. While it makes sense that a
> planing hull might beat a displacement hull, it seems a
> bit odd. Comments?

Any ship that goes much faster than its hull speed (which is about 1.3
times the square root of the length in feet at water line, answer in
knots) is going to be planing, even it's not a hull that's well suited
for it.  In a non-planing hull, it's a lot more expensive to go a bit
faster than in a planning hull, and it can be terrifyingly dangerous.



-- 
David Scheidt
dmscheidt at gmail.com