[gurps]_[VEHICLE]_of_the_week_632_-_Archvillain's_Yacht_(1920s_Version)

[David Scheidt]

On 12/20/06, Onno Meyer <Onno.Meyer at gmx.de> wrote:
> > Not with a length of 120 feet, it's not.  Speed of a displacement boat
> > is limited to about 1.35 * sqrt (LWL).  (LWL is length on water line,
> > typically less than overall length).   To go faster, you need to
> > plane.  To plane 700 tonnes, you'd need quite a bit more power.
>
> Speed   Minimum LWL
> 10      55
> 20      220
> 30      494
> 40      878
>
> Assuming that speed is in mph or knots and LWL is in feet, that
> doesn't feel right. Destroyers do 40 knots without the length of
> a cruise liner, but they don't look like planing hulls to me.
>
> compare
> http://en.wikipedia.org/wiki/G_and_H_class_destroyer
>
> Onno

Speed is in knots, lwl is in feet, yes.  I'm not sure I believe that
these ships were really that fast.  I'd like to see a source other
than wikipedia (or the book they cite, as many other web sites seem to
use it).  However, these ships do have lots of power.

The rough rule of thumb is that you need 5 hp per tonne of
displacement to reach hull speed.  These are about 2000 tons; they've
got 36,000 SHP, a surplus of 26,000 hp.  Assuming they've got the
props for it, they were certainly capable of going faster than the
hull speed.  36 knots is way past that, though.

There are other reasons to have excess power, though.  It's useful for
resisting currents, for towing, and making speed with a big hole in
the hull after you've been torpedoed.

-- 
David Scheidt
dmscheidt at gmail.com