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

[Thomas Thrien]

Onno Meyer schrieb:
>> 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
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>
>   
The formula 1.35 * sqrt( LWL ) is a given fact for ships with a
conventional hull form (whatever "conventional" means in this context).

But boat builders have invented special shapes for boat hulls in the
1910s (namely Claus Engelbrecht and Arthur Tiller) that allow higher
speeds for displacement vessels. One attribute of such a hull is its
length-to-width ratio of 5:1 up to 10:1. Looking at the G and H class
destroyers Onno mentioned, they have a length of 323 ft at a width of
33ft, so this may fit here. This special hull forms allowed 25% and more
speed above the "bare hull speed" (up to 160% as stated in one article ...).

To be honest, I do not understood the hydrodynamics behind this,
although the articles are written in German. But it looks like that the
Archvillain's Yacht COULD be as fast as stated by Onno, even by the
given length, if it will have the proper hull shape and enough power (I
did not check the power). As Engelbrecht and Tiller made their invention
around 1910 also the time frame fits (there is a newer concept, called
DG Hull, invented by Theodor Eder in 1990 that looks for me to be even
more efficient).

Any specialists for hydrodynamics on the list? As I said above already,
I am not sure if I got it all correctly, so perhaps someone may lookup
the sources (using Google) and correct me where I am wrong.

Regards

-- 
Thomas Thrien
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