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PostPosted: Mon Sep 28, 2015 1:13 am 

Joined: Wed Aug 05, 2015 9:25 am
Posts: 2200
Location: Los Angeles and Houston
And, in case the above was not simple enough.

The motion of a fluid around an object can have the fluid moving in ways the fixed object cannot.

The fluid can undulate, twist, contort, etc. (turbulent flow).

While the "object," say a "rudder" cannot. It is simply a solid object.

The fluid and rubber affect each other, but in very different ways.

The fluid affects the rudder through what is basically a simple force acting on the rudder in a direction and magnitude.

But the rudder's affect on the fluid is going to be on each particle in the fluid, which then each affect the particles around them. This produces a multitude of varying motions from what looks like a single force.

Obviously this is a subject which, while I am capable of doing the math, is something that is far more involved than I had previously considered (due to having an education that applies the math I know to more stable systems). The physics I have did not go into Fluid Dynamics beyond very simplified models of idealized systems (perfect point-spheres moving through uniform temperature and density fluids of finite volume).

And without current access to the Library Database I usually used, finding useful materials on the subject is difficult.

But I would still like to find something that is capable of giving an estimate of the advance and tactical radius of turn.

If nothing else, it should be possible to just get a statistical measure of the various advances and radii from known ships, and extrapolate a generalized estimate (which I recognize would not be very precise. But it would be more precise than simply pulling a number out of the air).


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PostPosted: Mon Jul 02, 2018 8:07 am 

Joined: Tue Dec 13, 2011 1:52 pm
Posts: 11
Thoddy wrote:
ship wit one screw and 50000 PS will do 30 kn
how much PS will be required to achieve the same speed with two screws
exact values are not required but some kind of a approximative value would be fine.

I found a german statement of th K-Amt wich state -according to own experiments-
Propellerefficiency of a 3-screws ships was 0.48
and in the case of a 4-screws ship it was only 0.42

so the 3-screws ships requires less HP (about 15 percent) to achieve a given speed

they found no way to increase the efficiency of a 4 screw ship significantly.

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PostPosted: Fri Aug 17, 2018 10:56 am 

Joined: Wed Jan 02, 2013 1:15 am
Posts: 4299
The Iowa class BB's, the Alaska BB's and the Fletcher DD's all had very similar tactical Radiuses, a bit over 800 yds. For the Alaska's this was somewhat better than the turning performance predicted in the original model basin tests.

As with everything in ship design, a matter of some compromise.

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