Hi Talador Wood,
I suggest that you sign your posts using the name you choose to be addressed by, thereby allowing responders to know how to politely reply.
I also suggest you acquire a primer on basic naval architecture and when you are familiar with the concepts, read up on planing, Your physics background should allow you to pick up the concepts without great difficulty. A large part of the failure to communicate lies in your misuse of the term ‘planing’, which has a fairly specific meaning, which it has held consistently for many decades, and which is not significantly present in long , narrow, round bottomed hulls. Planing implies that the centre of gravity is raised above the rest position, as a result of dynamic effects, and the degree of planning is how much of the weight is supported by those dynamic effects. The rest of the weight is supported by buoyancy effects, and that part may be called the displacement lift or support.
Hulls are not “subject to” Froude number, it is a dimensionless number which represents gravity scaling, like Reynolds number represents viscosity scaling, Mach number represents compressibility scaling etc. All hulls that operate at the surface will have a Froude number depending on the speed and their linear dimensions. Those with similar geometry will create waves which are scalable by Froude number. When their geometry is significantly different, scaling wave effects by Froude number becomes unreliable.
Have you read the range of application for the Crouch formula? As an engineer you should appreciate that empirical formulae should not be applied outside the range for which experimental verification is available. I don’t have the information at hand, but if I remember correctly it applies to relatively wide hull forms. In any case, it is not new, and was not new when I was more familiar with it in the late 1970s. I doubt very strongly that it is applicable to hulls with L/B ratio of 12 or more.
You can safely assume that the range of Reynolds numbers for a full size proa, even a fairly small one, will preclude much laminar flow, but then you should be able to work out the Reynolds numbers for yourself, and see if they are in the range you are familiar with.
Cheers,
Peter
From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au]
Sent: 21 March 2015 04:57 PM
To: harryproa@yahoogroups.com.au
Subject: Re:: RE: : Re: : Re: : Re: : Re: : Re: : Re: [harryproa] Re:: Diesel Electric Drive
Peter, "Whoever you are,
1. We consider it civil to identify yourself by signing your posts"
Talador Wood is a character in a novel I am amusing myself by writing. I prefer to remain semi anonymous because of the open nature of the internet. No disrespect is intended to anyone.
2. Your misunderstanding of ship hydrodynamics appears to be deep. In spite of Rick and others remaining polite and explaining their points both accurately and in detail, using the standard meanings for naval architectural terminology, you persist in misinterpreting their responses to the extent that I am beginning to suspect trolling.
Except for the trolling part I somewhat agree. I think the standard meanings for architectural terminology aren't really applicable to modern designs so my fall back position is Physics terminology. And yes I do have gaping holes in knowledge about ship hydrodynamics, I am getting quite the education regarding the Monk effect right now from a NA.
3. You claim some background in aerodynamics and seem to think this can be applied without further investigation to a very different field of fluid mechanics. The people you are dismissing are knowledgeable in their field, can you produce any evidence that you are educated in fluid dynamics, so we can be persuaded to continue to take you seriously?
I am not educated in low Reynolds number fluid dynamics and you should not take what I say seriously. I certainly don't take what I say seriously.
However, I am trying to be truthful, my original post was simply to provide some ballpark numbers to help calculate hp and kW requirements for the Proa.
As an aside I have worked for TI, JPL, helped design the guidance system for the Tomahawk Cruise Missile, built and partially designed an airplane including designing the prop and transmission, created and sold a gaming company, blah, blah, blah got a couple of degrees in college, but mostly I just play.
4. A submerged bulbous bow and narrow hull are normal characteristics of a high speed displacement hull. Any similarity to a submarine hull is because they are both designed to work at high speed in a displacement mode, whether at the surface or submerged. Furthermore a Swath type hull would have a reduced waterplane area (by definition – look it up) which this does not have beyond the consequences of a generally slender hull. A submarine’s hull would also commonly have a smaller length to beam ratio to minimise surface area, for the given displacement.
I think the operative phrase here is "high speed displacement hull" which is not the same as a displacement hull that is subject to the Froude numbers. And I think that the Crouch calculations can be applicable to a high speed displacement hull.
Do you disagree? Really, I am not trying to start a fight.
Posted by: "Peter Southwood" <peter.southwood@telkomsa.net>
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