Planing hull wake shape...?

[PetterM]

Does any one have a good expression for estimating the wake shape from planing hulls?

[RANCHI OTTO]

Do you mean wake figures for planing hulls?

[PetterM]

Thanks for your reply. Need a simple expression for calculating the wake (wave) surface profile behind planing hulls (as illustrated in blue). I think Savitsky did some research and published a paper on this but then for rather large trim angels, not realistic for normal running. I have been looking around quite a bit but have not found anything that can be used. Any ideas?
I am trying to design a stepped hull at the moment a need a “quick” calculation method for the preliminary design.

Regards,

Petter

[RANCHI OTTO]

Sorry but I have never seen such formula because the transom wave profile depends form a lot of factors like speed, trim angle, bottom transom shape, propulsion system.....

[PetterM]

If the wake shape is unkown, how is conventional stepped hull performance prediction done? Is preformance determind using model test derived data?
We have done some work using Autowing, looking at the preformance of existining desgins, but it is not quick enough for doing the parameteric studies needed for deriving new designs.
Regards,
Petter

[RANCHI OTTO]

It's not easy to give you an answer....

I think that at the beginning each Architect is employing formulas derived from literature...with experience and age each Architect has his own formulas that in many cases are more closed to the real speed than empirical formulas...
I've a collection of data concerning high speed range based on KR coefficient (KR=(BHP)^0.551/(Displ)^0.476) with surface propellers....let me know if this can be useful for you.

Concerning hull shape quite all these boats have monohedron shape with 22/25 deg. deadrise.

I've designed a boat with a speed of 100 m.p.h. not using steps at all but based on my own hull shape named Arrow System Design because for me it is more important "how you reach a speed than how is the speed.."

[PetterM]

Good looking boat….thanks for your help.
Looks like I need to pull my old hydrodynamics books out then and start from first principle…
Regards,
Petter

[RANCHI OTTO]

Invest in your talent, read a lot a book and than......GO!
The first high speed boat design is like the first time with a woman.....

[PetterM]

This would depend on the woman as well as the boat…..

[RANCHI OTTO]

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