Peter R Payne-Sea Knife-Blade Hulls

Has anyone seen/know of one of these boats.

I believe they were built in Maryland in the 70s

I am also looking for a book Peter wrote "Design of high speed boats" ...has anyone got a copy

 

There are threads on here mentioning your subject matter. I would be interested in seeing a clear illustration of the shape of the bottom.

 

http://books.google.com.au/books?id...&resnum=4&ved=0CDgQ6AEwAw#v=onepage&q&f=false

Looks like a very tippy conveyance !

 

The Sea Knife was an interesting project. It clearly showed that if you increase the planing surface loading AND limit the increase in hull area that results from wave action, that your could have a big improvement in ride quality.

This is obvious, but it's a difficult thing to obtain. If you look at the HYSACAT (hydrofoil supported cataraman) you see much the same effect. The higher surface loading and the smaller change in surface area results in a better ride.

The question that I wonder about is could you get a similar effect with a planing pad that was coupled a higher deadrise angle. Deadrise angle limits result from higher drag, and poor stability as the angle gets high. But what would happen if you had a pad (wider than the very narrow pads on a bass boat), but one that still that resulted in a pretty high surface loading, and coupled that with a higher deadrise angle, maybe 45 or 50 degrees. Would the hull be stable enough as a result of the pad? The idea being that a flat pad would reduce the effects of too deep a V.. And, it might still ride well because it wouldn't slam as much as a higher surface area hull would.

If you think about it, that might provide a lower "spring rate" in that when the hull comes down off of a wave, the planing area would just sink in further, but since the area isn't increasing as fast, it wouldn't slam down as hard...

Just a thought...

 

Steep deadrise combined with a pad works with some power cats, but in a mono configuration it runs into stability problems, surely ?

 

If you apply that analogy bass boats would be tipping over all the time and they don't. I think it's likey an issue with the speed of the boat, the faster you are going, the higher the available force for righting and the better off you are. Also it doesn't mean that you would carry that high deadrise all the way to the sides, maybe you cut it back at some point, or trade pad area. I used the term pad here, but I'm thinking that it wouldn't be as narrow as a bass boat pad. More like a foot or two wide to provide more stability, but still have some capability to reduce the pounding.

 

This has been done in a number of designs (even some of mine), althouh not with a zero deadrise, but with a bottom of say, 5-10 degrees, together with a steep deadrise <45 degrees outside. If you for example look at Savitskys algorithms for planing hulls in a seaway, you will find that the optimum shape for a planing surface in waves will be narrower, longer, have LESS deadrise than what is used in the traditional designs, and run at a lower angle of attack.

See for instance:
"Hydrodynamic development of a high speed planing hull for rough water" by D. Savitsky, J.K. Roper, and L. Benen.

Unfortunately I did not copy the title of the book where it was published (SNAME????), but it should be possible to find through Stevens Institute of Technology, Hoboken, New Jersey, USA.

 

Thanks Baeckmo, that's exactly what I was thinking I just hadn't seen it in practice. I wasn't assuming that the pad would necessarily have zero deadrise, a small amount for improved stability would be fine, but a higher surface loading to improve the ride might just be an advantage.

Of course it's a matter of how fast you want to go in how rough a sea, and remembering that everything is a compromise. Just musing on the plus and minus effects and wondering out loud if it had been looked at. I'll have to look up the paper.

 

You did mention 45 degree deadrise, Yellowjacket, I doubt slicing off a wide pad from a mono of that ilk would be stable either at rest or underway. The Sea Knife looks like it would flop around at rest something awful. The concept has been around for a long time, no doubt has been considered by innumerable designers, but hasn't taken off commercially, and there has to be a sound reason for that.

 

The "Sea-knifes" had an open ballast volume, that emptied at speed. There is no magic in designing a double-chine hull with high outer deadrise; its just a question of basic knowledge in marine engineering - physics.

 

So where are they ? Had to be a snag there somewhere.

 

Narrow bottom

This is a boat with a narrow bottom and low deadrise for a smooth ride with low power requirements.

No snag here, just as calculations show, rather, slightly better.

http://www.youtube.com/watch?v=cXDfQqxJ_pM

js

 

That isn't the Sea-knife, is it ? Different thing altogether.

 

No, not really. The Sea Knife achieved a smooth ride by means of reducing planing area (increased planing surface loading) coupled with a very high deadrise so that the area didn't increase substantially as the boat rode thru the waves. The concept is similar to aircraft where an airplane with a higher wing loading rides smoother than an airplane with a big wing.

The idea behind the narrow and high deadrise approach to achieve a better ride is similar, but the Sea Knife is indeed a more extreme example.

Note also that the Sea Knife had a delta shaped planing area that was much wider than a typical planing pad at the aft end of the planing surface, which would provide more roll stability when planing.

 

Many years ago I built many models to find out how the Sea Knife works. It was intended primarily to reduce the huge resistance in the low and moderate speeds. It turned out that the type had its limitations, which also is discernible between the lines of the PP report. It was very sensitive to the ratio between the different parts. The boat was easily unstable. Therefore, I abandoned that track and spent myself first at Koelbel and Clement's Dynaplan to later develop my midship interceptor. On that way it is, apart from that developing the boats with double chine and narrow bottom and much more.
It is the bottom beam that makes the smoth ride, compare with multihulls. Not primarily the deep V.


js