Asymmetrical Hull Advantage ?

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Light Keeper's Kid
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Asymmetrical Hull Advantage ?

Post by Light Keeper's Kid »

Is there a hydrodynamic advantage over a reg. hull and do you get hydrodynamic push on the hull sides in the rear after the water passes the widest part of the hull :?:

Mike
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gerald
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Re: Asymmetrical Hull Advantage ?

Post by gerald »

Basically you can have three distinct shapes for small paddled craft--and myriad variations in between. Those three shapes are Fish Form (wider in front of the center of the boat), Symetrical, and Swede Form(wider behind the center of the boat). Generally if you want to do an asymetrical boat you should stick within 10% of the center though you can go more for certain reasons as long as you are aware of the tradeoffs.

Swede Form is generally acknowledge to be a trifle faster. Radical swede form can cause problems with directions stability. I like the way it looks best also.

Fish Form is also touted to be faster by adherents to this shape. Might be something to this because most REALLY fast surf skis and some K1 kayaks are a modified fish form. I say modified because it might not be totally apparent that they have more flotation volume in front of the center of the boat because it might be the depth and shape of the bow/rocker section and the stern/rocker section. Boats like this tend to need a rudder for directional stability. If I were to design an all out sprint kayak it would probably be like this--with a rudder. My 20' X 20" Stilleto is designed with a rudder. Interestingly enough you can design a boat that has more flotation in front of the paddler yet appears to be a swede form shape. The Stilleto is a little like this, but with a elliptically shaped cross section on the hull rather than paraboloic. This is for more stability. Stability?...with a 20" wide hull? Yes...as much as possible. As you can see there are degrees of variation in all boat designs. Simple little things--boat hulls...

The Symetrical hull is simple a middle of the roader. Some say this is best for speed, best for handling, best for....well....whatever. Everybody has their own ideas...
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Re: Asymmetrical Hull Advantage ?

Post by Light Keeper's Kid »

Redneck Translation,It'll make it look Fast :P

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gerald
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Re: Asymmetrical Hull Advantage ?

Post by gerald »

you hit it on the head. For general purpose designs it all boils down to what looks good to the designer or the future owner. Most of the technical details can be ignored...
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Re: Asymmetrical Hull Advantage ?

Post by bowgarguide »

This is a non supported view, just my take on the asymmetrical shape, it seems to be more stable since your weight is in the widest part of the boat. Looks good to.
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Re: Asymmetrical Hull Advantage ?

Post by preacher »

This discussion is causing me great PANIC. If my brother is wise as I think he is, he will let me paddle the boat FIRST. :mrgreen:

The more I look at his boat the better I like the shape, but my small experience is becoming a vast learning curve. At least I have one boat that paddles well and fishes better, I can always fall back on that design.
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Re: Asymmetrical Hull Advantage ?

Post by bowgarguide »

Preacher
Dont panic,I built a boat for my grandaughters that was 12 ft 28 inches wide at the bottom
asymmetrical ,it was super stable and a great little boat,the girls stand up in it and walk around,
I did have to add a keel strip
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gerald
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Re: Asymmetrical Hull Advantage ?

Post by gerald »

preacher wrote:This discussion is causing me great PANIC. If my brother is wise as I think he is, he will let me paddle the boat FIRST. :mrgreen:

The more I look at his boat the better I like the shape, but my small experience is becoming a vast learning curve. At least I have one boat that paddles well and fishes better, I can always fall back on that design.
Don't panic. I think your boat is an interesting project. If you build it--you have to try it first just to test what you did. That's what I always say...
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Re: Asymmetrical Hull Advantage ?

Post by AyJay »

Fish Form = less drag, but less length over which to initially displace water to max beam

Swede Form = More drag, but more lenth over which to initially displace water to max beam

These factors roughtly offset at most lenths if the shape offset is fairly conservative.
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