Can't help myself

What works and what doesn't. Share design ideas, references and contacts for paipo board builders.
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rodndtube
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Re: Can't help myself

Unread post by rodndtube » Wed Oct 10, 2018 5:57 am

My boards have had removable fins for like forever, probably since the early-1980s, initially driven by surf travel (during vacation and work travels). The beauty of removable fins is not being stuck with a static fin(s) placement and types. My center fin boxes are industry standard Fins Unlimited (true, there are different fin box lengths but I usually want 4 inches of freedom). For a long time I have been riding with a 3-fin setup, but not a true thruster as the toe-in is reduced with small side bites (about 2 inches tall, but ranging from 1.75 to 2.25, foiled but a rather standard fin shape). What I vary is the placement of the center fin depending upon the wave type and size. I usually use a 4.5 inch center fin, but have ranged from 4 to 7 inches. Flexibility is key.

I've had longboarder friends that were hating on their nice boards, complaining about how it didn't turn, turned to easily, etc. By suggesting and them trying out a different fin shape and size the board went from being a dog to "the best board ever."
rodNDtube
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nomastomas
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Re: Can't help myself

Unread post by nomastomas » Wed Oct 10, 2018 3:47 pm

Lots of good design-related issues being brought up in this thread. Here’s my $0.02:

Every good, i.e. “workable” design is an integration of all its functional elements, e.g. outline, bottom contours, rocker, fin placement, finless, etc. It’s very “Gestalt-ish”, where the whole is greater than the sum of the parts. It's important to understand how each design element influences all the others, otherwise you can end up with design elements that, while individually sound, are in conflict with others. This is what I call “purposeful design”; design based upon function, not just aesthetics.

The trial-and-error approach has been the cornerstone of surfcraft design throughout time. But, successful trial-and-error development requires both organization and purposeful design. Larry Goddard’s work is the perfect example of the trial-and-error approach applied to prone-board design. His methodology is as important as his designs themselves. To help train your mind to adopt this approach, you should keep a diary of each shape, recording your rationale for the use of every design element, notes on how the design functioned in real-life conditions, and what you might do to improve the performance. This approach will save you money in the end, because you won’t waste money on designs that are doomed to less than adequate performance due to design flaws.

None of my finned designs surf “better” or even as well without fins. The reason is that they are designed to be surfed with fins. Take the fins out and performance suffers. The front third of the rail is an up-rail which is a continuation of the belly bottom in the nose and is designed to be “forgiving”, to not catch and which, therefore, offers little hold into the wave face. Complicating that is the rear half of the board, which has a hard-edge, down rail that is designed to shed water for speed. Shedding water and providing “hold” are mutually exclusive. The design relies upon the fins for hold. So, it's not just a matter of tweaking a single design element, in this case adding or removing fins.

If you are going to use fins on a prone board, they should be placed where the rider will exert maximum pressure when turning. By studying photographic stills (both on top of the water and under water) of prone riders turning, and from my own experience it appears to me that the wave-side, rear corner is where that force is being applied on finless foam body boards. And, that makes sense given that the majority of the rider’s weight on 42" body boards is focused there when turning. But the shape of the outline in this location must also be considered. Boards are rolled onto the rail when executing a turn. A straight outline, which is what you see on most body boards, will resist turning more than a curved outline. So, having a bit of curve or “hip” in the outline in close proximity to the fins will shorten the turning radius. Likewise, having some bottom curve or rocker out at the rail will also enhance turning. Now, you could just stick some fins on a finless body board, but you would not obtain the full advantage of a finned-based design, because the outline would remain straight and the rocker would remain relatively flat. And, if you didn't add any fin toe-in, its likely that the board would feel stiffer handling. Or worse, too much toe-in and the fins would be in conflict with the straight rail causing a sense of drag when not turning.
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krusher74
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Re: Can't help myself

Unread post by krusher74 » Thu Oct 11, 2018 3:04 am

nomastomas wrote:Lots of good design-related issues being brought up in this thread. Here’s my $0.02:

Every good, i.e. “workable” design is an integration of all its functional elements, e.g. outline, bottom contours, rocker, fin placement, finless, etc. It’s very “Gestalt-ish”, where the whole is greater than the sum of the parts. It's important to understand how each design element influences all the others, otherwise you can end up with design elements that, while individually sound, are in conflict with others. This is what I call “purposeful design”; design based upon function, not just aesthetics.

The trial-and-error approach has been the cornerstone of surfcraft design throughout time. But, successful trial-and-error development requires both organization and purposeful design. Larry Goddard’s work is the perfect example of the trial-and-error approach applied to prone-board design. His methodology is as important as his designs themselves. To help train your mind to adopt this approach, you should keep a diary of each shape, recording your rationale for the use of every design element, notes on how the design functioned in real-life conditions, and what you might do to improve the performance. This approach will save you money in the end, because you won’t waste money on designs that are doomed to less than adequate performance due to design flaws.

None of my finned designs surf “better” or even as well without fins. The reason is that they are designed to be surfed with fins. Take the fins out and performance suffers. The front third of the rail is an up-rail which is a continuation of the belly bottom in the nose and is designed to be “forgiving”, to not catch and which, therefore, offers little hold into the wave face. Complicating that is the rear half of the board, which has a hard-edge, down rail that is designed to shed water for speed. Shedding water and providing “hold” are mutually exclusive. The design relies upon the fins for hold. So, it's not just a matter of tweaking a single design element, in this case adding or removing fins.

If you are going to use fins on a prone board, they should be placed where the rider will exert maximum pressure when turning. By studying photographic stills (both on top of the water and under water) of prone riders turning, and from my own experience it appears to me that the wave-side, rear corner is where that force is being applied on finless foam body boards. And, that makes sense given that the majority of the rider’s weight on 42" body boards is focused there when turning. But the shape of the outline in this location must also be considered. Boards are rolled onto the rail when executing a turn. A straight outline, which is what you see on most body boards, will resist turning more than a curved outline. So, having a bit of curve or “hip” in the outline in close proximity to the fins will shorten the turning radius. Likewise, having some bottom curve or rocker out at the rail will also enhance turning. Now, you could just stick some fins on a finless body board, but you would not obtain the full advantage of a finned-based design, because the outline would remain straight and the rocker would remain relatively flat. And, if you didn't add any fin toe-in, its likely that the board would feel stiffer handling. Or worse, too much toe-in and the fins would be in conflict with the straight rail causing a sense of drag when not turning.

It was interesting (but well known hydrodynamic theory) that on one finless board I tried a Hard edge on the back 12" of the rail. with the water shearing off the board was very loose/slid out. But with that hard edge sanded of to a 1/16th radius the wrapping water gave very good rail hold back with no slipping (used in 6ft g-land) So I think a finless and finned design can be very close. (but the best for each is maybe further away)

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