Finless T-Belly

What works and what doesn't. Share design ideas, references and contacts for paipo board builders.

Re: Finless T-Belly

Unread postby krusher74 » Thu May 31, 2018 2:35 am

Lots of interesting design elements going on there, will try to come have a go on it this winter! 8-)
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Re: Finless T-Belly

Unread postby zensuni » Thu May 31, 2018 12:49 pm

Do you have any video of the boards in action ? They look great and the design is intriging, I am very curious to see them in the surf.
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Re: Finless T-Belly

Unread postby nomastomas » Thu May 31, 2018 1:23 pm

On my to do list....
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Re: Finless T-Belly

Unread postby nomastomas » Wed Jul 11, 2018 9:58 am

I've had the opportunity to ride the FX a couple of times now, and I have received feedback from a customer who owns a G2, G3 and FX, as well as plywood paipos. Our consensus opinion is that the FX performs as well as any finless prone board. And as a a finless shape, it takes different lines than a finned prone board, requiring more of a go-with-the-flow approach. I had high hopes that the channels would significantly improve the hold, but that has not been the case. In fact, the channels are not worth the effort to shape and glass them, both being a PITA. As you would expect, the board is fast when it finds its line, and loose and eager to spin (if you enjoy that sort of thing). Not eager to take and hold a highline for more than the time it takes to turn back down the face. While faster than a soft prone board, it is definitely slower than my finned boards. Bottom-line: not my cup of tea....

My experience with the FX shape dovetails quite nicely with my recent fin experiments with the G5. I have been using less fin area by using the rear boxes for the largest fin and either a smaller front fin or no front fin. What I have found is that placing the larger fin in the rear enhances turn response, especially in smaller waves. But, hold in critical parts of the wave varies directly with the amount of fin area. During the recent Fabio swell, I ran a twin set up with 4.6" fins in the rear position. Seemed to be plenty enough fin area. On the drop-in on 5ft waves, I found that on landing there was a bit of drift down the face, maybe a foot or so, before rail and fin engaged fully. That drift feels like a slight wash-out or stall. With a quad set up, the board will fully engage immediately and almost leap forward on landing. I really enjoy that feeling and the lack of that feeling is what turns me off to finless. But the standard large fin front, small fin rear quad set up ends up being more carve-y than pivot-y, turn-wise.

Next steps will be (1) sell the FX to someone who appreciates the finless gig more than I, and (2) add a 3.7" front fin to the 4.6" rear fin in an attempt to strike a happy medium between hold and turn response.
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Re: Finless T-Belly

Unread postby bgreen » Wed Jul 11, 2018 4:40 pm

Thanks for the update.

I agree that a finless board draws different lines (and different finless boards draw different lines).

Whether the FX performs as well as any finless board is a big call. I've gone down a few different board design paths, one of these paths started with one of Larry Goddard's designs (I'm trying to recall the original model I replicated) . Now I am on number 7. I've ridden them all finless and finned, and have mostly left the small fins in (less than 5"). The exception is the current board, which I've only ridden finless. It rides as deeply in the tube as I'm capable of and I've not been tempted to try fins as yet. I have a trip coming up to South Africa, so that should be a good test.

I 've never tried channels, my latest board has a deep double concave. An interesting development will be what direction John Galera goes. He rides his finless boards in large Hawaiian surf. He has been given a twin fin which he is going to ride. I'll follow his experiences with interest.

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Re: Finless T-Belly

Unread postby rodndtube » Thu Jul 12, 2018 11:29 am

Nomas, I find the same thing to be true in using skegs: quickness with precision and speed coming out of turns. Much of this observed and experienced with a couple of other guys riding everything from Xylem wood (with and without fins), bodyboards, surf mats and finned paipos. It is a different way of riding, finned and finless, and everybody has there preferences and I can certainly admire both.
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Re: Finless T-Belly

Unread postby krusher74 » Fri Jul 13, 2018 12:53 pm

Interesting to hear feedback on the finless. (the FX looks to have a lot of curve in the template which would slow it up?)


The only experience I had was with the one fin-able board I had, when I took the fins out it felt much faster to me.

But the perception of speed can be an odd thing. I think as humans we feel a change in speed more than a constant. So think an acceleration from fins on a turn maybe make finned boards feel faster. But the finless could have a faster average :?

Does anyone know the actual science of fin drag? I read the faster a fin goes the more drag it creates. But do they actually create drive forwards or just aid direction change? And that finless just goes faster and faster as the wave goes faster. :shock:
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Re: Finless T-Belly

Unread postby nomastomas » Fri Jul 13, 2018 2:22 pm

The lack of scientific rigor plagues all surfcraft design theory. And, yes, we are all left with mostly subjective data on which we hang our design theories. Subjectively, I can say that surfing finned is to me more enjoyable than surfing finless, regardless of the size of the surfcraft in question. I can also say that, from experience, there are sections I can make finned, that I wouldn't make finless. But whether that is because I'm going faster or because I don't slide down the face, I couldn't tell you.

But it's not all about reducing drag. Drag, in general, reduces speed. The relationship is inverse; more drag = less speed. Fins do add drag to the total "form drag" of any surf craft. Total absence of drag leads to maximum speed, but at the cost of control. Drag figures heavily in control, whether it be increasing the drag on the rail of a finless shape to execute a change of direction, or using the drag of control surfaces, i.e. fins, to allow the surfcraft to reach and maintain position in the most powerful part of the wave. Turning up a wave face (finless or finned) slows my speed due the the drag I must apply to initiate the turn and due to the force of gravity acting against my intended uphill path. But such a maneuver sets me up for an increase in speed when I turn back down the face, stop applying drag, and stop fighting gravity.

And, just to muddle things a bit, those legs and feet trailing behind the prone rider also produce drag, and at times are used for control surfaces.

For me it all boils down to the lines you want to draw. The line I prefer is to land mid-face on the drop, regardless of the size or steepness of the wave, and accelerate immediately, without drift or sliding down the face. I then use that speed to execute my next maneuver, which could be could be a lip bash or a cuttie, or simply holding a highline, depending on what the wave has to offer. I have found that a properly finned board is the best way for me to achieve that line. If, like me, you can't draw that line on a finless board but want to, we should talk. If you can draw that line finless, then congratulations, you have little use for a finned prone board.
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Re: Finless T-Belly

Unread postby rodndtube » Fri Jul 13, 2018 3:48 pm

One naturally thinks that fins add drag, or slows the board. Thinking back to the series of studies and the book by Lindsay Lord, Naval architecture of planing hulls, he found that a 2:1 ratio (length to width) was the ideal shape for speed (coincidentally, this is generally the bodyboard ratio). If three large regular fins (e.g., 5 to 8 inches) were added to this 42 x 21 inch shape there would be considerable drag and one could conclude that natural speed is slowed down. However, if the fins were smaller (e.g., 2 to 5 inches) and foiled, the speed equation could change. For example, in "Surfboard fin science," at http://finsciences.com/surfboard-fin-science/, Doug writes:

    "Fins do two things, and only two things. In terms of science, fins create two forces, and two forces only. Surfboard fins create lift, and fins create drag. That’s it. In general, you want more lift per unit of drag–just like with airplane wings, boat keels, propellers, helicopter blades, and car spoilers. The laws of physics aren’t suspended for surfboard fins.

    When we’re talking about lift, we’re mostly talking about sideways (horizontal) force–it either helps you turn or resist turning by giving you something to push off of. (Of course I say mostly because fin splay (tips set wider than the fin bases) or in the case of our fins, winglets, give some component of lift vertically).

    In general, a fin moving faster generates more lift (side force) than a slower-moving fin. The design takeaway is that IF your fin is capable of producing good lift, THEN you can make it smaller, and THEN it will go faster, and THEN will produce even more lift–and THEN go even faster still. In surfing, we feel “more drive” as efficient fins generate lift (sucking force) with more speed. This lift or sucking force is why efficient sailboats like America’s Cup catamarans can sail toward the wind at several times the speed of the wind. Wings–and surfboards, are effectively sucked forward by the force of lift, and increasingly so with speed. In the case of airplanes, the sucking force of lift puts gets them airborne."

Then there are the holding and turning for speed aspects that Nomas mentions above. Nonetheless, we all enjoy riding different boards for different reasons and the enjoyment is at the heart of learning.
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Re: Finless T-Belly

Unread postby krusher74 » Sat Jul 14, 2018 2:33 am

So with a twin fins or quad the outer fins being single foil like plane wing can give lift. But central fins being twin foil would just create drag? :?

Tried these Thomas https://vimeo.com/24847687 (rastas "spiral" talk sounds like a loads of hippy bullshit to me. lol)
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