MyPaipoBoards Forums

Hi Bob
Like I see it as clear as day in my head?? The last 1/3 of the rail must flow water like a fin. You can take any fin example you want from nature or engineering but they all have knife shaped release points, most square shaped prone boards have round, oval almost squarish release points wanting to cause cavitation and slow it down, I think that’s why the ply wood paipos have that fast darting path, because they are so thin but if slightly off pitch they lose lift quickly, that’s my theory??

I get most of my best perspectives from under water shots of board tracks there are lots you have to surf the net a lot find them

Unlike a fin in water or a wing in the air or water, "flow" on a prone board is confined to only one surface, and that is the surface in the water, i.e. the bottom or hull. Yes, for proper release (of water) there needs to be an edge at the point that the water leaves the bottom. Water is actually sticky stuff, and will cling to surfaces until gravity pulls it away or until it encounters an edge. Hold a piece of PVC pipe or any round object under a faucet and notice how the water attaches to, and flows around the pipe until gravity finally pulls it off the bottom. Likewise, hold any object with a hard edge under a faucet and notice how the water falls away as soon as it encounters the edge. There is turbulence at the release point, as the laminar flow along the bottom is disrupted by the edge. (I wouldn't call this cavitation, which involves the vaporization of water due to excessively low pressure such as that produced by the rear-facing surface of a propeller blade at a high rate of spinning.) But this turbulence doesn't impact the speed of the hull, which has already moved past it. So, those bubbles that you see in underwater photos coming of the tail of a surfboard is the turbulence caused by a disruption in the laminar flow along the bottom created by the edge of the tail/rail. Now, if the release point is round, water will wrap around it and this will cause drag. "Squarish" release points are good, rounded release points are bad as far as preventing drag is concerned.

Chrispi,

I went looking through your posts to see if I can find what you meant by tapered. Your latest description was more about the rail shape than the boards foil, which is what I thought you were talking about.

Here are two photos of yours that I thought may show what you were talking about - thicker up front to a thinner tail.
Regarding hard rails, the first board of mine # 2 had rails so hard that when the board was washing around my feet on the shore, it superficially cut my foot. The rails have over time become rounder. Finless probably compensates for somewhat more drag as described by Nomastomas. I like the S decks and don't feel any great performance loss compared to the other boards that had a different foil.
Bob

Yes! Without fins, you need something to hold the rail into the wave face. Round edges hold better than sharp edges because they don't release water as well. The tucked-edge rail is a brilliant combination of round and hard. It allows water to wrap around (providing hold) but only until it encounters the bottom edge where it is released to (promote speed). I agree with S-shape foil (distribution of foam nose to tail) being ideal for prone boards. Over time I have moved the center of mass on my shapes more toward the mid-point of the board. It allows for a more level take-off position, and keeps the majority of the foam under the mid-section of my body.

Nomastomas,

I probably should have posted the full sequence. I've retained the S deck but have gone a lot thinner than Larry's original.The attached are Board #1 from the sequence. A fun board but it wasn't so easy to duckdive hence the move to a sleeker model which was faster.
Bob

Here is board 3 from the series, I wanted to see if I could go thinner and narrower and retain the speed of # 2. It wasn't as fast as I wanted & harder work. It would be interesting to ride it again and see what I think but it has gone south. Note the hard rails on the tail.

Board 1 dimensions 4' 5 3/4" x 21 3/8" x 2 13/16"
Board 2 dimensions 4' 5 3/4" x 21 3/8" x 1 7/8"
Board 3 dimensions 4' 5 3/4" x 20 0/0 " x 1 5/8"
Board 4 dimensions 4' 5 3/4" x 21 3/8" x 1 7/8"
Board 5 dimensions 4' 5 3/4" x 21 0/0" x 1 7/8"
Board 6 dimensions 4' 5 3/4" x 21 0/0" x 1 7/8"


Board 3

Yes, at a certain point, depending upon rider mass, low volume interferes with the shapes ability to plane effectively. I found the same thing as you when I dropped vol from 22L to 21L.

Very nice boards with some groovy channels and tail drops. Can these boards do spinners?

nomastomas wrote:Yes, at a certain point, depending upon rider mass, low volume interferes with the shapes ability to plane effectively. I found the same thing as you when I dropped vol from 22L to 21L.

Aloha, do you have video of you charging big suf ? What kind of do you ride? Is skeg or skegless?

I absolutely love this subject. And this forum holds huge amounts of information and in site much more than Swaylocks I think, they seem stuck on the same old tack forever. My can you improve body boards experiment has been running for about 20 years. The saying the more you know the more you know you don’t know has more meaning now than when I started this naive slightly egotistical project. I now have this large collection of past experiments and knowledge but I never collated it .That is the number one block to my project is verifiable performance parameters I’m not 100% certain about what’s going on under my boards .There are a few flat water flow pressure shots around but not on a vertically jacked water face . The only parameter I have is doing board swops in the water, when I get on the latest body boards, I am impressed with the bouncy for their size but fell like a wet blanket when riding. My boards have a hard crisp very connected felling when riding. I think the transition zone between been in and on top of the water is the most over looked part of wave riding, it happens twice on every ride cycle. I think???

I think the trailing edge should be as tin as possible , but makes serious injury possible but what is the cost for breaking out of the envelop , My leading edge has put 15 stitches in a carelessly dangled leg in the line-up . I have been experimenting trying to inlay Mylar strips into the trailing edge getting fish like fin geometry with some safety .

Howdy...no vids, don't charge anything over 10ft "Californian", ride Thomas Patrick T-Belly G4, don't ride anything without fins. Is there a point to your questions?

Hello Papa Paepo o ,

My background was stand-up surfboards. I've never tried to do a spinner in my life. Guys who have ridden boogie boards like Krusher & Trevor, probably do them routinely on their finless boards. My boards are also longer than theirs so I suspect spinners would be more difficult - but I could be wrong. I watched some recent video of Mike Stewart and he uses them very functionally. I've been meaning to post up a link.

Hello Nomastomas,

I don't think it was just reduced volume - I also reduced width. An alaia or a HPD and the paipo ridden in Hawaii can scoot.
Yesterday I was thinking of adding some width but retaining some scoop in the deck. A discussion I've not had with the shaper as I haven't fully tested out the latest board. I have a suspicion that I've been riding the board in the wrong sorts of waves - time will tell. The other variable, which was present on my fastest board, was a flat-as bottom. Later boards have had concave or concave + wings. My quest has been a board that duckdives with ease, is fast and can ride a tube.

Hello Chrispi,
The other big variable with your boards is obviously the foil. I'd be curious to see how the base went without a foil.


Bob

Sorry I seem to have got sweped away thierrrr I so whant to be normal and talk with the big boys

Chrispi,

I don't know what you are apologizing about or who the big boys are - I'm still tring to understand your comment: "That looks very nice , all it needs is to finish all the release points or were the water leaves the board with a taper".

I was wondering whether this design is ideally suited to your foils or whether you have tried it on boards without foils , hence my comment.

Interesting you mention a thin trailing edge, I found that a thicker trailing edge gives more run out onto the shoulder.
I like volume, flat bottoms, soft front rails and squared off trailing edges.Not very fashionable, but it's maximised for speed.

Surffoils,

How thick at the tail?

Bob

Can’t explain myself so I added some more thin trailing edges to my favourite board

Hi Bob, I see the trailing edge as the last buoyancy of the board. As you slow it naturally drops at the tail but by keeping the tail as thick as you can it delays that drop so you get more projection, especially off the wave into a channel or over a flat spot.
CHRISPI, your boards just kill me. I love the shape. So cool and exciting to consider the possibilities.