NoMasTomas,
I have moved my last post in the volume thread here. I am interested in your work and input. Here is the post you made that I commented on.
Thomas,
Very nice design work. Most impressive.
I started designing bodyboards 3 years ago. I built a couple of prototypes by hand. I came up with some secret sauce early last year and quickly realized hand-shaping would be too slow for rapid proto-typing and testing. There is a “minimum” of 54 potential combinations of shape elements.
My secret sauce has some very precise contours that would make hand shaping way too slow. The CNC shaping problems are somewhat similar to machine shaping a fish tail. I contacted a west coast pro shaper about prototyping. He said he didn’t have enough time and there were no shaping machines in his area that could do the job. He did indicate that Marko might have the needed equipment.
Nonetheless, buoyancy (volume) is a critical factor for bodyboards. I’m curious. What does your formula say about bodyboard length, width, thickness and volume for a rider that is 5’10” at 170-180 lb.
Bill
Boyoboy I have problems with the OP’s ideas. My SOQ: I spent time back in the day on the north shore of Oahu with several kneeboards in the mid-four-foot range, 22 inches wide. I used boards with deep-ish knee wells to try keep from bouncing out at speed when there was chop. You don’t want to get disconnected from the board when coming down the face at Waimea, even small Waimea, or Pipeline, or Sunset, and go skittering across the surface before you experience Armageddon (BTDT!). I suppose I weighed about 180 lbs then.
First, thin nose doesn’t matter for duck-diving. What matters is whether the rider can sink it and this is a matter of the rider’s weight vs boardbuoyancy (volume). Secondarily, it’s a matter of what one is used to. I’ve had a kneeboard with too much volume… for this we use ding strings and bail out when we’re caught inside, b/c you can’t (easily) duckdive a too-buoyant board.
Second, concave(s) on the bottom don’t provide lift, here’s why: It’s immediately obvious that water has to follow the nose-to-tail profile of the bottom. If the profile lifts, such as in the transition to a concave, the water must follow it, essentially being sucked up to keep in contact with the board. The only alternative is that the board will suck lower in the water. Neither qualifies as lift. If you want to use concaves, do so, but IMNSHO they are more about marketing than functional design. Flat bottoms rule - no “diversions” to try make the water do something it doesn’t want to do. Diversions cost energy, thus slow the board.
I do like the slight concave on the deck for the reason above. It gives some stability although staying on the board is much less an issue if riding prone. It also reduces volume, but that should be accomplished by paying attention to the overall thickness.
The longitudinal center of buoyancy should be rather to the rear, to balance the weight of the rider when paddling/kicking. Too forward and the board will push, and won’t easily get up on plane when taking off. Once you’re on plane, things change greatly and buoyancy is irrelevant. On plane, what matters is the center of lift versus mass distribution of the rider. If the center of lift is too far forward, the rider has to crawl much further to the nose to keep in trim.
Now one thing about paipo riding - the mass of the rider is so much greater than what the board provides. It is left to the reader to consider the implications.
Free $0.02–I agree about concaves not adding “lift” but it seems to me that what they accomplish is to straighten the rocker curve down the middle of the board while leaving more rocker at the rails. So in theory (which is so often different from practice) the board should be faster while retaining the turning ability of the rail rocker.
Also, important is that if the transition side to side in/out of the concave is soft curve (vs the sharper edge of a channel), then when the board tries to slide sideways, like it a very hard carve, the convex shape the water is driven over will tend to suck the board into the water somewhat, adding hold.
Feel free to argue this!
Hawaiians have been riding paio boards for millenia, most of us began our surfing journey on a wooden paipo. I rode knee boards a lot too, but my right knee hurts when I knee paddle and riding on my knees is painful.
Last year I had surgery and had to stay out of the water for a bit. Then the spot I often surf at closed off a nice walkway forcing everyone to back to foot trails down a 200+’ cliff. While I was drydocked I decided to make a paipo and start back in the water with something I can easily scale the cliff trail. I ened up making 3 before I decided to give up and just ride regular boards because my legs weren’t as strong as I thought they were. These are my findings.
I made all my paipos very thin (half an inch thick) to be able to dive deep under bigger sets, if I sit one them my neck is barely above water. I expermented with outlines, rockers, bottoms and rails. The first one was based on the old Makapu’u style shape, but I added concave in the tail. These boards usually have no rocker, but with a turned up nose. I ended up making mine a little too wide, so carrying it up and down the cliff wasn’t easy. I also didn’t feel any advantage with the concaved tail. I had a hard time setting the edge and making bottom turns.
I went in the opposite direction for paipo 2, very narrow, an Alaia shape but a slight bit of rocker and a lot of Tom Wegener’s bottom and rail designs. I think this one was maybe 18 wide, and so small that it barely floated me. I had a blast riding this board and felt like I had way more control but I wanted more flotation, so I did another thicker board.
Paipo 3 had a lot of weirdness again, but it was about and inch and a half thick. It doesn’t work as good as number 2, but 2 small fins on the rails would probably fix it.
If I made another paipo, I would make a copy of the second board, but make it a bit wider and longer and closer to an inch thick.
I strongly recommend using Tom Wegner’s ideas for the Alaia designs for the rails and bottom. No rocker needed, but a bit of nose kick is good.
In response to Honolulu
“First, thin nose doesn’t matter for duck-diving. What matters is whether the rider can sink it and this is a matter of the rider’s weight vs board buoyancy (volume). “
I would argue that a thinner nose is less buoyant than a thicker nose and that a foiled, pulled-in nose offers less resistance to being submerged than a full, blunt nose. For a 160lb rider, a 30L shortboard is easier to duck-dive than a 30L mini-Simmons. But I agree that buoyancy versus downward force exerted is also a critical issue in duck-diving. Obviously, a 250lb rider would have little difficulty duck-diving either of the previous examples. Why not have both, low buoyancy and low-resistance?
“Second, concave(s) on the bottom don’t provide lift, here’s why: It’s immediately obvious that water has to follow the nose-to-tail profile of the bottom. If the profile lifts, such as in the transition to a concave, the water must follow it, essentially being sucked up to keep in contact with the board. The only alternative is that the board will suck lower in the water. Neither qualifies as lift.”
Water only “follows nose-to-tail profile” when paddling, or when the nose is pointed straight at the beach. When surfing, water flows in a variety of directions along the bottom, but mostly at a 60⁰ angle to the stringer as the board moves across the face of the wave.
“If the profile lifts, such as in the transition to a concave, the water must follow it, essentially being sucked up to keep in contact with the board. The only alternative is that the board will suck lower in the water. Neither qualifies as lift. “
I disagree. While it is true that the the water molecules in the boundary layer remain adherred to the bottom, other layers of the laminar flow are subject to the influences of other forces, such as the speed of flow, disruption of flow, etc. The change in the direction of the flow caused by the concave creates an increase in pressure along the bottom (Bernoulli’s Principle). Additionally, the curve of the concave forces water down, away from the bottom, creating lift in the opposite direction (Newton’s Third Law of Motion). The combination of these two forces creates the lift used by surfboards and airplane wings alike. A simple demonstration of these principals is the “Spoon & Faucet” experiment: Hold the concave side of a spoon-bowl against the water flowing from a faucet. The bowl of the spoon wants to lift away from the stream. Then, reverse the spoon, holding the convex side of the spoon-bowl in the faucet stream. The spoon-bowl is pulled into the stream.
“The longitudinal center of buoyancy should be rather to the rear, to balance the weight of the rider when paddling/kicking.”
I thought this as well when I first starting designing/building prone boards. But I soon learned that the center-of-buoyancy (COB) needs to be further forward, generally, at about center. For a variety of reasons, smaller boards require a later, steeper take-off. With the COB in the rear half of the board, the board wants to over-tilt forward as the rear end is lifted by the wave at the critical point of take-off, with a greater likelihood of pearling. Moving the COB forward helped to defeat this tendency. I used a trial-and-error method, moving the COB forward in small increments over 3-4 iterations of the shape until I found what I felt was the best location. It does require sliding up maybe an inch to achieve maximum planing efficiency, but I’ve learned to make this adjustment while dropping-in.
I used to think water flowed accross the bottom of the board at a 45-60 degree angle until I saw this video 2 years ago.
In general, where the bottom of the surfcraft maintains constant contact with the water (remains immersed), flow is primarily parallel to the stringer.
The surfcraft moves over the water.
Actually…“The results indicate that the majority of the lift is coming from the transverse flow, and a smaller part of the lift comes from the axial flow.” -Camber Surfboards
I am not referring to leading edge flow at the point of board:water:air interface.
Watching the video, directional flow over the tail section appears to be relatively constant and parallel to the long axis.
Apparently the video is misleaading, as the Camber guys make it clear that their results indicate that “lift” is generated primarily by the “transverse flow”.
I think we are talking about different things: leading edge pressure vs. directional flow over the tail of the board.
The flow vectors on the CFD figure indicate the same.
A few things. I’ve had 20 plus bellyboards/paipos, ranging from the Paipo Nui style style board developed by John Waidelich in the 1960s & currently made by Paul Lindbergh, a couple of boards made by Tom Wegener, a 5 fin bonzer by Malcolm Campbell, a couple of John Galera’s NoFin paipo, a couple from Huie and a pile of other boards. I have experienced noticeable lift only on the bonzer and on a couple of waves. Having said that, lift isn’t necessary to having a lot of fun on a paipo.
What I ride these days is a board inspired by the designs of Larry Goddard from the 1970s: A Paipo Interview with Larry Goddard
At the bottom of this interview you can see a small number of the hundred’s of design sheets Larry drew. You will also see a work of art by Harry Akisada who rides his own style of concave bottomed finless boards, which are known for their speed.
My first 4 Goddard inspired boards had flat bottoms and didn’t deviate too much from Larry’s flat bottom S deck concept. Attached are three photos of board #7 in a series which show how the design has evolved. Shaped and glassed by Chris Garrett (Phantom surfboards), this board has a foil more akin to a standard surfboard and has more thickness in the nose than I usually have. There are concaves in the bottom. The board has been ridden finned only twice. How does it differ from flat bottomed boards? It is not as fast off the mark, still respectable but it doesn’t take off like a lemon seed squirted. However, it is a far, far better board for riding tubes. The thicker nose also makes duck diving easier.
Lift or no lift, paipo boards can perform in all sorts of waves, ridden with fins or finless. However, as Shark Country noted leg conditionining takes time.
Bob
I’m planning something different, a surf training board, which should be used in ponds or pools to build paddle strenth. Therefore it needs a lot of volume, because it should hold the surfer at least at water level.
After having studied an already existing foam version (see https://www.surfinshape.com) I designed something strange with boardcad, but after visualizing it in 3D, I think it will be rideable too. Of course it will be a mess to duckdive, but it should work for riding some small summer waves, at least prone, if not kneeing. JoB would definitely be able to stand on… 
I integrated some parts of a hotcurl into the thing, and if I will have finished my running project, I will build it as a HWS balsa, with a non slipping cork surface…
There has been interest in HotCurl BBs, notably from Jeff Quam, though you can alos see a Nomas drawing:
https://mypaipoboards.org/forum3/viewtopic.php?f=4&t=899&p=8890&hilit=hot+curl#p8890
Pool laps with bodysurf fins and a kickboard.
Had to glue two swim kickboards together to get enough “buoyancy” to keep my arms above water for laps.
(There was no re-positioning with the adhesive within 90 seconds after contact, as stated on the spray can.)
This is just a guess, but I think that board will plow. That’s a different topic, though, than your original plan/use for it (paddling in flat water).
One thing about bottom contours for finless: the more the bottom design directly emulates fins (e.g. deep concaves and sudden double barrels around a raised stringer line (that acts like a fin), the more drag, very much like a center fin creates, will come into play. The more the bottom when designed to act like a finned board produces hold and finlike stability and steering, the more the board acts like a finned board and negates the whole purpose of having a finless board, other than not getting “kelped” as readily as a finned board.
I’ve made about a dozen finless boards. I really don’t know how many, at this point. Some have emphasized channels (a la Derek Hynd approach), some have emphasized a “hot curl” (vee, or usually double-vee/double-hot-curl) type of design, and some have combined the two. I have paid as much attention to what’s out there as I have time to pay (I’m more compelled than most, probably, because I really, really, really want to eventually make myself a finless board I’ll want to ride very regularly). Most people are either doing channels or convexities, but inevitably the one creates at least some of the other other, so they are almost always working together (or, as the case may sometimes be, against each other).
This I know beyond a doubt: designs emphasizing channels and designs emphasizing convexities are different problems, but they are similarly complex and “nuanced” (i.e. small changes are or can be big changes). Unlike with a finned board, if you are reasonably skilled (int-adv or better), you will feel every change you make to the bottom, even seemingly very minors ones (e.g. 5 min sanding with 220 on a single channel in a board with many inter-acting channels). Many of the finless boards you see being ridden very expertly and smoothly on YouTube are not that good for most riders; what you are seeing in those videos is the virtuosity of the rider at work, not the great design of the board. For the majority of even pretty skilled riders, those boards will be very difficult to ride.
One under-discussed consideration, including by some people designing finless boards: if the rider wants to spend a lot of time going backward, and having the board perform smoothly as though its ride properties are on a continuum instead of a combination of herky-jerky tendencies that tend to suddenly switch from one mode to another with hard-to-manage transitions between them, you’re now into a whole world of considerations that aren’t in play if all you want the board to do is “go straight.” The finless designs that just make a line and hold, without having to perform and be responsive going sideways or backward, are totally different than the designs that will be best on the latter counts. The boards that produce hold via “horns” in the tail of the board, for example, whether asym or symmetrical, all have to account for what happens when that horn engages when riding backward, and the uneven drag it creates when an asym design is planing flat instead of on rail (usually, the board will show a desire to hook to the side of the horn, or even want to flip over); the design and the rider both have to account for that. The more skilled the rider, the less the board has to take up the slack.
That said, for riders who come to finless (prone, knee or standing) from a curiosity about Hynd, Burch, etc., this is the best finless board and design I’ve seen to date: https://www.instagram.com/p/BRPYTpdjsxb/
I’ve ridden one. It’s better than any I made, including 3 that took the “pontoon” (my made up term for the convex columns that produce hold in it) idea into consideration in the design. My next attempt will follow it more closely. It has a better and more natural/predictable balance of hold and slide, I think for the majority of above-intermediate level riders around, than any other I have seen or ridden. I can tell you from having ridden it and the ones that incorporated ideas from it that everything on the board matters: what the channels around them are like, if there are channels, the “toe” of the pontoons and channels and their length and dept (both depth as in “find depth” and the dept of the concavities around them if there are any), and how they relate to the rail lines, how these combine with rail style, rocker and foil.
Finless boards are the height of pure board design, imo. I’ve found channels (without “pontoons”) to be as exacting and complicated to get right on a finless than a design that relies more on convexities. With both approaches, everything matters.
All of which is not to correct, just to hopefully add to your considerations.
Am interested in making prone boards and kneeboards as well, myself, so am following this discuss with interest.
I agree.
IMO the holy grail of finless surfcraft is low drag tech that improves directional control.
Batfische,
I agree it all depends on the experience you are seeking. Tail slides etc and bodyboard spins don’t hold appeal to me. I grew up riding 70s single fins so try to draw similar lines on a BB. Attached is #6 in the design series. I ended up riding it with 1.5" keel fins because the board wanted to draw a straighter line than I wanted. I looked at the instragram link you posted. It had a bit too much going on for my liking.
Bob
Maybe I’m just lazy… on a test session on a low volume board on a big day I was driven deep. No leash but I held on for dear life. Damn - I was nearly out of air by the time I reached the surface. For some reason I was expecting the board to ‘help’ me get there. I know it seems easy enough - just point it skyward and kick, right?
Having ridden longboards a lot, I found myself missing the volume.
Regarding finless prone designs: it seems like there are various ways to control with drag. Feet, flippers, arms can all be used to help maintain position and direction.
On various idiosyncratic details I like to refer to Ryan Burch’s ‘slab’ Lord Board. https://vimeo.com/15614139