Right? I dunno if it’s the buoyancy of the rail so much as the additional planing area of the fat rail itself lifting it out of the water and the way it holds goes all to hell.
I’m a firm believer in thin boards, considering what I started out with that’'s no surprise- Newport Paipo Concave Vector
doc…
Gday Doc,
I’m not sure on which web-sites I acknowledged your assistance on, but this one I did: http://home.brisnet.com.au/~bgreen/world/World.shtml
There was a guy in Australia who made boards, with removable tails. It didn’t catch on as far as I know. It might be possible to make a modular board, where you could try different rails, tail, nose etc - “bolt” on and off. Not a commercial idea, but to test design parmaters. One for the mad scientists.
I see Krusher had some comments on hard rails - I sought to replicate my favourite board, twice. None were exact copies. Number # 2 in the series, tended to track a bit. I looked at the rails, with the shaper and they were harder. The board went better with more rounded rails (they were pretty sharp). This was on a board ridden finless. I loaned the board to a friend, and hope to get it back next year, when I do a trip down his way - he seems to have like the refined version.
I think on your advice, I got Huie to make me a 1" thick board. It was fun but I missed a few waves, because of the reduced volume. I’ll drag it out again one day.
Bob
Looking at the Slater/CI board, I see a linear channel with what looks like concave panels forward and on either side of the channel.
The physics principle of my design is all about the curves – in 2 dimensions.
Second drawing air into the channel would neutralize my channel’s curved contour effects – low pressure holding the tail in place. The curves of the sidewalls create a bit of an optical illusion relative to the bottom.
Charlie’s rail edge is fairly hard. But I would say the edge has at least a 1/16" diam. round. The rail shape I have been playing with uses top and bottom chamfers witrth a 3/4" rounded mid-section – not that there is anything revolutionary about that shape.
Finally, it would be very difficult to hand shape this channel by peeling back the bottom surlyn/polyethylene of a standard BB, especially the channel bottom contour.
The simplest way to evaluate this channel is try it in two boards of the same shape, one with and one without. Granted the one with the channel would have slightly less volume.
Does the physics of your design work differently than this? or any board with just a central tail concave that exits the tail?
Based on my understanding of the physics, yes.
I stumbled across the physics behind my channel design 10 years ago.
I made a quick beach bodyboard for the grandkids out of 3 sheets of unglassed, low density XPS housing insulation 3.5 years ago. After that, I decided bodyboard builds were a good way to develop XPS/FG build technology.
While trying some experimental XPS build tech, things kept going wrong, including a funeral in the midlle of a glass job. I put that build on hold. That’s when I saw an effective way to use the physics behind the current channel design. (Close to 2 years later, I finally salvaged that disrupted XPS bodyboard build tech project last week – functional but no showroom piece.)
So is the physics this:
Before he became focused on hydrofoil body boards, Dr. Terry Hendricks PhD, was riding body boards at WindanSea in the early sixties, that had a similar feature on the bottom that functioned much like a NACA duct. This ground was well plowed more than fifty years ago.
Dr. Hendricks was a talented individual.
Do you have pictures of the Hendricks “NACA duct?”
Thanks K-4. I am familiar with NACA ducts used for performance car air intakes.
Similar looking but a different final objective. And I believe pressure in the standard NACA duct is high.
My design parameters are different.
Mr. T indicates Dr. Hendricks used it. It would be nice to see Dr. Hendricks’ design and application.
Doc- so does eyesight. When I looked at it on my laptop, I thought your equation read “3x plus 1 equals 10”. Misread it! Damn it sucks gettin old.
My glassing skills with epoxy are mediocre. The biggest challenge for me on this channel was a clean glass job on the channel’s 90 degree edges and inner bottom angles. I figured Charlie could do it without problems.
While Charlie was working on this build, I was trying to come up with a good way to hand laminate the channel. The standard recommendation from several members has been to use spray adhesive to tack the dry cloth to the channel walls. The biggest drawback to that method is finding a spray adhesive that won’t melt EPS and that allows some small degree of re-positioning. I tested an idea last week.
I always have a little residual epoxy from any glassing session. I usually pour that into a paper plate so I can gauge when the mixed epoxy reaches the tack-free stage. So, I decided the way to do this is a channel pre-seal with epoxy (which I would do anyway), basting the walls and top edge surface first. Since I was playing around, I went for a narrow section at the bottom while I was at it.
I waited until the epoxy in the plate was still “slightly sticky” but not “tack-free.” I tested with the tip of a popsicle stick/tongue depressor (or a wood match stick). When the wood tip still barely sticks but the resin has set up, I draped the dry cloth over the top edge and wall, holding the cloth off the bottom. I smoothed the dry cloth onto the top first; then from top edge down the wall with a small plastic bodywork squeegee; press cloth lightly but snugly into the bottom 90 degree angle with squeegee while holding it off the bottom; then smooth cloth over a narrow section of the bottom.
I let the resin set to tack free. Then I wetted out the dry cloth with a 2" chipping brush. The test was done on a piece of low-grade packing EPS that formed a long 90 degree channel. The final lamination was clean and tight.
My future approach will be to hand laminate the sidewalls independently from the channel bottom.
Good job Bill. That looks like a very smart way to get your tight corners. The only water based contact adhesive that I could find that wouldnt eat the foam has a blue/green tint to it which might be a problem if your doing a clear layup.
Thanks Chris.
3M 78 won’t melt EPS/XPS and is sort of translucent. But it has a “lace” spray pattern. And while it says you can reposition for 45 seconds, in my experience that has not been easy to do with foam.
Bill
when are you expecting the board to be ridden?
You’ve mentioend the physics behind your design and the design parametrs being difefrent to the above photo, what is the idea behind the style of channel on the boad you’ve designed and what sorts of waves is it intended for? Wave type/size provides a context for understanding the theory. Thanks.
I’m pretty much grounded for any travel until there is an effective CoVid-19 vaccine.
Regardless, I’m too old to be a credible test pilot.
First, the design is intended to function as a “free-standing channel” in a fluid stream – not connected to a fluid distribution system. Channel dimensions will likely be affected by anticipated velocity.
Second, the channel contours are combined to produce an overall low-pressure effect under the tail. The objective is to hold the tail in place for tracking/directional control and to allow the rails to better engage. Perhaps too simplistic and over-generalized, the channel functions a low drag fin. It is likely there will be other performance effects related to contours.
My original design was a for a 42" bodyboard. The primary objective was/is to bring tracking/directional control to the standard “Boogie Board.” I have seen Bully Boards for larger riders. So the 48" was for larger riders and/or smaller surf.
After I started designing the channel, I decided I would like to try it for a finless fish. But it could be used for a variety of surfcraft.
The channel dimensions are intended to be dynamic rather than static – adjusted for preference, velocity and board size. The two current channels are the starting point for evaluation. At this point, it is sort of like asking, “What is the best fin size and shape?”
Without testing, I can only speculate about specifics based on the physics…
Charlie’s latest foam sculpture of my channel bottom BB arrived this afternoon.
42 X 21.75 x 2, EPS core with cork skins over and under FG.
Interesting.
