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.
this is great , THANKS everyone !
"
7 months ago
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sk8ment
Last seen: 2 months 3 weeks ago
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this build thread ans folloing dicussion is rad, make me pumped to get into the two belly boards i have half shapped in the shed, two edge railed beasts, inspired by greenough.
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@reclaim_surf formerly Skatement
(Adam) Sunshine Coast Queensland Australia "
hiya Adam !
just wondering if you have photos of your edge boards , please ?
cheers !
ben
That design is very wide-nosed and wide point forward. You would need the same board without the channel to truly feel its effect.
Moved.
Do you mean a shot of the rails?
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The nose is 0.78" narrower than the same section in a Retro Fish (relative to the widepoint).
With board thickness being thin at the channel exit and with lower pressure under tail, riding postion should shift forward a bit.
Over the last two weeks. I have been communicating with a professional, custom bodyboard builder. His comment about this particular bodyboard was, “Your design looks good.”
The channel effect should be fairly noticeable.
I think I can ride it.