In the process of putting together a small fishy thing w/ no stringer and some flex in the tail (various glass reinforcings here and there likely) (EPS w/ plain vanilla fiberglass probably 3 X 4oz on each side to start) (hey, have you priced carbon fiber to glass a whole board lately???) (I just wanted to add one more set of parentheses)(well two as I’m not sure how to spell the plural).
Have seen the Van Straalen flex keels made of carbon and they are pretty thin for that long of a base (I’m guessing from memory about 1/4 inch). I’m hopping to get twangy stff flex at the rear and have more like 3/4 inch thick at thickest point.
With nearly 8 inch chord, the angle from rear edge to thickest point is steep enough that I’m thinking I need to make a thinnish (1/8 inch?) glass core and then build thickness with something that will flex more easily than the glass by quite a bit so it doesn’t stiffen it too much and yet won’t break down under repeated flexing.
In pm, Dale has suggested Bondo since if use foam it is much more of a process to alter the keel outline or foil due to water leakage issues. Anyone got any ideas for material to build the thickness I’m all ears (eyes really).
Did I say bondo? It’s o.k. for cheap experiments, but is heavy and stiff. A mixture of resin and microspheres is much better. I’ve also used higher density 2 part polyurethane pour foam.
One nice thing about a laminate fin core with an exterior layer of resin/microspheres is ease of modification… at the beach or even in the water between waves. No worries about water absorption. The same type of experiments can be done with the rails and bottom of a board. I sometimes surfed with a half-curved coarse/fine file and a little 220 wet-n-dry sandpaper.
Hi Dr Strange -
Maybe a “spine” of roughly 10 or 15 layers of glass with a chunk of foam scrap added, foiled and then capped with a few more layers? This would give a pretty good sized “halo” of fiberglass around the foam that you could reshape.
The foam core area would obviously be the thickest part of the foil… is that an area you would want to have flex anyway?
I used some Last-A-Foam core recently on a hoop fin I made to increase the thickness of the foil. I also left a fair amount of glass “halo” for fine tuning at a later date if needed.
This is a pic before foiling and capping… it shows the glass spine and foam inserts being attached.
i’ll suggest sintered pvc foam or some resilient flexible plastic
Thanks for all the suggestions. Sorry Dale think I may have ADD’s on our conversation. Now I vaguely remember the microsphere/resin. Too bad nothing light and flexy has layers to show foiling like the glass does. Or plywood. Love the guidelines for grinding.
Too bad nothing light and flexy has layers to show foiling like the glass does.
I’ll say it again - sintered pvc foam…comes in different colors…look up “sintra”
“nothing…always…never”…absolute words I never use
An alternative to building a thick flexible fin section is to make the thick section stiff, and raise the cutaway slightly, allowing a short thin carbon fibre upstand to do the necessary twisting. . . this is what we do with our bulb tipped flex fins and it works nicely, the big trailing edge of the upper part of the fin has enough leverage to twist the lower carbon upstand, giving a twang to the fin and about two inches of movement either side at the trailing edge . . . . with a lower upstand the movement would of course be less
Will draw a picture if you like
If you use poly resin ,
Use boat lam and volan glass.Sand finish only.
That’s George Greenough’s method.
That Sintra PVC foam board looks really fine! Light, water proof, flexible. Pretty inexpensive too for amount needed for keel thickening.
This is Swaylocks at its finest. I now have a library of various tech ideas for the job. Many thanks to all!
Roy, I like that idea, I think similar in some ways to what Greenough has on the stage VI??? But for my purpose I want the paddle quite close to the bottom of the board, maybe 1/8 inch off. So the up post would have to be too flimsy I think to last and still be able to rotate.
Wondering about the structural integrity of the Sintra under load i.e. it will be building up the part ot the Keel that is where the attachment glassing goes. Maybe stop the Sintra buildup at the bottom of the blade of the keel leaving the post only thinner fiberglass and fill the dif w/ the roving in the attachment layup…???
