Hey guys, about to make some fins with a timber (not ply) core. As some timbers react differently to resin, would Pacific Maple & Raiata Pine (sunburst design) glass OK. Planning to run a bead (rovings) around the edge… a’la Berts step by step post. Fins will be glass ons.
Any ideas and input would be greatly appreciated.
Craig.
You can get glass to stick to almost any wood if you sand it & take off the surface oil. For poly resin, that just means wiping the wood with a little acetone; for epoxy, a little denatured alcohol. Let your treatment evaporate off & glass in low humidity. No problems.
The most important thing is to use woods of similar hardness so your foiling & sanding don’t make scallops into the softer one.
Someday I’m gonna make a set of fins with a port orford cedar core just to get a sense of how responsive the material is.
I’ll be using epoxy exclusively to keep the water out and strenghten the fin tabs.
Note: I have seen many beautiful wooden boats distroyed by the act of putting a poly-glass shell over the hull. Polyester resin makes a lousy bond and once there’s a pin hole there’s no stopping the rot that insues. I grant you Polyester is beautiful clear material but in a marine environment it would be my last choice of resins.
If you’re going to use a variety of wood for the fin take Benny1’s advice and use woods of a similar hardness. If you want flexibility stick with the conifers.
Any thoughts on African Mahogany marine ply as a choice?
Mahalo, Rich
Hey Gill,
Here are some fins that I just glassed. These are made the a’la Bert post, ‘thanks Bert, your method was really easy’. The multi layered fins are birch ply, the red ones are made from redwood fencing cutoffs, and the large single fin is balsa. The small fins are copies of FCS fins, but modified. The black FCS fins weighed 2.4 oz each, the birch ply fins weigh 2.6 oz each, and the redwood fins weigh 2.2 oz each. These fins were easy to make, no problems with resin sticking to the wood.
Poe Rava
the photos
Let me get my oar in about woods of different hardnesses. What’s said above about scalloping is correct, but ('scuse me) it indicates the wrong technique was used.
Most of us would happily stick together whatever light and dark woods we could get our grubby little hands on, and happily have at the foiling with our grinder and soft pad. Suggest a nice sharp piece of 60 grit works well. However, this is where the scalloping problem starts: the sandpaper cuts the softer wood more quickly, same as a surform cuts foam quicker than the stringer.
Solution: rough it out with the grinder and a soft pad, then switch to hand finishing with a suitable convex hardwood backing on the sandpaper, instead of the soft pad. The hard backing won’t let the sandpaper get down into the softer wood as the soft pad will.
And, yes, lam resin sets quickly but is an absolutely crappy glue. I set up some redwood/balsa strips once with lam resin and the next morning, though the resin was hard, I peeled each stick from the bundle with my fingers. Now I use plain old carpenter’s glue.
Scalloping can also be overcome by laying 3 or so pieces of 6 ounce, full height, on the fin when you glass 'em on, then use the soft pad to clean it all up after a nice thick hot coat on the fin(s). Better, since UV resin cures so quickly, you could lay the board on it’s side and brush a separate lam resin filler coat on each side of the fin(s) to make sure the weave is completely filled. I use an acid brush for this sort of thing…
It is always true that good results take careful attention to detail. Luck beats skill, but I won’t rely on it. You can recover from most mistakes, but better not to make 'em in the first place. Who am I fooling, I’m still learning the hard way myself.