Howard

As I envision this concept, imagine a single strip of 1/2" plywood that is 2 inches wide and 6 feet long. Now imagine 36 such strips stacked on top of each other. Glued together, they would make a single plank that would be 18 inches x 2 inches by 6 feet long, essentially the same overall size as the blank I glued up to make the CB. The edge grain of each plywood strip would be facing out, not fore and aft as would be the case if you laminated up 4 pieces of 18" x 6' long 1/2" plywood.

Plywood CB's and rudders seems to lose their strength and fail when repeatedly flexed across the grain (grain running fore and aft with the board). My notion would to turn the grain 90 degrees where the strength of the grain would resist the flexing. Same principle as vertical grain vs. flat grain.

Taken one step farther, if you drilled holes in the centerline to register the piece in the lamination stack, then started shaving fractions evenly off each side, you could start to build in the shape of the board as you stacked it up.

Good information. I would think if the were to swell to that much in either direction, it would blow the epoxy joints apart in the process? It will also be encapsulated in a layer or two of glass, so something would have to give there too. All good reasons to make sure it is well sealed and glassed, and hopefully, never breached.

Still curious about the plywood strip idea. It could be made from off cut scraps. Grain orientation would be right......each strip would be isolated from the others to avoid some of the moisture issues and if a person wanted to, they might be able to shave material off on the edge of each strip to get a head start on shaping?

Peter:

I seem to recall coming up one strip short and that one was available (and straight), so I used it.  I culled some staves that bowed like a banana once they were ripped out. Not sure whey as they came off the same board and had the same grain pattern as the straight ones did. Funny stuff, wood.

There are more than a few things with this board I have concerns about. Despite being kiln dried to begin with, and after being stacked and stored in a dry winter house for nearly 6 months, it appears to me the staves have dried and shrunk a bit more after they were ripped and glued up. I didn't notice any problem end spits when I glued them up, but there are small ones in the ends now. In the end, this one may turn out to be good practice, and keep it as a spare (if it doesn't self destruct).

I don't know what wood you can stick underwater that would not swell up some if it got wet, so yes, it will be glassed and sealed up with the intention of keeping it encapsulated and dry. My alternatives are Doug Fir and Cypress. I also have my eye on some piles of old lumber that has been stacked in a barn for decades. Outside, it has a weathered look to it, but inside, most is solid and dry. Most of that would be cypress, pine or fir.

BTW, plans say to use wood or plywood. I built a rudder out of plywood once and had no problems with it, but have also heard that plywood will eventually fail when a sideways flexing stress is applied over time, as would certainly be the case with this board. What I have thought about, but have never heard of anyone doing, is building a board out of a stack of laminations. In this case, a stack of about 36 - 2" x 6' strips of 1/2" plywood. That way, the grain would run straight to the load and stress vs. perpendicular to it as is the case when built from flat sheets. There is the exposed grain to worry about, but that is the case with any foil made from plywood. They always have to be glassed well.

Made some progress on the CB. Again, this is one of the things that needs to be done early on, as the finished width of the CB determines the finished width of the CB trunk. That would be after the glass is on, so even the lead tip needs to be poured and attached. The CB trunk gets installed as shortly after the hull is turned the first time and prior to the keel deadwood and glassing the bottom.

Anyway, for my first (and hopefully last) attempt at the board, I used yellow pine. Heavy stuff, strong stuff.....but I have concerns about it checking and splitting. We will see. Having gotten one this far, doing another does not seem like too big of a deal. Would probably use doug fir next time.

Plans suggest using the rope trick on the leading edge and hard epoxy filer for the trailing edge, but unless you inset these from the beginning, that means you are having to add and subtract from the board, if you want to maintain the shape outlined in the plan. I decided to inset them from the beginning.

Once the overall shape was lofted onto the board blank, I had a flat leading edge and cut out the blank to form the roughed in trailing edge.  I decided  to use a router with 1/4" flute bit on the trailing edge and 1/2" box core bit for the leading edge. The trick was how to get them centered. To draw a centerline, I used a spar maker's trick, which is a centering tool. Once the line was in, I used the same trick with the router, using two screws in the mounting holes, which kept the router bit centered down the entire run. Much simpler than trying to use a router table or edge guide, both of which get close to center, but are usually off a little to one side.

Once those were in, I backfilled the trailing edge with thickened epoxy and dropped my epoxy soaked rope in the leading edge channel. Both seemed to work well. The board has now had the finished shape roughed in and ready for final shaping.

In addition to the end game benefit of having an rope on the leading edge and sharp, and square edged epoxy on the trailing edge, both of these will serve during the shaping process. I've shaped a number of foils and when only marked off with pencil lines, invariably, I manage to mar my lines and thus lose my place. Hopefully, with these hard, straight centered lines, I'll end up with a better foil.

BTW, on the rope, I used polyester. I did some tests between polyester and polypropylene and found the epoxy soaking in better. Also, when I whacked the cured samples with a hammer, I couldn't see any change to the polyester. The polypropylene dented, which to me suggested the epoxy was in it, but not stuck to it. Also, last time I was at the store, I noticed a chart that showed polyester to have twice the strength and abrasion resistance, so went with it. To soak it, I used straight epoxy, except I added some 300+ grit walnut shell as pigment, so later on, during shaping, I'll know where I'm at. To saturate the rope,  I stirred it around, then hit it with a vacuum. Judging from the amount of bubbles that foamed out, that was probably a good idea. The only real surprise was to find my carefully measured piece had contracted somewhere between 5% and 10%. I managed to stretch it back out and held it in place with finish nails on the ends. I pre-wet the channel, but didn't have too. There was plenty of epoxy that worked out of the rope to bond it in place.

Winding sticks will reveal the twist, if any. With nothing to go on but the pictures, it looks pretty good as is.

As for the cooked epoxy, since the bow section is stressed to begin with, and will be stressed and tested even more when you use it, I'd want that out of there. The question would be how to do it. Grinding it out with a small angle head grinder is certainly one option, but not a good one (these grinders are a brute force method of removing material, but run the risk of doing a lot of damage in a hurry, not to mention the mess they make.......its possible that some CERCLA sites have been created by these). Since even cured epoxy will soften with enough heat, I might try to use an infrared heat lamp at point blank range (inside a foot) to soften it enough to dig it out with a putty knife. Same process as heating the wire, only bigger scale.

Not sure where you got your 5:1 epoxy, but for building a boat, I'd give up on that in favor of 2:1 mix. Experiment with various speed hardeners, but you will want at least one that offers a slow cure option. You need the really slow cure version to allow you enough time to mix it and disperse it, not to mention the ability to create a large fillet like this without it going off on you like this one did. The rate at which epoxy will cure is a function of the hardener used and ambient temperature it is used in. The curing process also generates it's own heat, so if you were to use a fast cure hardener on a hot day, it might go off in the pot before you can finish mixing it. A slow cure on a cold day might never harden. A big fillet like that will trap heat as it starts to cure and will act just like a large pot of epoxy. Once it starts to get hot, there is no stopping it. Given a choice on doing a large fillet like that one, I go as slow as I can. Not much bad happens when you go slow.