Help rebuilding a wooden daggerboard?

Hello!

I've recently undertaken the task of fixing up a late 1980's Scorpion (the tiny American dinghy by Pargo [discontinued]). I've read they're similar to sunfish, but the parts are model-specific.

The rudder and daggerboard were stored in a basement which had been flooded, and are now suffering some serious dryrot (although this seems a misnomer). Additionally, there appears to be neither paint nor sealant of any kind on the wood. Also, the daggerboard has sustained moderate damage with a few chunks missing on the lower stern side.

I'm looking to completely rebuild both these pieces, though i'm starting with the daggerboard because the rudder is more complicated, parts-wise. It appears to be a single (with the exception of the handle) piece of wood with the grain running vertically along the length of the board.

Am I better off using marine plywood or a single sheet of wood to build this?

While it's certainly not a keel, i'm assuming the piece has the potential to be under some serious side loads, and i'm trying to assess which wood (if not marine ply) would be ideal. I figure strength, weight, and cost are the three deciding factors.

Once the wood is chosen and cut to spec, I've got to worry about waterproofing it. A little digging here says something like the following might work, but my details are still a little vague.

(apply to sanded surface of the piece):
-stain (not anything wax or deck related)
I know this is optional, but it's for color here. How many coats/recommended brands?

-epoxy (marine grade, CPES?)
not very certain how to prepare the CPES, also, how many coats are needed, brands recommended, etc?

-polyurethane (for durability and UV protection)
i'm not really sure what brand, but i've read that 15+ coats is a fine job (repeat application of 1 coat/year).

Also, I've accepted that the board will eventually strike course sand/gravel and (hopefully not) rocks. Is there anything I can do (short of technique, of course) to improve the board's resistance to being chewed up, so to speak? would a layer of fiberglass within the epoxy (just on the lower portion of the board) improve strength in the worst case?

I'm not too worried about biofouling, as the board come up and out to be cleaned thoroughly with every launch. I don't want it to be maintenance free, but the work needs to be simplified.

Please point out any glaring errors in my process.

thank you very much

 

It would be best to use solid wood rather than plywood primarily because you can't easily buy less than a sheet of the kind of marine plywood that would stay straight and stand up to immersion in water, and a sheet of the good stuff is very expensive.
I would recommend quarter-sawn fir, honduras mahogany, or spanish/luaun mahogany. Fir because it is reasonably priced and available in your area (try a hardwood dealer for these woods). custom wood shops should direct you to their wood suppliers.
Treatment would be varnish, maybe 8-10 coats. This boat will be dry-sailed so no epoxy is required. Keep up the varnish (two coats a year) and expect a very long life.