I was working on my daggerboard this weekend. It is made of edge-glued cedar with the leading and trailing edge strips being mahogany. The whole was then coated for strength with a layer of light fiberglass. Over the years it picked up a few dings. But shortly after I got the boat a more extensive problem occurred. Previous owner had let the glass on the leading
edge separate from the wood. I patched it with some resin, and pondered how to do the job better. I went out sailing on a strong wind day and planned past every other sailboat on the lake (including a 470). But as the day went on, I had increasing trouble passing others. Well, it was getting late, so I started to tack in. Going upwind single-handed in such a strong breeze, of course I heeled a lot. And there exposed was the answer to my reduced speed! Earlier I had been going so fast that I had peeled the fiberglass back 3 inches on each side of the board, which now presented a 6 inch wide leading "edge." The glass had not separated from the wood, rather glass and a thin layer of WOOD had been ripped loose! I reglassed with glass tape around the leading edge so that there is no separation there any longer to come loose.
The relevance of all this is: I have never been satisfied with the repair. To really repair it correctly would require some fillers, and the clear finish will be lost. Remembering how great your rudder looks, I have just about convinced myself to finish my board the same way. So, being unfamiliar with the West System graphite-epoxy, I e-mail you with a request for information about it (where do you get it, how much, any special tricks in application, etc.).
Your daggerboard needs help, and I think that graphite epoxy will be the solution. However, that's the final solution. Before you get to that point you have some prep work to do.
Start off by sanding away the old fiberglass, but only enough that you have not lost the shape of the foil. You will expose some raw wood. Before you worry about fillers (for which the West system has a solution), coat/saturate one side with a clear coat of a mix of # 105 resin and # 206 hardener using a throw away brush. Work quickly and then take some low density fairing filler (#407) and mix enough of it into the epoxy until it feels like thick putty or spackle. Spread it to fill all the dents and nicks on that side. West makes a plastic spreader, one of which I will happily lend you, but any clean putty knife will do. Let the epoxy cure over night and then do the same thing to the other side. You need patience when you work with the West system or any epoxy coatings!
When both sides are sanded smooth with 80-grit sandpaper, mix another single batch of epoxy into which you stir a teaspoon or so of graphite additive. Use a throw-away brush to coat the mixture along the edges and, after that, pour the rest of the mixture onto the daggerboard and use a West roller (cut in half with a hacksaw) to coat the rest of the surface with graphite epoxy. Let it cure overnight and do the same thing the next day on the other side of the daggerboard. Sand the whole board again with 80-grit paper, to get it ready for a second graphite coat on each side. When that coat has cured, lightly sand with 80-grit and then wet sand with 220-grit wet-or-dry. If there are no places where the wood color shows through, you're almost done. If there are, you can either recoat the whole side again with graphite epoxy, or just coat the high spots and wet sand them down with 220-grit when the epoxy has cured.
My final finishing/polishing process involves hand rubbing with what fine furniture builders use. Use pumice stone with water and a small, soft rag for the first round of polishing. Rinse off this compound and then switch to rotten stone and polish the same way. I rinsed and re-polished with rotten stone a few more times until the whole board felt smooth as silk to my bare fingers. The last thing I did was use the finest steel wool I could buy to "burnish" the finish. I can supply you with the fairing filler, graphite additive and the rubbing materials, because I have enough to do another few dozen rudders and daggerboards. All you really need to buy is the West epoxy materials and tools. BOAT US has usually had the best prices, but you can also buy West products from West Marine or M&E Marine. Unless you plan to do many projects, I suggest you order the "A" sizes for the epoxy and hardener and get the appropriate pumps. Per their latest catalog, BOAT US will charge you: $22.89 for 1 quart #105A resin; $10.99 for 0.44 pint #206A hardener; $3.95 for 4 pairs of disposable gloves; $13.83 for #850 Solvent; $7.39 for #301-A mini-pumps; $4.89 for roller frame; $3.49 per pair of roller covers (get a bunch); $0.47 each for mixing pots (you can reuse them so buy 4 or 5). If you buy from BOAT US, they'll send you the West System manual, which is great!
Amine blush (related to fairing)
Amine blush is not a problem when you use additives like graphite or fillers in applications where a clear coat is not the intended result. Besides, the sanding you need to do will remove it anyway! Using a roller puts the finish on thinner, smoother and faster. Once its on, use a foam brush to even out any bubbles. On the first coat, where the epoxy will be saturating bare wood, it is actually displacing air in the wood fibers and that creates surface bubbles. In those areas, stand over the work as you may need to dab on a little more epoxy now and then until the exposed wood cells are filled. It really is an amazing process!