Building a Sailboat Keel Fin
Materials
Two sheets, 3/32 Balsa and one carbon fiber material
Fin trunk thickness is determined by the mating opening in the hull
Epoxy glued fin board. Dried on a flat surface with moderate pressure ( use 5 to 1 epoxy, strong and water resistant.) In this example we use Balsa sheets and Carbon fiber fabric. Multilayer plywood or basswood can also be used.
Carbon fiber center may not be needed if the wood core is strog enough to hold the lead keel
Aluminum roof flashing.
Aluminum roof flashing 6 inch wide. From Home Depot or Lowes
Carbon Fiber sheets may be used in place of the aluminum for the outer surface
Mark the blank with the keel fin shape.
Cut the wood blank to the fin shape. Make slots for the attachment bolts -
The top trunk and bottom may be made undersized so that after gluing together a epoxy filler can be added to seal the wood from water.
The Aluminum sheet outside should be marked. The inside surface should be roughed up so the epoxy glue will adhere better
Use a razor to score and cut the aluminum fin to shape. The width should be larger than the black since it must go over the balsa blank
Then use sandpaper to chamfer the edges to maximize the contact area
Shape the wood blank's surface to the airfoil curve
The usual shape has the max thickness at the 40 percent point from the front surface-
Sand the blank smooth.
Position the attachment bolts. Use epoxy or epoxy putty to position the bolts
Finish gluing in the bolts. Sand smooth after curing. Correct any bumps. If the wood is porous, like balsa, you can seal the edges with CA glue or other wood sealing product.
Cover the outside surface with masking tape ( blue tape) to protect it from the epoxy glue. The leading chamfered edges should be glued together using CA and clamped together at a acute angle. In this case I used magnets to make the angle
Use a straight wood block that will not bend with clamps to hold the edge together. Careful not to over tighten and damage the skin. Allow the edge to cure.
After it is set you can add more CA or epoxy from the inside surface and let gravity spread the glue
Insert the wood core into the formed cover. Check that the core fits well, the open edges mesh together and that the trailing chamfer is good.
You can use CA on the chamfer edge as a surface prep for the epoxy. Use a good 5 to 1 mix epoxy, covering the wood core and carefully insert the core into the shell. This can be a messy task and care should be taken to keep things clean.
Use wide masking tape to close up the training edge. Clamp it just like the leading edge but being careful not to allow the escaping glue to harden onto the clamps. The closer to a smooth curve and exact fit of the cover, will require the least amount of glue and the neatest job.
After the epoxy is cured, remove the blue covering tape.
Use CA and seal any exposed wood. Several coats would be good.
You can under size the top (trunk) core blank and bottom and after curing use epoxy paste to make the edged. No wood would then be exposed.
Mount the bulb and attach it to the hull. The two key pins help align the bulb to the fin. Some filing and sanding may be needed to make a good fit to the hull and bulb.
EPMYC.org rev A FinBuildPopUp01 11/24/2017