SECTION IX B - WOODEN BOAT RESTORATION AND REPAIR
Often our technical service people take a telephone call where the question "I bought this old wooden boat and I was wondering if your product can be used to restore it?" The caller often hopes that slathering on a coat of System Three epoxy will turn the boat into a beautiful modern wooden boat. More often than not we end up dashing his hopes for a quick fix simply because there isn't one.
Modern wooden boat construction takes small pieces of wood in some form and uses epoxy resin to laminate the pieces into one large piece in the shape of a boat hull. This so called monocoque (single piece) structure is very different from traditional wooden boat construction wherein the various pieces are mechanically attached to each other in such a way that movement is allowed. Indeed, it is the movement caused by the swelling of wood by water that keeps these boats leak proof.
Jim Brown of trimaran fame uses the analogy that a traditionally built boat is like a woven basket where a modern wood/epoxy boat is like a bowl. To be watertight the basket must be allowed to swell a little when wet so that the strands press against each other. For the bowl to remain watertight it must be sealed to keep water out - the very antithesis of the basket. Therein lies the problem with slathering epoxy on a traditionally built wooden craft. To do it you must first dry the hull, which causes shrinking of the wood planking. At this point it is no longer watertight. Epoxy coating the planking will prevent it from absorbing water and swelling. It will remain leaky.
While it is possible to stuff thickened epoxy into the opened seams of the dry hull, fiberglass the outside and produce a leak proof hull the results are apt to be temporary as the planking will pick up moisture elsewhere and swell probably cracking the fiberglass. Dry wood picks up moisture and swells producing forces that greatly exceed the strength of epoxy resins.
If the boat owner is aware of the risks and is prepared to sink a lot of labor into the project some traditionally built boats can be brought into a modern monocoque condition. The key to success is devising a way that will eliminate or reduce the movement of the various wood members permanently. The problem is that no one possesses the crystal ball that predicts such success. The following will give a rough outline of the techniques involved. Be advised that there are no guarantees and the situation may deteriorate rather than improve.
These pose no problem in restoration as they are essentially built as modern plywood boats. Dry the hull thoroughly. Remove all coatings and take the boat back down to bare plywood replacing any rotten plywood. Make sure that the frames are in good shape and replace any that aren't either by sistering in new frames or building new frames and installing them. Epoxy coat the bare plywood and fill depressions, screw holes, staple holes, etc. With System Three epoxy and microballoons. Sand fair. Lay down fiberglass cloth and reinforce the chines, bow, corners, etc. Finish as described in this book. If possible, the inside should be taken down to bare plywood and epoxy coated. Remove any oil or grease that would interfere with epoxy adhesion.
Carvel Planked and Caulked:
The important thing here is that the planking has got to be immobilized against both mechanical movement and moisture swelling.
Remove all caulking by using a router or saw blade. Dry the hull thoroughly and remove all outer coatings down to bare wood. Remove any damaged planks and replace. Make sure that the frames are in good shape and replace any that aren't either by sistering in new frames or building new frames and installing them. Refasten any loose planks. Fill the seams with thickened epoxy or glue in wedge shaped battens if the gaps are wide. Fair the hull using System Three epoxy and microballoons.
At this point a crucial decision must be made. The planking must be sheathed with an outer layer that is structural. We believe that the best way is to use a double diagonal layer of veneer at 45 degrees to the planking. The veneer is then finished as a new hull. An alternative way is to use a structural fabric and orient the fibers so that they lie perpendicular to the planking. As added insurance the inside of the hull planking should be taken down to bare wood and epoxy coated. This may not be possible without gutting the boat. If you go this far put nice generous fillets in the corners formed by the frames and planks.
Restoring these boats is quite similar to carvel planked boats except there is no caulking to remove. Make sure the hull is dry, the planks well fastened to the frames and each other regluing the planking where required. Follow the outline above.
We do not recommend restoring this construction method with epoxy resin. Restore boats built of traditional lapstrake construction using original techniques.
- Tags: The Epoxy Book
- STR Staff