Space saving Alternatives to a Single Hull

By Paul Butler

illustrations by Marya Butler

Small Boat Journal #63, November 1988

Ever try to fit an 8-foot dinghy onto a 7-foot foredeck? Lift a rowboat onto the top of the family station wagon? Squeeze a 16-foot rowing dory into the back of an 8-foot truck bed? Prams, dories, and rowboats, small as they are, are often subject to severe space restrictions like these, and trailers are usually more trouble than they're worth. But there is an option for owners of plywood, coldmolded, and fiberglass boats.

By using epoxy and plywood, it is possible to install back-to-back watertight bulkheads in a small hull, which, by removing a few fastenings, can be easily and quickly taken apart and reassembled. Bolted together, the bulkheads function as watertight dividers, and they stiffen and strengthen the hull. Unfastened, the sections can be carried or lifted more easily than a single hull, and they will fit into a smaller space. One section may even nest inside the other.

The efficiency and sealing ability of epoxy is what makes this operation viable. But it needs a dry, tight hull to work best and is not recommended for traditionallapstrake hulls or hulls with aging chine logs and keels that weep constantly.

Strategic Planning

Because hull types and individual requirements differ, give some thought to exactly where the bulkheads should be placed. If you locate them precisely in the center of the hull, one half won't fit inside the other. If nesting is a priority, do some measuring to ensure that the smaller half fits inside the larger. Since bulkheads can go almost anywhere in the hull, it's possible to arrange for a specific use or to fit a specific location, like the cabin top of a larger boat or back of the family wagon. Use as many bulkheads as are necessary to accomplish the objective.

Preparing to Epoxy

With small boats, it's usually easiest to make a cardboard or thin plywood pattern of the bulkheads and then have a good long look at the pattern in place to see if there will be conflicts or problems. The top of the bulkhead can be cut away if it interferes with seating, rowing, or sailing arrangements, but it's best to leave the bottom edge of the cutout well above the waterline. Otherwise, you'll need a waterproof gasket between the bulkheads (Fig. 1-2).

Since the gunwale must be cut to accommodate the bulkheads, you may wish to add a small knee or gusset at the inwale location for added support. The only problem might appear in cutting through long skinny hulls that depend on fulllength members such as stringers, risers, and keelsons for hull stiffness. The builder must use common sense when severing these, but if they are butted solidly against the bulkhead, they will usually retain full strength. Additional hull bracing can easily be built against the new bulkhead by adding a flotation/dry storage compartment fitted and sealed with epoxy fillets. A screw-in hatch provides access to the sealed compartment while maintaining positive flotation. The compartment also doubles as a seat.

Epoxy fillets bind everything together. This is not a project for lesser glues. When preparing to glue double bulkheads into a sheet ply or cold-molded boat, scrape away all paint, varnish, or UV-resistant coatings and sand lightly. When working with fiberglass hulls, remove all gelcoat an inch or so back from the bulkheads because you need a large radius fillet for maximum strength and a good appearance. If you intend to reinforce the bulkhead with knees, cleats, or gussets, scrape and sand that area also.

A mix of approximately 75-percent silica to 25-percent microballoons is a good combination to begin with. Ratios may vary depending on the resin and working area temperatures. A red microballoon mixture will come very close to matching mahogany plywood and timber, and a pure silica fillet will weather to a yellowish fillet that looks acceptable on off-white fiberglass.