If you’re building a “frameless” boat, that is, a hull with only a few frames, or one that has no transverse frames, then you may use angle frames as a mold, and these will not remain in the boat. When you’re building the “mold” for a frameless boat, you may find it possible to eliminate every second frame when setting up the shape of the hull. When the designer prepares computer-designed lines, it’s usual to have only four to six control sections (similar to frames) and the remainder of the hull is faired through these sections. Most light-to-medium-displacement steel-chine hulls (not radius-chine) under, say, 40 feet (12.19 m), are suitable for building with the frameless technique. Contact the designer of your boat if you’re interested in using this method. Ask if some frames may be eliminated, either in the finished boat or in the setting-up mold. Some frameless hulls are built over a timber framework; this may be helpful if you’re building a metal hull under 35 feet (10.66 m) and have limited metalworking experience. You could build the timber framework yourself, and then hire an experienced welder to weld up the hull.

PREPARING TO BUILD STEM, BACKBONE AND KEEL

You’ll find that metal boats use many different sections for building the stem. Some boats feature a stem that is a flat bar on edge. This, in fact, is the material specified for many of our sailboat designs. Other designers favour solid round bar, round or rectangular tube, or rolled plate. In some sailboats and many powerboat designs, we favour stems that incorporate a rolled plate above the top chine. Your homemade bending machine will come into use for bending the flat-bar stem if part or all or the stem is to be formed from this material. As mentioned above some stems may include a conical section of rolled plate.

   The aft section of the backbone may be installed on-edge without your having to form it in a bending device. Some stems, such as those used in the Spray designs, may be constructed using a box section of similar construction to that used to fabricate the keel. You’ll need to make plywood or hardboard patterns for the sides of the box stem, and trial-fit them before cutting any metal.

   The leading edge of the keel will be flat bar, split pipe, full pipe, or rolled plate. Flat-bar leading edges for the keel are only satisfactory for very small powerboats. In most cases, a rounded leading edge—similar to the leading edge of an aircraft wing—will not only be stronger and less liable to damage, but will also offer a better passage through the water for the keel. The aft end of the keel is usually formed of flat bar on edge.

Bedlogs and Strong-backs

   For hulls built upside down, your plans should include details of preparing the base needed to set up the hull frames. This base can have one of several names including bedlog or strongback. In our plans, a set of bedlogs consists of a framework of suitably sized timber or steel I beams placed on a prepared surface. The surface can be concrete, packed earth, or other similar base. If a packed-earth floor is used, you’d be wise to install strategically placed concrete pads capable of supporting the bedlogs and the completed hull. You’re building a foundation, albeit a temporary one, and it has to support the hull until it is plated. In the case of a hull built upright, the strongback or setting-up bedlogs will be required to remain true until the boat is completed.

   The strongback is a framework that’s usually about 3 feet (910 mm) off the ground or floor. It’s used to support frames on a hull being built upside down. The idea of the strongback is to have the inverted hull set up far enough above the floor so the builder could easily climb underneath the hull to undertake the necessary tack-welding of the stringers to the inner hull plating before the turn-over stage. More recently, however, we’ve found it easier to simply extend the frames to a common headstock or upper baseline. Using this method, we ensure that the hull will be far enough off the floor to clear the stem, and allow a welder to have easy access to the interior of the hull. In all setting-up methods, a wire stretched tightly down the centreline will be an essential part of the procedure.

GANTRY

You may consider installing a gantry that can be used to erect the frames and assist in installing the plating. If you’re assembling your hull inside a commercial building, you may be fortunate in having an overhead gantry already available; otherwise you’ll have to arrange your own. The track will consist of a pair of channel rails made from some U-section steel that run full-length each side of the hull. Two sets of A-frames set to run on wheels in the channel and an I beam rigged with one or more chain blocks, chain falls, or a chain hoist (all the same device), will complete the arrangement. An even simpler gantry is a tripod with an attachment point for a chain hoist. You can use it to lift the plates and other large metal sections.

BUILDING UPRIGHT

Professional builders have many methods of setting up the frames, transom, and stem, to build a metal hull upright. These methods, while suitable for the professional, could in some cases cause problems for less experienced builders. For instance, they could allow errors to creep in, resulting in a twisted or otherwise less-than-fair hull structure. It’s the responsibility of the designer, especially when dealing with a less-experienced builder, to ensure that the method of setting up the hull is well detailed in the plans. This will make things easier for the first-time builder who otherwise may be unsure of how to proceed. Experienced welders, metal workers, and fitters who had no previous boatbuilding experience have built many fine metal boats but even they need some guidance when setting up the hull; so no matter how much welding knowledge you have please take care in these first steps of your boatbuilding project.

   For the less-experienced builder, the secret is to have a well-prepared building frame, strongback, or similar arrangement to allow the frames to be set up in their correct locations and to avoid errors. One method we have used is to build a framework for a shed-like structure, and support the frames from overhead rafters. Another way is to build a set of bedlogs and use pipe supports to hold the frames in position until the keel, stringers, chine bars, and stem are installed. With a hull built upright, once the keel is plated the structure can be more or less self-supporting, with the weight mostly on the keel. Additional supports should be installed under the ends and sides of the hull to avoid sagging during construction.