Fiberglass boats; hulls are available in different forms. A one piece hull supplied mold in one piece. A two piece hull has two half hulls which must be joined together by the builder. Hulls may come with edges reinforced and a mounting lip molded about the sheer edge. Often they come with a "straight" sheer; this means the modeled must put in a shelf or sheer clamp or gunwale strip in order to mount the deck and support the edge of the hull.
In the two piece hull trim the halves carefully. Hold the parts rigidly together with clamps or tape and laminate in a strip of fiberglass: across the inside joint between the halves. When the resin cures you will. have a one piece hull.
Before proceeding further you will need to build a cradle to hold the model in place while you finish building it.
If your hull is of the straight sheer type it will require a deck mounting shelf to be installed; proceed as follows. After trimming the sheer, laminate two strips of 1/8 x 3/8 spruce about the inside edge. This will give you a 1/4 plus wide shelf to support the deck. You may use other sizes and woods to fit your individual needs. Take care not to distort the hull at this stage. if necessary brace the hull externally to hold its shape. Do not fry to force the wood strips too tightly to the hull. This will distort the hull at the clamping points. Use a thixotropic resin to bridge the small gaps between the wood strips and the fiberglass. Another method is to use a small strip of fiberglass between the wood strip and hull with the saturated glass strip bonding to both the hull and the wood. On a racing model, remember weight should be kept at a minimum. Choose your building technique and materials with this in mind.
Locate the points at which the chain plates and various fittings will be attached. to the hull and deck. Locate and install load spreaders and back up blocks for such items as shrouds (stays), head stay or job rack, mast step, backstay and any other item which will need to be fastened after the boat is assembled. These back up blocks or load spreaders are generally blocks of light weight wood such as spruce which are bonded to the hull or deck so that when the fitting is screwed or bolted down to the fiberglass the pull is taken up by the block of wood. Remember that unless the load is widely spread out fiberglass, especially thin GRP as in models, can not stand tension loads. Arrange the blocks to spread the load or to put the fiberglass in compression loading.
The bottom of our model must support the weight of a heavy keel located on a long lever-like fin so it will need some sort of strengthening or "load spreading". If the keel is bolted on, the hull will need a keelson installed inside the hull. The keelson is sometimes called the hog or occasionally the keel. To do this you laminate a 1 inch wide strip of glass tape down the centerline inside the hull bottom. While this is still wet laminate three or more 1/8 by 3/4 inch strips of pine or spruce on top of this strip right down the centerline. You could use several layers of the 1 inch cloth laminated in place of the wood strips but they will weigh more. This keelson will give the hull thickness to hang the keel on and support fore and aft. Load spreaders will still be required on each side of the keel bolts. The "Sirius 45" calls for the keel fin to pass through the bottom of the hull and be glassed permanently in place. The keelson wood is needed only under the area below the mast step.
Check the beam measurements of your particular model; it may be necessary to spread the hull slightly or even to push it together to get the beam at the desired measurement.
This article Fiberglass Model Yacht Builders Guide is Extracted from a draft copy Book on Model Yacht Building by Dave Mainwaring, Framingham, MA
Copyright 1979
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