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BOATS: Lift Models and Lofting |
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By the middle of the 18th century, builders had developed another type of model, consisting of a blackboard cut to the shape of the hull profile, with the sections formed of thin plank secured at the desired mold stations. The sections were made fair, or capable of being planked smoothly, by battens at suitable locations. Finally, about 1795, the so-called lift model was developed, made of boards of equal thickness pegged together and shaped to the desired hull form. The shape of the mold frames was obtained by taking the model apart and tracing the shape of the lifts, or planks, in their proper relation to one another. By drawing lines across these shapes at frame stations, the transverse widths at the ordinates formed by the lift thicknesses could be determined. The lift model is still in use in many boatyards and remains practical for small craft. Lofting consists of drawing the full-size shape of the hull on a suitable platform or floor. The required drawing shows the mold sections, or transverse forms, usually five to seven in number. These sections usually are tested by drawing in some longitudinal curves, such as the sheer, and a few waterlines or level lines duplicating the so-called lift lines of a half-model. In addition, buttock and bow lines, longitudinal vertical sections parallel to the centerline of the hull, may be used. Diagonals, representing the batten curves over the molds, may be drawn in. In making the longitudinal drawing, the profile of the hull usually is drawn full size. Lofting is an important operation in boatbuilding, for it is the only way a design may be reproduced accurately or repeatedly. In the more advanced boatshops the structural details also are drawn full size, the lofting being done in minute detail. |
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