The recent development of extruded panels with integral stiffeners has provided the opportunity to further improve and speed up some areas of construction, where there is little or no double curvature. No fillet welds of stiffeners to skin have to be made with these panels and, in addition to reducing distortion considerably, only butt welds panel-to-panel are required, which are much more easily tested no-destructively.

Longitudinally framed vessels can most often be most easily built upside-down. A carefully constructed female jig of the deck and, if a sailing yacht, the main part of the superstructure is constructed. This usually consists of a steel frame on to which transverse panels made from heavy ply or chipboard are bolted. These are usually best placed one at each frame position. Longitudinal battens (housed flush in the transverses) are then run at the deck edge, the join of the deck and the coachroof, and the join of the coachroof coamings and the coachroof top (if this is being built at this stage). Some supplementary battens are often required for the foredeck and other large expanses.

The deck plating is then laid on the jig, having previously been joined up in as large sections as practical and these pre-welded. Hatchway apertures are rough cut at this stage, partly for access and partly to help control distortion. The deck plating is secured firmly to the jig. using tags screwed to the jig transverses and longitudinals, tack welded to the plating. The coachroof top and coamings are also fitted at this stage. The coamings stabilize both the deck egde and the coachroof edge against distortion. On a power boat, it helps if the design of the superstructure can allow at least an upstand around the inner edges of the deck as this again helps to stabilize the deck edge against distortion.

Now the deck and coachroof reinforcings are fitted, including the stringers, genoa track reinforcings, stanchion feet reinforcings, inserts in way of deck fillers, windlass pipes and so forth. All the items welded to the inside of the deck and coachroof plating can usually be fitted at this stage with advantage. It is necessary therefore for the design to be at an advanced stage by this time, so that the positions of all such items are know and fixed.

Meanwhile, the ring frames will have been constructed. It is preferable to complete the welding of the flanges to the webs and to correct any distortion, before the frames are set up. Before setting up, each frame is laid on its full size pattern (obtained from the loft floor or more likely nowadays from the CAD system) to check for accuracy, and any disparities are corrected. The frames are braced to allow them to resist the loadings applied as the stringers and plating are fitted and also to help prevent distortion as the hull is welded. Where bulkheads occur in place of frames, these will be fully constructed and checked out in the same way, before setting up. We can be confident therefore, once the frames and bulkheads are stood up in their correct placesand set plumb, that the hull will be intrinsically correct to the lines generated by the designer. As they are set up, the frames and bulkheads are also braced to keep them upright and prevent them twisting sideways.

Usually the next structural item to be fitted is the main centreline backbone or girder, and its continuation as the stem. This is slotted into the floor sections of the frames and bulkheads. This and the deck now stabilize the frames and bulkheads in their correct positions. The structure can further stabilized by wrapping a pair of longitudinal stringers around each side of the hull, taking care that the frames are not locally pushed out of position in the process. The stringers are only very lightly tacked to the frames at this stage, otherwise they will distort.

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© George Whisstock.