The Backbone: Tail Feather and Transom, Molds and Sheer

Getting it upright Let's assume that this keel is on its side, with stem and sternpost in place, and with ballast keel bolted on. Chain a timber to the exposed side and stand it upright to rest on two wide 10-inch blocks-one way aft, and the forward one at the toe of the ballast casting. The vessel is obviously down by the head. Secure it at the after block so that it cannot possibly slide backward or tip sideways. Now clamp a straightedge from the side of the sternpost to a temporary upright on the keel, forward, so that its top edge is exactly parallel to the designed waterline as marked on the sternpost and the stem (see Figure 6-1a). Go to the lofted profile, on the flbor, and determine how much the top of the keel rises from, say, station number 6 to station number 4, and be sure that the straightedge approaches the keel by the same amount in the same length. This, then, is your built-in water level. Jack up the forward end of the casting until the straightedge is truly level, and build up under the ballast keel with firm blocking. You'll wedge up three times before you overcome the settling of the blocking when the weight comes on it. Be patient and get it right, or you'll be in a mess from now on. Level the top of the keel athwartships, and brace it; plumb the sternpost, and brace it with diagonals, from the floor to the after face so that they'll be well clear of the rabbet. Now stretch a tight line from a midpoint on the after face of the stem at the sheer, all the way back to the middle of the sternpost at its highest (aftermost} point. Hang a plumb bob from this line to hit the top of the keel just aft of station number 3, where the centerline of the keel is still visible (Figure 6-lb). Push the top of the stem sideways, as necessary, until the plumb bob hangs exactly over the centerline, and secure it there, preferably with a horizontal brace from the top of the stem to the side of the shop. Brace it from forward also, trying to estimate and overcome its tendency to droop. You'll have a final check on this height when you have established the plane of the cross spalls on the molds and can project it to the 24-inch waterline marked on the stem. Fitting the tail feather We've still got the tail feather to fit before the molds go up, and the transom frame must be in place before the ribbands go on. Let's get these two settled. There are those who will argue that the tail feather as I show it is all wrong and criminally weak as compared to the old system, wherein the central member butts against the after face of the stern post and is locked there by the twin horn timbers (Figure 6-2a).The old system is good indeed, especially if you bring the top of the post all the way up and tie it to heavy deckbeams. The system I show gets worse and finally becomes very poor as the angle between the stern post and the tail feather approaches 90 degrees-as, for instance, in a normal powerboat or a motorsailer. But it is a perfectly good system in the present instance, where the joint amounts almost to a long scarf, so long as the bolts are big enough and properly located. It has to be strong. The backstay pulls upward at the end of the counter, and this normal load of a ton or so can increase to a frightening amount when a sea breaks into the foot of a big jib. But don't worry about that joint. The mast will explode before it pulls apart.