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.

Figure 6-1a

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.

Figure 6-1b

Figure 6-2a

Figure 6-2b

So much for that argument. Here we have a flawless piece of timber, 5 inches deep and 7 inches wide, which must be bored for the rudderport, rabbeted on both sides, and fitted at its after end to the transom frame.

Start with the rudderport. Same auger, same technique as for the shaft hole-we are not going to thread a tube through the timber in the usual way, and therefore we need only be sure of proper clearance for the l ½-inch rudder stock through the wood. You can line the port with a thin-walled copper or lead tube to keep the worms out, if you want to do the best possible job. You will eventually make a pattern for a bronze casting, which will be tapped to take the bronze-pipe rudderport and stuffing box, and which will be bedded and through-bolted to the top of the timber. Save this job for later.

Figure 6-2c

Figure 6-2d

Now the rabbet. Get the angles from station number 8 on the body plan; note that the rabbet lines are exactly 5 inches apart, to match the width (and therefore the rabbet lines) on the stern post. Study the cross section in Figure 6-2b, and if your courage is good, make both cuts with your portable power saw-from aft to a point 15″ forward of station number 8, no more. Save the rest of it until you have molds and battens to guide your chisel.

Figure 6-3a

Figure 6-3b

And finally, you are ready to make the cuts at the after end to receive the transom frame (Figure 6-2c). Get out the transom knee first its profile from the construction plan on the floor, cut from 4-inch stock-and place it in position atop the tail feather. Cut off the tail feather in line with the after face of the knee, but be sure to leave a jog at the bottom in way of the rabbet that matches the mitered ends of the planking-to-be, and simply carries the face of the rabbet across the transom. Note also that the bottom of the transom frame is in one piece across the end of the tail feather, and must be allowed for when you locate the knee and make that cut. A pad on the after face of the knee, from the top of this piece to the underside of the deck, provides a straight line for the transom planking to bear on.

Clamp the tail feather to the top of the stern post, and sight it like a gun-right down its centerline to the middle of the keel just forward of station number 5 (see Figure 6-2d) Drop a plumb bob from station number 8, and check its horizontal distance from station number 7 on the sternpost. Cut a narrow straightedge(¼ inch by l 5/s inches) and push it down through the rudderport to the keel. This proves the angle of the rudderport, gives the line to which the outer pieces of the sternpost will come, and will eventually support the skeleton pattern of the rudder, complete with the shape of the aperture and the location of the pintles.

Figure 6-3c

Figure 6-3d

Put it aside, for future use and bore those two forwardmost bolt holes, from the top of the propeller aperture up through the tail feather. Counterbore, as shallow as you dare, for the heads of 5/s-inch bronze bolts. Square off on top for washers and nuts. Poison the contact surfaces and drive the bolts. Fit a post from the floor to support the tail feather, just forward of the transom, and brace it strongly with diagonals to the floor. If you are sensible and methodical, you will now fit and fasten the two pieces of the outside sternpost (above and below the shaft hole).

Figure 6-4

These will of course be tapered from the forward to the after edge, and grooved for the rudder stock and forward face of the rudder. Use ½-inch bronze for all these remaining bolts. Plan locations of the three sets of gudgeons, and keep your drifts and bolts clear of them.

Bolt the transom knee in place-and be sure it stands absolutely true athwartships.

Fitting the transom frame
One last painful job remains to be done before the real fun begins. We need a transom, or at least the strong, exactly shaped, correctly beveled frame of a transom. If you love lofting, you can arm yourself with Chapelle’s Yacht Designing and Planning and go through the whole process of developing a full-sized transom, complete with bevels, on the floor projecting sheerline, waterlines, and buttocks, and using the stretchout. I did this twice, 40 years ago. Since then, I have become reconciled to an easier system that places faith in the designer’s ability to do the job in his scale drawing. If he hasn’t done it, ask him why not. If he can’t do it, regard him with grave suspicion. Half the transom will probably be shown on the lines drawing, laid off at right angles to the centerline of the transom in profile, and with enough points exactly located in its perimeter to define a fair curve. Cut off a 6-foot length of building paper, and fold it once, across the middle, end to end. Crease it, and lay the crease along the profile of the transom on the floor, with the ends aft. Tack it down. Lay off the transom widths shown on the drawing, square to the crease, at the appropriate intervals along the crease; these intervals are also· shown on the drawing. Bend a batten to the points thus located, and there she is. Cut to the line, unfold, and you’ve got the full transom to the outside of the planking, with the centerline nicely defined. Now all you’ve got to do is build a frame to that outline, arched to the proper radius, beveled to the run of the planking, and reduced in size, where necessary, to allow for the thickness thereof. (You will, of course, do all this in the best locust, white oak, black walnut, or dense hard pine you can get your hands on. This is the place where the rot starts first.) The transom frame is pictured in Figure 6-3a.

Begin with some handsaw work. Swing an arc on a board to a radius I inch less than that given on the plans ( to allow for the thickness of the transom planking) and long enough to reach across the full width of the transom. Saw this out, and use it as a pattern to mark at least two curved beams of 2-inch stock, which will temporarily bolt to the outside of the frame and hold it in shape until the transom planking replaces them. Now comes the tough one. You need a slab 1 ½ inch thick, about 7 inches wide and 30 inches long, sawn (or bent) to that same radius, which will make the bottom piece of the frame across the end of the tail feather. (Lacking a big, single chunk, or the means to saw something of this thickness, you can build it up with four layers sawn from 2-inch stock, doweled and glued edge to edge.) You will save yourself time and frustration if you now prepare an arched bed, on which you can assemble and clamp the various parts. Saw two boards to a radius 3 ½ inches less than that of the finished transom-to allow for the thickness of the transom ( 1 inch) and its frame (1 ½ inches) and the slats mentioned below ( 1 inch)-and separate them a distance slightly more than the height of the transom. Tack I-inch slats square across them, one to take a centerline, two on each side to support the vertical members and joining knees.

Fit the various parts together, face down, on the bed, as shown in Figure 6-3a, and apply the full paper pattern you made earlier for the final outline. (The paper pattern represents the outer face of the transom and includes the hull planking in its outline. For this particular boat, the pattern, if used for the inner face of the transom-i.e., for the shape of the transom frame-makes things come out about right. In other words, the plank thickness and the transom bevel just about cancel each other out. But be careful about using this simplistic approach on other designs-sometimes it doesn’t work. Another technique that might not work is that of ignoring the difference in expanded transom widths over the projected ones. The designer’s plan shows projected widths, and I’ve assumed, because there’s not much curve in this transom, that these can be used for making up the paper pattern. If your boat has a significantly radiused transom, you’ll have to be more precise here as well.)

Saw the individual pieces of the transom frame to the line, with a standing bevel sufficient to add wood enough for fairing in the finished bevel when the molds have been set up. The rough bevel along the bottom of the transom can be taken directly from the junction of the transom and the tail feather in the loft drawing. The bevel along the sides can be approximated where the transom joins the sheer on the half-breadth view in the loft plan. Finished beveling will come later. Reassemble. check with the pattern, pin the corner knee to the bottom and side pieces, and bolt your two temporary beams across from side to side to hold the true arc and tie everything together. Mark the vertical centerline on these crossbeams. Fit the 1 ½-inch by 4-inch vertical pad up the middle, the two intermediate vertical timbers, and the pair of big scab cleats that tie the sides to the bottom piece. Figure 6-3a shows all this better than I can describe it.

Now cut a notch at the bottom of this heartshaped transom frame to fit the angle at the end of the tail feather, and just wide enough in the forward face to match the rabbet lines (Figure 6-3b). Practice with a scrap piece until you understand the requirements. Hoist the frame into place now, clamp and bolt it dead center to the knee (Figure 6-3c), and prepare to square and brace it. To square it, you need a heavenly reference point. By eyeball estimate, project an imaginary line from the top of the transom knee, square to the line of its raking profile, and up to the roof of the shop.

Plumb up from the center of the keel in this general neighborhood, and drive (and bend) a nail there, to hold the ring in your long steel tape. The nail must center exactly over the middle line on the keel (see Figure 6-3d). Now swing the tape from side to side of the frame, and brace the frame from the floor, so that the twin points on the two edges are equidistant from the skyhook. If the boat you are building has an almost plumb transom, you can, of course, do this squaring from the center of the stem, or from the center of the cross spall on one of the molds. You can also square a raking transom from a point on a true centerline on the floor, extended well astern of the boat.

But this is not always an easy line to lay off, through all those piles of blocking. Stretch your tight line from the top of the stem to the top of the transom knee; check once more with the plumb bob to the centerline of the keel and tail feather, and brace strongly against sideward movement. You may by this time wish you’d picked a double-ended boat with a fine, simple stem at the back end, as well. I would understand and sympathize. Transoms demand thought, firmness, and constant vigilance in their handling or they’ll fool you, every time. But this one is locked, for the moment.

If you have a bell to ring, or a rocket to shoot off, now’s the time. You are about to set up the molds and see your boat full-size in three dimensions.

Set up those molds
Gather a level, a 2-foot square, a plumb bob, nails, a hammer, and half a running mile of pine scraps 3 to 16 feet long, and l inch square (or thereabouts) to use as temporary props and braces. Find two straight, clean, true, straight-edged planks that, butted end to end, will reach from the after face of the stem to the forward face of the transom knee. Mark centerlines on these, full length, on both faces, using string and the straightedge to get them true.

Fetch out mold number 5, and stand it on the keel as shown in Figure 6-4, centered, with the forward face on the station mark. Brace it with a prop from the top of the keel aft, plumb it fore-and-aft, and hold it level athwartships with two posts to the floor. Measure from the top of the cross spall to the rabbet line, exactly on station, and make sure that this agrees with what you laid down on the lofting floor. Set up mold number 4, then number 3, checking the height to the spalls and keeping the forward faces of the molds on the station marks. Brace these from number 5, well clear of the centerline on the tops of the spalls. Toe-nail the bottoms of the molds to the top of the keel lightly; brace number 5 forward, so that you can remove the braces to make way for number 6, which will stand with its after face on the station line. These four molds establish the plane of the spalls, which is of course precisely 2 feet above the load waterline.

Set up number 8 on the tail feather, with its after face on the station mark; set up number 2 on the stem, forward face to the mark. Stretch a tight string from the stem to the transom knee, touching the tops of all the spalls, and mark the stem and the knee precisely where this line intersects them. You will probably need to adjust the heights of the last two to agree with the plane established by the first four. You may find to your dismay that the mark for the 2-foot load line on the stem does not exactly agree with the string you stretched. Try to figure out what went wrong, and correct it; but keep those cross spalls in line.

If you raise or lower one or two out of that flat plane, you will perpetuate worse errors than the most careless designer could commit in fairing lines and scaling offsets. With this cross spall plane sacred and unbroken, you know that the sheer marks on the molds are right; you can extend the plane, by string, straightedge, or eyeball, and measure up to spot the height of the sheer on the transom-and on the stem, too, if any doubt exists. Finally, you can lay a fine strongback down the middle, and tie everything together square and true, thus:

Lay the longer of the two center lined planks fore-and-aft on the spalls; bevel its forward end to fit the slope of the stem; fasten it securely to the stem, centered exactly, underside on the corrected 2-foot load line mark. Let’s assume that its after end reaches 2 feet beyond the number 5 cross spall. Bring its centerline to the center of station number 5 spall. Plumb the mold fore-and-aft again with your level to the vertical post. Use your big steel square to set the cross spall precisely at right angles to the centerline on the under face of the strongback, and clamp it.

Finally, drop the plumb bob from the centerline to the keel top, and tie the strongback to the side of the shop so that it cannot budge off center. Anchor your long steel tape on the after face of the stem, dead center, just above the strongback, and measure to the two sides of the mold at the height of the spall. If these agree, it must be square to the centerline. Now, butt the other section of the plank to this one; cut it to length to fasten to the stern knee; join the two at the butt with a wide board cleat. Hang the missing molds in place; plumb, square, and fasten all of them. Tie the strongback to the shop wall every 8 feet and put a special tie, high up, on station number I-and she’s almost ready for rib bands.

Prove the sheer
For my sake, if not yours, let’s define and prove the sheer line with light battens. This is a process shrouded in mystery, mentioned in whispers outside the shops of the incompetent, accepted wordlessly as the final touch of the Master Craftsman-if you happen to like the way it came out. We’ve all heard of that taciturn genius who spends a day making minute adjustments to the batten, viewing it from his stepladder, allowing in his subconscious for perspective, haze, highlights-and finally achieving a line of ineffable grace, which even looks good when she’s out of the shop. I’m not in that class. I decided long ago that the designer probably liked to have the sheer come out about the way he marked it on his drawing. This assumption takes most of the glamour out of the business, but saves a lot of time and soul-searching.

Figure 6-5

Figure 6-6

If the molds are at their proper heights and spacing, and the sheer marks, taken from the loft floor, are clean and accurate on them, there’s not much need for inspired guessing. Start a batten at the stem, with its bottom edge at the mark, and wrap it around as far as it will go. Don’t pull it lengthwise and cause it to flatten its curve between molds. Tap another batten over it, top edge to the marks, and go the rest of the way aft. Measure up from the plane of the spalls for the height on the transom. If the curve has humps and hollows, go back to the floor and try to find your mistakes. After all, you are the one who laid her down. If some expert (other than the designer) tells you it ought to tip up more quickly up front, don’t just knuckle under. Tell him you’d like to see a half-dozen of his boats in the flesh, in order to study his individual style… and mark the sheer as it shows in the plans.

The line of the tuck
One more line should be determined and marked now, before the clutter gets too thick. I call this the “line of the tuck,” for want of a better name. It marks the division between two different areas of planking, and it’s important to get it in there, with a good ribband to follow it, just to establish squatter’s rights and keep others from encroaching on the territory.

Choose a long, flat batten, 1by11/2 inches, say, and start it at the point where the rabbet line crosses the joint between the stern post and the tail feather. Run it forward as if roughly parallel to diagonal number 2 in the lines plan, to cross mold number 3 about 9 inches above the rabbet line, and thence straight (without _sidewise distortion) to the back rabbet on the stem (see Figure 6-5). If you pulled a string tight between these two endpoints, and outside the molds, you would get much of the same line the shortest distance, or the nearest thing to a straight line between the points. Mark the molds at the crossings.

Finishing the rabbet
Go aft, now, and study the problem of the unfinished rabbet at the after end of the keel, up the sternpost and around the curve to the tail feather. Use plenty of battens to simulate planking. Twist a thin board from mold number 5 to the sternpost, to see where the garboard will lie. Cut with special care and caution at the top of the sternpost, where the angles change very abruptly. The battens will tell you what to do, if you are patient with them. Use your adze on the back rabbet on the keel arid up the stern post; use a chisel to cut the face of the rabbet all the way. Finish this chore by cutting all the remaining frame sockets in the keel, knee, and tail feather (see Figure 6-6). These last will angle aft, in order to lie in a true vertical plane athwartships. Clamp a matched pair in place, apply square and plumb line, and study them. You’ll get the point.

Bevel the transom frame. Bring the battens past it from mold number 5, and make saw cuts, in line with the battens, all around the edges of the frame. Cut to the bottom of the scores with an adze, a chisel, and a plane. Leave the final and exact cutting to be done one jump ahead of the planking crew.