Ship and Ship Models: Issue 79 – July 1954

TWO SHILLINGS | JULY _ 1954 The “A” Ciass Sharpie x and how to build her HEN the keel is shaped, but before it is chamfered off to its section, the skeg has to be fitted. The methcd is clear from Fig. 12. It is most important that the skeg should be vertical, and not lean to port or starboard. Likewise it is important ‘ to get the sternpost (back of skeg) vertical, or your rudder will not work properly. The skeg is cut from wood # in. thick. With the marking gauge, put two lines #; in. either side of the centre-line on top and bottom of the keel for the slot. Position the ends, and holding the keel in the vice at the correct angle bore two 2 in. holes to form the ends of the slot. You can either cut out the slot with a chisel or start with a keyhole saw. In the latter case keep well inside your lines and finish with a chisel. When cutting your skeg, you will have, of course, allowed for the part that goes through the keel. The top of the skeg will then assist in getting it in position. Put temporarily in position, and with a set square test it for thwartships alignment. Remove the skeg, and if it has not already been done mark the sides of the keel for planing to section. In this part of the boat take the measurement from Section 9, and remember that there is no } in. wide flat bottom to the keel. When the keel has been planed to section the skeg is glued in position. The after part of the keel is then laid aside until required. Fig. 12. Fitting the skeg Since the centre member of the backbone assembly is formed by the top part of the bread-and-butter fin, it may be advisable to deal with the fin as a whole before getting down to details. The lines drawing which appeared at the beginning of this series was not intended as a plan to work from, but simply to show the lines of the boat, and due to its small scale I omitted the two additional Continued from June issue, page 227 264 BY H. B. TUCKER waterlines situated } in. and } in. respectively above W.L.8. These and other details omitted from the small reproduction, all appear on the full-size drawings. Readers are, therefore, asked to refer not only to these lines, but also to Figs, 5 (pages 60-61 Feb. issue) and 13, bearing in mind that the bottom of the centre member of the backbone falls on W.L.7. From the bottom of the fin to the top of the keel from its forward end to } in. ahead of Section 6 is 8} in., and abaft this point it is 8} in. Up to W.L.8 would make eight layers 1 in. thick. Since the top of the lead falls exactly half-way between W.L.s 6 and 7, two $ in. layers will be used at this point instead of an inch layer, in order to save work when the pattern for casting the lead keel has to be taken off. See also reproduction of lines drawing pp. 60 and 61, February issue. Hence, when we glue up our fin for carving, we shall only make the lower joints for W.L.s_ 1-6 inclusive, leaving the joint between the 4-in. layers to be made after the lead keel pattern is taken off. The joint on W.L.7 is never made at all since this is where our detachable keel takes off. The joints for the two } in. layers on top of W.L.8 are made before carving the fin. Now let us examine the structure of the detachable keel (Fig. 13) in detail. This is shown with the joint slightly open. Instead of three or four keelbolts, only two are used but these are stout. To remove the keel, the butterfly nuts and washers are taken off, and the keel is then free. The locating studs serve to keep the ends of the fin in alignment with the hull. The contact faces of the removable fin are shod with brass plates held in position with screws as shown. To make room for these plates, the contact faces of the layers on W.L.7 are planed away for the thickness of the brass to avoid increasing the depth of the keel, which would probably put the yacht over rating. The keel-bolts remain permanently in the fin, and brass tubes are put in the hull for them to pass through. Rather hefty screws are put through JULY, 1954 SHIPS AND SHIP MODELS » EO CO € SelB py KS take out this temporary layer, it can be used as a ce ore A¢ IS a Fig. 13. The detachable fin : the broken line shows the extent of the lead when the boat is intended for radio control. the lower face-plate as they also serve to attach the lead to the 3 in. layer which forms the top of the detachable fin. The after screw is also large as it serves to keep things together. The locating pin at the fore-end of the lead prevents the lead being bent and keeps it in position. The locating screw at its heel serves the same purpose. Here is a little way in which we can save labour. Our face-plates will be made of sheet brass approximately 7; in. thick. It makes no difference whether the joint between detachable fin and hull falls exactly on W.L.7 or 7 in, above it. So instead of making the layer between W.L.s 7 and 8 of 1 in. wood, we can put in a temporary layer } in. thick and make the permanent layer { in. thick. This has the further merit that when our fin is carved and we WL7 ee We he es Si, trim the upper face back sharp to the marked line, but leave the rest of the carving until later. As the layer between W.L.s 7 and 6 is made up of two 3 in. thicknesses, screw these temporarily together, square the edges up, and mark in the centre-line and station lines as before. When it comes to making the template, we find from the plans that in the after part, the lower W.L. extends beyond the upper (see Fig. 14). Hence we have to cut our wood to a composite shape. First trace W.L.7, and then transfer the tracing paper to W.L.6 to get the shape for cutting. When actually marking the wood, you have to mark not only the composite shape on the top face, but indicate where the top face ceases to be the larger. On the bottom face you have to mark the shape as well, particularly the part where the lower face is the larger. In trimming to the line, you trim the upper face for the part where it is the larger, and the lower face where this is the larger. The same procedure applies to all the other layers. It should be explained that the object of trimming back the faces to the line is so that you know exactly where the lines fall, and thus have a guide when carving the fin to shape. The keel-bolts are made from + in. diameter brass rod, so holes have to be bored accordingly. These fall half-way between Sections 5 and 6, and 6 and 7. As it would be virtually impossible to drill these accurately after the fin is assembled, the individual layers are separately chilled. Mark the spots on the centre-lines of both faces of each layer. Start by boring about half through the wood from the top-face of one layer, turn it over, and bore the rest of the way from the bottom face. The holes should register. Do the same to the other layers. Your holes should now register right through the fin. Test this with your rods. template to mark out our brass-face plates for shaping. The wood for the layers has to be marked out. If you are working from your own enlargement from the lines plan published in this magazine (pp. 60 and 61, February issue) you will have to take out the two W.L.s $ in. and } in. respectively above W.L.8. Rule these on to the sheer plan and body plan. The former will give you the position for the ends, and the latter the widths on each section. Start with the layer between W.L.s 8 and 7. Since W.L. 8 is the larger face, our wood has to be cut to this. You require a piece 21 in. X 3 in. x $in. To make a template, take a tracing of the W.L.7, fold up the centre-line and cut out the double thickness, as you did for the moulds. | Before attempting to transfer this outline to the wood, the latter must have the basic lines put on it. Run a centre-line down the wood, square this round the ends, and repeat the centre-line on the other face. Mark in your station lines and square these right round the wood. Pin the template on to the wood, taking care to get your centre-line and station lines exactly in position. Run a pencil round the template. With a bow saw, or compass saw (sometimes called a “keyhole I= Whines e t saw ”’), cut out the layer, sawing about 4 in. outside the line. With a sharp paring chisel, Fig. 14. (To be continued) = 22 SN ~ an Plan of layer between W.Ls 6 and 7. 265