- Description of contents
© MODEL SHIPS – YACHTS- I/C. ENGINES LOCOMOTIVES: CARS: RADIO CONTROL ~ ies a . APRIL !I9 1300 Um CERAM \e) i im ie MODEL MAKER PLANS SERVICE é CLARENDON AD. 36, 3 waTFO RO . HERTS ‘ 2 3 Sphig ty ‘ \ =n) —” oo \ ) (a” PLY FIN NOTCHED \ ~~ MZ Kk YX NS we, INTO PLANK T LEAD LINE _— DISPLACEMENT 8’2 LBS BEAM . LOA . Ths 30° LEAD SECURED WITH WOODSCREWS OF DECK VARNISH HULL INSIDE AND OUT AND UNDERSIDE FIT CECK E:VARNISH, FINISH WITH UNDER AND TOP COATS SAIL PLAN 44 FULL SIZE APRIL, ee are many desirous of building a sailing model but are prevented from doing so by lacx of facilities. The 30 in. model herewith could be easily built on the kitchen table, the proposal being to build it from layers of obechi, which is easily available, in the usual bread and butter fashion, and after the layers are cut out and glued up the boat can 1958 LEO A 30 in. yacht of simple bread-and-butter be construction, shaped with a rasp and coarse glass paper. It is proposed to make the sails of polythene, which is quite strong enough for sails of this BY excellent for beginners W.J. DANIELS size. The model does not, of course, fit any actual sailing class but is a good, seaworthy boat, easy to handle and capable of excellent performance, As an introduction to model yacht building and sailing it is first class. Although the notes throughout refer to: obechi construction, the design lends itself well. to building in heavier timbers, etc., provided that the interior is hollowed a little more than indicated. You will require three pieces of timber 74 in. wide by 30 in. long, % in. thick. The lower layers will come out of the upper, as shown on the drawing. The pieces to bring up the sheer can be made from the inside waste. The fin should be of 4 resin bonded plywood, and everything can be cut with a padsaw or fretsaw. The inside of all layers, except the bottom one, can be 2 in. thick; in fact, if a soft grade of obechi necessary is to used, carve it would anything not but be really the inside “corners”. The lowest one must be left flat on the inside and should have the slot for the fin sawn before gluing up. It is not proposed to have a hatchway, and also that the mast shall be mounted on deck. In so small a model the mast can easily be braced by setting up the shrouds against the forestay and sighted in line with the fin. After cutting the waterline layers place them in position and draw a line round each in turn on the under face of the layer above. Then place each in turn, keeping the centre line parallel so that you get a line about half an inch-wide amidships. If you draw a line again around the lower layer this will give the inside line that will give an even thickness on ‘the inside when the corners are carved off after gluing. Use Aerolite 306 or a similar resin glue and cramp or weight the hull until the glue is thoroughly dry. After taking off the corners inside mark off the sheer and fit the deck beams. The centre line on the sheer plan will give you the amount of deck camber at each beam. The beams should be drawn out on } in. sheet and fretted out; the cross-section of the hull construction shows a typical beam. Arrange a deck beam directly under the mast position and fit a strut 1 in. wide under the deck beam to the top face of the bottom layer to take the thrust of the mast, and glue in position. The hull should now be thoroughly varnished both inside and out, also the deck on the underside, The deck can be of } in. obechi or 1/16 in. ply and should be varnished before fitting. Glue and pin deck on and fit a small block with a mast hole to locate the latter. The hull and deck can now be painted. It would be best to give the hull a coat of varnish to stop absorption before the undercoat is applied, and sufficient coats of flat paint to get a surface for the gloss paint. Whilst painting, the spars and sails can be made. Use a 2in. “clean” dowel for the mast, tapering the top third. The booms can be 5/16 in. dowel or } in. x in. spruce, etc., tapered off at each end. Varnish thoroughly. Screw a screw-eye into the mast 244 in. above deck, on the front face, and place another 2 in, above deck on the after face for the gooseneck. A third is required 334 in. up on the after face to receive the mainsail head. The main boom requires an open eye in the end to form the gooseneck and the usual sheet, etc. The jib boom is fitted with an eye at its forward end, engaging in an eye screwed into the bow; this also has the usual sheet. Deck fittings are confined to two wire horses of conventional type and the two eyelets for the shrouds. Make the sails from polythene sheet, using stitches plus plastic cement or, better. EvoStik, to form the hems. Sew in position to mast and boom and to forestay and boom. i MODEL MAKER CHINA BOY sizes. Part four of D. A. Macdonald’s Sharpie Marblehead—deck, leads, painting and general varnishing, finish and varnish is drying the nut patterns able for this. To ensure that your patterns will produce castings of the correct weight, the following process is worthwhile. First measure up a rectangular block of the pattern wood, calculating its volume and weigh it accurately. From this you can determine its “specific weight” as a fraction of an ounce per cubic inch. weight “=X OZ. per cu. in The volume of each half of the keel should be 14} cu. in. (radio version), so that, when finished, each pattern should weigh 144 times the specific weight calculated as above. The outline shape of the lead is marked on the wood, cut out and trimmed to the lines. The corners are now roughly rounded off and the block temporarily pinned or screwed to a flat plate (e.g. of spare 5/16 in. ply). Mark off on this plate the lines shown on the plan, representing axes on which the cross- section is semicircular. Make a set plates fig cut-outs of cardboard with of — tem- semicircular the correct i —— Full-size drawings showing all aa CT price 10s. 6d. post free. In addition “a ml con structional details for the hull, etc. J or other Marblehead yachts is available, MM/505, price 4s. 6d., plus 6d. p. and p., or post free with the China Boy plan. offered up to the on the end of 3in. length of O B.A. brass studding, insert this in the lead which has the deep counterbore and assemble the leads on to the fin in their correct positions, securing with another nut, which will project slightly outside the lead. (See Fig. VIII). Use two long screws to hold the ends of the keels in position. These screws go right through one lead and the fin and bite into the lead on the other side. Careful drilling of the clearance and starting holes for these screws is essential to ensure a good grip without risk of breaking the screw. Do not tighten the screws up fully at this stage. When satisfied with the fitting of the lead pieces to the fin, you should now remove them, to be finally fitted later. can be made for the lead keels. Obechi is very suit- length x width x thickness be version should not exceed 101b. On the free sailing version, however, up to 11 lb. is permissible. After cleaning up the flat faces of the lead keels they should be fitted temporarily to the fin. For this, drill a hole }in. diameter through both castings on or near the C.G. Counterbore the hole on the outside of each casting to a diameter of 4in. and a depth of $in. on one keel, and + in. on the other. Positian one lead piece correctly on the fin, and mark and drill a corresponding }$in. hole in the fin. Solder a Lead keels inside can by someone experienced in this work. The castings when received will be found scmewhat overweight, thus allowing for cleaning up and trimming, which will have to be done before fitting to the hull. The finished weight of the lead keels for the radio details The hull should first be given an inside coat of varnish, thinned by the addition of approximately 30 per cent. white spirit thinners. This should be brushed well into the wood and into all joints and corners. It will be found rather slow to dry and should have two days in a warm dry place. This is followed by three full strength coats, brushing well to ensure complete coverage. Care should be taken not to apply the varnish so thickly that it runs down and forms pools in the garboards and on the chines. Include all deck beams, runners, carlings, etc., in the process and also varnish any platforms and other wooden parts you intend to fit in the hull later. the, templates right cheeks of the lead are different. It is advisable to have the lead pieces cast at a foundry or at least Inside varnishing While These pattern to guide the final carving, and should eventually fit when in position on the axis lines as drawn. Spokeshave, small plane, rasp and sandpaper will eventually produce a shapely pattern which has the correct weight. It should also balance approximately in the C.G. position marked on the plan, but in checking this, be quite sure that the balance is checked on the correct axis. Two patterns have to be produced in this way as, of course, the left and The deck The outline of the deck is marked out either from the drawing or from the hull itself, and cut out about 3/16 in. oversize all round. The openings for hatches and mast slide are marked on the deck, and cut out 4in. undersize all round. The deck is then varnished on the underside only in the same thorough manner as the inside of the hull. While the deck is drying, the mast step can be made up from T section cut from brass curtain rail. Screw the mast step into its correct position in the hull, making sure that it lies exactly on the centreline uf the keelson. It is advisable to remove the mast after first fitting it, and seal the screw holes in the keelson with varnish before replacing it. This protects the base wood in the screwholes against an ingress of water which could affect the plywood. Platforms and other wooden parts not already fitted inside the hull can be added at this stage. To fit the deck, apply varnish liberally to the top of the inwale all round. Also varnish the top of the deck beams and carlings and the tops of bow and stem blocks. Attach the deck temporarily by a few pins, in its correct position (i.e. so that the hatchways, etc, are located exactly). Mark out a line of pinhole points at 1}in. intervals all round, +in. in from the sides of the hull. Pin the deck down by 194 - i ee APRIL, the same method as used for covering the hull. Trim off the surplus wood at the deck edge, and, before the sealing varnish is hard, sand the edges smooth with the top of the hull. The inside edges of the deck openings should then be trimmed to their SRASS STRIP 1958 RUDDER . TUBE correct size. Priming The entire hull may now be sanded down. A smooth file will assist in removing projecting pin heads. Give the edges of the fin and skeg a nice round finish, but leave the bottom of the fin and of the skeg quite flat. The hull and the deck top may now be given a “priming” coat of clear Valspar, thinned down with white spirit. Allow 48 hours to dry and then sand down lightly. Apply two full strength coats of the same clear Valspar to the hull, rubbing down after each coat with carborundum paper and soapy water. If the deck is to have a “natural” wood finish, apply two coats of gold size, also rubbing down after each coat. Fitting the lead The lead keels may now be finally fixed in position. It is advisable to seal the joint between lead and wood; if the castings have a smooth, flat face, varnish will provide an adequate seal. If these are rather pitted, a thicker sealing mixture is needd. Red lead powder and goldsize is excellent, or varnish may be loaded by adding some powdered whiting to make a thick paste. Clean off any surplus sealing matter before it has a chance to dry hard. If the following order is followed, no difficulty should be experienced :— (1) Hold the leads in position and fit the studding with nut attached so that the nut goes into the lead with the deepest recess. (2) Add the other nut and tighten with a spanner just enough to hold the leads against turning on the studding. aw Add the end fixing screws, and screw these tight. : (4) Tighten up the free nut, and finally tighten the end screws. % (5) Wipe off all occluded sealing matter. When the seal is dry (allow 48 hours for this) file off the surplus part of the free nut, and fill in round the nuts and over the screw heads with solder or “plastic metal”. Finally smooth off the lead with emery paper, and give the lead keels one or more coats of Valspar colour, rubbing down wet to provide a smooth finish. Painting A two colour scheme is tecommended, with the colours meeting on the chine line. The original boat from which China Boy developed had topsides of tangerine and undersides of turquoise, and looked very smart. Adding a spoonful of one colour to the other ensures that the two selected colours will _- look their best in harmony. Gummed paper strip should be used to produce a sharp line between colours, and careful rubbing down between coats with wet carborundum is essential for a good finish. Let the topside colour overlap on to the deck slightly; the join will be covered by a beading round the deck edge. Finishing the deck If the deck is to be lined or otherwise decorated, this can now be done. A protecting coat. of Valspar C/sk, FIXING HOLES % roD is applied over the lining and lightly rubbed down. Beadings of 4in. half-round mahogany are prepared and varnished, together with end cover plates of }{ in. thick material to match. These are pinned down, and a final coat of Valspar applied over the deck and beadings. Rudder It is advisable to select a piece of well seasoned timber for the rudder, as this must not warp. A piece of old furniture mahogany is suitable; this should be planed to 5/16in. thickness, cut to shape, and fitted to the }in. O.D. brass rudder post, using glue and long screws. The bottom of the post should be plugged and the hole drilled for the rudder pintle bearing. The rudder should be thoroughly primed and painted’ When fitting the pintle bearing to the skeg, seal the joint and screwholes with varnish or paint. Trimming weight Before fitting the hull out, it should be checked for correct flotation. The radio version depends on a correct disposition of the equipment to provide sufficient weight forward to correct for the positioning of the lead keel well aft of the C.B. With the equipment (or weights in lieu), temporarily in position, the hull should be floated in a tank or bath. The free sailing version should have its vane gear on deck for this test. If it is found necessary to add trimming ballast, this will be fitted under the deck just inside the bow or stern block (as the case may be). The amount required should be determined on this flotation test. Fixing lead weights inside is comparatively easy. Drill two No. 51 drill holes in the deck where the lead is to be fixed, and two corresponding holes right through the lead. Pass two threads through the deck, and draw the ends out of the hatchway. Pass these ends through the holes in the lead and tie them together. Now pull on the free ends of the threads, drawing the weight up under the deck. Drive 3/8in. No. 1 screws through the deck holes into the lead holes. cut off the threads and the weight is secured. Fitting out No special instructions are offered for fitting out. A drawing is available showing construction of mast spars and all fittings for M-class yachts, and if this is followed, no difficulty should be experienced. Remember, however, that this is a light displacement craft, and depends for its stability on a low centre of gravity. Rigging weights should therefore be kept as low as possible. Sails should be of Terylene, the new polyurethane coated material being preferable to the varnished Terylene now in general use. 195 i) _ _ as Tis Liat MODES MAKER! UCKER’S TOPICAL TALKS eT et will, therefore, be seen that at an angle of 20 degrees of heel, the C.B. moves aft a matter of 4in. Since on an L.W.L. of 48 in. this equals approximately 0.25 per cent., and a tolerance of up to 0.50 per cent. is permissible, the volumetric balance of the hull can be regarded as perfectly satisfactory. I next measured the areas of the in and out wedges on every section. From these I was able to calculate the volumes of the in wedge (158 cu.ins.) and the out wedge (107 cu. ins.). Thus the difference between the in and out wedges is a matter of 51 cu. ins., and as our displacement has not been increased the boat must rise in the water until her heeled displacement is reduced to the same as her upright displacement. By measurement it was then ascertained that the area of the L.W.L. plane at an angle of 20 degrees ~\ MORE ON THE VALUE OF TUMBLEHOME a y N my Talk in the December issue of the MODEL Maker, I pointed out that though some model yachtsmen have exaggerated ideas about the value of tumblehome, in reality it serves no practical purpose in yacht design. As a result of this article I received a letter from one of our best-known young designers stating that he could not follow my reason- heel is 351 sq. ins. Hence when heeled to this angle the yacht’s line of flotation is 0.15 in. (approximately 1/7 in.) below the original assumed heeled L.W.L. This rise in the water will shorten our L.W.L. by 11/16in. forward and 13/16in. aft (=1+4 in. in all), reducing the L.W.L. from 48.0 in. to 46.5 in. The whole of this reasoning sounds extremely plausible, and a novice can well be pardoned for being misled, but in reality the entire theory is based on the false premise that the boat is not under way and her heel is produced by moving weights aboard, and not by wind pressure on the sails. Actually when a yacht is sailing, the wind exercises pressure on the sails. The amount of pressure exerted depends on the area of the sails and the velocity of the wind. The pressure is also affected by the boat’s angle of heel, by the angle the course ing. For desired already not by these comparisons, it is assumed that the angle of heel is produced by moving weights aboard the vessel, while she is at rest, and wind pressure in the sails, or other external means, In a normal no tumblehome out wedge, and be increased if L.W.L. Since yacht with a small at all, the in wedge the displacement of she floated at the nothing has been tumblehome or will exceed the the boat would assumed heeled put aboard to increase her weight, she will automatically rise in the water until her heeled displacement equals her upright displacement, On the other hand, if by using a heavy tumblehome, we reduce the volume of our in wedge to that of our out wedge, our total displacement will not be altered. Consequently our hull will not rise in the water when heeled, and our assumed heeled makes with the wind, and by the trim of the sails. With so many constantly varying factors to consider, it is not worth trying to calculate this pressure exactly. At the same time we know that any given wind pressure can be resolved into three components —(a) side pressure producing leeway, (b) down thrust causing the boat to settle deeper in the water, (c) forward pressure causing the yacht to make headway. Heeling is produced by a combination of L.W.L. will actually be correct. Hence, at first sight it might appear desirable to give a yacht a big tumblehome, but further study of the subject will enable us to view matters in their true perspective, and we shall see that excessive tumblehome is more likely to be detrimental than beneficial. It will, however, give quite as much information if we examine a yacht with no tumblehome whatsoever. This boat happens to be an entirely new design, though based on the lines of a highly successful model. As she is destined to be built of fibreglass, I was asked to give her no tumblehome in order to facilitate the removal of the hull shell from the former on which she is built. As far as they affect the points under consideration, the main dimensions are: L.O.A. 58.0 in., L.W.L 48.0 in., maximum beam 10.75in., L.W.L. beam 10.40 in., displacement (approximately) 254 Ib. When I am making a design, I invariably make a most exhaustive check of the canoe body before I add the fin and skeg. and the figures cited below were obtained during this process. The section areas, both on an even keel, and heeled 20 degrees, of the canoe body were measured. From these it was calculated that the displacement on an even keel is 557 cu.ins. and the C.B. falls 0.155in. ahead of the midships section. In similar fashion the heeled section areas (taken up to the heeled L:W.L. drawn through the intersection of the upright L.W.L. and upright centreline) were calculated, giving a displacement of 608 cu.ins. with the C.B. 0.030in. ahead of the midships section. It (a) and (b). What percentage of the total wind pressure is represented by each of these three com- ponents depends mainly on the vessel’s course in relation to the wind direction. For instance, when the yacht is running dead before the wind, (a) is nonexistent, but (c) is at its maximum. As a matter of interest it may be added that it has been calculated that when the yacht is sailing at 4 points off the wind (which is as close-hauled as is advisable, even for a very weatherly craft), (a) represents 60 per cent. of the total wind pressure on the sails, (b) 30 per cent. and (c) 10 per cent. These percentages are to be taken as being approximate, rather than strictly accurate. The above explanation will suffice to show that the down thrust exercised by wind pressure on the sails is very considerable, and is equivalent to an increase in the vessel’s displacement as she heels, that is far- greater than any small uplift resulting from the excess of in wedge over out wedge. Further in a well-designed boat this down thrust will put her down to the point when she is sailing on the longest possible waterline her dimensions can afford. Hence there is no benefit in tumblehome. It should be observed, however, that some bz-ats do not settle down and use their overhangs. When this occurs, the source of the trouble can usually be found in the curves of areas. 206
