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OCTOBER 1970 THREE SHILLINGS (15 p) U.S.A. & CANADA SEVENTY-FIVE CENTS [o> HOBBY MAGAZINE OCTOBER Part Five —the ‘A3 FIG. 23 HARD CHINE HULL Bow Block method’ of building 1970 DETAILS OF FIN AND SKEG CB Hull, Transome Piece wk a hard chine hull |/4″ Mahogany Laminated 1/4″ Tufnol or 3/8″ Ply BODY PLAN By C. Griffin RACING MODEL YACHT CONSTRUCTION A HULL made by this method depends, as do all permitted under the Marblehead rules. The inwales and chines are best constructed by laminations of 4 in. thick by # in. wide spruce using Aerolite 306 glue. The fin is cut from ? in. thick marine plywood and extends through to the king plank, see fig. 23. The skeg and extension is laminated from two pieces of ¢ in. thick mahogany glued together with the grain of the wood reversed to prevent warping. If each layer of the mahogany is chamfered at the rudder tube edge before jointing this enables the rudder tube to be fitted into the recess so formed using epoxy and ? in. x No. 2 countersunk headed brass screws. See fig. 24 for details of a full rudder tube. hulls, on the accuracy of the initial building board, the marking out and the subsequent mounting of the shadows. The hard chine hull appeals to the novice builder because, compared to the round bilge type hull, it is easier to build. Secondly, the materials required for the construction of this type of hull are more readily obtainable, i.e. marine plywood, usually -4 in. thick. As with all methods of hull construction, the first task is to trace the shadows from the body plan, making the allowance for the plywood skins or planks. Fig 22 gives the details of a shadow; note that notches are cut to receive the inwales, chine stringers, keel plank and king plank. To build the king plank in with the hull still on the shadows makes removal of the shadows difficult when the hull is removed from the building board. Therefore, to remedy this situation the shadows should be made in two parts as indicated. This task is simplified if the shadow is made first as a whole, the necessary cross pieces screwed into place and then the shadow split by Fig 24A gives details of a short rudder tube where only epoxy is necessary to fix into position. The king plank is cut from 1 in. by 5/16 in. thick spruce extending from the bow block to the transom with slots to receive the upper ends of the fin and skeg. The planks or skins which form the hull are cut from either Imm. or 1/16 in. marine plywood; the former has a tendency to buckle if used for large unsupported flat surfaces but may be strengthened by the judicious use of balsa sheet. Where the final weight of the hull is critical, the use of 1mm. marine plywood and balsa sheet strengthening has obvious advantages. If care is taken in trueing sawing. See fig. 22A. Mount all the shadows on the building board as described in earlier articles, checking for accuracy and symmetry to produce a true facsimile of the original design. Note that here the process of checking is easier the chines and the skins are cut accurately, good close than that of a round bilge hull. The transom is made from 4 in. thick obeche and the bow block formed by three laminations of the same material with an integral bumper formed from 4 in. thick cork to give a thickness of 4 in., which is the maximum A SHADOW FIG, 22A. Saw Cut ———— Notch for chine Notch for (REVERSE SIDE) — Cross Pieces 3 Notch for king plank stringer inwale Mounting Block vi DETAILS OF SPLIT SHADOW | — Notch for keel plank ape Building Board —-[- 417 | Ye_\ a) – LH DETAILS OF L FIG, 22, glue joints will result and the hull will be of adequate strength for competition racing. There should be no need to screw or nail the skins although map pins may be necessary to hold the skins in position whilst the glue is drying. It is usual to cut the two bottom skins first and MODEL BOATS FIG. 24 LONG RUDDER FIG. 244 SHORT RUDDER TUBE TUBE-RAKED RUDDER FIG. 25 FIXING BOTTOM SKINS UPRIGHT RUDDER FIG, 25 A. OVERLAP OF SKINS SHOWING OVERLAP SINGLE 3/8″ O.Dia. Brass tube DOUBLE CHINE CHINE Overlep to receive Araldited in position side skin | 3/8″ O.Dia. Brass tube Cross sections of Skegs – Note reversed grain SEK 3/4″ No.2 Screws eee these are checked against each other for symmetry, then temporarily placed in position, allowing for a slight overlap on the chines. If the fit is accurate the skins can be glued into position. The next pair of skins which form the sides of the hull in a single chine hull are cut and checked for symmetry. They are glued to the chine inside of the overlap of the bottom skin and onto the inwale, allowing for an overlap at the inwale, if an inlaid deck is desired. When the glue is dry trim off the surplus overlap of the bottom skin. See fig. 25. If a double chine hull is being constructed leave an overlap to accept the third skin. Fig. 25A. Remove the hull from the building board, fit some temporary deck beams and then remove all the shadows. Brace the hull in the vicinity of the mast and chainplates to prevent the strain of the shrouds and the mast from distorting the hull shape. Fit the king plank and the deck beams at predetermined positions, giving the deck beams a camber of approx. 3 in. for a Marblehead, slightly less for a 36R;; this adds to the rigidity of the deck. Note that the deck camber can be assisted by raising the central king plank relative to the sheer line. This method can only be used if a built-in carrying handle or recessed hand grip or deck-mounted handle is fitted. For the same reasons a deck-mounted mast heel must be fitted. Should an opening or sliding hatch or a keel-mounted mast heel and mast slide be desired the king plank must be constructed as shown in fig. 26. The opening hatch is constructed from plywood and 4 in. thick obeche with a cork seal and must have some positive securing device (fig. 27). Sliding hatches can be constructed as shown in fig. 27A. If an opening or sliding hatch is fitted there must be some form of internal carrying handle cut or fitted on the line of the centre of gravity of the boat for ease of carrying. Cut the chainplates from 20 gauge stainless steel sheet as shown in fig. 28 and glue (epoxy) and bolt through the inwales into backing plates using 6 or 7 B.A. countersunk headed brass bolts. : FIG. 30. FORMERS ON Cut the deck from | mm. or 1/16 in. marine plywood and shape to fit either inside the sheerline skins or overlapping the skins. Cut out suitable openings for the deck hatch or hand grip and the rudder post tube. Drill 1/16 in. dia. holes around the edge of the deck approximately 2 in. apart and 3/16 in. from the edge, slightly countersink the holes. Fashion the garboards from obeche and glue into position, ensuring that the 1 in. minimum radius rule of the garboards is not infringed. Give the inside of the hull and the underside of the deck two thinned coats of varnish to waterproof the interior of the boat. Line and colour the deck if this finish is desired, then give all deck contacting edges of the deck beams and inwales a coat of either varnish or turpentine thinned Sealastic. Whilst this coat is still wet, screw the deck into position using 3 in. long No. 1 or 2 countersunk headed brass screws. When the deck is secure and the varnish has had time to harden, trim off any excess on the sheer skin if the deck was inlaid. Give the hull a coat of undercoat and varnish the deck. The stage has now been reached where the lead keel and the fittings need to be fitted but this will be dealt with later. There are two variations on the hard chine building method; it will be appreciated that the method just described is basically a ‘rib and plank’ type construction. As an alternative the shadows can be replaced by ‘formers’, fig. 29, which are left in position and form part of the hull. The formers may be cut to incorporate the deck beams; however, more time will be spent in shaping the formers and the final hull may be heavier than that of the method described. The second variation, strictly speaking, is a new method of construction; here the hull is formed inside a set of external formers mounted on a building board. This method lends itself more easily to mass production. The full outline of each former is traced from the section station of the body plan to a common datum line with no allowances for skin thickness or ribs or notches. The external formers are then cut from + in. plywood and mount- BUILDING BOARD FIXING BALSA STRINGERS FIG. 31. — Plywood Skin Balsa chine stringer Resin impregnated tissue SS all Balsa keel stringer r g | he Former 418 OCTOBER FIG. 26 CONSTRUCTION OF KING PLANK FOR HATCH OPENING FIG 28. =—II||| DETAILS OF CHAIN PLATES AND FIXING mu 9° AND KEEL MOUNTED MAST Choin Plate Chain Plate fh. 20G Stainless FITTING. 1970 — Inwale smarts Ni {}| 6BA Brass Bolts Backing Plate : — Skin Backing Plate 20G Stainless Steel DETAILS OF “PLUG TYPE” HATCH Pucreo FROM 1/4″ THICK OBECHE FIG 27A. DETAILS OF SLIDING HATCH = Se Cork or 3S y es — T 3/8″ x 3/8″ Mchogany Rebated |/16″ x \/8″ deep to take I/6″ Plywood | vas \/16″ Marine Plywood ed on a building board at the correct section spacings at 90° to the centre line and checked for accuracy, see fig. 30. All the skins are cut in pairs and each pair checked for symmetry and placed inside the formers. The chine stringers are made from + in. square balsa wood which is fitted into the angle of the skins, gently sprung into position and secured by the use of glass fibre cloth and resin, fig. 31. Alternatively, the chine stringers may be shaped from 4 in. thick by 2 in. wide spruce glued into place with Aerolite 306 glue and a second lamination fixed to the top surface, fig. 31. In both cases map pins are used to hold the stringers in position whilst the glue is drying. A bow block and a transom piece are fashioned from 4 in. thick obeche or ? in. thick marine plywood, recessed to accept the inwales and kingplank and glued into position. Strips of wood nailed across the top of the first and last former will hold the bow and transom in place whilst the glue is drying. The inwales are laminated in situ using 4 in. thick by ? in. wide spruce and Aerolite 306 glue. Map pins and clothes pegs will hold the inwales in place while the glue dries. The kingplank is 1 in. wide by 5/16 in. thick spruce with slots cut to receive the upper ends of the fin and skeg. Note that at this juncture provision has to be made for the type of mast fitting and the carrying arrangement, details of which have been described in earlier articles. A further variation of a carrying device is shown in fig. 32. Glue the kingplank into position after checking that it fits centrally in the hull; this is done by measuring the 7 distances from the kingplank to the former at each side at several section stations. Cut and fit all required deck beams, notching them into the inwales at the predetermined positions. Fit any FIG. 3IA. FIXING SPRUCE STRINGERS AND INWALES : Notch for inwales A an { Rubber Seating 3/4″ Deep Plug = 3/8″x 3/8″ Mahogany : S= FIG. 29. Notches for 9 stringers s FORMER AND MOUNTING BLOCK additional blocks that may be necessary to accommodate the deck fittings. Remove the hull from the building board. Fit the fin,through a slot cut in the keel plank or backbone and locate it in the slot in the kingplank. Fit the skeg in a similar manner, checking for true alignment in a fore and aft direction. Glue the fin and skeg into place and fit strengthening fillets around the root of the fin and skeg inside the hull. Cross brace the hull in the way of the mast and chainplates to take the strain of the shrouds. Shape the garboards from obeche and glue into position or build up the garboards with Plastic Padding, ensuring that in both cases the 1 in. minimum radius garboard rule is not infringed. The chainplates are made from 20 gauge stainless steel plate as shown in fig. 33, and glued (epoxy) and bolted, using 7 or 8 B.A. brass bolts, through the inwales and the skin as illustrated in fig. 33A. The deck is cut from 1/16 in. thick marine plywood and fitted onto the inwales and deck beams. The deck can be either flat or cambered, lined or painted and is cut to suit the predetermined mast fitting, carrying arrangement and rudder tube. Drill 1/16 in. holes approx. 2 in. apart around all edges of the deck. Give the inside of the hull and the underside of the deck two turpentine thinned coats of varnish, rubbing well into the wood to increase the waterproof integrity of the hull. The contacting surfaces of the inwales, deck beams and deck are given a further coat of varnish and, while the varnish is still wet, screw the deck into place using # in. x No. 1 countersunk headed brass screws. When the deck securing varnish is dry, undercoat the hull using a good quality paint and the hull is ready for the lead keel and deck fittings to be added. Plywood Skin FIG. 32. CARRYING HANDLE Folded Position 5/\6″ Tufnol ts Chain Plate Former FIG. 33A. CHAIN PLATE FIXING 419 MODEL BOATS 1970 BRITISH & OPEN ‘A’ CLASS CHAMPIONSHIPS and the YACHTING MONTHLY INTERNATIONAL CUP Above, fortunately the water was very warm. Chris Dicks and his mate were ceremoniously slung in by some of the other younger participants; Clive Colsell (nearest camera) overbalanced and followed Chris in, and instigator Mick Harris followed shortly after. Second photo shows wedgy appearance of winning boat, published in MB May issue. OSPORT this year returned to ‘normal’ for the week of the A Class — usually stronger winds are expected at Fleetwood, but of recent years it has seemed that Fleetwood had the light winds and Gosport the blows. This year saw, if anything, insufficient wind for most of the 32 entrants. The number conveniently divided into four divisions and in looking at daily scores it should be remembered that not all boats had sailed the same number of heats until Thursday. Sunday and Monday were sunny days with a light south-easterly (all days gave beat and run conditions) and the heavyweights made their mark. Kubernetes, leader on BRITISH A CLASS CHAMPIONSHIPS Reg. No. Boat Skipper Club Division Sun. Mon. Tues. Wed. 23 Thurs. — Fri heats 1 K877 Emperor C. Dicks 2 K884 Golden Fleece R. J. Burton R. Gardner Gosport G128 K896 Moby Dick Shenandoah KI. Pollahn K. Roberts Germany Birkenhead K787 Colleen Dawn A. Schollar Gosport 3 4 5 K879 Genesis 6 K789 8 K750 Serica K898 K790 7 FH 12 15 16 17 18 19 K822 K764 K876 G135 K875 K830 K839 K817 K865 K880 23 24 25 K722 K836 Philippa D 24 42 53 78 Eastbourne D 21 42 55 78 73 81 B Cc 12 24 40 38 56 59 69 71 82 71 A 10 36 58 63 63 B 15 Fleetwood Cc N. D. Hatfield Y.M.C. D 21 Kubernetes Blenheim R. Norton K. Jones Leeds and Bradford Birkenhead Kami Sama D. Lippett C Cc C D Colley Scheherezade Hamburg D. Parkinson Clapham H. Atkinson R. Cole Leeds and Bradford Guildford Fr. Jacobsen Germany Zerlina Odyssey Boreas Telstar Tiger Cat R. J. V. E. C. Harpoon A. E. Carter Serenade Gretal Fogaty Quinby Knapp Brown Mitchell H. L. Francis W. Poole D. Bush A. B. Frost R. Temperton Bournville Forest Gate 25 48 33 40 27 22 18 20 38 34 30 27 51 51 53 36 62 62 16 39 40 61 114 126 90 99 114 93 88 101 100 78 87 58 78 67 74 78 72 85 82 58 66 79 82 33 27 31 22 30 16 45 50 53 35 50 39 55 58 51 58 45 55 58 55 58 45 76 Ts 62 68 59 81 80 75 73 71 D 19 32 40 45 50 60 71 47 56 53 47 56 53 65 62 58 67 66 62 C A A Hove and Brighton Fleetwood 10 2 59 57 57 19 9 11 26 24 32 24 28 52 49 44 51 49 59 57 B 13 32 42 49 59 Cc 9 19 32 40 40 K852 Tabatha 29 KS567 2X Echo J.K. Smith Australia B B 6 18 17 24 18 28 30 35 31 32 K905 F56 Advonne 3JM R. S. Hawgood M. Bertoux Danson France B B 6 6 16 20 25 25 31 36 28 30 KA3 C. Colsell F. A. Johnson H. Shields S. London Scotland D 8 6 23 23 33 69 86 86 14 14 10 10 9 Wrong Direction W. Jupp 86 65 50 K897 Aegir 93 74 78 Trilby Hell Cat Lady Gay K895 109 62 66 65 63 K831 K871 K777 27 99 y hy / A A 27 58 91 D Gosport Gosport Leeds and Bradford Gosport Gosport 55 A A D A Cc B Gosport Gosport Y.M.C. Gosport Fleetwood 12 38 71 68 59 82 71 71 62 35 49 33 46 40 50 38 42 44 45 49 48 52 60 56 52 Sunday A and B 4 heats, C and D 7. Monday A and B 11, C and D 12. Tuesday A and C 20, B and D 15. Wednesday A and C 23, B and D 20. Thursday all boats 28 heats. 422 OCTOBER 1970 Left, ‘Moby Dick’ with a safe-looking lead over ‘Philippa’. Swans hung about all the week, but did not prove a serious obstruction. Below, top, ‘Emperor’ sailing ‘Hell Cat’; note modern mainsail leaches with roaches almost straight between battens to avoid curling. Centre, ‘Advonne’ is something of an experimental boat with enormous jib, pocket luff mainsail, and other interesting features. It would be interesting to see how she sailed with a more conventional rig. Second boat is Ken Jones’ ‘Blenheim’. Bottom, Roger Cole connects as ‘Scheherezade II’ sails gently in; ‘Zerlina’ being lifted out. | : : the first day, yielded on Monday to Emperor and Golden Fleece, but Moby Dick, another of the big boats, had a heat in hand and was only 2 points behind the leading pair. Quite a number of skippers were already thinking in terms of 75-80lbs. for their next boats by this time. Tuesday was again fine, but hazy, with a light, variable wind between N.E. and S.E. Though A and C divisions had completed 20 heats by the end of the day, only Shenandoah (59), Colleen Dawn (58), Odyssey (53), and Colley (53) were ahead of or equal to the leading boats in B and D, which had only reached 15 heats – Moby Dick (56), Golden Fleece (55), Genesis (55), and Emperor (53). Much the same wind greeted competitors on Wednesday, but with overcast skies which brought light rain in the afternoon. Although conditions still favoured the heavyweights, Emperor at 564 lbs. and Golden Fleece, even lighter, started to pull away and tied at 78 at the day’s end, five ahead of Roy Gardener with Genesis and 9 in front of Klaus Pollahn with Moby Dick. Shenandoah, 3 heats ahead, led the other half with 71. The rain heralded a temporary weather change, with heavy rain on Thursday, fining up by afternoon, and the wind light S.E. to moderate S.W. Three heats were sailed to bring all boats to the 23 heat point, then all sailed a further 5. In the 8 heats he sailed, Chris Dicks dropped only two runs; Bob Burton was less happy with 21 out of the possible 40, tying with Gardner who had made 26. This left Emperor 15 points ahead with 3 heats outstarding, needing only one heat or run to be unassailable; if he dropped all 15 and Golden Fleece or Genesis made all 15, there could be a tie. In the event, Emperor dropped one beat and despite Golden Fleece’s valiant 15 points, won by a clear 12. Genesis dropped a beat to come third. There was, in fact, a tussle for all the remaining places, as the table shows, and the very light S.W. air on Friday provided some keen sailing; there was just enough breeze for skill to count more than luck on the fairly tricky Gosport lake, and the Championship thus remained very much alive despite Dicks’ virtually having won by Thursday. Under O.0.D. Joe Meir the meeting ran smoothly and with good spirits. R. S. Hawgood, skipper of the newest (continued on page 427) 423 OCTOBER dramatic — hydro 66.8 m.p.h. and mono 41.5. We include these observations as some beginners have vaguely heard of high speeds with R/C hydroplanes and wonder if they would therefore do better to stick the prop out behind the transom, as the hydros mostly do. The answer is clearly to build the boat to suit the competition requirements, and competitions on this side of the Atlantic demand good turn characteristics. A lot of experiments have been carried out by fast boaters in several countries in the last ten years, and all the time they come back to the same basic answer — stick the prop well forward under the hull. One other factor has a bearing on shaft angle etc., and this is obviously prop diameter. Most 34 cc. engines will use a 14-1} in. prop, or the continental 40-45 mm. It would be unusual to use a larger prop. on a boat of the size and type discussed. If the centre-line of the shaft is set a full 1 in. below the hull bottom, tip clearance will therefore be a minimum of + in. on the largest prop, and 4 in. or so on the 14 in. prop. We have successfully used a 14 in. prop on a 34 cc. diesel, but this is again unusual, though the 3 in. clearance would be within the limits we -have suggested. Internally, flywheel diameter (and clearance to get the cord under it easily) is the crucial factor, and the only A CLASS (continued from page 423) and somewhat experimental boat Advonne, put up with a great deal of good-natured leg-pulling, mainly concerning his deeply dished foredeck, referred to as his private swimming pool or the fish-tank; there was even a fish found in it at one stage! The winner and his mate were pitched into the warm water at the end and it was perhaps only just that the principal instigators of this followed them in. Next year’s meeting should be remarkable for the number of heavy boats promised; certainly the impression made by, particularly, Moby Dick and Kubernetes was the strongest yet by the big ones. It remains to be seen whether this is because skippers are getting used to them or whether the gentle winds of the week were so much in their favour. A good blow at Fleetwood should provide the answer. INTERNATIONAL CHAMPIONSHIPS ‘YACHTING MONTHLY’ CUP 1970 (Reported by W. E. Long) Fe countries competed — Australia, England, France, Germany, and Scotland. Yachts and skippers as follows: Australia ‘Echo’ J. K. Smith England ‘Emperor’ C. Dicks France ‘3 JM’ M. Bertoux Germany ‘Moby Dick’ KI. Pollahn Scotland ‘2X’ H. Shields Four rounds of five heats in each round with the relevant bye in each heat were to be sailed, two on Saturday, 8th August, and two on Sunday, 9th August. The 0.0.D. was Mr. J. Meir and the other officials were appointed from the Regatta Committee with Herr Fr. Jacobsen as an additional umpire. A start was made on Saturday at 10 a.m. and the weather was fine with a light to moderate S.W. breeze giving a run and a beat. Fast times on the runs were not expected. Two rounds were sailed, one in the morning and one in the afternoon and England and Germany dominated the racing throughout, finishing all square with 28 points. France clocked the fastest time of the day with 2 mins. 17.5 secs. There being not much prospect of stronger winds, the 427 1970 thing that can be said is to keep the motor as far back as is practical, particularly if it is a heavy one. Ex-aircraft modellers are usually surprised that boat plans or kits seldom give a centre of gravity position, but this is something which is hard to do, since the required position of the C.G. will be affected by shaft angle, propeller, engine power, and overall weight. With an aircraft, the C.G. is critical and quite a small variation can crash the model on its first test flights; one starts off with the C.G. about right and trims for a glide, probably by slight wing and tail incidence, adjustment, and then for power flight by adjusting the thrust-line. In a boat, the thrust-line and hull angle are fixed, so one moves the C.G. to trim. The difference in speed between various power units or different weight models to the same design means a difference in the dynamic lift and the point through which the lift acts, requiring a different C.G. position. Where highish speeds are anticipated external trim tabs are desirable, and we will be discussing these later. As a very rough rule of thumb, the hull C.G. is likely to be close to 40 p.c. of the overall length forward from the transom, further forward with a narrow boat and possibly a little further aft where the transom is wide. Next month we will move on rudders. O.0.D. decided to start at 9.30 a.m. on Sunday. The weather was again fine with the same light to moderate S.W. breeze giving the same run and beat. Right from the start the Australian skipper, who had had a frustrating day on the Saturday, suddenly found his trims and made his presence felt by taking points from England and Germany as well as from France and Scotland, but at lunch time, after one round and one heat of the fourth round, England and Germany were still all square. England and Germany met each other in the fourth heat of the fourth round with England holding a one point lead and Germany having the choice of berth for the beat to windward. England won the run which gave a three point lead, and also equalled the fastest time of France which had stood since Saturday morning. Everything now depended on the beat, whether England won the Championship, or finished all square with Germany again. As the race started, with Germany in the windward berth, the wind shifted slightly toward the south, setting both boats toward the windward bank. The English, sailing a trifle more free, was the first to feel the shift back again to the S.W., and squared away for the line. The German boat under the bank did not respond so quickly and England won the race and the Championship by six points. The fifth heat carrying five points was not sailed. The Australian boat finished with 41 points. Had she had a better day on the Saturday, it is possible that she would have had quite a definite bearing on the destination of the Championship. The Deputy Mayor and Mayoress again presented the various cups, and Herr. Fr. Jacobsen, President of the International Model Yacht Racing Union, made a presentation on behalf of the Union to each skipper and mate of the five countries which took part. So ended the closest and most exciting International Championship for many years. YACHTING MONTHLY CUP 1. 2 England Germany 3 4 5 Australia Scotland France Emperor Moby Dick Echo Sat. Sun. 28 54 28 48 16 41 2X 3JM 12-25 16 22 Wing and Wing Cup (fastest time) England Johnny’s Cup (most windward boards won) and France. England, 12.
