- Description of contents
~*~” Vviodel MARCH 1971 S>EVEHNOTBY-BFYIVEMAtGASZINE, & t a =© DA U.S.A. & CANA . oe te [uas esc m MODEL BOATS SQUARE ONE Fred Shepherd’s ultra-simple 36 in. R yacht. Full-size plans for hull, ete. are available ref. MM 1104 price 50p post Model Maker Plans Service, free 13-35 from Bridge Street, Hemel Hempstead, Herts. PART THREE – FITTINGS continued Tiller and Rudder Assembly. Using an } in. rudder post rotating inside a { in. I/D brass tube may sound sloppy, but examination of the drawing will show that the post is located top and bottom by pintles. The rod needs a deep dimple top and bottom, and it is thus mounted clear of the tube. The bottom pintle is silver soldered into the sole of the pintle bracket, and the top one is in the form of a screw which is screwed down until the rudder is held positively in place, without shake, but completely free to swing; this is important. The blade of the rudder needs its foreside grooved to take the fin. rod, which is epoxied to it before assembly. All other components are clear from the drawing. Vane Pintle Mount. This projects beyond the transom (allowed under the rules of the class) in order to get an adequate linkage between vane gear and tiller. The mounting block is simply clamped against the transom by two screws screwing into a plate epoxied inside. The pintle, length to suit the vane gear used, screws into the top; ensure that it is truly vertical. Jackline and Sheeting layout. The sheeting arrangement shown has been used on all the writer’s boats for some four years, and has rarely given trouble. Cord, etc., is kept to an absolute minimum on the booms, but the important factor is that if one has to make a retrim, both booms move together; this saves a lot of time at the bank compared with having two bowsies to adjust. Although any circular bowsie could be used, the Seelastik tube top is neat in appearance and easy to grasp, especially as fingers may be wet and cold. Mast. Refer to the sail plans for jib luff attachLEAD CASTING MOULD SCREWS HOLDING BOX HALVES TOGETHER if POURING HOLE, APP, 1.1/2″ DIA 1/4″ THICK BRASS FORMING SLOT IN LEAD CASTING FOR FIN BOX. INSIDE 3″ A mast foot, sawn and filed from +in. dural, is epoxied into the bottom end of the tube, and this engages in the mast step, which is an integral part of the fin. With this fitting and the stiffness of the tube, no shrouds are necessary on this size boat, but in order to keep the forestay and jib luff taut, a cord backstay is needed, so all topmasts should be fitted with a spreader projecting rearward, and a clip-in or push-in spreader should be available to fit to the top of the tube when no topmast is carried. The backstay is hooked between the aft end of this and the plate bolted to the top of the skeg, and has normal bowsie adjustment. The Lead. Although casting leads has been recently covered, a brief reiteration may be permissible. A wooden pattern must first be made, using any wood, though preferably a softwood. Two boxes, slightly longer and wider than the pattern, are needed, one with a bottom and the other open. Fill the bottom box loosely with casting sand, push pattern in upside down, and ram sand all round till level with widest part of pattern (see sketch). Screw top box in place and sprinkle powder over surface of sand; Polyfilla has been found to work quite satisfactorily. This powder prevents the casting sand from sticking. Fill top box with sand, ramming as before. When full, cut a hole about l4in. diameter down to pattern. Gently lift off top box and tap pattern lightly to loosen it. The sketch shows a metal strip positioned to form the slot for the keel fin, and it is well worth taking time to line this up, as drilling and chiselling a zin. slot in lead can be frustrating. When satisfied on line-up, screw back top of box. Melt about 10 lb. of lead over a gas ring, lamp, etc., and carefully clear all the floating The lead should be poured as cold as possible, reduces contraction and also lowers the risk bubbles forming. SAND MOULD LONGER THAN LEAD KEEL, 4″ ment holes, etc. The main part of the mast should be dural tube, tin. or jin. O/D, up to the height of (usually) the third suit mainsail. Taller sails require wooden topmasts to be plugged into the tube. A jackline should be permanently hooked to the tube nd taped with p.v.c. tape to the mast at intervals, etween the hooks in the mainsail luff. This means that hooks in different suits must be in corresponding positions. Wire staples should be driven into the wooden topmasts to engage the upper hooks of the larger mainsails. WIDER. EACH SECTION FROM 2 x 3/4″ BOARD blowwaste. which of air Painting and varnishing. Any paint can be used, although the writer prefers to use one of the twopart polyurethanes. These have many advantages, the first being the standard of finish one can obtain. The 108 MAR. 6971 So drying time is so short that it is possible to get two coats on during an evening, and no rubbing down between coats is necessary. Around six coats are needed to get sufficient thickness to allow cutting down with a fine grade of wet or dry paper. Extra care is needed when rubbing down along the chines —it is so easy to rub through to the wood. Perhaps it would be worthwhile putting masking tape along the chines to prevent this happening. The waterline can be painted on using marking tape top and bottom of the line after scribing this with the gadget shown in the sketch. Two or three coats of varnish will be needed to give the deck that really good look. After rubbing down all over, ‘Brasso’ or a similar type metal polish can give the paint almost the look of a glass plastic hull. Should one want to put the name either on the deck or topsides, ‘Letraset’ or a similar type of dry lettering could be used. This will, of course, need a coat of clear varnish after. SCRIBING GAUGE FOR WATERLINE MARKING 1/4″ STEEL ROD (4″ WIRE NAIL SHARPENED) FAINT LINE MARKED BY POINT THEN MARK FOR PAINTING SCREWS USED FOR FIXING SCRIBE AND PAINT BEFORE REFITTING LEAD MIRRORS WITH LOOSE DOMED TOPS (THIS PREVENTS KITCHEN TABLE FROM BEING SCRATCHED $3) NOTE HEIGHT OF SCRIBING POINT CAN BE ADJUSTED BY SCREWING IN OR OUT DOMED SCREWS A AND B MUST BE EQUAL BEFORE SCRIBING WL. Next month — sail making MOTOR MART (continued from page 107) opened and it is possible to adjust the effective length of the slit at part throttle settings by unlocking the complete needle-valve and spraybar assembly and rotating it slightly. The system works well and Kavan carbs have been widely used by the R/C model aircraft fraternity during recent years. Perry carburettors Irvine Engines are now also distributing the American Perry carburettor, and among the watercooled engines for which this design is available are the Enya 45 and 60, O.S.Max 40 and 60F, Super-Tigre G.60RV and Webra 61. It is standard equipment on the Irvine marine versions of the K&B 40 Series 70F and Veco 50 and 61 motors. The Perry, like the Kavan, also incorporates adjustable automatic fuel metering. The principle on which it works (sleeved jet-tube) is similar to that of the Kavan, although its design and construction are totally different. The carburettor body is of a special plastic material and fuel is drawn directly into a small chamber in the carburettor body adjacent to the throttle housing. The jet-tube, mounted axially in the throttle barrel, projects into a sleeve housed within this chamber and picks up fuel via slots in both sleeve and tube. The idling mixture adjustment is via a large diameter disc which rotates the sleeve. Only very small movements of the disc are necessary. Overall mixture adjustment is provided by a needle valve mounted in the jet tube. Again, this is a carburettor that works well. It has an advantage over the Kavan in that it is possible to make adjustments to the low-speed mixture strength while the engine is actually running. It is, however, rather expensive at almost £7. Kosmic K-15 For use with the watercooled marine version of their 2.5 c.c. K-15, the makers of the Italian Kosmic racing glowplug engine have introduced a cast alloy engine bed incorporating a geared drive unit (see photo). The Kosmic K-15 (originally known as the Komet K-15 and produced in the Komet go-kart engine factory) has recently undergone some improvements which include modifications to the crankcase, cylinder-liner and head. It was with one of these engines that Horst Hachmeister of Germany set up a new 109 The American Perry R/C carburettor. This is standard on the Irvine marine conversion of K&B 40 Series 70F, Veco 50 and Veco 61 engines. European record in the Naviga Fl 2.5 class last summer. K.15’s also topped the results in the 1970 Italian Championships, classes F1 2.5 and B1 2.5. Kosmic engines are distributed by ‘Sportimpex’, Via Gressoney 6, 20137 Milan, Italy. The Kosmic K-15 and special geared mount that is now being manufactured for this championship winning motor. Racing Model Yacht Construction Part Ten By C. R. Griffin Jib fitting at left is not described as being a little heavy and rather complex to build. Example above is type sketched in Fig. 78D, for use with conventional jib stay. THE MAIN BOOM. The use of the main boom is twofold, firstly, it ensures that clew of the mainsail is kept at a constant distance from the mast and secondly, in these days of loose footed sails, it enables flow to be put into the mainsail. The main boom should be as light as possible without being fragile. If it is decided to have one adjustable mast for both high and low aspect ratio sails, this fact must be borne in mind when making the main boom _ and due allowance must be made for two adjustable points of attachment for the clew of the mainsail. The main boom illustrated in fig. 74 is the traditional wooden type and is within the prescribed limits for spars on a Marblehead, i.e. the cross section must not exceed the area of a jin. diameter circle. The main boom ferrule has already been described in the article on the gooseneck fitting. A band, detailed in inset 1, locates the triangular plate to which is attached the kicking strap, one end of the jackline and the woggle for the running sheet. A similar shaped band, inset 4, is made a tight fit on the end of the boom and carries the beating sheet woggle and the lug for the 4 B.A. mainsail flow adjuster. Note that the ends of this band are extended, silver soldered and drilled to receive the woggle hook. A braided terylene cord or ‘Sea-ranger’ fishing line jackline is run almost the entire length of the boom. Two circular bowsies, one for the beating sheet and one for the running sheet, work along the jackline. To enable sail trims to be repeated with accuracy, the boom is calibrated using either Indian ink subsequently varnished or small transfers. 2 46 CH ‘ et 8 CREWED ROD 4 ° ee ae ee ee DETAIL OF C kee Oo — Fl= O {> ¥ = I = 5 = m fo) ~ oO M4 o i od 116 BOOM-END MAINSAIL FLOW ADJUSTER, FIG, 748 b MARCH 1971 Also shown are two variations of the mainsail flow adjuster. Fig. 74A utilises 16 gauge brass or stainless steel wire to form a rail along which slides the hook in the clew of the mainsail. An outhaul working through a screw eye in the boom end alters the flow in the mainsail. Fig. 74B uses a similar principle but here a length of brass or nylon curtain rail provides a track for the sliding sail attachment point. An outhaul working on a short jackline allows for adjustment of the flow in the mainsail. Aluminium tubing, ?in. O/D, 22 gauge, is the material used in the main boom illustrated in fig. 75. One advantage of using aluminium alloy tubing is that fittings can be easily positioned by wire hooks or by some form of riveting. Two aluminium plates cut from 22 gauge sheet are fitted through slots cut in the boom and secured by overlapping either in- adjustment of both high and low aspect ratio sails, if necessary. A sliding collar, tapped 6 B.A., has a 1/16in. lug acting as an attachment point for the clew of the mainsail. The Tufnol bearing collar fits tightly into the boom but has ample clearance for the 6 B.A. screwed rod. Attach the knurled wheel to the screwed rod by a grubscrew or by silver soldering. Calibration letters or numbers allow flow settings to be repeated with accuracy. MAST EXTENSION. Where a single adjustable mast is envisaged, to save the weight of the unused portion of the mast it is necessary to alter the top section of the mast to suit either high or low aspect ratio sails. Fig. 76 illustrates the alternative top mast sections and the method of fitting. The locating spigot should not be too short as this is likely to lead to play, especially when the high aspect section is fitted. If jin. O/D aluminium tubing is used for the mast and the extensions, then the spigot should not be less than 2in. in length and preferably machined from stainless ternally or externally. A series of 5/64in. holes drilled in the plates provides adjustment of the flow in the mainsail. Vee-shaped hooks from 16 gauge stainless 5/65 ” HOLES FOR MAINSAIL FLOW ADJUSTMENT BI JACK LINE ‘ [S ovlans a 5 8 7 e 9 —u 8 1 17 ~ ae / KICKING STRAP 16G S, FIG. 75 t (oc 000000) o000000 5S CIRCULAR BOWSIE Al | SHEETING CALIBRATION NUMBERS eS ] f MAIN SHEET STEEL —__, SHEET HOOK MAIN BOOM & SHEETING 18G S, STEEL WIRE FOR SEPARATE BEATING & RUNNING SHEETS DUPLICATE JACKLINE & BOWSIE SECTIONS THROUGH 88] See X gd 3/8″ O. DIA, ALUMINIUM ALLOY TUBING 22G ALUMINIUM ALLOY SHEET 6 BA SCREWED ROD TUFNOL COLLAR ua ——— ees Bae Tee nadie Sse Poe BRASS OR PS aiEr tio 20G S. STEEL WIRE 77/252 uy Ma 44£ S, STEEL rs SSAANTNNANAANANAMATANATONATNT ANTM ~ 4 et KICKING STRAP TUFNOL COLLAR | KINURLED WHEEL DETAILS OF BOOM-END TYPE KICKING BA SCREWED ROD ae ennannnen « STRAP ADJUSTER, FIG 75A NYLON OR BRASS WHEEL steel are pressed into 1/16in. holes in the boom to act steel. It is essential that the spigot be a tight push fit as attachment points for the kicking strap and the in the mast and a main sheet toggle. Double eyed pins from 18 gauge stainless steel are used as anchorage points for the terylene cord jackline along which slides the circular bowsie carrying the main sheet. Calibration is achieved using either small transfers subsequently varnished or black paint. A kicking strap which fits into the free end of the boom is shown in fig. 75A. The Tufnol bearing collar is a tight fit into the boom and is drilled to provide ample clearance for the 4 B.A. screwed rod. The bearing collar is fitted prior to the flow adjustment plate. Thread the 20 gauge stainless steel kicking strap wire through a hole in the boom and connect it to the end of the screwed rod. Ensure that the boss of the knurled adjusting wheel is a slack fit in the end of the boom. Fig. 75B illustrates a variation of a mainsail flow adjuster. In this instance a 1/16in. wide slot is cut into the end of the boom, long enough to allow for sions. close clearance fit into the exten- Jumper wires and a wing spreader bar are necessary when using the high aspect extension. This prevents the top of the mast from being bent back towards the stern of the yacht by the combined strain of the mainsail uphaul and the backstay. It is the opinion of the writer that a mast-top forestay is a desirable addition as this does assist to counter the strain of the backstay and helps in setting a straight mast. The forestay can double as a spinnaker pole uphaul when the yacht is running before the wind. Before proceeding to the method(s) of erection of the mast and the fitting of the standing rigging, it is necessary to consider the jib stay and the related jib fitting. It will be appreciated that the jib stay is, in fact, the front leg of the tripod that supports the mast. It therefore follows that the jib stay must be capable of adjustment and strong enough to prevent the mast from moving from a predetermined position and rake. 117 6ULED) P| | 2 a Se ee a MODEL BOATS | ~ 1/4″ ALUMINIUM TUSING ad FORESTAY ic BACK STAY FIG. 77A RIGGING a JIB STAY & JIB FIC + 76 MAINMAST EXTENSIONS MAIN SHROUD STEEL S. STEEL SPIGOT-MACHINED PUSH WIRE JIB STAY a ALUMINIUM OR S, FIT IN MAST – CLEARANCE FIT IN EXTENSION – JUMPER – +9005″ WIRE I I ‘ ‘ ! ] ‘ | I ‘ ! ‘ ‘ | AT MAIN SHROUD I HIGH ASPECT RATIO EXTENSION 1 pt ~~ ~~ ‘ JIB HOOK tow Asrectratio eee EXTENSION ——— oe ‘ G eae S. RIGGING STEEL or , = 1 JIB STAY EGG JB STAY & JIB a TERYLENE = LAT CARD JIB an ‘ = SIE STAY ‘ tTstrouo I ‘| \ \ 4 | HOOK ; ; 1 ‘ |; \! 1 1 | 1 b dey MAIN stiroup ens \ \ ee, As there are several varieties of jib stays, there will be different means of attaching the jib stay to both the mast and the jib fitting. ‘ ! | : | : 1 utilises the traditional mast band and a stainless steel wire jib stay. The jib hook shown in fig. 77B is simple to make and saves weight when compared with the mast band in fig. 77A. This weight saving factor is important especially when considering the fittings of a racing model yacht. The use of a small diameter aluminium tube as a jib stay, in conjunction with a Figs. 77 A to C illustrate a few of the ways of rig- ging the jib stay and the jib to the mast. Fig 77A 24G, S, STEEL WIRE JIB 1B HOOK =) bo I 47 A ‘y oy i 1 ca. cohesion — a ee ‘ Ly / STAY double luff jib, is outlined in fig. 77C. This type of jib stay has advantages over the more conventional ones, when a deck-mounted mast is fitted. The jib stay hook illustrated is rather ‘fiddly’ to make but is effective. JIB FITTING. Type A — Rack and swivel. (Fig. 78A). The rack is best built from 16 gauge brass or 18 gauge stainless steel sheet, although it is possible to obtain tee-section brass. Ordinary brass curtain rail is not strong enough to stand the strain of the jib stay unless it is reinforced or has a multiplicity of securing screws. Use 20 gauge brass sheet for the boom ferrule and silver solder the jib stay-luff hook eyes and the swivel eye into position. Medium sized screweyes screwed through 3/64in. holes in the boom ferrule and the boom-end fitting hold these fittings in place and are attachment points for the terylene cord jackline. Make the boom-end fitting a tight fit, preferably by undercutting the diameter of the boom. Give the boom at least three coats of varnish to waterproof. It will be necessary to have a different boom for each jib. JIB SHEET Co) Cx ae c BRASS JIB RACK 16G. —+ FIG. 784 JIB FITTING – TERYLENE CORD JIB STAY RACK & SWIVEL ({ Jf 1/2″ x 3/8″ WOODEN BOOM / J yr 1Q = JIB STAY EYE jy loreOF ar a 89) i Er FIG. 788 JIBFITTIING 1/2″ DIA. BALL SLIDE 18G. pf BRASS DETAIL OF PIVOT POST – CLUB RADIAL 3/8″ x 22G. ALUMINIUM TUBING 1/8″ ©, DIA, BRASS TUBE 3/e” THICK TUFNCL ——— 3/4″ THICK TUFNOL 68A SCREW ADJUSTING WHEEL 4BA SCREW Fi (39 FIG. 78C JIB FITTING It is appropriate, at this point, to mention the radial jib fittings and to make a comparison with the rack and swivel type. When beating to windward using the latter fitting, the luff of the jib moves away from the central axis of the hull to a position slightly to windward. The effect of this is that the yacht sails off the wind. The radial jib fitting has its jib stay fixed to a permanent point on either the deck or the fitting itself. The luff of the jib remains on the central axis of the hull and, in theory at least, the yacht sails closer to the wind. The second difference between the two fittings and, in the writer’s opinion, the real disadvantage of the rack and swivel fitting, is that it relies upon the resultant force of the boom leverage (acting about the swivel) and the tension on the jib stay to hold the clew 20 – RADIAL 118 MARCH 1871 of the jib down. It is therefore necessary to slacken the jib stay to alter the flow in the jib, and difficult to alter the belly in the sail. The radial jib fitting has a kicking 3/16″ OR 1/4″ strap, similar to that of the main boom, which controls the lift of the jib boom and hence the belly in the jib. Any adjustment of the flow in the jib can be effected without touching the jib stay. It should be noted that the jib sheet in no way contributes to the ‘holding down’ of the jib boom, the sheet has only one function and that is purely to limit the side movement of the boom. 1/16in. wide slot extending from one end to within sin. of the other end of the tube. Silver solder an annular washer to the uncut end. The boom strap at the locknut end is silver soldered to the tube but the strap at the adjusting wheel end is not. Ensure that the brass slider, tapped 6 BA, is a slack fit in the tube and also in the slot. Silver solder the bossed adjusting wheel to the 6 BA rod, assemble the adjuster and fix in position by screws. Use 20 gauge stainless steel wire in conjunction with a turnbuckle for the kicking strap. Varnish the boom before calibrating. Note that only one boom is needed for all jibs provided that the slide is made long enough to accommodate the full range and that the length of the boom does not exceed the foot of the smallest jib. Type C-Radial. The fore and aft adjustment of this jib fitting, see fig. 78C, is achieved by using a series of 4BA tapped holes along the central axis of the bow of the yacht. The base plate of the fitting has two vertical lugs within which works the jib boom carrier. Cut the base plate from either a solid piece of }in. thick Tufnol as in the photograph or build up using two side plates. Fashion the jib boom carrier from gin. thick Tufnol; the extension through which operates the pivot tube should be at least 2in. in length to give a reasonable purchase for the kicking strap. Drill a sin. clearance hole through the extension to accept the pivot tube. Silver solder a small washer to the end of a length of 16 gauge stainless steel wire, thread the wire through the boom carrier via the cut-away portion and bend to form an eye. This becomes the jib attachment point. Drill a 1/16in. hole through the front of the jib boom carrier and bend 16 gauge stainless steel wire to form the jib stay eye. Silver solder 1/16in. brass lugs to two in. lengths of +in. I/D brass tubing to form the swivel pieces. Machine a trunnion from 3in. dia. brass to be a tight fit in the 3in. O/D aluminium boom, cut a 1/16in. wide jaw in the trunnion to fit the upper swivel piece. Saw the jib boom to the required length and make a flow adjuster plate from 22 gauge aluminium sheet, fit the plate into a slot in the end of the tube and secure by overlapping inType C jib fitting (Fig. 78C) is typical of the radial fitting where the jib luff stays on the hull centre axis. 119 i) FIG. CIEE 4 =) O,DIA, ALUMINIUM TUBING 6 780. JIB FITTING RADIAL WITH TUBULAR JIB STAY Ano DOUBLE WF DETAIL FOR DETACHMENT OF JIB 800M FOR DETACHME OF 18 NT 860M FIG, 77C RIGGING JI8 STAY AND Ji8 eye and the pivot post. Note that the pivot post is not joint should be an easy but not slack fit and is best made prior to fitting the U-piece on the boom. Use sin. O/D brass tube for the flow adjuster, and cut a V8″ | G.S. STEEL SLIDE : mounted on plates which operate in a deck slide simi- vertical but points towards the hounds. It is advisable to make the post reasonably substantial, i.e. 5/16in. reducing to fin. in diameter, as it can be subject to considerable strain in high winds. The ‘ball and socket’ = 3/8″ TUFNOL Type B. —Club radial. In this type of fitting, see fig. 78B, the jib stay eye and the boom pivot post are lar to the mast slide. Use 18 gauge brass or 20 gauge stainless steel sheet for both the plates and the slide. Drill a series of 1/16in. holes along one bent over edge of the slide to provide adjustment of both the jib stay ALUMINIUM TUBING FOR JIB STAY =—— ‘ U JIB STAY HOOK . 22G. S. STEEL OR 20G, BRAS s TA BASE PLATE 3/16″ OR 1/4″ ALUMINIUM TUBING JI8 BOOM CARRIER ternally. Position the two jackline eyes and the woggle hook, note that the forward jackline eye locks the tube on to the trunnion. Tie the jackline, complete with circular bowsie, to the eyes. Fit the kicking strap (described earlier) to the lower swivel piece and connect to the jib boom with 16 gauge stainless steel wire. Solder a short length of 3/16in. dia. tube to the end of the 6 BA screwed rod, locate it in the slot in the base plate and secure with a 16 gauge pivot pin. Place the adjusting wheel in the jaw of the boom carrier and screw down until the 6 BA pivot screw can be positioned. Note that it is necessary to have a different jib boom complete with trunnion and swivel for each jib. Type D- Radial with tubular jib stay. The fitting illustrated in fig. 78D utilises a small diameter aluminium tube as a jib stay in conjunction with a double luff jib. The photograph shows the same fitting rigged for use with a conventional jib and stay. Make the slide from 20 gauge stainless steel sheet, ensuring that (continued on page 122) Lateral Control J. D’Oyly Wright concludes his examination of keel effects in scale sailing Photo One, left, shows a ‘variable models lateral control keel’. D PPHE position of the C.E. can change according to – the alteration of a sail plan; wind pressure may cause the C.E. to move, but it may be the result of a difference in the angle of the hull (heeling), and with this the C.L.R. may well move forward more than the C.E., or the C.E. may not move at all. The CE. can change its position in another manner; the direction of the wind striking the sails determines its position, and while this is normally countered by trimming the sails, a gust at variance to the main wind stream could mean that the C.E. would move to an- other position. The consequential increase in the luffing action causes the model to swing, resulting in the C.E. moving again because the sails are now at the wrong angle to the main stream of wind, and so the procedure is repeated until the model is lying helplessly with her sails taken aback. These examples may explain the sudden and sometimes inexplicable luffing of a model, the fundamental reason for which seems to be simply that the distance between C.L.R. and C.E. is too little to allow for the accidental movement of one or both points without a rise in the force of the luffing action to a point where it takes over control. Possibly a model has a greater luffing tendency than the full-size version as the result of the grossly over-scale and disproportionate forces to which it is subject, and the addition of a sector seems to magnify either the force or resultant behaviour; it has been noted that two similar models but with different sectors took differing circles while swinging into wind prior to luffing, the gone with a deeper sector describing a tighter circle. So far in respect of the C.E. and C.L.R. the centre in one plane only has been considered; in fact. the sails are in anything but one plane, and in consequence there may well be an area of uneven pressure causing the C.E. to move. In this respect the spanker seems to be one of the chief offenders, as its employment often leads the model to luff. The hull is a three-dimensional body, and if, in fact, the C.L.R. moves in any way similar to its theoretical path, a change in position may result in a change of pressure, which, in turn, leads to a changed course. If the lines and ratio of beam to length are to be taken as a guide in respect of the luffing force, it is sug- gested that there is a smaller change in pressure between points Q, R and B (dia. 7) in respect of a small beam and fine lined vessel than in a larger beamed and fuller lined one; in this case the sector should be ‘of a larger SR than in the fine lined vessel. In concluding this section it should be remembered that the purely arbitrary ‘Force Scale’ at the side of these diagrams, which represents ‘a force’, originated from the angles of a rather large rudder, and using these diagrams in conjunction with a smaller rudder (whose size is about twice that of the model’s scale rudder) would mean that this force scale would rep- sent a large increase in force; therefore, the units shown should be divided into two or three sub-units, and where a rudder is being used in conjunction with a sector the F should not exceed 10 units of this scale, otherwise the rudder may not be powerful enough to effect a change of course. Practica! considerations for a variable lateral control keel Photo 1 shows the successor to the original keel. The sector ‘A’ slides along brass channels ‘B’ between the top and bottom bars ‘C’ and ‘D’, held parallel by means of struts ‘E’ on each side; these are braced against each other and are arranged so as to take the weight of the ballast ‘F’ directly back to the model by being near the attachment points ‘C’. The bars are regarded as an integral part of the hull for carrying calculations and should be kept as narrow as possible. The ballast was a problem as it could not be compressed, but it was solved by filling old cigar cases, which, of course, resulted in a narrower bottom bar than would otherwise have been pos- sible. The struts are lengths of channel brass, which was found to offer the greatest strength for its size. The requirement of the struts is that they shall offer the smallest drag (or turbulence) and yet have sufficient strength to prevent the keel from whipping when the model heels. This arrangement is not the only possible one, but is shown to illustrate how simple the arrangement for a moving sector can be; it has the advantage that the trailing edge of the sector can, if needed, be projected backwards beyond the bars and so act as a stabilised sector if necessary. Incidentally, the Thermopylae and Alabama both employed similar keels at the Round Pond and Hove rallies, where more than one person remarked on how well the models sailed. General notes In some quarters there is opposition to the attach- ment of a keel to a scale hull, and although agreeing on aesthetic grounds, the author cannot agree on 120 MARCH 1971 practical grounds, for the model is subject to out-ofscale forces and if a reasonable performance is wanted, then some form of correction has to be used. If one item can be used for correcting all the factors concerned and also made invisible while sailing, and yet be detachable at times so that the lines of the hull can be appreciated, what more is wanted? There are several shapes of keel possible, each with its own merit, and they should be carefully chosen for what is wanted to achieve or in respect of the model. It would appear that there is little justification for a bar keel, since most models could have the front portion up to the foremast removed, to the advantage of performance. It is thought that a stabilised bar keel would achieve no more than an asymmetrical one, which would be more suitable for most modern types; in the case of models with a raised poop, with or without deadwood, a stabilised asymmetrical keel appears to be the best choice. Where satisfactory control by some means other than the keel is achieved, the virtue of an asymmetrical keel centred at point B has already been noted. Where full control is wanted without any visible mechanism, then variable lateral control seems attractive, especially in the case of small scale models. The fundamental difference between this and the more conventional forms of control is that in Photograph Two, above, shows just how tiny the rudder of Cutty Sark actually is. If Variable Lateral Control seems an innovation, one may reflect that this too has been used for an equally long time, for the practice of trimming a vessel to obtain the best performance (this was done several times on a trip, especially in the tea races) resulted in the C.L.R. being moved. Another practice was that of taking in certain sails (moving C.E.) so that she would sail as near to the wind as possible prior to going about without use of the rudder. All this has been copied in the model world. The yachtsman ‘tunes’ his craft by adjusting the mast’s position (moving C.E.), and more than one author has (in this magazine) illustrated that knowingly or unknowingly he has felt the need to adjust the relative positions of C.L.R. and C.E. to obtain best performance from his models; e.g. L. R. Armstrong the latter a sudden rise or fall in the force of the factors concerned may render it inoperative, whereas in the former it appears that the forces equalise each other; if by chance they do not, then this can be compensated by a slight movement of the sector to obtain the required force level. The important advantages over any other systems are (a) if there is sufficient wind to move the model, then the control will function (b) its simplicity, and (c) absence of any unnets out-of-scale rudder controlling gear on the eck. A model should be able to go to windward, and in this respect leeway becomes important, and an attempt was made to assess this in relation to various sectors. Due to the inability to take three bearings simultaneously and the lack of suitable equipment, no consistent or reliable figures could be obtained, but it appeared that with a bar keel the leeway could be 5 deg., with a strutted keel (which almost corresponds to having no keel) it could be up to 10 deg. or even 15 deg., and with a movable sector (depend- — (topsail schooner), M. Garnett (Wild Swan) and F. J. Wilson (Nina). Owing to the lack of proper recording equipment and the inability to devote one’s whole time to proving this theory it is possible that errors may have crept into some calculations, but since the results have been so consistent with the predictions, it is felt that the errors that are present must be equally consistent and that their eradication would in no way CLR THERMOPYL DiA.7 Ceetnove,, 6+5° a = —— <) atte Jag” 5 ee +F40 eo y iene its size and position) anything below 5 deg. to 15 deg. Cutty Sark (ship) Wind 4-6 knots Conclusion = To some it may be a disappointment that no definite conclusion is reached in this article, but this is deliberate as the characteristics of different types are so diverse that no opinion can be made without practical testing, and to really ‘tie up’ the ideas of lateral control discussed here would be a ; LEC! fi Sector 7/2". 3" Leez “- .a'sa” THERMOPYL 4 (barque)Sector 5x4 scientific exercise involving models of all scales and types carrying instruments and sailed under carefully controlled and known conditions. The end product of all this would be a fair sized volume full of algebraical formulae comprehensible only to the scientist. A form of lateral control has been practised for a few hundred years; the shipwright found the correct distances between the points C.E. and C.L.R. by trial and error, which resulted in the rudders becoming efficient for controlling their boats. Note the size of the Cutty Sark’s rudder in photograph two; this had to control 2,000 tons odd which was being driven by acres of sails at speeds up to 18 knots, and consider the problems if its size had to be increased. ALABAMA (barque) Wind 6 Knots approx Sector { I I tI f l 3 ES i tS Pasel I I INCHES 121 wi a I I I I 4'x4" I I " l eo MODEL BOATS Diagram 8 is that of the Alabama (barque). The difference between the theoretical and practical L.E.C. is .5 deg. between points Q and L, and that of the point B, 3ths inch; the curve is very similar to the affect the underlying theory. So the author unblushen inflicts yet two more L.E.C. diagrams (dia. 7 and 8). During the winter of 1968-9 the old keel was one obtained with the Thermopylae, which had the same size sector, but the difference of the angle a/d scrapped and a new one built (Photograph 1). Using the theory just postulated new sectors were calculated; the theoretical L.E.C. in both diagrams is shown as a dotted line. Against this is shown the one obtained in practical trials (L.E.C. 2 dia. 7) and for comparison the L.E.C. shown in previous diagrams (L.E.C. 1 dia. 7) is included. It will be seen that despite the difference in angle to the axis, the nature of both curves is similar. On L.E.C. 2 dia. 7, the mean angle between point one and L is five and two-thirds degrees against an indicated angle a/d of 5.5 deg. B is the position found on trials and it will be noticed that that point and the point where L.E.C. is due to the Alabama having a smaller hull area. The other point worthy of mention is the positions and proportions of the three points along the theoretical C.L.R. path, \ These two diagrams are used to illustrate the apparent validity of the theory discussed and to show how using both the L.E.C. and C.L.R. paths a good idea can be gained of the keel’s efficiency and resultant F. So far no great deal of serious work on the fore and aft rig has been done, but with a topsail schooner (scale 1/96), starting with a bar keel and using a conventional rudder, she was uncontrollable in winds above six knots. The keel was shortened by one third, resulting in an improvement. Next a variable lateral control keel was used, with some success, for she sailed with suitable reduced ‘canvas’ in winds of over eight knots (which as far as the model was concerned, is equal to a full-blooded gale). Naturally, she had a rough time of it, but was 2 cuts the axis are very close to the point on the theoretical line, the maximum difference being threeeighths of an inch. The difference of point R on L.E.C. 1 and 2 is due to the difference of the efficiency of the sectors, but comparison of the theoretical paths of the respective C.L.R.’s show that r is the same plane. The Thermopylae was cut down to a barque rig and a four by five inch sector used; here the difference between theoretical and practical L.E.C. was angle a/d of 6.5 deg. against the actual one obtained of 4.75 deg. but there was only {th inch difference between the points B in theory and practice. The L.E.C. of this sector is not included, but for the interest the theoretical path of the C.L.R. is shown and it should be noted how the change in rig has altered the position of r. These diagrams show quite clearly how sectors of different proportions will affect not only the efficiency of a rudder but also the under control. If the ideas expressed in this article are taken up, it is most likely that the theory will have to be modified in the light of increased experience, but the basic idea seems applicable to both models and fullsize craft, irrespective of rig. To the more curious it may appear that some figures or statements are not substantiated, but this is not a deliberate omission, for this article was never planned, like ‘Topsy’, it just ‘growed’. From the moment a phenomenon was observed the author was principally interested in its practical application in achieving better control, not as a planned scientific exercise in the study of the action of luffing. At the time, one or two perplexing aspects, or facts, were not followed up, as they were considered to be of purely academic interest only. theoretical path of the C.L.R. The single point to the left of L.E.C. 2 simply shows that with the sector at that position the rudder, at a maximum angle of 25 deg., was powerless to control the model, but with the sector at B not only could it control the model. but it only took 2 deg. to send the model beating to windward and only 1 deg. to hold a course with the wind on the This may have been a serious omission, for when does pure academic knowledge cease to be academic and become the ‘practical know-how’? quarter. YACHT CONSTRUCTION (continued from p. 119) it is a good fit on the jib boom carrier, silver solder the feet to the slide and drill a series of 5/64in. holes at din. intervals along both sides. Cut the boom carrier from in. thick Tufnol, drill a tin. dia. hole approximately lin. from, and parallel to, the base and fashion the slot for the pivot adjuster wheel. Drill two 5/64in. holes, 14in. apart, in the carrier to coincide with the holes in the slide. Measure from the plan the angles that the high and low aspect jib stays make with the jib boom carrier. Place the ‘gooseneck’ on the wire and bend the wire to form an eye; this is the attach- ment point for the jib. Cut the boom to the required length from 3in. O/D aluminium tubing; in the fitting illustrated the boom end has been flattened to form the flow adjuster. This operation is best performed by heating the tubing before compressing in the jaws of a vice. A rule of thumb method of checking the temperature of the metal is to rub soap on the surface prior to the application of heat. When the soap mark turns black, the metal is ready for flattening. Drill a deck and calculate the mean. Drill a 1/16in. hole vertically through the carrier at this determined angle series of 3/64in. holes in the flattened portion to accept the jib clew hook. Make and fit the jackline eyes and and widen the lower end to give the correct movement. Silver solder a short length of 3/32in. I/D brass tube to the end of the 6 BA screwed rod, feed through the tin. hole in the carrier and position the pivot adjuster wheel. Construct the kicking strap adjuster as described in earlier sections and make the ‘gooseneck’ by silver soldering two #in. wide U-shaped pieces at 90° to each other. Drill 1/16in. holes through the centre of all faces. Silver solder a small washer to the end of a length of 16 gauge stainless steel wire and thread it through the kicking strap adjuster eye, the tube at the end of the pivot adjuster and through the the woggle hook, using 18 gauge stainless steel wire, add the jackline and circular bowsie. It is necessary to have different jib booms to suit the different foot lengths of the jibs, therefore the boom is made detachable by using a ‘D’-shaped pin, as shown in the inset. The tubular jib stay is attached to the jib boom carrier by a din. wide U-shaped fitment with the tubing passing through a hole in the top of the fitment and being belled out. Three holes are shown to give a degree of adjustment. 122
