Model Maker: Volume 5, Issue 53 – April 1955

SPACE SHIP DEVELOPMENT CONTROL CAR LAUNCH : : JETEX FIREBIRD ASTON : MARTIN “LORETTE” REMOTE BEGINNERS’ : CIRCULAR ARC DESIGN : SILENCERS : USE OF PORTABLE ELECTRIC DRILLS : MODEL YACHTS FOR BEGINNER S APRIC, 1955 CIRCULAR ARC DESIGN BY THE ORIGINATOR OF THE SYSTEM, GUY BLOGG I WAS very pleased to read the article in the February issue concerning canoe-bodi es with of radius 10 in. between 6 =55° and 6 =70°. The areas of segments of same subtending form profile. None of the three boats referred . to has shown any particular vice in perform- respective radii, therefore, a segment of 10 in. concentric circular sections fittin g a true arci- angle are proportional to the squares of their radius possessing the char acter need, would have an area of ance and each can put up a good show with the best of her class. They plane efficiently, particularly the one with a main section subtended by the smallest angle, where @ —60°. SUBTENDED @ which we 10° 4.38? x 15.5=81 sq. in. nearly. The chart shows that the relat ive character of such is 67°, SUBTENDED ANGLE. Our main section is therefor e one generated by a radius of 4.38 sq.in., 6 being 67°. The height above water of the centre of this section (and all sectional centres) will there- total displacement of 12lb. and a maximum beam of 9 in. To be on the safe side we will aim for 11} 1b. and a maximum beam of 8.76in. She will have a 2in. forward overhang and 1in. aft overhang, so that her static L.W.L. will be 33 in. In motion the 3 in. total overhang will become effective except for } in. at the forwar d extremity, so that her effective dynamic L.W.L. will be 35.5 in. : First we must calculate the area of the submerged portion of the main section to provide a displacement of 11.5 Ib. on a L.W.L. of 33in. Now AxL.W.L. x .0225 (where “A” sq. in. represents the area we seek) equals the total pounds displacement including normal fin and skeg. In this case A x 33 x .0225=11.5 A=15.5 sq. in. Our main section must therefore have a 8.76 radius of ——-=4.38 in. and a submerged area 2 15.5 sq.in. We need now to find profile arc, which is radius of the IO” RADIUS 80 A Tt a SQ. INCHES for a 36 in. Class model where we are limited to therefore 4.38 — 1.71 =2.67 in. We can now calculate the 8 To illustrate the method of design, I suggest we proceed to develop a suitable canoe-body fore be, 4.38 cos 67= 4,38 x .390 = 1.71 7 in. The depth below water of main section is nw | ie al isa 50 out the oe Gs Sn a 1 specific value of 4 (i.e, value of the half subtending angle) for a radius of 4.38 in. to generate a segment of 15.5 sq. in. To facilitate such calculations, I appen d a chart showing the areas of all such segments 207 40) ss° 6″ HALF 6s” SUBTENDING ANGLE : 5 al MODES MAHER! AT LEVEL OF CENTRES & ABOVE. ae ee , 1] ABOVE CENTRES FREEBOARD 1S VERTICAL. 6543 21 = : “109 876 Sectional Bech Section : Centres 1.71 in. Displacement LW.L. L.W.L. No. 1 2 and 10 3and 9 ; Profile Radius 1.35 in. 3 eT in: Fw’d Meh: 2.9010. end 8 – Radius Overhang +. 5 – 33.00 in. – 52.318 in. – 2.00 in. 1.003 ore ” 3.72 in. L.W.L. 6 (main) » 4.38 in. W/L Beam – – 8.064 in. 11 2782. 150 4ns Greatest – 8.76in. : Freeboard 3 at 0 wad . = JteS 1b: Beam – 33.00 in. 2.5 in. 2.0 in. THIS DRAWING IS ONE-SIXTH FULL-SIZE 4.125. ‘S45 ee Ol ‘f i 2 yee3 L.W.L 8 d Wis) Tear 7 6 5 4 aes es 8 4 Pee Se CENTRES L?+4 d? 4.125″ 4.125” 4125” AADS 4.125” a ‘9 it” ed 10 I he co creernee {Oa where L=L.W.L. and d=Depth of Main In this particular case it is 337+4(2.67)? Section SSS a = 52.318 in. 8 x 2.67 A profile drawing can now be made. First describe an arc of radius 52.32 in. Within this arc draw a chord 33 in., which is the longtitudinal L.W.L. Parallel to this line draw a line above it at a distance of 1.71 in. This is the line of all sectional centres. At mid-point of the 33 in. L.W.L. depth of main section will be found to be 2.67 in., otherwise an incorrect profile radius was used. Let the profile arc extend backwards for a horizontal distance of lin. to form the aft overhang undersurface. Let the profile arc extend for- wards for a horizontal distance of 14 in. to create the forward overhang. From that point it curves upward through a horizontal distance 208 of Lin. to join the deck line. A 1/6 scale drawing of what we have done is appended, and a sectional plan has been. (Continued on page 234) made from it. | APRIL, LT.-COL. C. E. BOWDEN 1955 ON PLANING YACHTS & RADIO CONTROL PART TWO Radio racing possibilities and limitations At the moment of writing, the tuned reed multichannel system of radio is the only practical method developed adequately for sailing more than one boat together on the 27 megacycles band. The questions arise, how many yachts can be raced comfortably together to suit the helmsmen, and how many can be raced together to suit technical limitations. Last year Mr. Lindsay stated that up to 30 yachts could be raced together if a superhet receiver were to be employed. Such a receiver for model racing Is not yet produced as a practical proposition, to cost a lot of money and time. In the mean time the “tuned reed” system is here and well develope d to an excellent state of reliability. Furthermore, I do not believe for a single moment that 30 model yachts could successfully be raced together . It sounds thrilling, but would result in chaos! We find that 30 keel one design “X” boats racing at Cowes Regatta Week in the open Solent is a stiff headache at the start, and when grouped around the marks, even with each helmsman right there on the spot. Experience of model racing by radio, has already shown the difficulty of judging two large “A” Class yachts to within inches of each other around the distant marks, and I believe we will find that four boats together will prove the greatest number for sound racing, with a reasonable chance of avoiding fouls. This number will provide all the necessary thrills and interest for helmsmen and spectato r alike. Even two radio yachts racing together around a triangular or other course draws a far bigger crowd of spectators than a normal Vane controll ed race. If we accept four as the maximum, with much longer courses than have yet been attempted, more like the real thing, the question arises, how we can race four boats together? This is where Mr. Tucker’s Vane may have to be used, but not for that vital personal rudder control. We obviously would like full rudder and sheet control by the helmsmen. This can be done for two boats, or modified for three boats. Four boats may have to use Vane sheet trimming. My own personal preference is for two or three boats and personal handling of rudder and sheets. Two “reeds” are required for “inching” rudder and two “reeds” are necessary for “inching” of sheets in and out. This reauires eight reeds for two boats, without interference, which we know from practical trial is perfectly feasible. Keen competition by the author and G. Honnest Redlich at Poole with rjc yachts. Two marker flags may be seen on the right. (Photo by L. R. Gwynne, Bournemouth) but might become fact in the future when various difficulties have been overcome. This develop ment is likely It may be possible to use 12 “reeds” for three boats, but the radio equipment may have to be rather specially accurate, and this may put up the cost. Alternatively, we might race three boats together using the original system that HonnestRedlich and I had in our craft, namely two reeds for inching rudder right or left, and a third reed operating sheets in and out in sequence stages. This is quite effective but not so much fun as with sheets controlled exactly as required like the real thing. It is the system I have on my smaller Marblehead model. This would require nine “reeds” for three boats racing together, which is feasible. Incidentally, up to 15 “reeds” have been employed, but the gear becomes more expensive because of the very accurate construct’on involved. Redlich and I are using four “reeds” each at present giving us real sailing control. Only further experiment and trial will decide the best arrangement, but I would say that we can have very great sport with even two yachts racing together in heats with full control of rudder and sheets each. and it may not be sound policy at this stage to become too ambitious until radio racing has become better established. I would, however, like to try four boats out in the Marblehead Class fitted with two “reeds” each for rudder and Vane sheets control. How to control a radio race It has been suggested that an O.0.D. with his flags will find difficulty in deciding whether a competitor has suffered from radio fai’ure or has committed a breach of the racing rules should he touch another boat. I consider that we should follow full-size practice, and make the owner responsible – for his gear. If anything carries away he often has to retire. Radio is now sufficiently reliable to hold the owner responsible for its correct working. There is then, no need to employ a flag wagging O.0.D., for any 217 2 SS See that I have been operating on in my rig experime nts, allowing, of course, for other factors that influence a particular problem. The Flying Series keels are high aspect ratio swept back “sectioned” hydrofoils with a fairing at the top THE LOW ASPECT RAT/O A/RFOIL (4 AND THE HIGH ASPECT RATIO AIRFOIL (4 HYORCSO/L) HYOROFO/L )-SHORT SPAN & WIDE HAS A LOW DAAG ANGLES HIGH LIFT RATIO AT LOW OF AFTACK. /T STALLS EARLY AT CHORO~CAN WORK EFFECTIVELY AT FAR GREATER ANGLES OF ATTACK, SUCH AS ON SAILS WHEN REACHING & RUNNING. COARSER ANGLES OF ATTACK — ——=—= A NARROW CHORD Good —_ — _ DOES NOT PERMIT AIR FLOW SMOOTHLY ATA B/G ANGLE OF ATTACK and a faired in streamlined weight below acting as an “endplate” to prevent “tip losses”. This is how it should be, and Mr. Tucker is quite wrong in his description of this clever keel. The old “flatplate” high drag incorrect aspect ratio and quick stalling TO THE LONGER FLOW AT bulb CHORD split second decision each “mark” is correctly rounded, and finish the race by giving the winner a gun. No helmsm an should be able to claim radio failure dispensation. I can speak from experience, as I touched my competitor at the start during the 1953 radio race at the Poole Regatta. My left rudder failed as I luffed up to give water to my opponent. I retired automatically, and could not We actually raced after this in order Fibreglass construction, combined not to disappoint the crowd of spectators. I ultimately lost this demonstration race. Later we found area. All keel yachts operate planing keel. special aspect ratio. their keels at a low This provides a low drag and high lift The model has an experimental, very light and light fittings and very high A.R. hydrofoil conventional planing model hull. But I do not anticipate emploving Mr. Tucker’s recommended conventional shifting of bollast we’ght fore and aft by radio. for the Flving Fifteen tvne of hull can plane without shift of weight, which is, of course, angle of attack when on the wind, and at no angle of attack when off the wind if the skipper knows how ratio. S»ch a foil stalls early at large angles of attack, when a low aspect ratio foil comes into its own with anti-stall attributes. Therefore, a yacht’s keel should be high aspect ratio, and the sails lower A.R. because they overate at big angles when reaching and running. All this is slowlv becoming recognised by designers, and these are the lines in general sails keel and other devices to try out one form of semi- keel A hydrofoil operating at a low angle of attack (this also applies to an airfoil) should have a high asnect ratio special low aspect ratio battened rig that I have also fully tried on a full-size Flving Fifteen and dinghy hulls. The model is 6 ft. 8 in. long with 71 in. beam. and was at the National Boat Show at Olvmpia. I have since taken off a very light glass hull from the original female mould, which I may fit up with craft must have wetted surface reduced in the keel, and owing to the increased sveed this can be of less to trim out rudder drag with his sails, etc. low strong “glass cloth” cant’lever rotating mast, with my keel appendage the Flying Fifteen, and Flying to a “Seal flipper, only a bulbunder a new alias”. Nothing A and under radio control, and the model has a fine turn to windward, with its slightly modified Flying-type cedure and custom of yacht racing. The present M.Y.R.A. rules have similarly been developed over the vears to suit the special conditions of vane gear racing. truth. above has sailed very nicely on open Poole Harbour water many years experience to formulate, so why should anyone imagine himself more comretent fo create new rules, which will compl’cate other sound pro- the the ticularly around the gunwhale area but. nevertheless. Some individuals want to form special rules, but the full-size R.Y.A. rules of racing adequately cover all circumstances of free racing, and ‘have taken be further from in task. It was, therefore, built unnecessarilv heavily. and it had all the mistakes of an initial effort, par- The rules of racing could fail The model illustrated last month was made as an exploratory “exercise” to learn the technique of full-size dinghy fibreglass construction, before I set about the that there was an unusual transmitter fault causing instability of note. But this is very exceptional, and should be tested more fully before race day. Aspect ratio and the Mr. Tucker likens Series, cutaway keel fin in a fancy dress to, yacht, and accordingly the hull changes appreciably. It is a terrible mistake to condemn the Flying Fifteen keel out of hand for its specialised job. It may well be developed along an even more drastic high A.R. line. The modern designer cuts down wetted surface as much as possible, allowing, of course, for good stability and sound windward work, owing to the more effective hydrofoil keel used. This matter of keel, or hydrofoil, is one of the big secrets of the modern yacht’s greater speed. There is, however, a lot to be learnt by designers on the subiect. Perhans the Yacht Research Council will help in useful discoveries. when so many rules are employed, and when there is so much manoeuvering during the race. The O0.0.D. should start the race by gun, mark up that win the cup. them have become far more keel conscious of recent years, in that the hydrofoil keel has a great effect on the sailing ability of a the race, when, as in full-size racing, a protest committee of at least three experienced helmsm en listen to the protest and give a judgment. It is too much to make a likens ably in future years. Modern yacht designers GREATER ANGLES retire, or be protested against by the other man after expect one man he I think it is safe to prophesy that aspect ratio of hydrofoil keels and airfoil sails will change consider- FORMS AN EASIER competitor who feels he has offende d a rule should to keel respects. Fig. 2 explains aspect ratio and angle of attack, in broad principle. Kept lak necessary in a dinghy. Unfortunately, I have little spare time for these interesting experiments, in spite of Mr. Tucker’s belief in this direction. When I do get down to the planing model. I will most ‘kelv produce a “hideous bastard craft” that Mr. Tucker deplores, instead of the more conventicnal planing craft. My hope is that many other modellers will have a go at model planing vachts with a dual personality—a mixture of displacement and planing virtues. Although they are unlikely to win in all types of weather. they will prove of great interest. No harm can be done by some failures, but a lot may be learnt. 218 MODEL MARKER) ~ UCKER’S HOLDING TOPICAL = ENTHUsIAsM TALKS IN. CHECK Me ks GURELY Mr. A. F. Hill’s letter in the March MopeEL Maker should have been headed “Thoughts on Sail Plans,” rather than “Thoughts on Sail Areas’? promising generation. Alan Hill is a young skipper of the post-war Last year he sailed a “Duck” into 3rd place in the 36 in. National Champ ionship, being only beaten by two other “Duck s”. Mr. Hill’s enthusiasm for the fad of the moment reminds me of my own youthful enthusiasms when I was lucky enoug h to be his age. The craze for enormous jibs is no new thing. Boats of the 1890/1900 period had immense jibs of low aspect ratio. From these the pendulum swung to the oppos ite extreme, and about 1930 we had a period of over-small jibs. During the period when over-small jibs were in vogue, some of the more knowledgeable designers considered these too small and the opinion was expressed that headsails should represent between 33 and 36 per cent. of the total S.A. This is probably not far out, thou gh undoubtedly the question of what is the optimum ratio must be influenced to a certain extent by hull design. however, knowledge that to-day provided It must be remembered we by have wind s additional tunnel tests which prove the value of high aspect ratios for sails. No scientific reason has been adduced to show that while this applies to mainsails it does not apply with equal force to jibs. The logical thing is, there fore, to make both mainsail and jib of approximately the Same aspect ratio, taking into consideration height limits permitted by Rati ng Rules, Mr. Hill details alterations he has made to the rig of his “Naiad” which was built in 1935, when small jibs were fashi onable. My own design “Chloris” was publ ished early in the same year in “Marine Models”. Two have turned up recently, and I have had correspondence about their mode rnisation with vane gear and a new rig. Mr. Hill tells us that he took “four inches off the base of the mainsail and added 3in. to the J measurement of the Fore Triangle.” I did not keep a copy of the new plan I made for “Chloris”, but memory, I curtailed the foot of her mainsail by 4in., and added 51 in. to the base of her Fore Triangle. From one over-enthusiast let us turn to from 222 another, Colonel C. E. Bowden, who this time, points the whole shooting match at me, because I dare to differ with practically every idea he has put forward! If the Colonel had read my notes carefully, he would have realised that he is tilting at windmills. Colonel Bowden accuses me of statin g that Uffa Fox’s “Flying” series are not plani ng keel boats. Everyone knows they are plani ng boats with a seal-flipper fin-keel appen dage. What I said is that they are not displ acement type boats. In displacement type yachts, the weigh t ratio of crew to boat is so small that the crew’s position can be changed with little or no effect on the fore-and-aft trim of the vessel . In nondisplacement type boats, the weigh t ratio of the crew is such that the fore-and-a ft trim can be changed at will by moving the crew. From this it is obvious that a displaceme nt type yacht always remains the same boat, but a non-displacement type craft is several different boats contained in a single hull. are obviously full displacement Model yachts types as all weights are fixed. Again, Colonel Bowden states that I con- sider “manoeuvre is not essential in model yacht design.” I deny having said anything that could be thus interpreted. A yacht’s ability to manoeuvre arises from her being mobile and steerable. Further, to enable a model yacht to sail a good course up and down the racing water steered by just these steerability. same vane geer, qualities she must possess of mobility and The colonel then makes the concession that vane gears steer a helmsman. Major M. boat better than a human I have never claimed this, thou gh Heckstall Smith considers them equal to all but the best helm sman. Interest in R.C. racing appears to turn on whether you are interested in making your boat sail at her best, or twiddling knobs and turning buoys. It is not a question of preju dice, but of preference. I think most model yachtsmen prefer a straight race under M.Y.A. rules to sneaking round buoys under R.C. Elsewhere, Colonel Bowden accused model yacht designers of being unpro gressive. The real truth is, of course, that finali ty in yacht design is never reached. As an instance, look at the 10-Rater class, which after about 70 years is still going strong with produced every year. new designs MAKER) (3) The hull must have adequ ate sailing length. The maximum speed at which a hull STARTING ON THE RIGHT TACK AN can be driven depends upon its effective length, and provided there is adequ ate driving power, the greater the length, the greater the speed. In the 10-rater class attemp ts to obtain sailing length much greater than the INTRODUCTION TO MODEL YACHT RACING PART ONE—THE BASIC REQUIREMEN TS measured L.W.L. must not result in excessive BY D. A. MACDONALD overhangs, which make the boat unseaw orthy, [NX the past few years ther e has been a great drive (see (4) below). (4) The hull must be easily driven. This is the main requirement for fast sailing in light airs, and to achieve it, the hull lines Increase in the popularity of or coarse hull lines, model yacht racing. Each season bring s a welcome influx of new competitors and and championship new boats to club racing. This season will be no exception, and now that sO many designs for high-performance craft are readily available, it is to be expec ted that many newcomers to the sport will model yachting careers be Starting their with yachts capable, if handled correctly, of acqui ring championship honours. It is therefore appro priate at this time to carry out a brief investigation into all the factors which contribute towards success in racing, beginning by an attempt to formulate some basic requiremen ts, covering design, construction, equipment and sailing. Later in this series we can consi der how some at least of the principles we lay down in this first study can be put into practice. Although correct design is one of the main requirements for success, the subjec t has been covered in outline by recent contributors to these pages, and is too great a subjec t to lie within the scope of these notes. But it is, I think, important to set down a few basic requirements for a successful yacht design, since if these are not fully met, there will be a deficiency in performance which might be difficult to make good in other ways. To be successful, a yacht must sail both fast and straight, and to do both, it must have the following qualities. Basic Requirements (1) The hull design must be accurately balanced, i.e., it must have no steering tendencies when heeled. When running before the wind, it must not bore, submarine, or sit on its tail. (2) It must be sufficiently stable to carry its full sail area under normal sailing conditions. A yacht which has to canvas down before its opponents is immediately at a disadvantage. 230 which make it hard to must be as long and easy as the length and displacement requirements will allow. The ability to heel a few degrees in a light air makes all the difference to light weather performance. These last three requirements, (2), (3) and (4), can to some extent conflict, and the successful design is that which achieves the best all-round compromise. (5S) The sailplan must be designed to provide the most efficient drive for the hull for which it is extended. The whole subject of sails will be dealt with later, and at this Stage it is only necessary to say tkat there is just one best sailplan for any hull, very often some experimenting with and varia- tions of the designed sailplan will be necessary achieve the maximum performance. to Obvious? To many readers, the foregoing remarks will be no more than a statement of the obvious, but it is regrettably true that, even nowadays, new craft are being hopefully launched which fail in one way or another to meet these design requirements. Although they may have particular virtues which produce an occasional high performance, such flashes of brilliance are often misleading, and the average performance over a period proves disappointing. It therefore behoves every skipper who aims at success in racing to be certain from the outset that the design of his craft is in order. In certain cases the name of the designer is in itself a sufficient guarantee, but this does not imply that there is any monopoly of success in this field. Besides, it is in the best interests of the sport to encourage the work of new designers. An experienced and _ successful skipper will generally possess sufficient technical knowledge to give sound advice to a novice on the selection of a suitable design. APRIL, 1955 Construction Other Considerations Let us now assume that the design of the yacht has satisfactorily fulfilled the require- The builder’s contribution to a successful yacht is far from finished with the completion of a sound and accurate hull. In fact, it is from this point onwards that most yachts begin to fall short of the best. We shall, therefore, need to set out the essential requirements for the fitting-out stages of the work. First. the paint and varnish must provide complete protection against water, good protection against bumps and abrasions, and provide a suitably smooth surface for minimum skin friction. It is well worth the extra effort involved to secure a finish that will last out the whole racing season. To withdraw a yacht from racing at mid-season for repainting can result in the racing trim being lost. At the same time, the paint must not be allowed to add undue weight. Secondly, the mast and standing rigging must provide a light but rigid assembly upon which the sails can be set up accurately, without strain on the sailcloth. The term “rigid” deserves emphasis, since any tendency for the mast to bend or the rigging to stretch under the pressure of the wind must inevitably alter the trim of the sails. Thirdly, the running gear must be adequately strong and efficient. It is essential that all cordage affecting the setting of the sails must be incapable of shrinking or stretching. Kicking straps, except possibly on very small models, should always be metal, and must be capable of precise adjustment. Fourthly, the sails provide the driving power for the hull, and determine its speed under any wind conditions. Nothing but the best can be tolerated, either in material or in workmanship. Some of the biggest differences between boats which should perform equally can be attributed to the sails. A yacht should have an adequate complement of efficient sails for racing under all reasonable sailing conditions. Finally, the steering gear (we assume it will be vane type), must be mechanically sound, efficient, and capable of quick adjustment during racing. It must be light in weight, carefully balanced, and cali- ments I have enumerated, and turn to the question of construction, ie., the execution by the builder of the designer’s intentions. I feel that this definition should be underlined, since it is the specific function of the builder to put into practice what the designer intended. It is not part of his work to carry out “improvements” in the design—if these were needed they should have been done on the drawing board. The essential requirements for successful hull building are:— (1) the ability to read and transfer to timber the designer’s drawings. (2) Proper planning of the whole building operation. (3) A conscientious (but realistic) regard for accuracy. (4) The use of suitable materials. (5) Careful attention to weights. Boats to the same design by different builders usually perform differently, and often do not even look alike. Two boats built to the same design with the same materials by the same builder can perform differently whereas an experienced builder like Arthur Levison can produce a number of hulls to the same design, with varying materials, all with an identical performance. This is because the work has been done systematically, and with due regard for accuracy. Until sufficient experience has been gained for work to become virtually a routine, I strongly recommend the production of a plan of action before any work is commenced. This would list all the operations in their correct order, and the list should have provision for notes on each stage. The work should not be commenced until each stage is fully understood, and difficulties which have to be explained by reference to books or to the advice of an expert should be covered by the necessary notes. Care should be taken to ensure that the right tools and materials are available for each stage, so that there will be no temptation to accept a makeshift of any kind in order to overcome delay in construction. My last word of warning on hull construction is that any error which results in the hull not being identical on both sides is intolerable and will make the boat a failure from the start. The greatest possible care must be taken therefore to ensure that, for example, the backbone of a planked hull is true, the shadows symmetrical, and templates and marked-out layers carved hulls are identical on both sides. for brate. The whole system (skeg, rudder, tiller mechanism, vane gear, feather) must be carefully planned and made to suit the boat on which the gear is to be used. A yacht which has been designed, built and equipped to fulfil all the foregoing requirements can be considered capable of competing for the highest championship honours, and the owner who aspires to success should do all in his power to ensure that these requirements fully met. 231 il (To be continued). are == ‘i CIRCULAR ARC DESIGN (Gontinued from page 208) | MAKE THE It will be observed that above a transverse OF horizontal plane through the line of sectional centres, all sections are cazried upwards vertically. This is done to facilitate planking. It is high enough above water to affect flotation only at heeling angles exceeding 25°. MOST YOUR Ss KI LL My drawing gives her a 2.5 in. freeboard at bow and 2in. at stern, which I consider adequate. The C.B.of this canoe-body is obviously at 33 2+—inches=184in. from forward extremity. 2 If the waterlines of the fin are so shaped that its C.B. is not far aft of the vertical through | the C.B.of canoe-body, the metacentric balance (in theory) will be more perfect. In the case of the three models already built, no attempt to do this was made. Without drawing any lines at all, the position of any point on the surface of the canoe-body can be deduced from a few equations, which any interested person may have if he cares to apply to the writer, care of this journal. 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