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KEN FIVE” BOAT PROCTER’S “TWO CHAMPION : “CRUSADER” JETEX POWERED : RUSTON BUCYRUS MODEL MODERN ‘“PATEKE”’ : COMPLETED CARGO BOAT : THE DEAN DOOLINGS FOR 1956 : “TORNADO”, : MINIATURE BOAT A NEW ELECTRIC VAN MODEL FOR R/C : MODEL MAKER TROPHY AT BOURNVILLE : B.M.W. WORLD RECORD M/C AND SIDECAR A LATHE APRON : VANE GEARS AND APPARENT WIND : MAKING y LI MODEL MAKER system is used, that the rudder be mounted in such a way as to give, as nearly as possible, a frictionless movement. A favourite method is to employ puintle STARTING ON THE RIGHT TACK AN INTRODUCTION TO MODEL YACHT RACING PART FUUR—THE STEERING GEAR BY D. A. MACDONALD I HAVE purposely left the very important subject of the steering gear to be dealt with in a chapier of its own, rather than including it in the fitting-out stage, because an efficient steering gear is a vital necessity for a racing yacht. Wide differences in the performances of yachts, particularly in variable winds, can often be attributed mainly to differences in the steering arrangements. A study of the yachts competing in any open tournament will show that opinions differ widely on such matters as the best shape, size and position of rudders, the correct size and shape for vane feathers, and also on such matters as linkage ratios and the use of stops and‘tensioners. In fact, in many racing centres, the Braine gear still continues to fight a stiff rearguard action against the growing popularity of the vane gear, and in fact, can still enable the skilful yachtsman to spring a few surprises on unwary opponents. aS Obviously there is still a lot to be learned about vane steering gears, and,I will therefore attempt no more than a simple, and, I hope, rational approach = to the subject, so that the beginner Cc will at least start “on ff rT | | ee ] a the right track” and not be a saddled with steering system which is a box of from _ the tricks outset. I will there- fore start with the constructional as- pects of the steering gear, and deal theoretical with matters later, when we ULL: come sider use. the to con- gear in It is essential, steering whatever api DECK WS SSS SSS. bearings at both ends of the rudder post, but there are mechanical difficulties involved in devising a top pintle arrangement, and furthermore these top pintles require constant re-adjustment to take up wear. A simpler method of rudder mounting 1s shown in Fig. 1. ‘The rudder post A, consisting of stout brass tube (4 in. o.d. is suitable for racing class yachts), is plugged with brass rod silver soldered into both ends (B and C). At D, a collar in the form of a ring of brass wire soldered to the rudder post, gives a free fit, without excessive play, in the rudder tube E. The plug B is drilled to an appropriate depth to receive the bottom pintle, which is silver soldered to the pintle base F. The latter is a substantial brass plate (1/16in. to 4in. thick), screwed to the skeg, being shaped and rebated into the latter, so that no projections or cavities result. Fig 3 RUDDER This simple arrangement will be found completely effective and reliable in practice, and the troublesome top pintle problem has been avoided. It is essential however, that there is a good clearance between the inner diameter of the tube E, and the rudder post A. For the smaller classes I suggest the tube 5/16in. o.d. with 24 s.w.g. wall thickness, and for larger yachts 3 in. o.d. x 20 s.w.g. An alternative type of top bearing is shown in Fig. Il. In this case a plate or washer A, is drilled to allow a free but not sloppy fit for the rudder post and is screwed to the deck, the rudder tube B, being finished off flush with the deck surface. The washer plate now provides a top bearing equivalent to that provided by the ring D of Fig. I. To improve rudder efficiency and reduce resis- tance, the skeg and rudder should be nicely streamlined together. The waterline section of Fig. III illustrates this. The rudder tube A, is continued as a curved strip screwed into a rebate in the trailing edge of the skeg. The rudder post B, is let into a similar groove or rebate on the leading edge of the rudder, and the contours of skeg and rudder are such as to produce a continuous streamlined contour to the complete assembly. This is a much more efficient arrangement than the flat plate form _ usually employed for both skeg and rudder, and is well worth the extra work and care involved. The rudder should be fixed to the post by long screws (fin. x 2 are suitable) and the joint should be bonded with synthetic resin glue. The rudder tube itself will be in the form shown in Fig. TVa, and the method of fitting to the hull is shown in Fig. TVb. Watertight sealing at deck and keelson can be achieved with synthetic resin or thick varnish. If the tube is not a tight fit into the keelson, a brass washer is soldered to the tube, and screwed and sealed to the keelson as shown. Finally, Fig V shows the bottom pintle in detail. With the rudder assembly complete and operating freely and without undue play, we can now proceed to consider the tiller arm. In the author’s opinion, all moving parts of the steering system should be independently balanced. Only in this way can one 238 MAY, 1956 difficulties with vane gears designed for mounting aft of the tiller, because of the latching arrangements which would work in reverse unless the gear is suitably modified. Assuming, however, that we have a conventional yacht to equip, the arrangement on deck, so far as we have described, will be as in Fig. VII. The balance weight A, is adjusted finally ) a ERS EE 8 i | ensure that the gear is always balanced however adjusted. I therefore recommend that the tiller arm be provided with a counter balance so that when the hull is immersed and heeled, the tiller arm remains central. A simple tiller arm is shown in Fig. VI. This consists of a flat strip of brass, with slots at each end, screwed and silver soldered to a collar. “Extruded” quality brass strip is recommended for this purpose. The dimensions should be adequate to provide rigidity, without excess weight. A width of 5/16in. will be adequate for all but the largest classes of yacht, which may need 3 in. The thickness will vary from 22 s.w.g. to 16 s.w.g. according to the size of the yacht. The main slot should provide a free but not slack fit for the linkage pin. The other slot is to accommodate a balance weight, the position of which is adjustable. The collar is secured to the rudder post by grub screws—details of the collar fixing are shown in Fig. VII. By providing two grub screws 120 degrees apart, a much more secure fixing is achieved than that providing by a single screw. The length of the linkage arm of the tiller should be such that it just clears the vane gear. It is a great mistake to have the tiller arm too short as this means that high linkage ratios cannot be achieved. The distance between the rudder post and vane pintle will in most cases be determined by the space available. Efforts should be made, however, to secure a minimum of 4in. between centres, and up to 6in. on the larger classes. In some cases one has to be content with 3in. or even less, and one must then ensure that the best possible use is made of the restricted space, by ensuring that the tiller arm is made as long as ever possible. On certain M class yachts the rudder is so far aft that the vane pintle has to be mounted forward of the tiller; this causes HOLE FOR TENSION LINE pas SLOT FOR LINKAGE PIN i i +p 0 SLOT FOR BALANCE WEIGHT 239 by floating the yacht artificially heeled, and moving the weight to and fro until a position is found where the tiller arm counter-balances the buoyancy of the rudder, and takes up a position along the centre line of the deck. To decide on a suitable weight before flotation tests, it can be adjusted approximately so that it just fails to overcome the weight of the rudder in air, when set to its midposition on the arm. The weighted extension to the tiller arm conveniently provides for a_ tensioning line (B in Fig. VIID. A very light phosphor-bronze or stainless steel spring is satisfactory for this tensioner, and such springs are easily made up from suitable thin wire. The spring tension is adjusted by a conventional cord-and-bowsie arrangement. A fairlead C, ensures that the centring spring always pulls on to the centre Jine of the deck. This tensioner is normally used in very light winds or under conditions where calm patches occur, to ensure that the tiller does not come to rest in an off-centre position when the yacht is becalmed, thereby causing her to wander off course. It is also a valuable accessory for sailing off the wind, and in this connection, the length and elasticity of the spring have important effects on the behaviour of the yacht when the tensioner is used under these conditions. A short stiff spring will allow a small easy move- ment of the tiller and strongly resist any further increase of helm. A long “soft” spring will allow considerable movement of the tiller without much increase of tension. Some experimentation with different lengths and strengths of spring is therefore advisable. As a general rule, a tensioner should allow about 20 degrees of tiller movement with only a light tension, and offer an avoreciably increased resistance as the angle is increased further. If the vane pintle (D in Fig. VIII is fastened to the deck, the latter must be t) reinsubseeither by a ‘: L.— V¥e—x} 7 t SILVER SOLDER veil deck beam, or, pre- aes if Ove forced ferably a post between deck and keel. (Continued on page 254 i \ 4 TAPPED 4B.A, MAY, 1956 Model Maker Trophy for Marbleheads BOURNEVILLE POOL THs year’s MopEL Maker Trophy—open to novice skippers sailing Marbleheads— was held over the Easter holidays on the Bourneville M.Y. & P.B. Club’s water at Valley Parkway, which, incidentally, was also the scene of the inaugural trophy race in 1952. Ten entrants only competed, made up of skippers from the home club, Birmingham and Nottingham, a disappointing total in view . of the general popularity of M class racing, which must be put down to the early season, and counter attractions of a public holiday. However, contestants made up in enthusiasm for any lack of numbers, and as popular O.0.D. Mark Fairbrother remarked at prize presentation, “all skippers and mates were to be complimented for giving him such an easy task by showing such excellent sportsmanship and good clean sailing throughout the whole race, an on AT Above: Joe Meir’s Hopalong (932) sails against 3rd boat Puffin Below: A. Penn’s Zoe (912) in a board with local man Ron Harris’s Black Ajax Winner proved to be Joe Meir from Birmingham*M.Y.C., with his Hopalong, which, it will be remembered came sixth in last year’s Open Championship at Hove. Second was his clubmate, A. Penn, sailing Zoe, which -had also run at Hove in 1955, but finished well down the field on that occasion. Third was local entrant J. Sills, with his Puffin, and fourth, who also took the most distant entrant prize, was A. L. Waite from Nottingham, who sailed Red Witch. A steady N.E. breeze on the first day proved a good test for skilful handling, and racing generally resolved into a series of duels with the younger element intent on snatching points from their more experienced elders, who were not allowed to relax for a single board. The day ended with Hopalong, skippered by Joe Meir, mate Dennis Lippett, nine points ahead of clubmate Zoe, with Chance, G. H. Leeds, Bourneville, lying third. Second day offered – a variable but mainly N.W. breeze, which created difficulties, and again gave the youngsters opportunities of shaking up the old hands. However, Joe Meir held on to his lead and won by four points from A. Penn. Altogether some very pleasant racing: with grateful thanks to all at Bourneville who helped to stage it. 247 Las —_ EE A NEGLECTED SUBJECT “Sti BY A. WILCOCK iv ‘PRE principles of calcu- Lisso’ rio4o” -7°?°’ lating the direction of the apparent wind, and the influence of vane gear linkage ratios, were dealt with in the MopEL Maker. The present article will extend the information to cover the other points of sailing. It may be as well to start by postulating the conditions that will be met on these other sailing Free reaching is the fastest course in a given wind, so we find that from the close beat to the free reach, sailing speed increases and then falls again to the full run, at least when not carrying a spinnaker. The additional sail area obtained with a fiat spinnaker, possible on the free reach, and a balloon spinnaker as the full run is approached, goes a long way to maintain or exceed this speed. The helm requirements however change with the setting of any spinnaker and the two cases will therefore be dealt with separately. It will be recollected that the beating course was 45° to the wind, with the axis of the boat at 30°, the difference of 15° being due to the leeway made. The course now to be considered is 60° to the wind, the boat axis being 50°. The speed is again dependent on the class (size) of boat. Fig. 1 is the apparent wind diagram for the 60° course, with an estimated speed increase of 20 per cent. over the beating course. The apparent wind, it will be seen, is now 16°25’ for the A class, 13°50’ for the 10R, 10°40’ for “M”, and 7°20’ for the 36 in. R West of North. Assuming. as we did before, a 3:1 linkage ratio and 2° offset for developing some pressure on the feather, the feather has to be 11° offset for 3° of helm. On this 60° course the helm will require to be very slightly increased, say 4° making the feather setting 12°. The table. equivalent to the one in the earlier article, for this course of clarity. The next course for analysis is a broad reach. That is the boat’s course is 90° to the true wind. Again on this course, some leeway is made, so that the axis of the boat is a little closer to the wind than the course sailed. 5° has been assumed. A further 10% increase in speed has been allowed and Fig. 2 is the apparent wind diagram for the four classes on this course. In calculating the feather angles, allowance has to be made for a further small amount of helm, say another 3° making the feather offset relative to the apparent wind 13° in all cases. Table 2 shows the respective angles. The final course to be drawn in full is at 120° to the true wind. On this course, leeway can be neglected, but both helm angle and feather offsetting for wind pressure must be increased. For the former, another }° is probably sufficient, and one more degree making 3 in all for wind pressure has been allowed. These offsettings relative to the apparent wind, now total 15°. Fig. 3 is the apparent wind diagram for this course. Boat speeds have in this case been increased by a further 5°. Table 3 shows the angles and final feather setting. Sufficient has now been written, and the methods detailed to enable the reader to calculate and draw other courses. Attention is, however, drawn to the following. (1) It will be found that on the courses nearer to the run the angle of the apparent wind gets smaller until on the full run it is zero. (2) The reduction in the strength of the apparent wind as determined by measuring the length of the jig. and the fact that without a spinnaker set, more helm is required, both call for additional feather offsetting to overcome water pressure on the rudder. The setting of the spinnaker on any course, on which it is suitable to carry one, reduces the amount of helm required to sail a straight course. The amount will depend on the spinnaker, and how it is set, but it is easy to see how much was allowed in the feather offset for helm and adjustment must be within that range. So far we have considered only one wind Some strencth to simnlify explanations. thought is now given to the variables. With is then as Table 1. Having gone into considerable constructional 251 snlilbtehined r’*® Li 6t4s’ points. UNUSUAL ARTICLE ON details in Figs. 3 and 4 of the earlier article, opportunity has been taken to combine the information in single figures now without loss rer ‘ PART TWO OF AN te as ae a eee eee ea en —- Mi FEATHER ANGLES & APPARENT WIND MODEL MAKER an increase of wind speed beyond the example taken, the boat speed increases only slowly for two reasons, (a) sail has to be reduced, and (b) the hull is being driven at a speed at which the driving force has to be increased considerably for small increases in speed. The direction of the apparent wind therefore moves slowly closer to the direction of the true wind. For reductions in wind speed, the rate of reduction in boat speed is less much depen- ding on the quality of the finish of the hull— the apparent wind is therefore at a greater angle to the true wind. It is interesting to note here that as the “M” 10 R and A classes have sail area restriction, while the 36 in. R_ has not, it is possible for a 36-in. R to sail through an “A” fleet in light airs. In concluding, it must be stressed that boats are not sailed on theory. Theory in this connection is of value to guide one on how to improve one’s trim and understand what is happening. I am sure it would be true to say that the vast majority of “top notch” skippers racing to-day have found their trim by trial and error, and practice until they are “at home” with any wind and course. These notes are not really for them, they are for the newcomer struggling to master the vane and get a better performance. Nevertheless, I am sure from my correspondence that experienced skippers are concerned with theory as an aid to understanding what is going on, and how they might performance. 10° “squeeze” i 14°45′ 23°45’ bit more in delicate balance of sail trimming and feather trimming. Once you have the jib and main set so that they are both pulling evenly, try small changes of vane feather setting about the one that gives you the required course, and see the great difference which small changes of the feather angle and therefore helm, make to the sneed without seriously affecting the direction. Then practice getting that optimum combination. As in all the arts, it is practice that achieves perfection. TABLE TRUE MM wino 19°30″ that Three important conclusions can, I think, be drawn from the foregoing exercise. (1) That feather angles should be different for the same sailing course with different classes of boat, because the direction of the apparent wind is dependent on boat speed. (2) That to hold a rudder slightly off centre, i.e., giving helm, requires some force to overpower the water pressure on the rudder. This force must come from the wind on the feather, To develop some force, the feather must be offset (a feather flying in the wind has no power because there is equal pressure on both sides), but to reduce the offset to a minimum, the linkage ratio of the feather arm to the tiller must be large. (3) With vane steering, the course sailed is to a limited extent variable with wind strength since the direction of the apparent wind changes with a change in the ratio of the true wind to the boat speed. Finally, a further word to the novice. Optimum performance is obtained with a vf} TRUE Ff WIND Boat Class .}, 6o° | 50° | 12° ei of RS) ae s\283\96 40°. | 50° 12°. 2664 | TABLE npr a (c) |% 7°20’ | ae ae | 51° 20’ 3? Se”) 48° 10’ eel 54°40’ eo eeca 2 36’r 90° 85° 13° 10° 88° M 90° 85° 13° 14° 45’ 83° 15’ 19° 30’ 78° 30’ 23° 45’ 74° 15’ 10R 90° A 90° 85° | 85° 13° | 13° TABLE 252 oe | ’ Wael le eae eae eae My Gee 6\6 Apparent ertionfy (a) Mo} FoR Vane Course Shits ser ois 36″r Fig? | | 3 36’r 120° 120° 15° 10° 125° M 120° 120° 15° 15° 15 124° 45’ 10R 120° 120° 15° 21° 30’ 113° 30’ A 120° 120° 15° 27° 30’ 107° 30’ fe) S,0 A feature of the ‘Revmaster’ on test was the consistent, vibrationless running. Current values were held steadily at all load speeds and there was a complete absence of ‘drumming’ or resonant vibration common to many motors of this type. Self-starting characteristics were good, there being no measurable ‘null’ points on turning the arma- is 20 quite moderate provided it is operated at relatively high speeds, and brush wear troubles /0 02: O the PERMANENT motor ‘Frog’ rate \ OVERALL L WA L 45000 2000 3000 4000 5000 6000 7000 8000: We would make the further comment that the manufacturers would be doing modellers a service if they also made a gearbox unit which could be used with the ‘Revmaster’ and other small motors in their range—something compact and simple which could easily be coupled direct to the motor shaft and enable power to be taken off the low speed shaft. Apart from the spindles, the whole job could be plastic. it best in Ta A RPM. should be practically non – existent. We would, in fact, \ 50 It is a very efficient motor for demand : Bare ak Summarising: a compact and extremely powerful little motor which the average modeller might well pass by on account of its current |— ELECTRICAL V/ sO ounces. size, pe MECHANICAL 60 Total weight of the motor, with driver, is 3} appearance. —_ 70 brackets being drilled out to take 4B.A. size screws. For fastening down to a hardwood base, woodscrews would be quite adequate. its | | EFFICIENCY CURVES 80 ture slowly with current applied. Mounting is straightforward with a well spread ‘base’, the ‘> —_— oi the range. i ee TUCKER’S TOPICAL TALK (Continued from page 260) Of course, practical considerations prevent our going to the full 9 : 1 aspect ratio for windward work, but if we consider this as the optimum for four points off the wind (45°), which is as close as any vessel can sail with advantage, and compare with the 1:1 aspect ratio, which is best for running dead before the wind, i.e. 16 points (= 180°) off the wind, we see that theoretically an aspect ratio of 5: 1 might be the average. This would give the best sailing at 10 points off the wind (= wind 224°) abaft the beam. However, 4:1 is the utmost aspect ratio that can really be used profitably, but it must not be forgotten that at 45° to the wind, this has been increased to approximately 5.3: 1. It is common knowledge among all yachtsmen and model yachtmen that it does not pay to carry sail beyond a certain point. An over-canvassed craft labours and makes a lot of fuss, and possibly appears to be travelling very fast, whereas, reefed down, she would be going easier and faster. The point at which it pays to reduce sail can be judged by study of the tables above. A yacht is at her best neither upright nor on her beam-ends. She needs to heel a 259 certain amount to attain her maximum sailing length, but once that is reached further heel reduces speed and weatherliness. This optimum angle is in the region of 20° to 25°. The skipper’s difficulty is caused by the fact that wind strength varies continually, and his boat may well be undercanvassed one moment and overpowered the next. Only experience and judgment can guide the skipper as to exact point when he should change down to a smaller suit of sails. In this connection, it must be remembered that just as S.A. varies according to the angle of the heel, does effective lateral area. At the same time, lateral area gains in value as speed increases. Hence a boat travelling fast makes less leeway than one travelling slowly. In consequence, if you punish a boat by over-canvassing her, you will not only reduce her lateral area because of her great heel, but reduce the effectiveness of the lateral area because of the lower actual speed she will be making. This applies, of course, purely to windward work. Off the wind, you can give your boat all the canvas she can stand without broaching or pitch-poling. a ee MAY, 1956 MODEL MAKER! fi Tucker’s Topical Talks = a ]N a fresh, whole-sail breeze, wind pressure on sails is approximately 1 lb. per square foot of area. This pressure, however, can be mathematically resolved into three component forces. The largest of these is lateral pressure, which causes the vessel to make leeway. The second component is downward thrust. This is roughly half as powerful as the lateral pressure, and is what enables a vessel to increase her displacement as she heels. The third, and much the smallest force, is propulsive forward pressure, and it is surprising that so small a proportion of the wind When closehauled, it may be a mere 5 or 10 per cent. Taking it power is available for this purpose. at 10 per cent., then lateral pressure is 60 per cent. and downthrust 30 per cent. Naturally, these proportions vary with the course and sail trim, and the proportion of energy available for propulsion increases as the yacht’s course brings the wind more free. It is, however, lateral pressure that is reduced, not downthrust which remains practically constant at all angles to the wind. With the wind dead aft, lateral pressure is eliminated, and about 70 per cent. of the wind-force is available for forward propulsion. In order to see how this all works out, let us take a very simple instance, a cat-boat with una rig. Her sail is a Bermudian of 1,000 sq. in. having a luff of 80.0 in. and diagonal of 25.0 in. Now as the boat heels her effective S.A. is reduced. It is quite simple to calculate this reduction by the formula S.A. cos 9, @ being the angle of heel. In making this calculation, it must be assumed that the foot of the sail is at right angles to the wind. Now as the foot of the sail will remain constant at all angles of heel, the reduction will be solely in the height of the sail plan. Hence it is a simple matter to work out what the effective height of the sail plan will be at any given angle of heel, and see how this reduces the aspect ratio. Angle of heel S.A. 0° 1000 25° 30° 35° ? 45° 905 866 819 766 707 15° 20° 966 940 Dimensions | Aspect Ratio 80.0×25.0 3.2:1 65.5×25.0 61.3×25.0 56.6×25.0 2.9:1 2.8:1 2.6:1 2.5:1 2.3:1 77.3×25.0 75.2×25.0 72.5×25.0 69.3×25.0 3.1:1 3.0:1 The height of the C.E. drops proportionately as the height of the sail plan is reduced from approximately 26.8 in. above the boom at 0° Heel to 24.8 in. at 20°, and 18.5in. at 45°. Taking both these factors into account the Heeling Moment of the sail plan is:— At in calculating the actual Heeling Moment of a sail plan. Some authorities take the height of the C.E. above the C.L.R., others take is height above the L.W.L., and yet others again as height above C.B. or M/C. My figures are rough figures to show the rapid decrease of heeling power as the angle of heel increases. ON SAIL FORCES AND HEELING MOMENTS N In taking out these figures I have ignored the fact that it is not the height above boom that is taken x 26 8 = 26800 0° Heel, Moment equals 1000 940 x 24.8 = 23312 3 3 che DOT 707x 18.5 = 13079 53 a his 45 Now let us examine this question from another point of view, and see what difference course and ‘trim make to effective S.A. and Aspect Ratio. This time the height of the plan remains constant. Dimensions | Aspect Ratio Angle to Wind S.A. 90° 80° 1000 985 80.0×25.0 80.0×24.5 3.2:1 3.25:1 60° 50° 54° 866 766 80.0×21.7 80.0×19.1 3.7:1 4.2:1 70° 940 707 80.0×23.5 80.0×17.7 3.4:1 4.5:1 From the figures we have arrived at, we can carry matters another step forward. Let us assume our cat-boat is close-hauled and sailing four points (45°) off the wind, heeled to 20°, from our table of Angles to the wind, we see that her sail is reduced in effeciive width to 17.7in. and from our Heel table that the effective height is 75.2in. Our effective S.A. is thus reduced to 4 (75.2 x 17.7) = approx. 666 sq. in. There is a nice whole-sail wind with a pressure of approximately 1 lb. per sq. ft. (= 1 lb. per 144 sq. in.), so that the wind pressure on our sails is 4.6lb. Of this 2.76 lb. is lateral pressure pushing our yacht to leeward, 1.381b. is downthrust increasing her displacement by this amount, and only 0.46 lb. remains for the forward propulsion of our craft. It is also of interest to observe that our aspect ratio has now become approximately 4.25: 1. All these calculations savour of X-chasing, and are never indulged in by practical designers, who simply work on broad principles and experience. They are, however, given in this article to show how some of these principles have been arrived at, and why they are correct. Far too many articles on designing are written by people without practical experience who have never designed a successful boat in their l-ves, and from that standpoint criticise those who prefer to rely on practice and experience, rather than on sheer theorists’ impractical ideas. Neither yacht sails nor yacht keels have anything to do with the design of either aeroplanes or steam-rollers. The design of sailing vessels was in a comparatively advanced stage before either steam-rollers or aeroplanes were thought of, and in its latest developments owes nothing to either of these useful mechanical contrivances ! At this point, we can, with advantage, summarise what these figures show us. We know that an aspect ratio of 9:1 is theoretically best for windward work, and 1:1 for running. From our calculations we see that whatever our aspect ratio as taken on actual sail measurements, it is greatly increased as we come on to the wind. On the other hand, while the aspect ratio of our mainsail by itself remains the same, as our course frees from wind abeam to wind dead aft, the aspect ratio of a jib-mainsail plan becomes narrower because the jib is gradually blanketted by the mainsail. By setting a spinnaker we can correct this and maintain the utmost width our sail plan permits. (Continued on page 259) 260
