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| «JANUARY 1957 MODEL MAKER) 4 GLASS FIBRE By A. G. STAINSBY MODEL YACHT HULL Part two of a most helpful and instructive account of the construction of an all-glass-fibre ’ Marblehead Class yacht The mix is painted on as evenly as possible, work- ing it well into the corners and eliminating bubbles. For this the better brush is used. When completed wash the brush immediately by dipping in acetone and squeezing with newspaper, then soap. After a time, which depends on the quantity of accelerator and the. temperature, it will begin to set. These things are under one’s own control and one must decide how long the job will take, or, better still, make a mixture with plenty of accelerator but do it in the cold. In the winter time, one can do the whole job, then bring up a couple of electric fires to speed up the setting. Don’t get it warm enough to start melting the wax, 60° to 70°F is quite hot enough. When it is tacky, the next stage can be started. We now have a smooth resin surface and we wish to reinforce it with glass fibre. As the mould will have no rough treatment, glass mat may be applied next. Feel the resin, and if it has hardened it will need another coat of resin before the layer of mat is applied. In fact. this is probably the easier way for the learner, although it is not the professional way. This does ensure that you cannot push any fibres through the coating of resin, and it allows a small thickness for rubbing down if this seems necessary. Cut a piece of glass mat the full length of the boat with sufficient to wrap round the ends and form a wall against the putty. Allow a bit extra as it is difficult to place it very exactly. Now mix up some resin for impregnation, this time 8 oz. of resin (with thixotropic) will be enough. No tale is required this time. Using a cheap brush, paint a layer over the first coat then push the glass mat into it and dab it with the end of the brush. Work from the centre to the ends, trying to use as little resin as possible and trying to bring all bubbles to the surface. Push the mat well into the corners and up the putty walls. If at the end some resin is left over it is worthwhile increasing the thickness of the centre flange by an extra thickness of glass fibre. When this has set, some circumferential ribs can be added to increase the rigidity as it is most important that this mould should not deform when used later on. This is done by putting up putty walls on the outside of 30 the mould and sticking glass fibre or cloth to these. I tried both and two layers of cloth gave a very rigid rib. 2 oz. of resin were required for this operation in which ten ribs were fixed at the ten station lines. These ribs are seen in the photograph of the mould. The whole should now be left for one or two days to harden. Although setting takes place rapidly the resin continues to harden for several days and it is most important that no distortion should occur. On no account let curiosity get the better of you at this stage and attempt to free the half mould from the male mould as it will not go back again exactly. The putty along the centre line may now be removed and the resin cleaned with a litile turps or linseed oil. A new wall must be built around the gheer line of the other half. If the batten protrudes so much the better, if not, care should be taken to smooth the putty as exactly as possible to the sheer line. The glass fibre sticking up along the centre line should be trimmed off, leaving a wall of resin lamination sticking up. The resin wall must now be given a few coats of polish, taking care not to fill the angle that the wall makes with the male mould, as this will later cause flash during the next moulding and worse may cause sticking. Coat the remaining half of the male mould and the resin wall with P.V.A. and allow to dry as before. Then once more build up a lamination exactly as the first half. When this has hardened, drill some quarter-inch holes through the wall and bolt the two halves together with quarter-inch nuts and bolts. These should now be slackened off and the female mould removed from the male. It should come away easily if a thin knife is pushed in at the top to start it. The inside of the F.M. should now be washed in water to remove the skin of P.V.A. which will be sticking to it. Examine the inside carefully. If there are any pin holes or bubbles in the surface these can be filled with resin and rubbed smooth with glass paper, always remembering to mix a filler in the resin if it has to be rubbed down. If the mould is generally satisfactory, it should be clamped together and waxed. If, however, the surface is not perfect, it can be smoothed off with flour paper prior to waxing. JANUARY, The Canoe Body of cloth where the keel and skeg will go to give extra strength there. ; We now have the shell in its outer mould with a If the mould is satisfactorily polished it can be given two coats of P.V.A. and it is ready for use. Insert the dowel pins into the mould and grease them, these will now form the location for the keel and skeg. lot of surplus whiskers sticking out at the top. These can be trimmed with metal shears and a fine hacksaw then planed down with a Surform and finally sandpapered with coarse sandpaper to bring the sides level with the sheer line which was marked in the outer mould. Doing this one should get an exact replica of the sheer of the original mould. The next process is the insertion of the inwales. Where these are placed will depend on wheiher it is decided to fit the deck over the top or to let it in. In my case. I decided to let the deck in so that It is assumed that the colour for the boat has been decided. It has to be the same colour all over, and possibly white is the best, since any colour may easily be painted over it as desired. The colours are obtainable from the retailers of the resins and the quantity required varies with the colour used. If you wish for a transparent finish in another colour such as blue or green, this can be obtained, but | think most yachtsmen will prefer an opaque finish, in which case some talc filler will also be mixed in the gel coat. the edge was not exposed. The inwales for the M Class boat were }in. square. There was also a transom piece both fore and aft. This is necessary since there is little strength in a flat laminate. These transom pieces were cut to fit. inside the moulded. For the boat itself, I used one layer of glass cloth and one layer of 1 oz. mat. The glass cloth is to provide additional strength which was not required in the mould. For this purpose 12 oz. of resin (with thixotropic resin) was mixed with 2 oz. of talc and about { oz. of white pigment, and the catalyst but hull and grooves }in. square were cut in the top to take the inwales. The inwales were cut to length and checked in position. A gauge was made up which could be run along the sheer and gauge that the no accelerator was added at this stage. This was thoroughly stirred then allowed to stand to remove bubbles. It is most important to get rid of small inwales were exactly the thickness of the deck below the upper edge. Having made sure that everything would spring correctly into position, the wood was removed, the inside of the hull was coated with thixotropic resin for half-an-inch down from the upper edge. The wood was also coated with resin, placed in position and checked with the gauge. If the wood has been correctly cut it will spring into position correctly. If, however, it does not fit well the wood can be held in by toolmakers’ clamps or wedges. The whole mould is then turned upside down so that any resin forms a fillet beneath the wood when the boat is upright. Further strength can be given to the inwale by sticking strips of cloth on the underside. Finally, a keel piece must be put in to take the weight of the keel. This could be of solid resin loaded with chopped glass or. wood can be used. In my case, I used a piece of wood which was shaped to fit roughly into the bottom of the boat. This was fixed with a liberal supply of resin. When set a drill the same size as the dowel pins was put through the wood so that everything lined up. In the same way a strip of 1 mm. ply was stuck to the inside of the hull where the skeg would fit. Slots for deck beams are made in the inwales with a chisel and the bubbles in this mix as these will spoil the surface of the boat if they appear. This resin was divided in two. The cloth was cut into suitable pieces for laminating then the accelerator was added to one half of the prepared resin. This was carefully brushed over the inside of the mould, trying to get as uniform a coat as possible. When this had become tacky the cloth was pressed into the surface and accelerator added to the second half of the resin. This was applied with a stiff brush by dabbing like a stencil brush in an endeavour to get rid of any air bubbles. The importance of this layer cannot be over-emphasised as the whole appearance depends on elimination of bubbles at this stage. The time this operation takes depends on the size of boat and size of brush. and this must be borne in mind when adding: the accelerator. It is desirable to complete the whole process before the resin sets, otherwise there may be differences between the two ends of the boat. Here again the temperature is another important consideration. The use of a wooden roller is recommended by the makers to help in this process, but one of a special design would be necessary to get into the curves. Suffice it to say that it is not essential. 5 i cee 1957 deck beams are fitted by screwing and gluing. A layer of 1 oz. mat is applied as soon as the cloth is in position, and this is once more pressed into the resin which is there, and more is added as necessary using the stencilling technique to push out the bubbles. There is now no need to use a filler or colour in the resin, but thixotropic paste should be added to prevent draining. The quantity used for this part of the process was again about 12 oz. If at the end of this process there is still some resin left, it is worthwhile sticking in some strips The canoe body is now complete. The female mould is removed and the hull is washed to remove the P.V.A. If all has gone well there will be little smoothing required, and rubbing with flour paper should be sufficient. If there are some blemishes these can be filled later, but unless they are serious they can well be left until after the keel has been fitted. This view of the completed female mould shows clearly the circumferential stiffening ribs and the joint line flange running along the entire length of the hull 31 MODEL MAKER Another view of the completed model, which has a first class finish and an excellent performance The Keel It is assumed that a keel and skeg have been carved and that the lead has been cast and inserted in the usual way. There are now two ways of proceeding. Perhaps the most logical is now to form female moulds and cast the keel and using chopped glass mat as a skeg filler. in solid This, resin portant how- it with glass cloth. be The wooden keel and skeg were fitted and glued into position with resin, the lead was also glued into position and fixed by the keel bolts in the usual way. The rudder tube and brass step for the lower rudder pintle were also fixed. Keel, lead, and skeg were then painted with resin containing colouring material and some filler. Strips of glass cloth were spread over each before it became too dry, making sure were not of. much that may otherwise importance. Weight of canoe body with deck Deaingunt to. 5, oak io\ Deadwood of keel plus skeg and rudder mee aed Deck t. A iz Paint and varnish, approx. There a-half As gether two. -In any The final ADL Lb OZ. i 10 oz. 10 oz. 4 to 6 0z. is thus a saving of something between one-andand two pounds over a conventional hull. a postscript, I took the boat in the car towith the family including number two aged During the journey he lurched against the went away on business for seven weeks. On my return I have looked for the dent but it is now invisible. Evidently the glass and resin slowly For painting, cellulose or worked itself back into a relaxed position. of course, im- to say, I was delighted. . 8 S z i book form?—any thought you may have helps us to plan your future reading nrat- @ S ter in the way YOU would Ike it—and you, after all, are the person who matters, so do please card ! drop us @ main sheet and/or unbalance his vane gear to give excess weather helm when heeled. Many other examples could be given of the way in which a yacht’s imperfections may be either assets or liabilities according to conditions, but the foregoing should be adequate to draw certain basic conclusions:— 1. If your yacht has wayward tendencies it is best in the long run to eliminate them if possible before the yacht is raced. 2. If they cannot be completely and permanently eliminated you have to decide, each time the yacht is raced, how they will affect performance under the prevailing conditions. 3. If you can use these tendencies to advantage in the race, take every opportunity of doing so. 4. If they are handicapping you, do everything possible to counteract them. Finally, a perfect yacht can easily be made to sail imperfectly if it is an advantage to do so. An imperfect yacht cannot readily be made _ perfect or easily given opposite imperfections. There are, therefore, no substitutes for thoroughness in design, construction, fitting out and tuning if consistently good performance in racing is to be achieved. BOAT 3. 4. 5. ASSOCIATION Single or twin i/c engines limited to I5 c.c. with a concession up to 30 c.c. for multi-cylinder engines of four or more cylinders. Power/Weight handicap of li Ib. per c.c. of cylinder capacity (Ballast may be added to bring boat to required weight). Steam and Electric craft—No special restrictions at present. Col. H. J. Taplin (Birchington) has offered a Trophy for International Competition, and it is hoped to run this next season. Provisional date for ANNUAL GENERAL MEETING is Saturday, January 19th, at Central Club, London, E.C.I. Will Secretaries. be confirmed by circular to all Club 0000800000 000000000 wind pressure. Changing the trim of the yacht will normally transfer it from one such course to 1957 MODEL MAKER | above Tucker’s Topical Falk COMPARISON AND OF RIGHTING Gravity. of essence, Buoyancy. of of kLffort. e = Heelin Movement of Centre of Effort. UO rvenbe: “Talk”, the diagram which illus- intricate calculations are fallacious, and put forward a suggestion of my own for their amendment. In doing this, I specifically invited readers who are interested in X-chasing to air their own views on the subject. This invitation drew two answers—one from Mr. Guy Blogg and the other from Mr. A. G. Stainsby. These letters appear in full… Dealing first with Mr. Blogg, it will be remem- us back to Admiral Turner’s = 11.519 in.-Ib.=184,32 in.-oz. Mr. Blogg calculates the Heeling Moment:— the stability equation (Righting Moment= Heeling Moment) is satisfied. The orthodox method of finding the Righting Moment is by the formula: — Weight x (GM sin @) Where GM=Distance of M/C above C.G. and O =Angle of Heel. The Righting Arm by which the weight is multiplied is thus the distance that the C.G. has moved in a horizontal direction at the given angle of heel. Thus, when the yacht is upright since the C.G. is still on the upright centreline, the Righting Arm is nl and there is no Righting Moment, but as the yacht heels the Righting Moment increases with the so_to (S.A. cos@ P )x x(H cos @) calculate the Wind Pressure, we have the following equation: — (644 x 0.94) x P x (17.44 x 0.94) = 184.32 605.36 x 16.39 x P= 184,32 P=0.186 in.-oz. From the Table of Wind Pressures and Velocities I gave in November we see this is equivalent to a wind of 8 knots. By my method I got a wind of 12 knots. Now I well remember the little boat from which my figures are taken, and she was a very stiff little boat for her size. Hence I feel very dubious if an 8-knot breeze would have heeled her to as great an angle as 20 degrees. angle. Of course, unless the yacht is a Metacentroid, the height of the M/C changes with the angle of heel. the brings The Righting Moment is: — Weight x GM sin @=10.3 x (3.27 x 0.342)= 10.3 x 1.118 the sails is equalled by the righting power of the hull. In other words she heels to the angle at finding this 17.44 in. bered that I stated the problem:— When the breeze strikes the sails the yacht heels until the heeling power exercised by the wind on of the Since the Righting Arm is the distance the C.G. has moved from the upright position, I consider the Heeling Arm should be the distance the C.E. moves when the yacht heels from its original upright position. Hence I calculate my Heeling Moment:— (S.A. cos ATM)xPx(H sin @) Now Mr. Blogg evidently agrees my contention that the M/C must be the fulcrum for our balance and measures his height to that point. By making this. H. cas@, he allows for the drop in height of the C.E. as the boat heels, in the same way as effective S.A. decreases. However, he still uses a horizontal Righting Arm and a Vertical Heeling Arm. Let us see how this works out for the same little 36-in. yacht I used in my November “Talk”, and see what pressure it takes to heel her 20 degrees. For convenience, I repeat her relevant measurements here: Weight 10.3 lb. C.G. below M/C (GM) 3.27 in., S.A 644 sq. in. Height of C.E. above M/C trated it took a 20-degree list to port, as the line CMBG should have been vertical. As the same diagram is needed for reference again, it is repeated but this time on an even keel. The principal subject of my November “Talk” was Stability Calculations, and the fact that the data they provide as to a yacht’s ability to carry sail is unreliable. I tried in this article to see why the orthodox methods of working these Iengthy and method or the hull and another for the sails. NFORTUNATELY in the final make-up of my The orthodox Moment is: — the C.B. Theory of Rolling Motion on which the well-known system of balance (the “M/C Shelf’) is founded. The M/C is not only the pivot point about which the boat rolls, but also the intersection point between the upright and heeled centre-lines. It therefore seems logical that it should be the fulcrum for balancing Righting and Heeling Moments. I have used it accordingly, instead of using one point for Arm. = Centre Effort C!=Heeled . entre which above We also see that in heeling, the yacht turns about the M/C. In fact the M/C is its pivot point. In MOMENTS Centre others Moment for every angle of heel, including when the yacht is on an even keel! HEELING (Not to Scale) Centre L.W.L., C.G. is below the M/C, we would have the same A= Angle of Heel. B= Bi=Heeled the C.L.R. To me it seems that if we are balancing the Moments of Righting and Heeling, we must employ a common fulcrum, not measure them about different spots. Further, it seems inconsistent that the Righting Arm should be horizontal and the Heeling Arm vertical. As we have seen above, it is obviously correct to calculate the Righting Arm by this horizontal movement, as if we employed the vertical distance the Now cannot turning fact that Heeling to understand Mr. A. why he G. Stainsby’s draws attention letter, to I the Weight= Buoyancy. This is merely another way of stating that a boat floating disvlaces a volume (S.A. cos \xPxH Where P=Wind pressure per sq. in., and H= Height of C.E. Some authorities measure the Height of the C.E. of water having a weight equal to her own weight. Quite true, but is this relevant to the subject under discussion? (Continued on page 50) 48 JANUARY, De Pf Readers write… HEFLING MOMENT— JOIN OUR 1RIG CLASS! Mr. Tucker’s invitation to X_ chasers is too hard to resist and I should like to offer my views on the subject the heeling of yachts under pressure from the wind. Refercing to the diagram of a heeled yacht—Fig. 1, it is seen that we are concerned with four forces acting at different parts of the boat. i. The weight “W” acting downwards at the centre of gravity “G’’. J li, The force of Buoyancy “B” acting upwards at the centre of buoyancy “C B” and crossing the centre line of the boat at the metacentre “M”,. — iii. Next the force “‘S” due to the wind’s ressure on the sails. Assuming no riction of the wind on the sails, this force must act at right angles to the mast at the centre of effort “‘E’’. iv. Finally, the reaction ‘‘R” of the water to the lateral push of the wind. This can by definition only operate at the centre of lateral resistance “L” and if the boat is smooth it will be at right angles to the centre line. Assuming that leeway is negligible, these forces must be in equilibrium =B S=R and we have two couples heeling and righting ; the boat. We have to resolve the vertical forces along and at right angles to the axis. Righting moment = W sin @x GM. Heeling moment = Sx E , There remains the value of S, this (as I believe Guy Blogg has already written) is given by the pressure of the wind x Area of sail which the wind sees x the resolute at right angles to the mast i.e., P x (A cos 9) x cos @ The equation is: W sin 9 GM=P.A. cos? §EL. rg? FON .. : (i) Fig! To illustrate by an absurdity that the metacentre is the wrong place about which to take heeling moments, imagine an extreme skimming dish hull (Fig. 2) carrying its storm suit. The centre of effort might be below the metacentre and E M would thus be negative making the wind pressure cause the boat to heel to windward! Also if Mr. Tucker’s expression using sin 6 were correct: if the boat became upright, sin 9= @ the heeling moment would be zero even when the wind got up, i.e., it never could heel! Finally, if when equation (i) is worked out it still does not give the right answer, don’t blame the equation, but remember that the position of the centre of effort, the instantaneous metacentre and the centre of lateral resistance al] depend on the angle of heel and the velocity of the boat relative to wind and water. A. G. STAINSBY. Oxhey, Watford. Dear Sir, With reference to Mr. Tucker’s article in your November issue, he arrived at the following equation relative to his diagram :— Heeling Moment=Righting Moment. SAcos6PxHsinO=W sin@GM The heeling arm, or crank, of the Wind Force is not Hsin §, I suggest, but H cos @. A more correct equation is therefore: SA cos? PH = W sin§ GM. London, N.W.3 Guy BLoa«. SUPER SHIPS WANTED Dear Sir, ‘ As a keen working model shipbuilder, I would like to endorse Mr. J. C. Castles comments on scale models, and I would certainly like to see more scale model ships in the MopEL Maker, particularly modern ships, as there is another magazine which seems to find bags of space for “‘full rigged models’’. I am one of the “metal hull brigade’, “a la Norman Ough”, and at present am working on a fully detailed working model submarine, 4in.—lin., to one of his drawings. These drawings are the finest of this type available in the country. Could not perhaps the Editorial staff persuade Mr. Ough to contribute to the MODEL Maker as they have L.B.S.C. ? His latest drawing is to 4in.—lin. of the wartime destroyer Kashmir, and to my knowledge has not been published in any magazine. I’m sure builders of model warships, who read MODEL MAKER would be inspired by the detail and gen of these drawings, and it would certainly bring in more readers. D. Lewis. Honiton. CONTEST CALENDARS Dear Sir, Why all the argument about too many pages of the MopEL Maker devoted to ships! M.V. Pateke — fullsize version with Reader Holst’s drawing of bow-plaque below. NEWS OF M.V. PATEKE IN N.Z. Dear Sir, In the May edition of MODEL MAKER you gave the line drawings of M.V. Pateke, one of our New Zealand coasters. You stated that only line drawings had been obtained from Mr. Hill, and therefore had only details from what could be seen in photographs. She paid a visit here (not usual) a short time ago, and so I took the enclosed photograph. It can be seen that you have got most of the detail right. Omitted from the drawings inscription, so drawing of this. New Zealand. however, I have was also the bow enclosed a R. J. Hotst. L.S.D. OF L.B.S.C. isagree. I have been a reader for three or four years, and there seems to me to be fewer articles on model ships and boats than there was a year ago. I would like to see the MODEL MAKER devoted to model boats. I know I am sticking my neck out when I say this, and sit back and wait for the rude remarks. I also dropped a certain magazine because there was too much steam and settled down the MopEL MAKER—now blow me down if the chap isn’t following me around; for heaven’s sake don’t start publishing articles on traction engines—this will be the last straw. Now to a serious point. I do think that a portion of the magazine should be devoted to competition and Regatta dates, so as to keep everyone informed. As Marine Secretary of the local Cub, I ran into difficulties this year by—unknowingly, arranging Regattas on dates which clashed with Poole and Birmingham—and which had to be subsequently cancelled owing to the small number of entries. A certain magazine used to do this, but discontinued it this season. Come on Mr. Editor, what about it ? Let everyone know what and where it is happening during the summer months. Dear Sirs, Reader Paxton seems to have gone off at half cock. I too thought that building a live steam locomotive was quite out of my HAPPY BALSA BASHER Frankly, I was on the point of cancelling my order, when L.B.S.C.’s article was announced. Now I am glad to say I can enjoy his serial whatever else you like to give us. For Bro. Paxton’s benefit, I would like to point out that I have just completed a 341n. gauge loco. to Curly’s “words and music”, Although it took me over four years, I made it for under £2. When I began I had no lathe, or prospects of one | Brighton. ARTHUR T. SALLIs. Dear Sirs, Surely there is another magazine especially for those who want “to play at loco builders ?” Leave the MopEL Maker for “those spineless people whose limits are balsa wood and electric rail cars’ Some of us can only afford to work on the “‘kitchen- table”’—and we thoroughly enjoy it! ! Buxton, T. F. Starr, 49 reach until I enrolled in a Model Engineering class, run_ by the local Education authority’s evening institutes. For 15s. per term I am able to use the machinery and tools, obtain valuable assistance from a well-versed instructor, obtain most materials at nominal cost and meet others in the same position as myself, Why not have a bash at “Mona”, Mr. Paxton, I am, you don’t really have to be a millionaire, I’m not. Bournemouth. E. W. PEARCE. P.S.—You cannot make a loco in five minutes; over a period of time the expense will not be too great. Dear Sir, I became a regular reader of MODEL Maker, not because of the interest in ships. boats and yachts (I can’t stand ’em), but because Prototype Parade occasionally produces plans for a decent racing car. However, lately we have just been presented with obsolete junk or modern production stuff (this month excepted). MONEL MAKER) but with a little patience and a well filled junk box, I gradually built her up. Cylinder and wheel castings were all it cost me. When I need to run this loco. I must take it to Edinburgh, which is over 50 miles away; farther than for Bro. Paxton. If the above gentleman cannot build a loco. under these conditions (provided he is able to do anything but criticise), then let him stay with his hammer and nails. As for myself, L.B.S.C. will give me my “*two bob’s” worth. Hawick, Roxburghshire. E. J. BREARLEY. Dear Sir, I am a new reader of your magazine, so am not in a position to comment on your past policy, but quite obviously, from the current controversy, your readers fall into the two categories of those who make models and those who assemble kits. Surely the ultimate aim of the genuine ‘Working Model” maker is to produce his model, including power plant, from basic taw materials, and there is no greater satisfaction to be had in our hobby than the first uncertain motion of a home-built power unit. Reader F. G. Paxton would be well advised to find his nearest Model Engineering Ciub, and meet a few enthusiasts who are enjoying the hobby to the full at very little expense; I have been secretary of a club for a number of years and can assure him that we have no millionaire members, although we do have a track and six L.B.S.C. locomotives, either built or building, and noting Mr. Bellamy’s remarks concerning model makers’ workshops. I agree that few of us have expensive workshops, but a great number have lathes of some sort from simple home-made jobs upwards. Finally, I would add that, although my own interest is in model power boats, I have been a regular reader of L.B.S.C. for just over 27 years, and owe most of my knowledge of lathework and steam plant design to his lucid-instruction. Hatfield. F. W. DUNHAM. Dea: Sir, I have always considered that MopEL Maker has been aimed at the modeller with little or no workshop equipment, that is, I think the average modeller. I have no objection to articles by L.B.S.C. or anyone else, concerning models requiring the use of a lathe. I find such items most informative even if my chances of access of a lathe ate negligible. However, the attitude of Mr. Castle annoys me intensely. His criticism of such materials as balsa and papier mache, together with his condemnation of electric rail track racing, suggests a very short sighted outlook for a model engineer. Epsom Downs, Surrey. R. BLEASBY — ——_—— TUCKER’S TOPICAL TALK (Continued from page 48) Our Similarly, he tells us that Wind Pressure on the sails=Lateral Resistance, but this does not prove that the boat, in heeling, rolls about her C.L.R. This idea reverts to Norman Skene’s method given in a textbook published about 1920, of which I have a copy. However, we will later work out our little 36-inch boat by this method and see how it compares with the results obtainable by Mr. Blogg and myself. Mr. Stainsby contends that the M/C is the wrong point to use as a fulcrum is balancing Righting and Hecling Moments, and to prove this he adduces an instance which he very rightly calls an “absurdity”, and illustrates it aptly with an equally absurd diagram! While this is evidently not to scale, it is not even vaguely credible. If we examine his Fig. 2 and assume it represents a boat with 15 in. L.W.L. Beam (which incidentally has no topsides), by taking 1ough proportions, we see he has placed his M/C about 10.25 in. and his C.E. 9.3 in. above L.W.L. If we allow for 3 in. Freeboard and for the top of the main boom to be 3 in. above deck (both conservative figures!), we see that the mainsail of his “storm suit” has a luff of not more than about 9 in. length. This is certainly very reduced canvas for a boat with 15 in. L.W.L. beam! His position for the M/C 1S sanally improbable even for an extreme skimming dish. Mr. Stainsby then proceeds to proclaim that my use of the movement of the C.E. as Heeling Arm is wrong. It possibly is, but his arguments against it, and the conclusion he draws, are on a par with his reasoning about the use of the M/C as a balancing fulcrum. Our friend tells us that since my Heeling Arm is nil when the boat is upright, she cannot heel when the wind gets up! Now by every method of calculation, including the one advocated by Mr. Stainsby, the Heeling Moment is obtained by multiplying the Pressure of the Wind on the sails by the Heeling Arm. When there is no wind, the Pressure is nil, so whatever one uses as a Heeling Arm, the Heeling Moment is nil. So according to our friend the boat could never heel. But it does not end here, as what applies to the Heeling Arm applies with equal force to the Righting Arm. The Righting Moment is obtained by multiplying the weight of the vessel by the Righting Arm. When she is upright, the Righting Arm is nil, and the Righting Moment is likewise nil. So if Mr. Stainsby’s argument is correct, if heeled, the boat could never right herself! 50 friend concludes by telling us that if the equation does not work out satisfactorily we must not blame the method, but remember the C.E., M/C, and C.L.R. are all points that continually move about. We all know these points move with every change of wind force and direction, but Mr. Stainsby cannot invoke this easy way out. In order to test our boat we are trying to ascertain what force of wind will heel her to an angle of 20 degrees. In the case of the litle 36-inch boat used I worked out her C.G. accurately, likewise her M/C for 20 degrees of heel. The calculation of the effective S.A. when heeled gives an accurate result. The calculation of the C.E. when heeled gives a reasonably correct result, as apart from the effect of the heel, its main movement is forward. Surely our objective should be to find some new method that will produce reasonably reliable results, instead of trying to boost methods which have been tried and found wanting. Admittedly many formulae used by naval architects have been evolved by rules-of-thumb methods and have no scientific explanation. The main thing is that they work well. A good example of such a formula is that giving the Ratio for Comparison of tthe relative Speeds of Vessels of different sizes. This is :— V : Sq. Root of L where V=Speed in knots, and LZ the L.W.L. length in feet. This gives remarkably accurate results and in consequence is universally employed when such comparisons are required. _ By way of final comment on the method advocated by Mr. Stainsby, let us work out our 36-inch yacht that way. All necessary measurements are given above except the Height of the C.E. above the C.L.R. which is 21.4 in. As Mr. Stainsby uses the same method of finding the Righting Moment as Mr. Blogg and myself, we can take this at 184.32 in.-oz. as already ascertained. Here then is his equation, but as for some reason he has used different expressions to those usually employed by naval architects, I have Stated it in the normal fashion: — (S.A. cos@)xPx(H cos@)=184.32 (644 x 0.94) x P x (21.4 x 0.94) = 184.32 (605.36 x 20.12) P=184.32 18180 P=184.32 P=0.0151 in.-oz. This equals a wind of about 7 knots, which seems more off the mark than ever, since our problem is to find what velocity of wind will heel this rather stiff little boat to an angle of 20 degrees.
