- The “A” Class Sharpie and how to build her “K.N.” Part 2 By H. B. Tucker. The yacht’s hull has to be built upside down on a jig (or former), so our first task is to construct this. The jig consists of a number of ‘‘ moulds ” (templates) erected on a stocks (or baseboard), round which the planking is bent to shape.
TWO. SHILLINGS FEBRUARY 1954 The “A” Class Sharpie and how to build her HE yacht’s hull has to be built upside down on a jig (or former), so our first task is to construct this. The jig consists of a number of ‘‘ moulds ” (templates) erected on a stocks (or baseboard), round which the planking is bent to shape. It is, therefore, obvious that the greatest accuracy is required in making these moulds and erecting them, By H. B. Tucker . to ensure the hull’s fairness. Actually, the first steps in. building are all-important, and should on no account be rushed. Once the jig is erected and faired, the remainder of the work is straightforward. As a preliminary a certain amount of paper work has to be done. If one is working from a small scale plan, full-sized drawings will have to be made. This enlargement has to be done with great care, since any error is multiplied by the scale. For example if one has to work from plans one-sixth of full-size, every error is multiplied by six. Hence an initial error of 0.05 in. would become an error of 0.3 in. in the actual boat. However, arrangements have been made whereby intending builders can obtain large scale plans from the offices of this magazine. These include lines plan (full-size) and full-size drawings of all essential parts. The first thing to do, if the designer has not already done so, is to rule a “‘ datum line ” on to the lines plan and body plan. This should by 6 in. above the L.W.L. and parallel with it. On the sheer plan (i.e. the plan showing the yacht’s profile), this should extend 3 in. beyond the full length at either end. Since the boat is 71.5 in. long, our datum line must be 77.5 in. long. On the body (or section) plan, the line will extend 2 in. either side of the centre line and be 4 in. long in all. This datum line represents the upper face of the base- board (commonly called the “* building board’’). In building a boat as big as an A-class, it is essential for the building board to be a very stiff, rigid structure, ‘so this will be built up as a T-girder. The cross member (or top member) will be a piece of good wood, without splits, bends or shakes, measuring 77-5 in. X 4.0 in. X 1.0 in., and its top face must be planed dead flat and true. The upright member measures 77.5 in. X 3.0 in. X 1.0 in. While some slight variation might be made in these measurements, the above would make a most suitable building board. The top member is firmly screwed to the upright member, with its better face on top. Before assembling the building board, take a marking gauge and very carefully run a centre line longitudinally down the upper face of the top member. (Continued from January issue page 29) Exactly half-way along the board (i.e. 38.75 in. from either end) square a thwartships line right round the board. Now the section stations are spaced 5.4 in. apart, so working forward and aft from the line representing the mid-section (No. 6), square lines for all of the section stations (i.e. from o-12) round the board. The positions for the stem and transom station lines have also to be found. If reference is made to the drawing showing the building jig (Fig. 5), it will be seen that a spare piece with an ear is left at the top of the stem to secure it to the building board. Our stem will be made from wood 1.5 in. thick. This is rather thicker than is usual for the stem of an A-class, but this is partly due to the wide cutwater, and partly to the fact that our yacht is a sharpie. From the broken line, showing how the stem would have run had pure sharpie technique been used, taken in at right angles, our stem is 3.0 in. from back to front. The little extra piece added on the fore side for the sake of appearance adds about 0.2 in. to this, but we have also to allow for the ear on the extension at the stemhead including the ear used to fasten the stem to the building board. The stemhead when finished will measure 3.25 in. from front to back, and the ear should extend about an inch forward of this. Using the broken line as a guide and measuring at right angles 3 in. in, draw in the back of the stem and produce it to meet the datum line. It will be found that the back of the stem produced cuts the datum line + in. ahead of Section ““O”’. This gives us the station line for the stem, and this can now be squared round the building board. There remains the station line for the transom to place. Our transom is to have a total thickness of % in., and will consist of an inner transom $ in. thick and an outer transom ¢ in. thick. Drawa line in. forward of the transom on the profile plan and parallel with it. This will be found to cut the datum line 3% in. abaft Section 12. This is the position for the transom station line, and it can be squared round the building board accordingly. The building board can now be assembled. In 59 DATUM LINE (| (RED fe a L.W.L. Rip RATING PARTICULARS WW di nent) ona Sian age he tn BG QUARTER BEAM. — =~ 31875 EW. BEAM Sees aoee 2 ee . e Q.B.L. ALLOWED WITHOUT PENALTY .__51-197 CB (AC TOAL creme wees ho ottas B18” O\BPENALIVE te L.FOR RATING ed 26} MIN. 3/0. ALLOWED WITHOUT PENALTY.___Il -20 ACTUAL PHO Ps ve Sle! lies) FOB PENALTY! one 3 5 1-16 MARE le ISI. 3 ah “EW De ane Baya er ENTS ae ATING. = 54-61+ a 39:00 , + = 23-40+ 15:97 L.O.A. 71-5″ L.W.L. 54-0″ = MAX BEAM DRAUGHT TABLE OF WEIGHTS SQ. INS. OVOO & VARNISH ——y IMMING J i i [ae Fe ede 54-61 x 39-00 ie i-b me a uf a a esr eee pe Soe a— W.LS. = = = W.L4 2s Se — O74 ee W.L3 Nore ts W.L.2 = 4 WLI n [2:0° 1 o7. < ——E Bet, Me ” + na pie Somes 2 Ca Te ee CG DECK ]LINE UPPER | CHINE eee iy LOWER| CHINE a BALLAST... Keele sos) 25 ¢ CURT = _= i =n Med eo io LOWER = 13-6" RIG (INCLUDING SPINNAKER). 2. ° LEAD, an sh SE 2 8 VANEIGEAR. ee W.L6. \C el 39-37 Re deries acti ee ei = DECK WITH HATCH.......... 1. 10. FIT ING Sor ane = _—_ LOWES i Wie rae) HULA eee ae aia. 2 \5,""G, PAINT hae = & M52 vs 3 1519 ee = 0:04 gh fOR RATING FORMULAE iene, —e Gl 2 2 Reec ee e ES: if MIN. FREEBOARD WITHOUT PENALTY_..___4- 15” AVERAGE FREEBOARD (ACTUAL) ss 4-5" DISPLACEMENT...___._____-‘51-5 LB. = IS90 CULINS. pier ee ° FORMULA. 54-61" — ee Fa Sul eres o . eae er | és fos 75° ete 3004 aaa or Bye etrie 51.8 | i I fo) 1 2 3 I oa TOP OF| FIN po tee : ee 6 Hull Lines and Sail Plan of A class Sharpie“ KN”. Draw screwing this together, screws should be positioned about half way between station lines. Ordinary iron wood-screws can be used for this, and in fact for any part of the jig, but any fastening that is to be incorporated in the boat itself must be non-ferrous metal to avoid rusting. Next take a piece of wood 1 in. x 1 in, (1 in. square) and cut off 13 4 in. lengths. Square a centre line round each of these (i.e. dividing the length into two). These form the cross-pieces to which the section moulds are secured, and will be clearly seen in thediagram. There are 12 pieces for Sections 1-1 25 and the 13th is for the transom. For important reasons which will be clear in due course, the cross-pieces in the forward part of the boat (Sections 1-6) must have their forward faces on the section lines, and those in the after part (Sections 7-12) must have their after faces on the section lines. These station lines are in the thwartships lines across the building board. Be careful to locate these cross-pieces exactly in their correct positions, and see the centre line that has been squared round them lines up with the centre line down the building board. Now in order that the boat may be got off the former, the screws N Construction Plan showing model on building board T-SECTION a BUILDING [NO 6 SECTION N sae aS - ‘ Res ee eas TO ARCS OF THE SAME RADIUS ALL DECKBEAMS ARE TO BE CUT SKEG %@ THICK MO itpeer ee ea cs ——— “NORMAL LEAD LINE (39-258) LEAD LINE FOR USE WITH RADIO CONTROL (34:75 LB) See a) N / ” OO eae on / @, el CPS pa ere Pe rio on / ‘ / eS, 820 oo \\, : \ Teee rr) OnY VO \ 8 sale urd 00 \ \ D = io OP ; ome) x1 2 + — 8 9 A-CLASS 10 Ti 4 12 AO z a 3% xin w g a => ae | ° rg a oO > og ae fon Wi x = aS 3 Z a tz > & Ao =e “S Alternatively put the building board on the edge of underside of the board. To enable you to line up your work table and screw through the upright into properly, start by putting a couple of screws in from _ the side of the table. the top. Turn the building board upside down and Dealing with the cross-piece for the transom, this put in two more from the bottom for each crosshas to be bevelled off to the rake of the transom. piece. With the board once more right way up, Take a marking gauge and set to in. Run it along remove all the top screws. This sounds like double what will be the top face of the cross-piece. Witha work but saves trouble later on. small plane now shoot the corner off from nothing at Incidentally, when you are working on the building __ the lower after corner to the gauged line on the upper board right way up (and this applies to the rest of the after corner. Fix to the board in the same way as building processes), hold the board with the upright _ the other cross-pieces. part of its T-construction held firmly in the vice. (To be continued) ase 2a, e | 5 BOARD a 4 3 2 ol|se. a 22 swing in our Plans Series Ref. SY16 is full size for model holding them in place must be driven from the 2 < @202 Aas S SHARPIE “KN” DESIGNED BY H.B.TUCKER Q Low O3 IMs a qi coy o
