DABCHICK ASSOCIATION OF SOUTH AFRICA PART 8
DABCHICK BUILDING NOTES
These building notes are designed for the person who has never built a Dabchick before, but may have useful tips for the experienced builder. It is recommended that the first time builders have a careful look at competitive Dabchicks and talk to the owners of these boats with reference to any good or bad pointers, and to do this frequently while building their boat. 1.
MEASUREMENTS AND MATERIALS
All measurements on the plan have a 15mm tolerance on either side, except where a maximum or minimum is stated. The wood sizes are only recommendations.
4mm Plywood is recommended to keep the weight down, but 6mm plywood may also be used with fewer stringers.
ABE Epidermix 372 and 365 are recommended for the glueing work. 372 on stringers and 365 on the ply edges and surfaces.
ABE Epidermix 389 is recommended for painting of inside of hull and underside of deck. In case of difficulties obtaining ABE Epidermix epoxies a good alternative, which is also cheaper, is the Ivory series available from Ivory Industries “Epoxies for Yachties”. The equivalent products are: Epidermix 365 372 389
Ivory 320 319 340/5/LF
Type Slightly thicker than 365, good gap filling and can be used for all purposes. Similar consistency to 372. Low Viscosity penetrating sealer. Apply 2 coats wet on wet to all surfaces.
Ivory also provides an excellent polyurethane (Ivory 400) that is much easier to use than Glatex 8 and is more flexible. Libra also has a similar product viz PU. Type “A” 1.5
Material Requirements: a) b) c) d) e) f) g) h) I) j) k) l)
Sheets of Marine Ply 2440 x 1200 4½ sheets Meranti centre board framing 15 x 12 x 900 4 off reqd. Meranti forward spine framing 12 x 12 x 1500 4 off reqd. Meranti forward spine framing 12 x 12 x 1750 4 off reqd. Meranti edge stringers 12 x 12 x 3500 4 off reqd. Juluton bottom stringers 18 x 12 x 3800 4 off reqd. Juluton bottom stringers 18 x 12 x 2750 4 off reqd. Juluton top stringers 12 x 12 x 3650 4 off reqd. Juluton top stringers 12 x 12 x 2650 2 off reqd. Juluton seating stringers 12 x 12 x 1100 8 off reqd. Formica (suggested lining to centre board case) 600 x 600 1 off reqd. Jig 3700 x 1100 wide 1 off reqd. with positions of bulkheads, A,A1,B,C,D,E and bow located in relation to transom. A number of clamping devices are required to keep spine straight and flat on jig as well as maintaining cross frames in position.
N.B. Ensure that jig has adequate strength to take heavy loading from bricks/sand bags when fixing underside and deck to frames. It is recommended that the sheets of ply are weighed before purchase, as their mass can vary considerably. A mass of less than 5kg per 3mm sheet is desirable.
Page 1 of 8
Cutting wood for framing and stringers : If you have access to a radial-arm or circular saw and wish to cut the wood yourself, it is recommended that you save by buying rough wood in the size 30 x 150 x 3850 mm which can be cut down easily.
Plywood and cutting lines for the bulkheads : 4mm plywood is used for the bulkheads because it is lighter and easier to use accurately. Draw all the bulkheads on a sheet of plywood as shown on the plans. 4mm should be subtracted from the bulkhead measurements for bulkheads A,B,C,D,E and Transom to allow for the sides, deck and bottom skins. 8mm should be subtracted from the bulkhead measurement for bulkhead A1, to allow for butt joint backing plus sides, deck and bottom skins.
Centreboard case : Varnish the inside of the centreboard case before you glue the two halves together. Formica glued to the centreboard ply can be used as an alternative to varnishing as it is maintenance free and provides added strength to centre board case. Glue top and bottom stringers to both sides of centreboard case allowing end projections to form joint with forward and aft spine. The stop-ends to centreboard case should be grooved to allow the ply forward and aft spines to be securely glued to them. The two halves of the centreboard case plus the stop-ends are glued together. Ensure that the inside of the centreboard case is not twisted when you glue the two halves together.
Forward and Aft Spines : Use 4mm ply for the spines and frame the top and bottom with Meranti stringers. Provide semi-circular cut-outs for bulkheads. (These are positioned at the measurement stations). Provide lightening holes taking into account the positions of the mast step strengthening and jib attachment fixing blocks.
Bulkheads : 12 x 12 Framing strips should be glued to bottom of bulkheads to increase the glueing surface with the bottom. a)
Cut the slots for the top and bottom stringers, side stringers, and spine.
Cut holes in each bulkhead for about 40% of its area to reduce its mass.
A 12 x 12 Jelutong framing strip should be glued round the edge of the transom to increase the glueing area. The strip should overhang the ply and be sanded to correct angle to suit incoming angles of sides and bottom. When putting in the stringers you should only cut grooves in the Jelutong and not the ply.
Fit a central hardwood block on the transom for the rudder pintles or gudions. This should be slotted to provide for the fitting and glueing of the aft spine to the transom.
NB. Extreme care should be exercised when forming this connection as the forces on pintles and gudions are very high!! It is suggested that only the best pintles and gudions are used for the rudder as cheap varieties are prone to failure.
Page 2 of 8
FITTING THE FIRST PARTS OF THE BOAT ON THE JIG Contact your Association to try to borrow a jig, otherwise make one.
Ensure that the jig is level.
Glue the forward and aft spines to the centre board case and fix this assembly to the jig, ensuring that the top of the spine is straight.
Glue the bulkheads into the spine, then attach the bulkheads to the jig. Check that bulkheads are upside down and that the larger side of centre board case is in front.
Glue the transom hardwood block to the aft spine and fix the transom into position on the jig. NB. Ensure that bulkheads are at correct measurement stations and that the edge height of frames above jig are identical on either side.
FITTING THE BOW TO THE JIG
The Bow is made by laminating strips of 4 x 4mm ply = (16mm) together. The grain of the bow strips must be vertical to enable one to bend them sufficiently. Adequate retaining stop blocks should be fixed to jig so as to ensure correct curvature of bow.
Laminate the bow strips into position allowing outside ply to pass aft of the bulkhead E and the 3 inside plys to stop at bulkhead E. Half the perimeter of the bow is 637mm (maximum length allowed), measured around the outside edge, from 3300mm from transom (bulkhead E) to the front centre of the bow. Screw front centre to spine. Screw through bulkhead E into the 3 ply layer that has stopped short.
ATTACHING THE STRINGERS
Stringers should be flush with bulkheads except that stringers at the A1 bulkhead stick out by 4mm.
Work from the inside out so as to prevent buckling of bulkheads.
Use wire as a clamp to hold the stringers in place when glueing them.
Stringers aft of bulkhead A1 and forward of bulkhead D are tapered to approximately half thickness so as to reduce weight.
Hold the stringers at the bow in place with a strip of wood over the stringers, at about 90 degrees to the stringers, held in place by a clamp.
Recess stringers by 4mm at frame A1 and use 4mm ply backing for supports for the bottom and side.
Check the measurements of the bulkhead widths.
Page 3 of 8
ATTACHING THE SIDES
Chain plates are bolted to hardwood backing strips between top and bottom side stringers and are fitted before sides are glued into position. This positions the chain plates inboard of side ply.
Glue the sides to the side stringers and bulkheads. Clothes pegs can be used as clamps while glueing on the sides.
PREPARING THE FRAME FOR THE BOTTOM SHEETS OF PLY
a) b) c) d)
(DO NOT FORGET!) Cut the water grooves in the bulkheads. These are positioned on the high side and directly adjacent to the stringers. The grooves should be 5mm deep. Grooves should also be cut behind bulkhead C from the side to the centre line. Check the measurements of the bulkheads.
FITTING THE BOTTOM
Cut the front bottom and back half sheet of ply down the centre. Short screws through some scrap ply has been found to be very successful in holding the edges of the ply down. Weights, bricks, sand bags are used in the middle of the ply. The screws are removed when the glue is dry and the holes are filled.
Glue on one complete side of the bottom, when dry, plane the overhang at the keelson down level with the keelson.
Glue on the other half of the bottom.
When dry trim all ply overhang back and cut the centre board slot out.
MAST STEP and FORESTAY NOTES
Cut the sides down to the level of the bulkheads at each bulkhead/side joint. Shape the sides with an even curve. Shape the stringers level with the sides. Shape the keelson level with the stringers and the side.
The boat is detached from the jig and turned right-way-up for these fittings.
Two chain plates are recommended for the forestay on either side of spine ply.
8mm thick hardwood fixing blocks between top and bottom framing of spine are used for fixing jib forestay.
The holes for the bolts for fixing the chain plates in place should be drilled before glueing the blocks in place.
A strong mast step is recommended - 10mm hardwood blocks between top and bottom framing of spine.
TOP STRINGER and BACKING BLOCKS The top stringers are fixed as per bottom stringers. Backing blocks (3x4mm ply) should be fixed for jib fairleads, toe straps and cleats. NB.
Fully measure and record positions of backing blocks so that once deck is glued on these positions can easily be found.
Page 4 of 8
VARNISHING THE INTERIOR ABE Epidermix 389 is suggested as it not only strengthens the wood but is compatible with ABE Epidermix 372 and therefore simplifies the glueing of the deck sheets as no marking of deck is required. Care should be taken not to paint top of stringers especially if ABE Epidermix 389 is not used!.
Attaching the deck and varnishing the interior of the deck. (If ABE Epidermix 389 and ABE Epidermix 372 are not used) two or more people are needed for this as the glue sets quickly.
The boat, especially the transom, must be supported so that it will not twist when the weights are put on the deck.
Spread glue on the surfaces of stringers and bulkheads to which the deck will be glued.
Put a deck ply sheet in position to make a print, remove it then varnish between the glue marks.
Re-glue the surfaces when the varnish is dry and place the ply in position and secure it with weights while the glue sets.
Drill a hole where the hatch cover is to be, as a breather hole.
Attaching Deck. (If ABE Epidermix 389 and ABE Epidermix 372 are used) a)
The boat, especially the transom, must be supported so that it will not twist when the weights are put on the deck.
Paint the interior of the decks with Epidermix 389 and before the paint dries completely.
Spread glue on stringers and place deck into position and secure it with weights.
Fibreglass (Optional Extra) a)
Fibreglass over all the corner plywood joints is an optional extra.
All the edges are rounded, except the transom which doesn't get fibreglass.
The fibreglass matting, 50mm wide, should be inlayed less than one veneer of plywood or about 1mm.
The fibreglass should be filled and sanded until it is level with the plywood. Resin, Epidermix or car body filler can be used.
It is recommended to sand out the bumps in the plywood before any painting. It is suggested that the edges be sanded round, except for the keel/side edge from the transom forward 2/3 of the boat's length.
Glatex 8 or equivalent good (polyurethane or polyacrathane) yacht paint should be used.
One should aim to put on at least four layers of paint.
After two coats of paint first 220 then 400 waterpaper should be used to sand the boat. After the third coat 400 and 600 waterpaper should be used. The final coat on the bottom should be sanded with 400, but mainly with 800.
Page 5 of 8
It is recommended to put silicon marine sealer/varnish in with the screws when putting on the fittings. Stainless steel selftapping screws should be used.
For the hatch cover you should only make a small hole first then make it bigger to fit the cover when you know the position of the stringers, because you do no want to cut a stringer.
Two strips of sail cloth, 40mm wide, should be glued under the centreboard case to prevent water from spraying up the centre board case. Commercially obtainable centre board gasket is available which could be used as an alternative.
CENTREBOARD and RUDDER a)
Make plywood templates of the shapes shown in the plan.
The laminated centre board should be about 27mm thick: it is then sanded down to the thickness of the centre board case, less 1,5mm for the paint. It should be made longer, then cut to size when shaped to allow for error.
Only shape the underwater parts of the centre board and rudder. If possible have hardwood for the leading and trailing edges.
If you can use a radial or circular saw, draw the template shape on the bottom of the centre board or rudder, then line the saw blade depth with the depth of the template shape. Cut four slots as guides of the depths on both sides then shape down (I use a coarse plastic sanding disk) to the template shape.
When fitting the similarly laminated rudder, ensure that it is positioned on the centre line of the transom as well as vertically to the deck.
MAST and BOOM a)
A straight mast section as shown on the plans is recommended. This section can be tapered at the top or purchased ready-made from a commercial supplier.
The thinner tube section with a track riveted onto it can be used but it has been found to be too weak.
Page 6 of 8
FITTINGS Hull a) b) c) d) e) f) g) h) i) j) k) l) m) n) o) p) q) r)
Rudder pintles Rudder retainer clip Pulleys for aft-sheeting Saddles for aft-sheeting Mainsheet block Swivelling cleat for fixing main sheet block to deck Toe straps 800mm long Toe strap plates Jib fairleads Adjustment cleats Pulleys for adjustments (Kicker 2, outhaul 4, cunningham 3, jib cunningham 2) Saddles for adjustments pulleys Cleats for adjustments Mast step Chain-plates Hatch covers Bung plug Centre board gasket
2 1 2 2 1 1 2 4 2 7 11 1 7 1 6 2 1 0.9m
Boom a) b) c) d) e)
Hangers & shackles for mainsheet pulleys Attachment for fixing kicker Mainsheet pulleys Recessed outhaul pulleys (Metal) Monal pop rivets 5mm x 13mm
2 1 2 2 40
Gooseneck Mast heal Halyard pulley (metal) Halyard lock (toothed rack) Monal pop rivets 5mm x 13mm Burgee holder
1 1 1 1 40 1
Mast a) b) c) d) e) f)
Rudder & Centreboard a) b) c) d)
Rudder gudions Tiller extension Centreboard retaining rope Eye for retaining rope
2 1,1mm x 16mm tubing 1m x 3mm 1
Page 7 of 8
Rigging a) b) c) d) e) f) g) h) i) j) k)
Aft-sheeting bridle 3mm x 2,0m Mainsheet 8mm x 5,5m Jibsheet 6 or 8 mm x 7,0m Adjustment rope (Kicker,outhaul, cunningham, jib cunningham) 6mm x 9,0m Kicking strap lever 1 Outhaul rope in boom 3mm x 3,0m Strop in boom 2,5mm x 1,5m Halyard strop (for internal halyard) 2,5mm x 4,2m Halyard rope (for internal halyard) 2,0mm x 4,5m Stays with chain plates 2,5mm x 2,94m 2 Levers for fixing stays to deck 2
Page 8 of 8