SANDWICH DECKS AND CABIN

For sandwich decks, the choice of core material is either PVC foam or end grain balsa. Check with your suppliers for the best material to use. There are now some PVC foams that are suitable for decking.   The thickness of the core and the laminate requirements should be specified in your plans.   Your plans should also clearly show if any supporting beams and girders are required.   A well-engineered sandwich cored deck should not require extra beams – the strength is in the sandwich and the supporting bulkheads.   Boats over 40 feet [15 metres] may require some reinforcing in the deck especially if built to survey.

MASTER DECK MOULD

Your first job should be to cut the master camber board; sometimes your full size patterns will include this otherwise, you will need to draw out the camber from measurements.  You should make up a full width plywood or timber camber pattern.   By using a wide plank, which can be edge laminated to a suitable width, you can make both male and female patterns with the one saw cut.

   Next job is to build the master deck mould.  This mould will serve to mould for all the deck and cabin top panels and even curved cabin fronts can be laminated on this mould.   Make the mould wide enough to fit the widest section of the deck or cabin on your boat.   This may be the aft deck, poop deck or perhaps the cabin top.   On sailboats and on some power boats, the camber is often greater for the cabin tops than the deck, however for a power boat with a flying bridge, it is best if the standard deck camber is used for all purposes.  The reason for this is you do not want a heavily cambered deck in the flybridge area.

   The length of the master deck mould should be a few inches longer than the longest panel required but, as panels can be joined, 16 feet [4.9 metres] long is sufficient for most boats up to about 65 feet or [20 metres].  Build the deck mould without sheer (fore and aft camber) as when first moulded, the deck panels will be flexible enough to bend to the shape of the hull.

   Build the master deck mould using similar techniques to those used to build the hull mould.  Set up the structure on bedlogs and build the mould with the camber in reverse.   Use the female camber boards as the frames and install battens to receive the mould lining.   Waxed hardboard will serve well as the mould lining.   Attach the mould lining with contact cement and nail only where necessary.   Any nails will show up in your finished moulding so try to avoid excessive nailing although most areas will have to have non-skid applied so this is not a major problem.   Prepare the mould by waxing with non-silicon wax and, if necessary, apply release agent. Tests can be made to see how well the mould releases.

   Place temporary beams across the hull in the areas where the deck moulding may need to be supported – these mouldings should almost be self-supporting straight out of the mould.  Supporting beams should be inside the deck shelf so the pre-laminated deck part can sit flush on the shelf.   Make a pattern of the section of the deck you are going to laminate and transfer it to the mould.   To make the pattern, you can use strips of plywood stapled together to get the approximate shape and then use a spiling block to obtain the exact shape marked on to the pattern or, trim the moulding once it is in place.     Use masking tape, to outline the shape on the deck mould.  

   It is probably better not to use gelcoat as you will have to paint and apply the non-skid after moulding and joining the parts.   It is possible to apply a non-skid pattern to the mould surface however this can be tricky and should not be attempted without experience also, you will later be bonding the deck in place and would probably spoil the effect of the mould-in pattern.   Use a similar laminating technique to that used for the hull, no more than two layers per day or whatever the manufacturer recommends for the particular resin that you are using, otherwise the deck piece may distort and pre-release from the mould.   It is important to remove the deck part from the mould as soon as it can be handled.  This means that it will be “green” and can take up the sheer, if any, of the hull.   Therefore,  make sure the centre of the panel is well supported,  camber boards set right across the hull at every 3 feet [1 metre] apart should be sufficient.   Check after you install the first piece.

   Any deck beams, girders or special stiffening called for in your plans should be laminated on to the panel while it is still in the mould.   Allow for the deck shelf when installing beams as they should be shortened by the width of the shelf.   If you want to use interior gelcoat, then should be applied to the deck panel while it is still on the mould.   Keep the gelcoat away from the edges where it will later be bonded to the deck shelf.   Keep any cored material stepped back from the edge to allow the inner and outer layers of laminate to join by way of a tapered edge of the core as shown in the drawings.   Side decks can usually be laid up flat on a piece of hardboard on the ground or on a bench.

You will be surprised how quickly you can make the deck and cabin with this method.