Building the Scarab 350 trimaran.

This boat was my favourite boat to build. It was small and quick. Most of the time was spent making the foam sandwich panels see Manufacturing foam sandwich panels but it would be much quicker and less expensive built using plywood. Stitch and glue construction. Boat is built using 4mm plywood for the hulls and 10mm for the centreboard and rudder blade.

The building frame was built using plywood. The building frame longitudinals and bulkheads have slots and fit together egg crate fashion.
The cut panels are attached to the building frame (drywall screws for foam and staples for plywood). If you mark the position of the bulkheads on the inside it will help position the permanent bulkheads.

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All the panels were added. It is important to ensure the chines are fair at this time. The chines were filled and sanded and then taped. If you use strips of peel ply the weave will be filled with resin making it easier to finish with minimum sanding.

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The hull was turned and the chines taped. A quick neat technique is to use a wet fillet. The bog is applied in a rough fillet and the glass tape is applied over the wet fillet. Using a compactor, squeeze out air bubbles and shape the fillet wiping off any excess filler. The all the bulkheads were taped to the hull using wet fillets. The outside was filled and faired.

mainhull Scarab 350

A plywood stringer to strengthen the deck was added between bulkhead no.2 and no.4. A carlin was added between bulkhead no.8 and no.4.Supports were added to support the side deck.

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If a prodder is desired then it is built at this time. Glass is laminated over a metal tube covered with cardboard or something similar. A stem web and a forestay web are attached. The assembly is mounted in the nose of the hull and taped in.

Scarab 350

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Scrap foam or plywood is glued to the inside of the hull to support the deck. Deck is glassed, trimmed and glued to the supports using soft metal. The aft deck and the side decks are attached. An edge is built using foam between the fore and aft decks.

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A mast support tube is made from glass laminated over a metal tube covered with cardboard or similar. A plywood mast support was added and a hole cut in the hull bottom for the centreboard. The dagger-board case was made of laminated foam and taped to the floor. A dagger board support was added around the mast support tube and the dagger case. The inside of the hull was filled ready to paint.

Floats

The building technique for the floats is the same as the main hull. The same longitudinals are used. The temporary bulkheads are in the same position as the permanent bulkheads so it is a good ideas the mark the inside of the panels at the as they are added. This aids in adding the permanent ones in the right position and saves levelling the bulkheads. The panels added to the frame and joined with drywall screws (foam) or staples (plywood). The chines are taped and hull turned over.

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All the inside chines are taped using wet fillets. The float is levelled or you can use the markings that you added when attaching the panels. The bulkheads are added and taped in.

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The sloping transom is added and taped to the hull. Doublers were added around the edge of the float to hold the deck.
The deck is added. Plywood will bend in a fair curve but laminated foam is too stiff to bend. A solution is to score the laminated foam partly through, glue the deck down and add bog in the scores. Trim and sand the joints. Then the deck can be glassed over the edges.

mainhull Scarab 350