|Article 6 - Fitting out the Hull Shell|
|Related Topics: | Virtual Javelin Index | Home ||
In last months article we described the process of building a hull shell using vacuum bagging techniques. In this article we describe the fitting of internal frames, bulkheads, decks and floor. Three boats have now been taken off the mould. The first boat is in Wellington, and the second boat is in Palmerston North.
Building the Hull Cradle - When the hull is removed from the mould care must be taken to ensure the shape remains correct until internal strengthening is added. To achieve this a cradle was constructed in fibreglass over the hull shell whilst it was still on the mould.
Removing of peel ply / Preparation of shell - After the hull is off the mould and in the cradle it is prepared for fitting internal framing. This involved removing the peel ply added during the lay-up of the internal skin. The peel ply leaves a roughened surface (rather than a mirror surface) that allows good adhesion of the frames without sanding, and potential damaging the inside skin.
Frame Templates - A benefit of a computer designed hull was
that we could produce templates for the internal framing. This
saved a lot of time during the fitting process. Templates were
printed onto paper, and then transferred onto 3mm hardboard.
Templates were made for the transom, main bulkheads and underfloor
Fitting Transom and Frames - The transom was fitted first to help keep the hull in shape. A chipboard template, matching the correct outside shape of the hull at the transom, was temporarily attached at the transom. By screwing this template to the shell the hull was pulled back into final shape. At this stage particular care was needed to ensure the transom was fitted in the correct place to ensure the boat did not end up too long. The transom was glued in using an epoxy resin / filler powder mix with a layer of 400gm double bias e-glass tape for additional strength.
Once the transom was in place, a string centreline was placed through the hull to help align the frames. The underfloor frames were glued in using a similar method to the transom except 15mm radius fillets were used instead of e-glass tape as the additional strength that the e-glass provides is not required.
Main Bulkheads and Mast Step - The main bulkheads are angled from the mast base to the chainplates and act as a space-frame to take the rig loads. Because of the high loads an additional layer of 400g tape was placed under the bulkhead, fore and aft beam and mast step to stop point loading the hull. The bulkheads were also taped on both sides to maximise strength. In the area where the chainplates are bolted to the bulkhead the foam is replaced with plywood for additional strength.
The mast step is another structure, and is designed to transfer loads from the mast into the main bulkhead and the fore and aft frame. It was constructed from several layers of laminated 10mm foam sandwiched between 4mm plywood.
Attaching the Centrecase - The centrecase was the next to be added, a little bit of double checking, and a little less beer was consumed to ensure the boat would sail in a straight line. The centrecase was constructed over a male mould, and was made of a strong laminate that included 2 layers of 400g kevlar. The centrecase was again e-glass taped in for additional strength.
Attaching the False Floor - The false-floor was constructed with curvature that enables the water to run out the back whilst sailing on a slight heel. The floor section aft of the main bulkheads was made from 8mm foam and the floor in front of the bulkheads was made from lighter 5mm foam. Only the inside glass layer was put on the floor before fitting to leave the floor floppy allowing it to be bent into shape easier. The false floor sits on top of the sub-floor frames and a strip of foam around the inside edge of the sides.
After the floors were cut to shape, and before they are glued in the layout of the running riggings needs to be thought out. Foam is not a strong enough material to screw or bolt into, the locations of the fittings on the floor needed to be determined so that the floor can be strengthened. A router was used to remove the foam where fittings are to be attached, plywood blocks were then glued into the floor to replace the weaker foam.
The floors were then glued to the frames. This is a simple process involving lots of glue on top of the frames, and a lot of weight in the form of anchor chain (courtesy of Macduff Industries) and bags of cement to hold the floor down while it set. After the floor was glued in a couple of layers of glass cloth were laminated on top of the foam and ply blocks.
Side Decks - The side decks were constructed over a female mould. An aggressive curvature, around 30mm radius, was used on the inside edge of the side deck to form a strong self supporting finished shape. To bend the foam this tightly during the moulding process it has to be slit down its back edge and bent when softened with a heat gun. Small sub frames are attached under the deck to help support the deck in the span from transom to main bulkhead.
AROUND THE YARDS
Things are very busy for the class at
the moment, with 9 or 10 major building projects underway at
A new plywood hull has started construction in Auckland, to the builders own design. A lot of hard work may see this boat racing by Christmas.
Two boats are underway in Australia, with a new mould being planned for the Western Australian fleet.
The class website, and building progress has stirred up some more international interest. Plans have been sent to Atlanta, Georgia where two boats are being constructed, to the McNeill design, for the upcoming Florida boat show. Interest has also been shown from the Caribbean, and from the Netherlands.
For more information, stay tuned to the website, www.javelins.org