Making the mould

Crusader 2 model build


With the plug primed, flatted a few times and with 8 coats of wax applied, we can progress to creating the moulds. Ordinary A4 printer paper was placed end to end along the centre line of a copy of the plans and sellotaped to hold in place. The outline of the broadest section was then cut with scissors, stuck to a plywood sheet and cut with a steady hand on a band-saw before being transferred to another piece of ply and joined.

That frame is carefully lowered over the plug until it sits on the horizontal split line. The boundary is sealed with plasticine and a hot glue gun from the underside before any gaps in the top are filled with the release wax. When the mould has been taken, remove the wood and turn upside down, re wax the model and place upside down in the newly moulded upper section. Again seal any tiny gaps with wax to make a second boundary longitudinal down the central line of the boat. From this take another mould, remove the wood, re wax and take the third and final mould. It’s a little more complex than that with joint alignment hard wax buttons but that is the basic process.

Moulding wax was used to infill the plug to the frame. Locating buttons were formed first by rolling a small amount of wax into balls about the size of a large pea. Using a Stanley knife blade four flats tapering out on the bottom (pyramid shape) were cut. PVA releasing liquid was applied and left to dry overnight. Grey pigment was mixed with the gelcoat and painted on. Not very pretty but it’s the best way to get a good internal finish. Finally, chopped strand glass layered on to reinforce the mould along with a wooden external frame. Work also began on the sponson moulds.

The completed half mould came apart, thankfully with no nasty surprises – no sticking to the plug. The mould release PVA liquid (the blue liquid on the surface) really helps while the yellow moulding wax gives a clean sharp edge with no resin creeping down the sides.

Although the same needs to be done for the sponsons, the moulds to create the body panels for the hull are now finished and will be ready to use with a little bit of cleaning up. The final picture below shows the plug along with the two moulds created from it.

A few pictures of the sponson attachment and shoes under construction. Len made a wax casting frame and then produced a sponson planing shoe on his 3D printer. The shoe is fitted to an attachment point on the mould but then removed before casting. The reason for this is that although it seems that Railton favoured a V shaped bottom to the shoes, on the wooden model they are flat and it’s not clear yet what V section he had in mind. By making the shoes changeable, we can experiment to get the best results on the test runs. Replacement sets of shoes with different degrees of angle will be made (probably carbon fibre 3D printed) to slot into the base of the sponsons.

To see more about the previous stage of building the plug, click here.

The next stage is to assemble the bodysee more here.