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Duck Board

Weight ;   30 kg     Centre of Effort ;   750mm behind station 9

An interesting challenge.
The plan is for the duck board to fit between the hulls and be able to be lowered and raised using 2 cabin roof support tubes which are to be moved behind the aft beam. The support beams for the duck board will slide inside the outer tubes. Fully raised, the duck board will act as a deck extension behind the aft beam and a transport platform for the dinghy. Fully lowered, it will be used as a swim platform and for launching and retrieving the dinghy. As the electric motors will be inboard of the 2 hulls this platform will provide access to the props and rudders.

The platform had to be made to support the weight of people and the dinghy plus, not be too badly affected by wave action when lowered.

A design was drawn up on the computer to match the curve of the aft beam. 20 mm slots were drawn at 80 mm spacing. The 80 mm was made up of 20 mm slot, 20 mm bevel, 20 mm flat and 20 mm bevel. This design will relieve the effect of water pressure when lowered to water level.

For this panel we used 20 mm GS foam which was machined with the pattern as described above. The unslotted sections had 2 layers of foam to increase stiffness. The lay up was as follows. Sandable gelcoat. 3 layers of 450 gram chopped strand. Foam panel. 3 layers of 450 g chopped strand. We used chopped strand to help with the complex shaping of the underside of the panel.The uni glass would have been too stiff to follow all the slopes and flats of the panel.

Below are the shots of the panel before infusion showing the plumbing with the vacuum line closest to the camera.Note there is plenty of bag to cater for all the humps and hollows. The second shot shows the successful completion of the infusion with all the resin arriving at the vacuum line at the same time. Travel was very slow as we were relying on movement through the chopped strand.

After the panel was removed from the table and cleaned up it was placed on the CNC machine. The outside edge was trimmed. The two holes for the support tubes were cleaned up and the slots were machined allowing a 2 mm bonding joint between the inner and outer skins. Below are the photos of the underside and the topside of the completed panel.

Stiffening ribs have to be hand laid on the underside to support the tubes. 2 ribs radiate backwards from the holes starting at 160 mm down to 40 mm. A rib runs across the front edge to a depth of 160 mm to support the tubes laterally and take most of the flex out of the 40mm maximum thickness. The 90mm diameter high density fibreglass tubes have been machined to be a press fit into the 200 * 90mm tubes. When pressed home a dowel will be inserted through the tube to secure the support posts to the duck board. The dowel also acts as the anchor point for the lift mechanism. The Bridge deck roof support tubes are 100mm inside diameter. Correct bushing will ensure the duck board support tubes slide smoothly inside the outer tubes. The duck board has been painted Claret to blend with the hulls. To soften the visual effect of the red colour as a work platform, an "off white" non skid material has been machined to overlay the top surface with a 3mm red border left around the slots.
Below are the photos of the finished duck board, showing the stiffeners underneath and the top view with the tubes in place and the non skid stuck down. The edge buffering has not been sourced yet. It still remains a problem to be solved.