Step by Step #8

Now would be a good time to paint the sub-assemblies, and doing it this way saves a dust-sheet on the floor beside grovelling around at that level. And you can have them any colour you like so long as their black.

Step by Step #7

The centre-deck is assembled using the self-same techniques, and in this case foam sheet is applied to the underside. The format of the foam panel is identical to that in the pontoons and between them they displace sixty pounds (27 kilos). This is easily calculated in metric viz. 42 x 87 x 2.54 cm or 9,281 cubic centimetres apiece. No, it's not going to be the world's largest cruise-liner but yes, it's expected to float.

N.B. in the scheme of things each of those spars is supposed to be identical in length at three feet. One reason for a re-build at a slightly reduced size ~ aside from material constraints ~ is that it can then be toted on the roof of the car instead of trailered. On the vehicle in question the distance between the roof-rails is three feet, so the overall width of the craft has to be just that. In view of the fact that the hydroskis overhang the pontoons by an inch and a half, the net effect of this is that the cross-spars have been reduced by around five inches. 

Step by Step #6

With the foam in place and leaving just one side of the pontoon laminated in view of its oversized thickness, run a filet of silicone around the edges. I've used black here because that is the colour of the spray-paint we'll be using. You could of course use a glue to fix these components, and I use silicone only because (a) it's cheaper and (b) it allows fast-builds to be pulled apart and modified as part of a fast-prototyping effort. 

Now to build the second pontoon, simply rinse and repeat...

Step by Step #5

Before popping the foam into the void in the frame, run a seam of silicone around the margin to secure.

Step by Step 4

Here's my re-used PIR insulation being cut to fit the void in the picture-frame. It is 25mm thick, so the pontoon floats can only be skinned to one side. 20mm sheets are available, in which case we could apply laminate to both sides of each pontoon.

Step by Step #3

Fix the laminate to one side of the frame to form a shear-web. To avoid measuring the screw-holes, simply park them in the middle and repeat the process.I've secured with a dozen screws that were hanging around the workshop like a bad smell.

Step by Step #2

Draw around your sheet laminate, which here is leftover three-ply 1mm hardwood that has proven remarkably durable. A tragedy of chopping down every tree in sight is that we'll lose varieties of timber with extraordinary qualities, along with the experience of using them. But don't worry, in the event of apocalypse we'll still have smartphones to hit each other with, and EVs to live in.