Rossco, Did Ross Trinder use 4mm or 6mm ply on his longer Water Rat? With my 9' Water Rat I used 4mm with a full length centre stiffener of 1/4" x 4" western red cedar ( from an old verical blind) plus some smaller ply pieces and a pair of heel pegs, between the centre stiffener & the chine.You can see these in the photos I put up in Duckworks Magazine forum under "Water Rat".The bottom seems quite stiff enough with these, plus of course,the fore & aft facing seat mounting cleats. My Water Rat weighs only 17kg,which is very light,so using 6mm will probably increase it to about 25kg which is still very portable. Would "rowerwet" be better advised to use 6mm if he intends surfing his boat? Al Burke
Ross Trinder used 6mm ply on his long version of Water Rat and she turned out to be about 28kg (62lbs) which is quite heavy. However, he said that he used locally-sourced "Pink" BS1088 ply. In Australia "pink" ply normally means Pacific Maple (Meranti) or a Malaysian hardwood like Keruing all of which are quite heavy. If built from 6mm Gaboon (Ochume) the plywood weight of all of the panels in a 10.8 ft Water Rat should weigh 10.5 kg (23 lbs). I'll leave it up to your judgement to work out how much the timber, glass, and epoxy would weigh.
As Al Burke points out, the boat can be made from 4mm material, but stiffeners will be required in strategic locations. The stiffness of a panel increases (and decreases by the cube of the thickness, so 6mm ply which is supported around all edges is 3.375 times the stiffness of the same panel in 6mm!
Here is another one from my mate, Al: -
Monday, December 12, 2011
Answers to a few comments
I apologise for not having replied to the last few comments, but I've been snowed under with other duties and this is my first opportunity: -