V Twin

Originally posted by r2d2 I like the way the V twin brand is being rolled out :-) Other than 16(?) and 90 foot, What other lengths do they come in?

Originally posted by JimC Originally posted by G.R.F. no, it's got to be 50kgs, That's a reasonably challenging weight for a wood build with a boat of those dimensions. The lads will be doing well if they all achieve it without cutting inadvisable corners..

Graham,
plywood is a composite enginearing material, and used propperly can produce something alot lighter than a glass boat.  all in the aplication and being carefull with your epoxy fillets, and ensuring that you keep it dry and well aired

I think we need minimum weights in class rules. Just look at the current crop of Volvo 70s as an example, they built the hulls very light so they could maximise the weight in the keel bulb. The hulls are so light that only 1 of them made it through the southern ocean without having to stop for repairs. I wouldnt be surprised if they changed the rules so that next time there was a minium hull weight to ensure that the hulls were made sturdy enough. I would sooner have a reliable/sturdy boat than one built to a minimum weight that was more likely to fall apart. The VO70s are built by the worlds best builders and they still have delamination issues so what hope have smaller builders got?

Graeme, the limiting factor in making a light dinghy is robustness. You could make a boat which, if reinforced in the right way, could handle the global loads, and be ridiculously light. It would be expensive both in materials, and in time taken to design and build it. If you tried to draw on it with an HB pencil, the pencil would puncture the skin. Don't even start on pulling it up a beach!
This need for robustness drives the minimum panel weight - i.e weight per unit area. In short, you will really struggle on any boat with 200gsm skins or lighter on say a 80kg/m3 core.
You can get away with it a little on smaller stuff - i.e. if I made a hollow windsurf board, I would use a layup that light or lighter (exept for around mast track / footsraps/ finbox etc) becasue the energy imparted into the structure when its weight of 5kg is taken on a single pebble, will be less than that of the energy imparted when a 45kg boat is point loaded on a single pebble.

So based on this minimum area weight necessitated by robustness, your limit is hull surface area. Andy P's quoted weights are really low because a) he is a skilled experienced builder using fairly high tech materials b) I dare say he has poured a fair few hours into each in a way you couldn't if you were production building under subcontract, and has used spraypaint which is lighetr, but much more labour hungry than gel. But most importantly c) they are all very narrow boats - that is to say that given their length, they have a low surface or panel area.
This is also why the Vtwin is not as light as you'd hoped, despite pretty light modern constrcuction - there is a lot of structural area.

I am pretty sure that, if designed accordingly, and well, you can build structures in sheet ply which are competitive in weight and stiffness with pretty exotic composite.  You can build in an analagous way, perhaps with less capacity for compound curvature, in sheet composite. See the gougeon brothers book on wooden boat construction, if nothing else for the 70s/80s b&w pics with guys with amazing moustaches and lumberjack shirts. Pioneering stuff on light construction in wood and epoxy (without mechanical fasteners) by many methods inc stressed ply.
I think that for any V twin derivative it may be tricky to apply - these techniques lend themselves to narrow craft without too much compound curvature - i.e moths canoes and cats. With big flat panels you have to rely more on internal structure to stiffen

Re the 3.7 and most similar classes with weight limits, a sensible / achieveable / conservative minimum weight is there such that sufficient panel weight exists that the boats are robust enough, and that the materials and techniques necessary are within the scope of an amateur enthusiast in his garage. You can take twice as long to build to drive a couple of kilos out with exquisite detailing, but again that isn't hugely desireable to most.