V Twin

Anyway G.R.F you know you should have build this like I said.



40kg ALL UP. Rig, Sails, Foils everything. PBO rigging etc... problem is it was so dam light and fast anything over F3-4 and the guy couldn't keep control of it! Nothing to do with the crew weight, just how lively it was off waves etc... the sailing equivalent to windsurfing.

G.R.F...

I can't remember having a conversation with you about the 3.7 with regard to it's hull weight. Certainly not one where there was any passionate discussion ending with anyone being close minded.

The 50kg hull weight is there because it is an achievable weight that an amateur boat builder can realistically build to in wood. One of the great things about the class - plus 50kg is light especially when it only costs around £500 for the materials! But the class allows wooden boats to be built as light as 45kg. Dam light and achievable if your skills are up to it (Max 5kg correctors). The rules also allow composite hulls (which carry spinnaker equipment) to be built down to 35kg (Max 15kg correctors). So as not to handicap those wanting to sail for fun with the kite when (edit: (not) racing.

so... I'm sure if you wanted to build a composite boat that light and sail without correctors at your club. No one would mind. Just tell your race committee and put your correctors in if you come racing with us.

As for fleet numbers.

There are 4 boats being built (possibly another if G.R.F's mate builds over the winter), plus mine, so 5. With several interested people waiting for Dave Butler to finalize his costings and his demo boat.

So G.R.F why not join us and when the class is formally launched and it's appropriate, get enough signatures and votes for your ideas and you could change that close minded situation.





Edited by Jack Sparrow - 21 May 12 at 6:51pm

Where is there a restricted class fleet that renews all its boats annually?
Probably the most competitive restricted class, the Merlin Rocket, had its nationals won by a boat several years old, despite that boat being beaten in most of the races by an even older boat. The Merlins could easily reduce their weight, it's been debated, as most of the boats less than 15 years old carry a fair amount of lead. But it is not in the interests of the class to do this, it would undermine the grass roots and open circuit where you get many older boats turn out for competitive racing.
Rather than warming over 90's designs with  a few kilos less, I would like to see a few new designs built lighter. Have there really been no advances in hull design since the RS400?
Yes a boat buit lighter might be more fragile, but it might also be nicer to sail, and faster for the same power.

The problem is not many people can afford a new boat on a speculative basis, it's much more sensible to buy a boat with a class rule behind it. That way it might cost the same, but the depreciation is reasonable.

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.

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?