I translate this roughly into :

Average singlehanded crew weight Boys and girls 10 - 19 years of age = 50.5 kg's

As it is better to sail underweight then overweight the F12 should be optimised for 55 kg.

My 3.90 mtr design is now down to 65 kg when build light but stirdy (55 kg was/is planned) and has an optimal weight of 53 kg with a competitive range of 38 kg to 62 kg.

Of course it will carry ALOT more weight in a recreational sense.

I think the initial choice to develop a 3.90 parallel to the 3.66 is turning out to be a smart one.

Making the hulls out of unglassed 3 mm ply will make the platform around 58 kg ready to sail and make it have about 70 kg as max crew weight limit.

I seem to remember A-cats used to be made out of 3 mm unglassed ply so a shorter F12 should hold up if they did. Of course these would require more care when handling on the beach and trailer.

Currently I'm also below the laser-1 as cost price (that does include several bought items like rudders, sails, blocks etc).

I'm trying to get close to the optimist cost price. I won't be able to get down to the lowest cost price that is of the Topper dinghy as that is 2000 US$ and that is darn cheap but it is also as slow as a snail. So that is alright.

I've looked at little a rotomoulded materials and found some very interesting info from a knowledgeable source.

If these F12's are ever mass produced then I starting to prefer Twinex and corematt material over rotomolded. Stiffer and is more durable over hard use. With core matt I mean two layers of glass on either side of a layer of sprayed on resin with 50 % microballs. Should be the same weight as ply I think. Please correct me if I'm wrong here anybody !

As the middle layer is resin itself (no foam) the hulls should both be impact resistant and stiff. The latter because of the glass fibre cloth on both sides.

Spraying should really cut down on labour costs.

Wouter