Glass layup schedule?

Evening all,

Been doing a bit of reading around on this forum regarding glass cloth weights & numbers of layers. Of particular interest was KIWI & Goose’s AC120 build thread where Claudio recommended 4 layers of 80gsm cloth. Obviously the point of the AC120’s is relatively light weight racing machines with what appears to be watching every gram - or rather avoiding them where possible.

At the moment I’m planning to produce a fibre glass hulled J class ‘Enterprise’ using Claudio’s amazing drawings etc from the scale sailing thread (like many others, I’m completely in awe of his design abilities & workmanship). I’m sticking with his 1/28th scale so that the finished hull will be manageable in terms of transport & weight and was wondering what sort of layup weights and numbers of layers I should be looking at.

In terms of materials available (what I’ve got ‘in stock’) is 165 gsm glass twill & 280 gsm glass twill. I’ve also got 175 gsm 50mm wide glass tape & a reasonable quantity of peel ply. I’ve never molded a model yacht hull before - infact the last glass work I did involved using 600 gsm CSM, lots of layers, even more epoxy and eventually ended up with new engine bearers on a ‘full sized’ yacht, so producing model yacht hulls is a bit like brain surgery instead of orthopaedics!! (No offence meant to any ortho surgeons out there)

Looking forward to getting any advice / info.



PS: At the moment I’ve got as far as a sort of completed male plug - unfortunately got a bit carried away with the initial sanding & now it’s in primer I can see rather too many flat spots - seriously kicking myself for that. I know with ‘big boat’ fairing they use long flexible ‘longboards’ to sand the hull - do you guys use anything similar or are you just more careful ? !!

PPS: Once I’ve worked out how to, I’ll try and post pics of the construction process

Are you looking for info to layup the mold or to do the hull layup in a finished mold? There is a lot of information in the “composites” forum over in on mold making.

In general, two layers of 4 oz glass is lighter than a single layer of 8 oz glass. Many areas of a boat hull gain strength from the shape (compound curves), and can do with thinner layups. Also, many areas do not need to do anything but hold the water out!

Yes, I use a long board to sand my plugs. Of course long is a relative term when you are talking models. a 1" wide strip of foam board that is 12" long works for me. Glue sandpaper to it and go over the plug lightly and you can feel the high spots and low spots. The more time you spend on getting the plug perfect will pay off for you in less work on each hull you pull from it.

If you are only going to use it for one or two boats, you may be better off using the “German Rubber” method and laying up hulls directly on your male plug.

Many thanks for that - I’ve had a look at the link and as you say, plenty of info on mold making etc.

The info I’m mainly after is for the actual hull layup. I understand your comments on compound curves etc - the basic hull shapes, by virtue of the inter-linked curves do make for extremely strong structures. The classic ‘wine glass’ shape of the more traditional hull form also appears to lend itself to ‘intrinsic’ strength for want of better terminology.

As I said in my first post, I’ve not actually laminated up an rc yacht hull before so any previous experience I’ve got re general laminating doesn’t really count - I suppose info regarding overall numbers of glass layers and weights (hopefully utilising weights I already have) is what I’m after. Life was so much simpler when I built my first rc yacht - it was a Marblehead design called ‘Skippy’ by Stan Witty and displaced an incredible 18.5 lb (approx 8500 grams), positively tank like by modern standards! All planked up in 3mm x 9mm mahogany, reducing to 3mm x 3mm for the turn of the bilge and with a sugar-scoop or open transom - very advanced in its day.

Also, your suggestion of the ‘German rubber’ method appeals although I guess there’s a certain amount of trial & error establishing the right sort of tension in the sheeting and also how far into the curing process (or straight away?) that it’s applied.

When I first started looking at Claudio’s drawings it all seemed so simple - make a plug, bit of sanding & fairing, wax it and then pop off a hull mold. Ignorance was blissful !! I’ve just realised that it was last November I decided to have a go at building ‘Enterprise’, where the hell does the time go?!!

Looking forward to any further info & experiences you and others may have.



I would use two layers of the 165 gsm (4.8 oz/yd2) and try to change the orientation of the second layer so that the fibers are at angles to the first layer. You may not be able to get them at 45*, but angle them some. The more directions the fibers of the two layers are going, the stronger the hull will be. Then add another layer or two where the fin box/mast box will attach, where the rudder post will go and and other “flattish” areas of the hull. Try to devise a structure for the finbox area that will transfer the tension of the shrouds down to the mastbase and incorporate into your design. Some builders will assemble all of that structure onto the underside of the deck molding after it is laid up, and drop it into the hull as the last step.Then all of the rig tension will be carried by this internal structure instead of the hull itself.

Cheers for that - it certainly gives me a good starting point to work from.

Fortunately I don’t need to get involved with the intricate / accurate moldings of a fin box with ‘Enterprise’ as it’s an integral part of the hull, with the ballast being cast to fit inside the hollow of the ‘fin’.

It’s amazing how time & technology improves our understanding of the materials we use. I can vaguely remember seeing a grp marblehead about 30 years ago and the hull must have been getting on for 1/8" or 3mm thick - the bare hull must of weighed at least as much as its wooden counterpart.

Time for some more filling & fairing - got to lose those flat spots! Once again, cheers for the info,