how much fiberglass??

hi, i' m building a 15ft hydroplane and am about to order fiberglass. what thickness/weight shud i get and how many layers?
also as for tissue, how many layers and what weight?


is it worth double skinning? and how much strength would it add?

thanks, Robert

 

What does your plan recommend?

 

i dont have plans, taking from a wooden mould

 

If you are talking about Epoxy / Glass on plywood, I would say, 2 layers of 160 gram m² biax should do the Trick on a 15ft. Apply a thin EP coat (no thinner) first, otherwise the wood sucks the resin out of your layup. Work wet on "sticky", not cured resin, if possible, to get a perfect chemical bond between layers.

Sasha

 

thanks, but i'm actually using the wooden boat as a mould and makinjg another boat from it from fiberglass. the boat i'm taking the mould from was made from plans last year (glass over ply) but the wood inside was left untreated and has began to rot badly, so i'm starting over making just from fiberglass. is white pigmented epoxy resin ok? i used polyester b4 and it was rubbish...just cracked

 

You can leave the EP unpigmented for better technical properties. You have to paint it anyway to make it UV protected.
But if you use Polyesther (much cheaper) I am not the one to comment, I do´nt know much about poly.
And Sasha,
that was too much on a hydroplane! Two coatings and one layer 160gsm underwater was the way to go on a wooden boat. One layer 100gsm on the upper part......
Regards
Richard

 

You'll be hard pressed to make a strong enough and stiff enough single skin GRP hull that doesn't weigh a lot more then the wooden version of the same boat, especially if you use polyester. Even with epoxy and S fabrics, you'll be pushing the envelope to keep it light enough, yet stiff enough to tolerate the slamming loads up on plane. This of course assumes you'll not be employing the exotic fabrics.

When working with something as highly loaded as your little hydro, the laminate schedule has to be carefully worked out.

It would be helpful to know which hydro you're looking to "splash".

 

hi, cant find the old plans i used for the boat, i got them from absolutelyfreeplans.com . do you think i should just try another glass over ply then? i'd rather more of a cruiser anyway...maybee 16foot ish, or a catamaran. if anyone has any plans i'd be very grateful!

thanks

 

Maybe start a new thread setting out what you would really like for your boat in terms of size, power load carrying ability, etc.

Good plans with material specifications are worth paying a bit of money for.

My view for easy home build is to use flatpack construction with glass on corecell. You can make your own panels providing you have a flat area and a vacuum pump. You end up with a light, strong boat that takes shape very quickly. It makes better use of the expensive materials so cost is likely to be less than a solid fibreglass hull. The weight saving reduces costs throughout its life.

The linked thread has some good detail on flat panel method although the panels were factory made and pre-cut:
http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-11.html
In this case the core is end grain balsa but corecell would suit your purposes.

Rick W

 

Easy to make your own flat sheets using a nice big sheet of window glass, cheap to obtain from any glazier as they regularly have large sheets that they throw away.

 

ah, so instead of ply i construct it similarly but with fiberglass panels? sounds promising, and i suppose the wooden frame would be the same? i'll just cover it in fiberglass afterwards to protect it and prolong its life.

it probs sounds a bit mad, but as this is my 3rd boat, i'd like to try and design my own from scratch...i have a scottish NQ in product design so can fulfil specificqatios easily enuf which i can write down, have good graphics skills and can use autocad/autodesk fluently. any tips/do's and dont's? thanks

 

Do,s ............use the same wooden frame !
Do´nts ... cover it with glass. EP is just enough to make it water resistant, no need for the weight of glass.

Regards
Richard