Building in a female mold

[Adam_melb]

Hey everyone,
you'll probably be seeing a bit of me around here from now on.
my mate has the molds for an "oarski",which is a open-water capable single person rowing skull, and has asked me to build him one. I dont have vac bagging facilities so it will have to be a wet lay-up. At the moment i am thinking of a glass either side of coremat (Felt like core material for fibreglass laminates. Provides stiffness and lighter weight in fibreglass fabrication work. Ideal for automotive panels, boats, canoes and industrial panels.3mm thick. 1m wide) I am unsure of whether i should gelcoat inside the mould or paint with 2-pac after removing the hull from the mould. if i choose to gel coat do i lay the fabric before it has cured, and would it be advisable to to do a layer of tissue?

The other issue i am unsure of is what weight and type (i.e. twill, satin, plain) of cloth to use. Please note that this is not a really high performance craft, and i will be happy to make small sacrifices in weight in the name of durability and ease of construction.
I plan on using polyester resin

Any advice is greatly appreciated and i am open to any suggestions.
Cheers adam

[johnpt]

I have an 8 ft pram / sail equiped , and I plan to cover the exterior in plastic film ( saran wrap ) then cover it in glass/ resin to make a fiberglass copy , it is a wooden boat my father built and it needs attention... so a copy is an alternative to repairs.. has anyone else made a boat this way / or similar to ? how many layers ? weight of cloth ? and I plan to gel coat the exterior , but paint the interior ... ideas ?

Hi Adam,

Your layup will really be dictated by how big the boat is, and what you want to do with it.
ie
does open water mean Port Phillip Bay lazy sunny summers day for an hour or two, or record attempt mid winter Bass strait crossing?

Either way it is a real gain that you already have the mold (assuming it is in good condition)
It is well worth the effort to set up for vacuum layup, especially as you have a mold and if you think there might be other things you could build (the main thing you need is a reliable vacuum pump.)
Coremat does spread the laminate skins, but it does so by absorbing resin which makes it heavy. Vacuming makes it easier to use a light core and achieve better strength/weight allround. Which is nice as you have to power the thing with your own steam.

On the other hand, for a you can use a single skin (no core at all), as are most production kayaks, dinghy's, runabouts etc.

Assuming the mold is in good condition (with a nice gloss) the only reason you might use 2-pak would be to give the boat some cool and funky paint job, or possibly save a (very) small amount of weight. If you use gelcoat the finish of the mold will equal the finish on the part, which relates to how well the release agent is applied and how fine the mold finish is. Gelcoat is also much easier to repair/refinish than 2-pak's. I think I'm saying go the gelcoat...

Using Gelcoat:
put it on
about 2 hours after it gel's put a first skin on (something like 300gm csm) in colder weather put more on.
when that has cured put the rest of the lam. on

a possible laminate schedule for a dinghy might be:
gelcoat
300gmcsm
300gmcsm
600gm Bi-axial
300gmcsm

Of course that particular schedule is pretty much meaningless as it is not related to your circumstances. ie boat size, number and location of ribs, bulkheads, stringers etc. Does the boat have a deck etc? Is it a hard chined boat or not,
It would make it easier for you if you could copy a boat already built from that mold, a similiar one, or talk to the original builder.

Anyway, good luck with it.

Rob

[Adam_melb]

Rob,
Thanks heaps for your detailed and informative reply. Sorry about the delay in getting back to you.
At the moment the project has been put on hold for a few months. When the time comes i will definately be looking at getting my hands on a vac pump as there are a number of other building aspirations i have that will require a pump.
Cheers adam