tiki 21

[redreuben]

why build a male mould?

[ricardoribeiro]

Originally Posted by redreuben

The tiki is a simple shape, build your mould in female frames with laminex (Formica?) coated sheets like mdf, ply or chipboard, any radii can be made with plasticine and a suitable tool drill bit etc. wax, gel coat and lay up!
cheers.
Reuben

a good idea, but that layup?

[redreuben]

What is wrong with the layup given to you on Multihull forums by Steve Turner? Sounds on the money to me. If not consult the designer or get a layup from your materials supplier. At some point you are going to have to make a decision and start building. My only advice at this point would be use a top quality gelcoat and use a vinyl ester tie coat behind or all ve layup.
Cheers,
Reuben

[Angélique]

Originally Posted by redreuben

What is wrong with the layup given to you on Multihull forums by Steve Turner?

Link please?

Regards,
Angel

[ricardoribeiro]

http://www.multihullforum.com/
The best forum off multihull!!!!!!!!!!!!!!

[Angélique]

Thanks!

But what I meant was a link to the mentioned post with the layup given to you by Steve Turner.

Regards,
Angel

[jamez]

You will need to log in/register to read it.
\The thread is http://www.multihullforum.com/forum/...?TOPIC_ID=3988

[redreuben]

in full Steve Turner said,

"Hulls:
Gelcoat, 200 gram powder bound CSM skin(tie coat),300/150 gram biaxial combination mat,Lantor Coremat XM 4mm, 300/150 gram biaxial combination mat. Extra layers along keel, stem, stern etc.
Decks:
Same layup but substitute 10mm PVC foam for coremat eg Airex C70.
Beams:
Make standard wooden beams, or use aluminum alloy tubes, 4" (100mm) OD x 10 gauge wall (3.3mm)
Are you planning to build a female mould, or make flat panels?
If flat panels, you will need to join them before laminating the inner skin.
Are you an experienced laminator? If not, hire one and labour for them!

Steve"

[sngatlanta]

Here’s a reply from Richard Woods on the method I received via email,

Sorry for the delay in replying to your question but sailing and Christmas got in the way

Some general comments

In principle any flat panel hulled boat can be built using solid grp panels. Having said that I have found that you cannot "torture", ie compound curve, a grp panel like you can a plywood one.

Solid grp is always heavier than plywood (it sinks, specific gravity 1.2 at best). So plywood is the lightest for small boats. 1/4in ply weighs about 20lbs a sheet, or 2/3 lb/sqft. You have to be a good laminator and use a lightweight foam panel to get anywhere near that weight using grp.

My Strike 18 trimaran outriggers are Morelli and Melvin designed 18sqm cat hulls. They are solid glass with paper rope stringers. Even when it was designed (mid 1980's?) I would have designed foam cored hulls especially on what is obviously a pure racing boat.

A rule of thumb is that you save about 1/3rd the weight using a foam core. So, to keep the numbers easy, say a solid laminate was 3oz/sqft (say a typical 8ft dinghy/yacht tender. Then you could use 1oz on each side of a core for the same strength. You'd be lighter and also stiffer. However the 1oz skin would be very prone to impact damage (so OK on a racing dinghy that is looked after and gently handled ashore, but not for a hard-used yacht tender)

So a thicker skin is often needed for non structural reasons.

Boats are usually strong enough, but not usually stiff. So you need either bulkheads/stringers or a cored hull. Or a very thick grp hull, as in the early grp boats from the 1960-70s

I have built solid grp paneled boats, but I found that adding the stringers, necessary for the stiffness, was time consuming and also heavy. So I decided that a foam core was preferable, especially when it resulted in a cleaner interior.

The only time I suggest using solid laminate is when the panel size is narrow. Typically the Gypsy hull bottom, for example, or the Romany lower chines. These panels become extra stiff when the chine joints are made and it is easier making a joint if the panels are solid rather than cored. And of course abrasion is more of a potential problem on the hull bottom than topsides.

A compromise to solid grp on a smaller boat, like the 21fter you asked about, is to use Coremat or similar. However that uses a lot of resin and, surprisingly, I haven't found the skin bonding as reliable as when using foam.

If you built a typical 21ft cat hull in solid glass the laminate would be about 6oz/sqft. If you use a foam core (say 1/4in) then you'd use 2oz each side. So you would save about 5oz/sqft or roughly 30lb per hull. But you'd need to add stringers, say 10lbs. So maybe you'd save 20lbs per hull. Up to you to decide whether that is a worthwhile saving. Then add in the extra condensation, the reduced space because of stringers and extra frames, etc

Hope that helps

Best wishes

Richard Woods of Woods Designs Sailing Catamarans

I think this backs up what most of the others on the forums have been saying all along. It can be done but not a good idea.