Help choosing building method

I'm working on the drawings for a female mold, once done I will post the drawings here.

 

Female mold

I draw full size on plywood, half side only, cut the pattern, flip it over, and do the second half and join them together.

I nail the pattern to the floor, taking care baseline is straight. Alignment is very critical at this point. Take the time to check and countercheck.

Do a full form. Not left and right. you will be inviting trouble. Brace a lot. Fiberglass when fully laid up is heavy. Full transom. It is what holds it together.

Lay up the second layer when the first layer is cured but not tacky. say two hours after first lay up. That means, if it took you 1 hour to layup the 1st layer, wait 1 hour and start where you first laid up. Do not hurry on the second layer. The resin heats when curing. It could twist your whole form when you try to laminate all at once. Do not laminate below 21degree C.

Overnight curing is ok but you have to abrade the surface to get the next layer to grip. Helps remove the slivers too. A # 80 grit will do.

More than 24 hours, the laminate is fully cured. This will be a secondary bond.

Attach some pictures. you will get an idea of scaffolding.

 

Core?

Core is a choice.

You can do single skin with closer frames and stiffener and thick plating or skin, (more frames and stiffener, more labor extensive, cheapest)

or you can go sandwich (cored) laminate with thinner skin on both sides of the core and more distant frame spacings.( less frames, less labor, but core more expensive)

Rx

 

Rx where are the pics coming from? is it a textbook?
I'm planning on having all the woodwork done by machine cut all the mold will be a big interlocking structure with 5 longitudinal sections on wich transversal sctions will be locked...very easy and very low error margin...a lot of wood though.
Planing on using 19 mm MDF for the sections and plywood for mold surface,I will have to figure how to finish the surface then...is it enough to putty fill it and spray it with something ? (poliur. paint? )
How separation should I use between stations in straight parts (toward transome for example)
At the bow I'm using up to 15 inches spacing.
Thanks for your precious help.

 

Safety

JFBlouin,

I will be busy next month so i will jumpstart on the lamination safety. You will rarely find this notes on any boatbuilding magazines.

If for whatever reason the resin supplier sells you un accelerated resin and gives you cobalt to mix later in your resin, never, never store this or let it come into contact with your MEKP. several Milliliter of cobalt and MEKP when it mixes has the explosive power of a stick of dynamite.

When laying up, The volatile styrene and acetone, being heavier than air, tends to collect in the bottom of the mold. Use a blower to suck it out. We had a naked bulb that accidentally broke before and there was an spontaneous combustion. We nearly burned the boat.

Be careful of catalyzed and unused resin left in the can. It could ignite spontaneously. Many factories have burned that way. During cold weather, laminators "bump up" the curing time by adding more mekp. Resin heats up during cure and could generate between 150 to 220 degree C of heat. Add to that the volatiles collected in the can and you could burn your boat, not to mention your house. Our next door factory fabricating fiberglass burned to the ground during a coffee break. they rebuilt it but a month after, it burned again. So much for safety.

A laminate that is curing properly should be warm to the touch or bearably warm. If it starts to smoke, get your fire extinguisher quickly. you have an overcatalized resin.

Read all safety manuals provided by the material suppliers.

 

Mold

Fede,

I have tons of materials here. Txtbooks, magazines, literatures. anything i can get a hold on. I buy, beg, borrow, steal, copy,download.

Seems your choice of material is correct. No need to interlock. Get another piece of wood and lap join it together. nothing fancy because you are going to destroy it anyway after lay up.

Plywood is the best choice but you will have to spray it with dark gel coat mixed with micro balloons. Seal all nail holes with polyester putty. If you can find gypsum board with finished surface ok. pressed board with good surface also work. formica coated surface is best but expensive. just make sure it bends slightly to conform to the slight curvature. On the forward end where you have slightly concave surfaces, use strip planking laid up at 45 angle. You will have to finish it though.

 

About Core

I'm affraid to have a bad bond under the core and if I understand core dynamic, any void will be a weak spot..

 

Finishing

Polyurethane paint sometimes stick to gel coat. use a light coat of gel coat with wax solution. make sure it cures completely. say 3 to 4 days after coating. you may have to do some final sanding and polishing. Apply carnauba wax based release to the mold several times and spray Poly Vynil Alcohol (PVA) as an insurance. It is best to play safe than have your part stick to the mold.

Others may have different ways and may be better. If it works, listen to them.

 

Hi Fede,

Take a look at www.navaldesign.it FOTO GALLERY/GALLERY COMPLETA / 23 m vetroresina. You can contact me through the emails on the site