Vacuum infusion Male vs Female

Sure, I understand, but a hull with say a 22mm core has a safety factor already in place; so a 1mm sanded section is less than 5% deficient...like I said; fairly mute point if class rules apply

What type of core is used on the outside for infusion? Is it channeled or is a mesh used?

 

If this is correct, I'd be glad to use this method with male mould.

 

One 50ft racer I helped build.

Plug of stations and battons.
Heat shrink
Infused inner skin.
Foam core
Fairing the core
Infused outer skin
Some additional fairing and paint.
Rolled into a cradle for interior work.
The deck was traditionally moulded to incorporate non-skid surfacing

 

It will be very expensive if you do, you need to buy thicker foam. The resulting surface will still not be perfect, fairing and painting still required. Foam fairing is done as light as possible to smooth the gluelines.
Your best bet for getting a good surface on a direct female mold (direct as in not making a plug first) is to sand a lot using a two man sanding board. Strip plank the mold with wood without glue between the strips, just screws and nails, countersunk very deep. Fair the wood as good as you can, then put a good layer of CSM with polyester over it for stabilization and making the mold airtight. Now you can use polyester based fairing putties to make the surface as fair and smooth as you can. Sand to 400 grit, wax and layup your hull. If you use a thick layer of gelcoat, you can then polish it up to remove imperfections.
It's a lot of work, and the result will only save you some kg's of fairing compound on the hull.

 

Thank you
In your opinion, what takes the biggest part of the cost of building a mould with method you wrote?

 

well, you certainly can't fair foam with a longboard in a female jig....but the idea is to build the female jig and infuse the inside; then bulkheads go in, then pop out and fair a wee bit of foam to reduce the outer fairing work, infuse outer skin, fair and done

but, honestly, the discussion is a little beyond my expertise...I would be a bit nervous about building a plug and then a female mould to pop out one boat...also, gelcoat is not light!

for one off construction, I really think the way to go is female jig mould..lots of ways to minimize fairing...

my guess is you might end up with well under 100 pounds of fairing and paint...keep in mind, I was focused on the thing looking perfect, not necessarily ultralight

 

How much would gelcoat weigh for that hull?

 

For me probably sandpaper and filler, but it is location and worker dependent. Compared to a "normal" male mold with stringers you would use at least 50% more wood, but wood is cheap (spruce, pine, fir, etc.). That is why I am a big on getting the wood as fair as possible, price. Screws and nails can also be the cheapest on the market. Then you have to glass the mold with the cheapest fiberglass and polyester resin you can find, to get it airtight and minimize wood movement. If you have big humidity changes during the build it would be wise to glass both sides of the mold. It eats a lot of resin, especially with CSM. Then it's fill and sand, and here it pays to use good filler and sandpaper, your surface finish depends on it. How much you use depends on how good a job you can do.
One way to minimize the cost for the mold would be to not throw it away after use. Sell it cheap, even if you get 50% of money back, it is still better then nothing.
One word of caution, this way you build the hull twice, it takes more time. Infusing the foam on an open mold is faster, and probably cheaper in the end.

Here is a blog with some photos of a similarly constructed mold, but male.
Boatsmith Shavings: Wharram Fiberglass Ariki Catamaran http://boatsmith.blogspot.com/2011/09/wharram-fiberglass-ariki-catamaran.html
Boatsmith Shavings: Waxing Ariki Catamaran Mold http://boatsmith.blogspot.com/2011/11/waxing-ariki-catamaran-mold.html

 

Depends on what is under the gelcoat, hand layed CSM or a sprayable filler, since without them you have print trough. Can be anything from 1-3kg/sqm depending on how the actual layup is. Polyester done on a male mold and faired with vinylester or epoxy fillers can be lighter but it depends on the craftsmanship.
Epoxy in a mold then final fairing and painting is usually lightest.

 

Pironiero, what resin system are you planing to use for the boat? Poly/vinylester or epoxy?

 

probably epoxy, because its safer and has virtually no expiration date.

 

With epoxy I see no reason for you to use a labour intensive female mold, the hull will have to be filled and painted anyway. If you want to minimize fairing you can use a female mold lined with something that has a good surface already (some thermoformable plastic like pvc). A "perfect" female mold is only usefull when using gelcoat as a finish, where you don't touch the hull after infusion.

 

Why not use linen? im pretty sure that it can be used as mould mat, some even use it for boatbuilding, like Baltic yachts and flax 27

 

Fiberglass is normally cheaper then any natural fiber fabric.

 

I may be wrong but a brief search shows that linen is cheaper here.