building a mould for canoe

[ocpaddler]

I am new to boat building and am shaping a plug to build a mould for an outrigger canoe. I have searched for information regarding this, but thought simply to ask in this forum. Two questions;
1. How many ounces of fiberglass cloth should I use to make the mould (i.e., is 1 layer 6 oz glass enough)?
2. I have read alot about creating a flange for the hull and deck of the canoe (it will be a two part mould, hull and deck). What is the easiest way to create this flange, and does anyone have a link to something relating to this?
Thanks in advance for any advice.

[marshmat]

Moulds need to be really, really rigid. Something like 10 layers of the cloth you mention, then a rigid trussed wood frame glassed onto that, would be typical.
The flange can be tricky; I've never done one for something like you describe so someone else may have more tips.

[John ilett]

There's plenty of advice or instruction out there but more so in books than on the internet I think.

More common for average moulds is CSM (chop strand mat) rather than cloth. This is far cheaper and will build up your thickness much faster. Also a good idea for fast thickness is to use coremat also.

Eg Gelcoat (brushed is easy)
2 layers of 225g CSM as a skin layer, let cure.
2 layers of 450g CSM , let cure
1 layer 3-4mm thick coremat + 1 450g CSM, let cure
2 layers 450g CSM

This would give a mould thickness of about 6-7mm.

The flange can have a little extra, just two more 450g CSM

Timber or steel frame for support. Simple way is bend some small steel tube around the flange and glass on.

Beware fibreglassing mould frames etc directly to the mould as resin shrinkage can make pull marks at the frames which will show up in the finished boat.

[JEM]

What are you making the molds from? Foam? Wood strip?

[SamSam]

I am new to boat building and am shaping a plug to build a mould for an outrigger canoe. I have searched for information regarding this, but thought simply to ask in this forum. Two questions;
1. How many ounces of fiberglass cloth should I use to make the mould (i.e., is 1 layer 6 oz glass enough)?
2. I have read alot about creating a flange for the hull and deck of the canoe (it will be a two part mould, hull and deck). What is the easiest way to create this flange, and does anyone have a link to something relating to this?
Thanks in advance for any advice.

1
You have to make it thick enough to not deform when removed from the plug.
For just a few canoes 1/8" thick with bracing will work, for production make it
1/4" or more. I'm assuming polyester resin, so use mat. Gel coat the plug, let cure. Laminate on a 3/4 or 1 1/2 oz layer of mat with a resin/hardener mix to give a slow cure, you don't want to build up heat which might distort or cause pre-release from the plug.Let it cure. Put on another layer of 1 1/2 oz, let it cure.Put on a couple layers 1 1/2 oz, let it cure. When thick enough, put on bracing. Try very hard not to introduce hot spots in the laminate with too much hardener or too much laminate all at once or hard spots with hard bracing directly against the mold or untapered reinforcements covering the bracing or weak areas.
2
Do you want to make a two part mold that you bolt together and make a one piece decked canoe, or do you want to make a hull mold AND a deck mold that gives you a seperate hull and deck that you attach together to make a decked canoe? Sam

[ocpaddler]

Thanks for all the replies. I plan to make the mould from foam (Lastafoam) as it seems to be easiest to work with. I was originally looking for a block of foam meeting the dimensions, but found the cost too high. I will strip build the plug, but using foam strips instead of wood. I've had a difficult time locating good sources for foam that would be relatively inexpensive and the Lastafoam seemed the best option. Any other recommendations on manufacturer?

[ocpaddler]

Answer to SamSam. I want to build a few canoes from this mould and appreciate all the advice. I also plan to build a two part mould that will not be bolted together. I will attach hull to deck after completion of both for various reasons. I need to run cable for rudder system on the inside of the deck and the canoe is a sit on top with footwells, etc. While I have your attention, what is the best method for joining the two halves together for completion? Like I mentioned before, I am new to this and appreciate all the advice, hope they are not silly questions.