Originally Posted by PorkyPig

yes, chopped matting that comes in sheets (not the blown in stuff)

first 2 layers are 1 oz. and next 2 1.5 oz...

2 layers of regular gelcoat (molding gelcoat is too expensive and you can't buy it in small quantities)

I'm not trying to tell you how to make hulls but that's not what the IOM boat builders use in the UK to my knowledge, I would think the chopped matting is going to make a heavier boat

Originally Posted by ToniGe23

I'm not trying to tell you how to make hulls but that's not what the IOM boat builders use in the UK to my knowledge, I would think the chopped matting is going to make a heavier boat

He's making the mold.
Don

ah ok!

Boat Lay Up Schedule

For those who are thinking about building their own IOM, it can be quite the mystery to determine (guess) the ideal fibreglass cloth layup schedule (weight, quantity, orientation and order). Last year I read an article written by one of the Oracle builders who said vary the strands as much as possible.

I've also noticed a hull with hard chine(s) has more and sharper corners so the shape is naturally stiffer than a soft chine hull. Ideally I want as light of hull as possible but strong enough to survive T Bone impacts from other boats.

When I started building my first IOM (2009) I used a lay up 3 layers of 4 oz. I had a few pin holes. A friend told me about using a layer of 0.75 oz. closest to the water (1st or last layer depending f you're doing a male or female mold. Males are less work and work well for one offs. Females if you are going to make multiple boats of the same design.

On my PP4 I did a layup of 3 layers of 2.5 oz and 1 of 0.75. That was just marginally too light. On my next boat I think I'm going to replace the middle 2.5 oz. with a 4 oz. Considering it has 3.5 pairs of chines (lots of sharp corners), I think it will be lots stiff enough and will allow me to have lots of corrector weights to fine tune the fore and aft trim (within the rules).

Early construction photo's of Wiz

Originally Posted by FWAL

Early construction photo's of Wiz

Wot no chines

It does have chines which in fact are quite aggressive in the midships due to the freeboard being rebated. This feature a long with what I have planned for the foredeck should visually set this design out from the crowd.

Originally Posted by PorkyPig

Boat Lay Up Schedule

For those who are thinking about building their own IOM, it can be quite the mystery to determine (guess) the ideal fibreglass cloth layup schedule (weight, quantity, orientation and order). Last year I read an article written by one of the Oracle builders who said vary the strands as much as possible.

I've also noticed a hull with hard chine(s) has more and sharper corners so the shape is naturally stiffer than a soft chine hull. Ideally I want as light of hull as possible but strong enough to survive T Bone impacts from other boats.

When I started building my first IOM (2009) I used a lay up 3 layers of 4 oz. I had a few pin holes. A friend told me about using a layer of 0.75 oz. closest to the water (1st or last layer depending f you're doing a male or female mold. Males are less work and work well for one offs. Females if you are going to make multiple boats of the same design.

On my PP4 I did a layup of 3 layers of 2.5 oz and 1 of 0.75. That was just marginally too light. On my next boat I think I'm going to replace the middle 2.5 oz. with a 4 oz. Considering it has 3.5 pairs of chines (lots of sharp corners), I think it will be lots stiff enough and will allow me to have lots of corrector weights to fine tune the fore and aft trim (within the rules).

Have you ever considered using a small amount of chop mat ? my dad has been making a couple marble head boats using 1 layer of cloth ( not sure on weight ) and one layer of chop mat as an experiment and they have come out so stiff that you cant even push the sides in.

I recall reading a spec sheet for a Britpop! from Vinaixa Yachts. They are using 2 layers of 165gm/m2, about 5.8oz, S-glass.

Interesting thread BTW. I haven't tried designing my own yet, but I've been trying to learn all I can about it before having a go.

Glen

Originally Posted by FWAL

Early construction photo's of Wiz

Looking good! Is this a one off balsa boat or are you making a mold?

Originally Posted by D design

Looking good! Is this a one off balsa boat or are you making a mold?

Just a one off experiment which should last until this time next year when I'll probably tweak the design again

About PC. In general a higher PC will let the boat go a little faster. Do you think it matters whether the higher PC comes from fattening the bow, or the stern? The modern designs are full in the bow, but I wonder if that is more of an anti nose diving choice. Could you achieve the same PC by fattening the stern and still keep the entrance angle to a minimum? I'm thinking a generally light wind boat that would stick with a modern hull in the puffs? I think I've answered my own question here but I've typed for this long I'll post it anyway.
Don

Hi Porky,

I use 3 layers of 75 gram silk weave with an extra layer gunwale to gunwale through the keel area on my IOM's. It's a bit of a buggar to lay up as it doesn't stretch and creases are hard to remove. And I use bracing from keel base to gunwale to transfer rig loads. This is a really light layup and you may need a bit extra around the mast step area as the keel tries to pop out of the bottom. Completed ready to paint around 450-475 grams.

I've also used this layup on my Gothic Marblehead. A bit of a cheap skate and didn't use carbon.

A trick to cut down on pinholes - use peel ply - wait for bubbles in the resin to dissipate before using and layup at night when its cool so you don't get solvent popping (gassing) so much.

Tony

One reason narrow hulls have such full bows and sterns is to have enough boyancy to be class legal.

I think D design is right there. I think the forward buoyancy is what help the latest generation hold they're bows up high whe sailing to windward, particularly in chop.

I use 3 layers of 107 gram 'satin weave', or multiple axial cloth, which is fantastic at going around and into complex curves etc. Craig Smith taught me that one....

By taking the top layer just over half way when laying in from each end, you get an extra layer in the midship area, where all the loading is.

In order to minimise pinholes, I really wet out the first layer, then use the remaining to absorb resin, and add as needed. I then use paper towels to absorb excess resin, or use peel ply, which seems to help consolidate the whole laminate.
I too have tried a thin layer of chopped strand mat, at 25grams,to reduce pinholes. Its like tissue paper! I now only use this on carbon hulls, and it works well...