Spray Foam

[catsketcher]

Hello all

I am looking at increasing the volume of my little cat. I would like to add about 300l to the 6 metre hulls. The displacement is 600kg and the boat sits fine with no one on it but in a chop it could do with more volume.

Does anyone have any experience with foaming up a hull to gain volume. I had thought of using extruded polystyrene or polyurethane surfboard foam. I know you can get two part polyurethane for ice boxes. Is there anything else out there?

cheers

Phil

[Ad Hoc]

I think you're going to have to distinguish between the method of apply volume, and that of the effects of adding volume, to your boat.

Do you have a sketch or drawing of your boat?

[CDK]

Spray cans containing polyurethane are not suitable. The material needs moisture to harden, so in close confinement only a skin is formed around a liquid core which slowly collapses. 2C polyurethane fully cures but forms a lot of open cells: in contact with water, the foam becomes a sponge.

Styrofoam has closed cells but as far as I know is only available in extruded form, like sheets, blocks or pellets.

[PAR]

Are you talking about skinning the outside of your boat with foam to increases it's displacement?

[catsketcher]

Thanks for the replies. Ad Hoc - the boat sails really nicely but being a catamaran she depresses the leeward hull as the wind comes in. Due to her flared shape this causes an abrupt change of buoyancy. I want to increase the volume so that she has a higher immersion rate and higher displacement when the transoms are immersed as well as lessening the flare. I already have a second, more voluminous set of hulls for the next version. It is just that she is such a sweet thing I want to make her better.

I have found a supplier of surfboard type polyurethane blanks. In the 60s a big cat was built using spray foam - it was a Rudy Choy design - Glass Slipper - I think. I was wondering if anyone else had used this technique.

cheers

Phil

[Frosty]

I think he intends to glass over it afterwards.

I am interested in this as I am going to do the same thing to my bulbous bows and make them more shaped.

I was told I could use spray can type foam but the cost was way more than buying A&B mix from the air con shop.

[Pericles]

If you are contemplating the suggestion by PAR, try PIR as discussed at

Plywood vs foamcore-how do they compare?

[catsketcher]

I would like to put about 60mm all over the two hulls. Then I would glass over them with about 400gm biax. I would be leaving the whole current hull as is (but grind off the filler to try to save some weight before adding the foam)

I will probably go the polyurethane foam blanks cut into strips. Lots of work with the torture board but not impossible.

cheers

Phil

[Pericles]

Or you could use the existing hulls and do this:

http://bateau2.com/howto/foam1.php

Bigger, lighter, newer.

[michael pierzga]

Years ago we needed to change the rating of a racing yacht fast by adding more volume, buoyancy, to the hull aft to force the bow down and change the waterline length.

This was a fast, I dont care how much it cost , nor how long it lasts , between regattas job. . .

We epoxied wood strips to the hull as a a guide....faired the wood strips in...then used spray foam to fill the voids between wood strips......then faired the spray foam to the wood strips ...then glass sheathed the new foam hull.

Quick and dirty.

I would say that conventional sheet foam core would be superior in technical specs and as a result more durable than spray foam . .

[catsketcher]

I like the idea of the fairing strips. I know how much I want to change the shape so these would be good. Pericles - I had thought of making whole new foam hulls for the cat but I reckon the time involved in cutting up and setting up moulds would be greater than the time involved in putting foam on.

I saw the 35kg/m polyurethane foam. Its not bad and $30 for 600mm x 900mm. Probably go that way

cheers

Phil

[Pericles]

catsketcher,

The price you quoted seems high.

In the UK, I was able to purchase PIR as "seconds" for insulating our extension to the house. I paid £30 including 20% VAT for each 8' x 4' x 5.5" (1220 mm x 2440 mm x 140 mm). http://www.aandainsulationservices.com/

PIR is an improvement on PUR. http://en.wikipedia.org/wiki/Polyisocyanurate

The PIR I purchased would be too thick for your purposes, but I think 2" (50 mm) sawn (very easily) into strips as per the link below and moulded onto your catamaran would work well. No setting moulds, just turn the cat hulls up & pin the strips on.

http://bateau2.com/howto/foam1.php

PIR is available in Australia.

http://www2.dupont.com/Formacel/en_U...ads/h39903.pdf

http://www.bradflo.net/bradflo/au/da...20Brochure.pdf

Good luck with sourcing "seconds". Lay up, lash down, launch & hang on.

[catsketcher]

Thanks Pericles

I didn't know there had been an improvement in foam but polyurethane is pretty old now. I would love to get some sheets like the ones you bought but I have only sourced much smaller ones and only up to 75mm thick.

I will see if I can get some of the panels you bought. I will add the foam in the manner you suggested and would prefer to use some sort of spray foam to glue the foam strips together. Epoxy filler will be expensive, heavy and slow. I will epoxy the foam strips to the hull though.

I will start digging down here

cheers

Phil

[Pericles]

Builders Merchants are what we call the suppliers in the UK. It's insulation for houses. They make the stuff over there, not all sheets are produced to first class quality.....

The sheets with wrinkles or with thickness variations have got to be offered somewhere. Even in OZ, not all things are of the finest quality. For example, your manky politicians are as crap as ours. Your PM is a Welsh import FFS.