Insulating a steel hull.

[alienzdive]

I am thinking of using white polystyrene as an insulation material on my 47ft project steel hull. And then panelling with 6mm oak ply.

Do I have to worry about condensation between the exterior of the hull and the internal linings? Or do I need to incorporate an air gap?

Is it better to use a different insulation between the area above and below the water line?

 

[Stemar]

No pretentions to expertise, but fwiw, here's my 2p's worth:

Expanded polystyrene is cheap & a great insulator but, in the thickness you'd want, it's quite rigid, so you will have an air gap between the hull and the insulation. It's impossible to make it completely and permanently airtight, so condensation WILL form.

To my mind, however, the biggest disadvantage is that it's inflammable and gives off VERY toxic smoke (including cyanide). There are spray -on insulations that would protect the hull better and be a lot safer in the event of a fire.

 

[DavidMcMullan]

The inside surface of my 37ft steel yacht was spray insulated with 1-inch of fire-rated foam down to the waterline. The company who did it was Paul Homer, who now trade as http://www.insulationsprayfoam.co.uk/index.shtml.
The quotation in 2001 was approx £700 + VAT.
The sprayed foam sticks to the paint primed surface and prevents any further corrosion.
Hope this helps.
David.

 

[Gumpy]

IMO there is ONLY one choice.
That is Sprayfoam, warm in winter cool in summer and NO condensation at all You need at least 30mm and it needs to be done by a professional.
I have lived with polystyrene, and rockwool, Parglena has sprayfoam and I wouldnt change it for the world. Its not cheap but works.

Mine was done by
http://www.webstersinsulation.com/


Julian

 

[rogerthebodger]

Spray on polyurathane foam is the only way to go. I you use sheets of any kind you will get water (leaks,condensation) behind the sheets that will cause the steel to rust from the inside.

Only cover insde down to waterline and not below

 

[wanderlust]

As per the other replies, spray foam is the best way forward. If you use any product that is rigid you will have problems with adhesion and air gaps. You can use a flexible foam and glue it in place but you need to use foam no thicker than 6mm and at least two layers. You need to overlap the joints and vapour seal the whole thing by taping all joints. Very time consuming and not as good a job as spray foam.

 

[ianabc]

Using anything BUT sprayed on fire retardant polyurethane foam allows moisture behind the insulation, resulting in condensation and rusting.

BUT spayed on foam in minutes after application develops a skin that is hard and this skin should be painted with fire retardant paint.

Polyurethane foam with fire retardant still generates toxins (Cyanide gas is created while setting and by combustion of whenther they be glues or foams) in a fire and any combustion will be close to unstoppable.

Most commercial fishing boats and many commercial passenger vessels have polyurethane foam and crew are liable to jump overboard in a fire.


So painting the foam with fire retardant paint works!

We used an expensive bathroom paint that did not contain arsenic or other toxins, just minerals that thickened the paint and prevented bathroom mildew and fungus growth. Left a painted piece outside and althoug here in B.C. ( wet coast as they say) anthing organic left ou is covered in fungus in 6 months or so. The paint works!

It is important from the I don't want to cut back the foam point of view, when sanded or cut the foam is exposed beneath the skin that forms on setting. The itch is horrible, so set battens in place at the top height of any required foam.

As the operator is trying to avoid cyanide and skin contamination he will wear a full suit with a pressure air feed. That means that he will have difficult seeing the places to foam and those top avoid so plastic sheeta and do not foam here signs may be necessary.

700 pounds for the inside sounds good.


Don't forget the icebox ( 6 inches all around would be good)
We had it foamed later and it cost almost as much as the entire inside foaming!

I suggest a minimum of 2 inches under the deck and 1 or more everywhere else.

Hope this helps