Very good comment indeed Steve. I'll also keep for later usage. Would your
recommandations also stand for an aluminum hull ? I know it has to be
insulated but i remember to have read that in order for adherence to the
aluminum, this later has to be etched and primed.

André

"Steve Lusardi" wrote in message
...
Michael,
I am a builder and owner of a large steel boat. Insulation is absolutely
necessary in a steel hull. Corrosion is no problem on the outside, but can
be a nightmare on the inside. Condensation is the culprit. The solution is
to seal the interior metal surfaces from exposure to air. This is
especially true for those surfaces that are hard to get to. That
requirement is best met by sprayed urethane foam on top of a quality paint
scheme. It has incredible adhesion qualities. It is fast to apply, but
extensive masking is required. It has some disadvantages, it is expensive.
It is not a closed cell foam, so it can absorb liquids over time, which
are not removable without gutting the foam. It outgases for a long time,
some of which can be harmful. When exposed to fire, the gasses created are
deadly. Once sprayed and cured, it should be painted with a waterbased
flame retardant paint. This will seal the foam countering the
disadvantages somewhat. Polystyrene foam is another choice. It is of the
closed cell variety, it is less expensive, it is not as messy as urethane
and it has a better R rating. It is harder to use because the adhesives
are slow curing. Volatile adhesives will dissolve the foam. Because of
this, it is slower to apply, as clamping is required. It does NOT seal the
steel from exposure to air, so the foam must be additionally sealed with
plastic sheet and outgassing in fire is also a problem as with urethane.
Another choice worth considering is rock wool. It is less expensive than
styrene, faster to install than styrene and can be purchased in a roll
with one side bonded with a plasticized aluminum foil which will aid in
sealing the metal surfaces from air as well as having a much better R
rating and an infra-red reflector. Probably the most endearing quality
Rockwool has is ease of maintenance and accessibility. It is easy to
remove and replace if it gets wet, as well as being fast to remove in an
emergency. One last point that is related is bilge protection, which is
also critical in steel hulls. Your insulation must not go much lower than
the waterline, typically only to the cabin sole. So where water
congregates requires special attention. There, you want to derust at well
as possible. then use a rust converter like a weak solution of phosphoric
acid or a commercial equivalent like Fertan, wash out well with water.
then an etching two part epoxy primer followed by a compatible bilge
paint. But, where water can sit, additionally spray that area with a
special marine paraffin based wax similar to Ziebart for cars. This
material never quite hardens and continually seals against water.
Completing these steps with just occasional maintenance will allow the
hull to remain viable for well over 100 years. One last note, commercial
ships and super yachts use Rockwool and the paraffin wax solutions almost
universally.
Steve



"Michael Prewett" wrote in message
...
I'm considering purchasing a small steel-hulled yacht, but she does not
have any insulation. I would imagine that the immediate problems in a
European summer will be excessive heat,condensation, and to a lesser
extent, noise. Retro-fitting insulation is an option, possibly in stages,
and I'm wondering whether anyone would have some views on this. My
initial thoughts tend toward the use of foam board, room permitting. (I
know that Alubat offer foam insulation as an option on their aluminium
boats, fitting boards between frames, but I don't know what material they
use - I would imagine that it is some form of polyurethane).

Michael Prewett