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