Hi Steve,
Thanks for your insight ! Altough my cruising ground is fresh water, i do
have an aluminum boat which turns 40 years old next year and it has no sign
of external or internal corrosion whatsoever. It was built from 5032-H34
alloy. I agree from my studies in chemistry that in salt water any
contact with another metal would create a cell and Al has very low
electronegativity. This is why i have 2 magnesium anodes instead of zinc.
The boat can be seen here;
www.langevin.biz/marinette34
I am currently budgeting the cost for building a 45 feet aluminum sailboat.
Thus i have to take account into my budget that the aluminum hull has to be
primed inside. But your "rock wool" idea is very interesting also. It
could save me for priming the inside of the hull. Do you have any idea the
basis for comparing wool versus foam or another ? Is it a matter of price
or sound insulation ?
André
"Steve Lusardi" wrote in message
...
Andre,
Yes, it does, with caviats. Aluminum is very reactive in salt water. The
5000 AISI series is specifically intended for marine use. Do not use other
aluminum alloys. Do not electrically connect any other metal above or
below the waterline. Do use a cromate based primer. Do not believe any
paint company's assurances of performance from cromate free paints without
making tests yourself. I have seen many, many failures. In fact I have
only seen one truly successful aluminum yacht. It was built by an
Australian Navel Architect. It was 35' in length. He was so anal about
mixing metals, everything was aluminum, including the prop and shaft. I
was there when he took it out of the water on the Isle of Wight after 3
continuous years of cruising. He had 10' long grass growing from the hull
and absolutely NO corrosion. So it is possible to be successful, but you
will not acheive it with out of the box components.
Steve
"André Langevin" wrote in message
...
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