Alluminum boats and corrosion

[James448]

Thank you noelex that’s very a friendly and helpful comment. From what I can understand most of these French build boats are well constructed and well finished. One question I did have is about the insulation on the inside of the hull. is it common to paint behind the spray foam as this seems to be a problem area for condensation and then corrosion. I will be hoping to find a boat that is in paidnted from the water line up and made of a suitable 5 or 6 series alluminum. Do you mind me asking where you are based and if you Have you any idea about alluminum construction and the issues. Particularly the wiring modification part worries me with stray currents I understand cause rapid corrosion.

 

[Neeves]

Here's a nice one in your price range. I can recommend the design.

http://www.dbyboatsales.com.au/listing/camper-and-nicholson-55

And from a look from the outside when she is in the water or on the hard she is absolutely stunning. I used to see her regularly but she has been moved and I have not seen her for 6 month when she was last 'serviced'.

Jonathan

 

[noelex]

Insulation is one of the features that makes aluminium boats very practical. There is no condensation on the walls and ceiling. The boats are noticeably warmer in winter and cooler in summer compared to fibreglass boats. This keeps them free from mould, and very quiet, especially if you can find a boat with 75mm insulation.

Very few aluminium boats are un-insulated, but there are some racing boats that were built like this to save weight. If they are subsequently converted to cruising boats it is often not practical to add the insulation.

Spray foam insulation is the most common. Corrosion under the foam is seen in steel boats but is rare for aluminium boats. Five series aluminium will not corrode even with no surface finish (paint etc) when placed in seawater. Hence the number of boats with unpainted hulls. The only danger is crevice corrosion under the foam. The foam itself sticks to the aluminium like glue and unless there is a deck leak (and one of the features of aluminium boats is that this is very rare, or even impossible if the boat has welded fittings) and there is also defective insulation, which has not stuck to the aluminium, there will not be water under the foam, which would is necessary for crevice corrosion to form.

It is very hard to scrape off all the foam. It sticks much better than paint, but it needs to be well applied and this comes down to quality of the builder.

There is some debate if the uninsulated bilges should be painted or left raw, with pros and cons both ways. On boats with painted bilges the paint will extend for a short distance under the foam which may give the impression the whole interior is painted. Painting the whole of the interior is occasionally done, especially with boats with stick on foam sheets for insulation (instead of spray foam) but is not common.

 

[KellysEye]

>If the aluminium becomes exposed it will develop a white powder on the surface of the metal, this is the corrosion. It can lift paint off in the same way rust does.

In the Caribbean we saw lots of aluminium boat whose hulls were not painted they go white through corrosion but that protects the aluminium below.

 

[npf1]

Thank you noelex that’s very a friendly and helpful comment. From what I can understand most of these French build boats are well constructed and well finished. One question I did have is about the insulation on the inside of the hull. is it common to paint behind the spray foam as this seems to be a problem area for condensation and then corrosion. I will be hoping to find a boat that is in paidnted from the water line up and made of a suitable 5 or 6 series alluminum. Do you mind me asking where you are based and if you Have you any idea about alluminum construction and the issues. Particularly the wiring modification part worries me with stray currents I understand cause rapid corrosion.

Joining the site I mentioned earlier will give you lots of knowledge on all of these subjects. It well worth the few dollars to join as it has tons of articles discussing these very issues, as well as displacing the myths.

 

[Neeves]

Here's a nice one in your price range. I can recommend the design.

http://www.dbyboatsales.com.au/listing/camper-and-nicholson-55

Pasha is 50 years old, she seems to illustrate that with care (and love) corrosion is something that can be managed.

 

[vyv_cox]

Pasha is 50 years old, she seems to illustrate that with care (and love) corrosion is something that can be managed.

I have been trying to find the whereabouts of War Baby for the purposes of this thread. She has had several names, not making the search easy. We saw her in Crosshaven in about 1992, when she was already in middle age. As soon as the warps were on the anodes were over the side.

 

[Neeves]

A far as I know Pasha had permanent anodes. They were huge about the size of very large dinner plates (200mm diameter??) and about 20mm thick, 2 off. I saw her on the hard about 12 months ago and the anodes were lying alongside, ready to be 'installed'. I only know they were anodes, because I asked. For some reason I think they were installed in custom recesses - so they were flush.

I confess that aluminium hulls are not of major interest to me, too niche (and I only know of two large yacht in aluminium here (though there may be many more). I did not probe on Pasha and have not probed in general.

I did think she was, and still is, gorgeous but required, as is (or as was), too large a crew in order to sail her to her potential (no different to any bluewater performance yacht of her vintage). I can sail our 38' cat single handed (with the other single crew off watch) and hit averages of 10 knots over 100nm and peak at 16 knots - I don't think I could do that with Pasha - she would need some money spent - to allow her to be sailed short handed and I doubt you could make long passages with a crew of 2. This has nothing to do with her being built from aluminium. I did fleetingly consider buying her.

She was well, and professionally, maintained (I know the yards) and had some decent upgrades - so I suspect corrosion was knowledgeably (and maybe expensively?, maybe cheaply?) managed.

I think she is now down in Sydney Harbour and we are up on Pittwater - so normally we would not cross paths.

She looks very cheap - I suspect aluminium, particularly here, has the wrong reputation.

Jonathan

 

[Sybarite]

Strongall thick aluminium guaranteed against galvanic action

http://www.actunautique.com/2015/12...tion-construction-strongall-ou-aluminium.html

http://www.meta-chantier-naval.fr/web/notre-histoire/histoire-du-strongall/


Sorry it's in French.