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Old 08-04-2019, 14:39   #46
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Re: Need help with an Aluminium boat

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What alloy did you use when you built the boat?
Seawater resistant AlMg 4.5
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Old 09-04-2019, 07:26   #47
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Re: Need help with an Aluminium boat

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Coasties leave them bare, will find out what they do with the stripe.
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Old 09-04-2019, 08:10   #48
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Re: Need help with an Aluminium boat

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Seawater resistant AlMg 4.5
Eventhough there are various versions of AlMg 4.5, this is the right series of alloy.

Any black plastics or rubbers permanently attached to your boat? Black rubber and plastic often have Graphite in them and are even worse than copper when it comes to causing corrosion.
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Old 09-04-2019, 11:26   #49
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Re: Need help with an Aluminium boat

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Eventhough there are various versions of AlMg 4.5, this is the right series of alloy.

Any black plastics or rubbers permanently attached to your boat? Black rubber and plastic often have Graphite in them and are even worse than copper when it comes to causing corrosion.
Yes I have black rubber mat inside the cain locker.
But there i have no problems.
Overall I would say I can manage the problems.
The biggest mistake was, not to sandblast inside and to spray with epoxy.

If any dirt stays with moist and salt thats a problem.

So my opinion is, Al have not to be painted but than, it haved to be washed once a week or so.
So to avoid that, I would rather cover.
Than epoxy without sandblasting not good.
Waterbased paint very good experience. On deck or inside. 1 k paint ok.
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Old 12-04-2019, 00:48   #50
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Re: Need help with an Aluminium boat

Hey guys

Thank you so much for all your input, you're awesome!

This weekend a surveyor (Paul Fay of faymarine.com) is going to check the boat for 2.5 days, and then we'll see if we have found what we were looking for. I'll keep you posted!
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Old 14-04-2019, 20:16   #51
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Re: Need help with an Aluminium boat

Looks to me like a terrible welding job. Not as common in aluminum but very common in steel. It's the reason welds need to be properly spanned to ensure no voids. It's the voids that quickly deteriorate and ultimately lead to failure. This is of course only a quick response to a quick look at a picture but if the PO is saying electrolysis I'm inclined to agree.
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Old 14-04-2019, 21:20   #52
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Re: Need help with an Aluminium boat

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re:
"...electrolysis..."

Are you certain of your terms?

Based on your information, you appear to be describing galvanic corrosion.

The difference is significant. An experienced surveyor will know the difference.
An experienced surveyor and Certified Marine Corrosion Anakyst would not use the term "electrolysis" in reference to any marine corrosion.
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Old 15-04-2019, 05:37   #53
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Re: Need help with an Aluminium boat

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Looks to me like a terrible welding job. Not as common in aluminum but very common in steel. It's the reason welds need to be properly spanned to ensure no voids. It's the voids that quickly deteriorate and ultimately lead to failure. This is of course only a quick response to a quick look at a picture but if the PO is saying electrolysis I'm inclined to agree.
Did weld my Al boat from scratch. Never ever problems with welds.
I did not allways a perfect job. But if you weld from inside, then grind out from outside, then weld from outside again then it must be a huge mistake that it comes to failure.
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Old 15-04-2019, 06:11   #54
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Re: Need help with an Aluminium boat

It takes a few days to paint the inside of an aluminium boat. Then a few years to carry the paint out in little pieces. Been there and still doing the latter. It is VERY difficult to sandblast or otherwise clean the inside of aluminium boat for a good paint job.
Outside our paint on deck has lasted 5 years because of exposed edges. On the cabin and cockpit, 15
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Old 17-04-2019, 03:17   #55
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Re: Need help with an Aluminium boat

So here we are, and we have refused the boat.

We have surveyed the boat with Paul Fay (faymarine.com) who did an excellent job and just is an overall cool guy.

We have for example found pretty bad corrosion in the water tank, which has obviously never been opened, which has eaten down the hull in certain small spots up to about 5-7mm.

Furthermore, some mechanic has put fiberglass mats in an area between the keels under the motor room on the hull on the outside of the boat. There has been corrosion too, and for stopping the corrosion (or hiding it, however you want to call it) they have done this job. Any comments on this?

The gas system was laid out so poorly from the kitchen that the owners have basically been sitting on a bomb should there ever have been a leak.

And the list goes on.

It has just turned out to be too much of a project boat with tons of repair jobs to do und too many uncertainties. Also the owners were pretty shocked and will work out some of the points before even putting the boat back on the market.

The search goes on.
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Old 17-04-2019, 13:20   #56
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Re: Need help with an Aluminium boat

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So here we are, and we have refused the boat.

We have surveyed the boat with Paul Fay (faymarine.com) who did an excellent job and just is an overall cool guy.

We have for example found pretty bad corrosion in the water tank, which has obviously never been opened, which has eaten down the hull in certain small spots up to about 5-7mm.

Furthermore, some mechanic has put fiberglass mats in an area between the keels under the motor room on the hull on the outside of the boat. There has been corrosion too, and for stopping the corrosion (or hiding it, however you want to call it) they have done this job. Any comments on this?

The gas system was laid out so poorly from the kitchen that the owners have basically been sitting on a bomb should there ever have been a leak.

And the list goes on.

It has just turned out to be too much of a project boat with tons of repair jobs to do und too many uncertainties. Also the owners were pretty shocked and will work out some of the points before even putting the boat back on the market.

The search goes on.
Only one option, buy the boat very cheap ( if the surveyer agree) than throw all the interior away.
Repair the bad spots, sandblast inside outside and paint.
Renewing the interior is a half to one year job not such a big deal.
And still if you buy a used boat with all the interior you can end up with repairs for years.
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Old 21-10-2019, 22:16   #57
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Re: Need help with an Aluminium boat

You can install a corrosion meter (see photo below, I always have trouble getting these photos to stay upright).[/QUOTE]
I've lost count of the aluyachts, boats I've built



if i were to build one again for myself, I.d do this
polish topsidesto 320, with a RANDOM orbital
leaves no tracks, acid wash, then whilst damp hit hard with alodyne Heavy sand bottom, again wash anf hit with alodyne, then 300 DFT(Dry film thickness), this can e mearured with a wet film gauge--- quality poxy then antifoul whilst bottom paint is soft
painted topsides esp those that are not alodyned are going to corrode, at some point, free design
under
it is a nightmare
for trailered boats polish with alu prepping polish as they do road tankers
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Old 25-10-2019, 09:23   #58
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Re: Need help with an Aluminium boat

Just like Erik de Jong, I'm dutch. In the Netherlands, France and Germany many boats are build in metal. Steel or aluminium.

My boat is 63 years old (1956) and build out of cold-riveted aluminium. It's still without pitting. In the early days her underwater paint was coal tar, no fancy etching primers. Nowadays it's epoxy painting. In her life she's been grit blasted 3 times. That's once every 20 years!

There are a a couple of rules
1. be careful with shore power and earthing your hull (don't in any way)
2. if you add another metal (screw on hardware ie), the aluminium will corrode. The more mass the added metal, the worst the corrosion. Only one screw for a plastic cleat for example, won't do any harm. A big bronze chrome winch will definitely create some nice currents.
3. prevent any "environment" which can not breathe on the aluminium surface. Dirt, blisters in the paint, trapped moisture etc.

3.... The aluminium oxide skin that forms the naturally protection of the metal can't handle any envoirement that has a PH lower or higher than 7 (natural). Water trapped inside a void WILL go acid and that keeps attacking the alu oxide protection layer. Bad things happen when you ignore this situation for an extended period of time.

4. Do not believe anything you hear and laugh at "penny in bilge" stories. They are urban legends and complete nonsense.
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