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08-04-2019, 14:39
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#46
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Registered User
Join Date: Jan 2019
Posts: 20
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by Erik de Jong
What alloy did you use when you built the boat?
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Seawater resistant AlMg 4.5
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09-04-2019, 07:26
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#47
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Registered User
Join Date: Feb 2015
Posts: 269
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by jmorrison146
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Coasties leave them bare, will find out what they do with the stripe.
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09-04-2019, 08:10
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#48
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Registered User
Join Date: Mar 2012
Location: Sitka, Alaska
Boat: Custom designed and build 52'
Posts: 117
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by Norbert1
Seawater resistant AlMg 4.5
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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.
__________________
We operate our "Bagheera" in the high Arctic for scientific, skiing, mountaineering, diving, research and adventurous expeditions.
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09-04-2019, 11:26
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#49
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Registered User
Join Date: Jan 2019
Posts: 20
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by Erik de Jong
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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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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12-04-2019, 00:48
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#50
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Registered User
Join Date: Mar 2019
Posts: 63
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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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14-04-2019, 20:16
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#51
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Registered User
Join Date: Oct 2015
Location: Newfoundland
Boat: Beneteau
Posts: 671
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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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14-04-2019, 21:20
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#52
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,060
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by LargeMarge
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.
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An experienced surveyor and Certified Marine Corrosion Anakyst would not use the term "electrolysis" in reference to any marine corrosion.
__________________
If you're not laughing, you're not doin' it right.
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15-04-2019, 05:37
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#53
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Registered User
Join Date: Jan 2019
Posts: 20
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by nortonscove
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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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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15-04-2019, 06:11
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#54
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Registered User
Join Date: May 2006
Location: Quathiaski Cove, British Columbia
Boat: Garcia Passoa 47
Posts: 167
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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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17-04-2019, 03:17
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#55
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Registered User
Join Date: Mar 2019
Posts: 63
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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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17-04-2019, 13:20
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#56
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Registered User
Join Date: Jan 2019
Posts: 20
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Re: Need help with an Aluminium boat
Quote:
Originally Posted by Fidu666
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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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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21-10-2019, 22:16
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#57
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Registered User
Join Date: Mar 2009
Posts: 152
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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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25-10-2019, 09:23
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#58
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Registered User
Join Date: Jun 2018
Location: Netherlands
Boat: Nonsuch 36
Posts: 152
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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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