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Old 21-08-2018, 11:57   #1
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Protecting aluminum hull.

I'm seriously considering buying an all aluminum 42' sailboat. Consequently I've been reading up on galvanic corrosion, and scaring myself silly. It will be used as a liveaboard in the ocean full time. Are anodes sufficient protection? Is an impressed current system the way to go, OR is aluminum just too much hassle in the electrolyte(ocean)? Thanks in advance for your help.
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Old 21-08-2018, 20:31   #2
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Re: Protecting aluminum hull.

The oxide layer does an almost perfect job of protecting the hull. Old airplanes at the bottom are still looking good sometimes because they often have a pure AL coating on the sheet metal called Alclad. Pure AL is soft so it can only be used as a coating but it is very corrosion resistant.
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Old 21-08-2018, 20:49   #3
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Re: Protecting aluminum hull.

With respect to Ecos, while it is true that the oxide layer can protect aluminum from environmental corrosion, it is useless in terms of galvanic corrosion, or stray current corrosion. They can cause serious damage to a boat in a short period of time.

And rjtaylor12, you are right to be concerned, but no need to be scared. Just use your concern as motivation do things right. There are a LOT of metal boats out there, and they live long and useful lives, if they are cared for with knowledge and diligence.

Some things...

Your shore power connection should be through an isolation transformer. These are much cheaper, smaller and lighter than they used to be. This will dramatically cut the risks associated with bad wiring in marinas. Cuts risk... does not entirely eliminate. Marinas with derelict boats should be avoided!

Be sure the boat has a "floating ground". Basically this means that your entire DC electrical system is a closed circuit. ALL power that leaves from the positive battery terminal can ONLY return to the negative terminal through insulated wires. No connection to the AC ground, and none to the hull, or anode bonding system (if any). This can only be maintained with regular monitoring, either automated or manual, for ground fault leaks that can cause stray currents.

Anodes... yes! Regular monitoring of protection levels, YES!

As much as possible eliminate other metals in contact with the hull, and if that is not possible, be sure the installation follows best practices. Keep bilges as clean and dry as possible.
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Old 23-08-2018, 10:13   #4
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Re: Protecting aluminum hull.

Thanks guys I really appreciate the info.
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Old 23-08-2018, 10:33   #5
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Re: Protecting aluminum hull.

Just dont try to keep paint on it. You may be disappointed.
Friends of mine had a quality built 48 ft cutter. In 10 years use they had it painted 3 times. First by a high cost yard in US , second in Trini, third in the SW Caribe.
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Old 23-08-2018, 14:08   #6
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Re: Protecting aluminum hull.

Just the bottom right? I don't want to paint topside... I like the aluminum look...work boaty
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Old 23-08-2018, 14:56   #7
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Re: Protecting aluminum hull.

Quote:
Originally Posted by rjtaylor12 View Post
Just the bottom right? I don't want to paint topside... I like the aluminum look...work boaty
their paint was hull and deck/cabin. Did the usual bottom jobs every 1-2 years.
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Old 25-08-2018, 08:51   #8
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Re: Protecting aluminum hull.

New high voltage galvanic isolator for Aluminum boats, 2.4 volts.
https://www.defender.com/product.jsp...032&id=3929406
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Old 25-08-2018, 16:48   #9
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Re: Protecting aluminum hull.

We almost bought a 42’ aluminum boat some years ago. Neat boat, schooner, but was sorta home built, the welding had been done by a bunch of different guys, some understood the schedule, some didn’t. Chain plates were buried behind cabinets. Bottom welds stood 1/4” proud. Other non-hull related issues also.

We reluctantly walked away at survey, made a few people very unhappy with us. Oh well.

I would buy an aluminum boat but there is always some risk, same with steel or glass. Talked to a guy with an about 10 year old Kanter, he reported a leak in an integral water tank I think. I looked at another boat that had a hole in a water tank. Don’t know if that’s common or just coincidence. Hull repairs, if needed, are not bad at all, provided you can get to the inside without destroying the interior of the boat.

Look around for poster Funjohnson, he has rebuilt an abused aluminum hull, I’ll bet he has some good advice.
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Old 26-08-2018, 08:24   #10
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Re: Protecting aluminum hull.

Post #8 Andina Marie
I reviewed the documentation for your GI+ and cannot find reference to the third party testing required by ABYC A-28. Without this testing and certification, your product does not formally meet the requirements of ABYC as you state on your website.
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Old 26-08-2018, 08:43   #11
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Re: Protecting aluminum hull.

billknny Post #3
Some very good advice but there are a few caveats.

Your shore power connection should be through an isolation transformer. These are much cheaper, smaller and lighter than they used to be. This will dramatically cut the risks associated with bad wiring in marinas. Cuts risk... does not entirely eliminate. Marinas with derelict boats should be avoided!

Comment: Good advice. Also ensure that all shore power inlets are electrically insulated from the hull. Mounting the inlet in a piece of Starboard and then mounting the Starboard to the hull works well.

Be sure the boat has a "floating ground". Basically this means that your entire DC electrical system is a closed circuit. ALL power that leaves from the positive battery terminal can ONLY return to the negative terminal through insulated wires.
Comment: Good advice.

No connection to the AC ground,
Comment: Bad advice, and potentially dangerous. There is no good reason not to follow the ABYC Standard and connect the B- buss to the AC safety ground that was derived at the secondary of the isolation transformer.

and none to the hull,
Comment: Most, if not all, metal boat experts will recommend a single connection between the Vessel Ground (aka, B- buss) and the aluminum hull

or anode bonding system (if any).
Comment: Impossible to accomplish as the anodes are bolted to the hull so the hull becomes the bonding system

This can only be maintained with regular monitoring, either automated or manual, for ground fault leaks that can cause stray currents.
Comment: Absolutely!! An aluminum or steel hull must have a built in corrosion monitoring system (manual or automatic) that constantly checks the hull potential. An excellent source is Electroguard http://www.boatcorrosion.com

Anodes... yes! Regular monitoring of protection levels, YES!
Comment: Highly recommend aluminum anodes. See above.

As much as possible eliminate other metals in contact with the hull,
Comment: ESPECIALLY copper, or copper bearing alloys, even condensate water with dissolved copper. Copper in a wet aluminum hull is exceptionally damaging.

and if that is not possible, be sure the installation follows best practices. Keep bilges as clean and dry as possible.
Comment: Absolutely.
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