Just bought a 36' aluminum hull trawler!!!

[Steve DAntonio]

Congratulations on finding the right vessel, I hope the survey goes well. For an aluminum vessel the surveyor should be well-versed in corrosion issues, preferably with an ABYC Corrosion Certification. He or she should, among other things, carry out a reference electrode test.

I tell those who are considering owning an aluminum vessel, you need to be part metallurgist to do this successfully and enjoyably, for two reasons. First, to avoid corrosion issues with this alloy, which is the third least noble, or most likely to corrode, after zinc and magnesium. Second, to avoid being mislead, and frightened, by those who believe they understand corrosion and what causes it, but often don't truly understand the various causes of corrosion, particularly with aluminum.

The most common causes of corrosion for aluminum vessels are galvanic, or dissimilar metal, and poultice. Both are explained in detail here https://stevedmarineconsulting.com/understanding-and-preventing-aluminum-corrosion/

Painted aluminum presents it's own unique challenge, this article covers corrosion associated with it https://stevedmarineconsulting.com/paint-and-aluminum-how-to-ensure-a-good-mix-2/

(In Kaohsiung, Taiwan)

 

[Wayfarer]

Congratulations on finding the right vessel, I hope the survey goes well. For an aluminum vessel the surveyor should be well-versed in corrosion issues, preferably with an ABYC Corrosion Certification. He or she should, among other things, carry out a reference electrode test.

I tell those who are considering owning an aluminum vessel, you need to be part metallurgist to do this successfully and enjoyably, for two reasons. First, to avoid corrosion issues with this alloy, which is the third least noble, or most likely to corrode, after zinc and magnesium. Second, to avoid being mislead, and frightened, by those who believe they understand corrosion and what causes it, but often don't truly understand the various causes of corrosion, particularly with aluminum.

The most common causes of corrosion for aluminum vessels are galvanic, or dissimilar metal, and poultice. Both are explained in detail here https://stevedmarineconsulting.com/understanding-and-preventing-aluminum-corrosion/

Painted aluminum presents it's own unique challenge, this article covers corrosion associated with it https://stevedmarineconsulting.com/paint-and-aluminum-how-to-ensure-a-good-mix-2/

(In Kaohsiung, Taiwan)

Thank you for posting these articles! I'm in the process of buying an aluminum boat myself, and this is exactly the sort of thing I needed to see.

 

[rgano]

As told to me by the chief engineer of the USS New Jersey:
Somehow or other the active cathodic hull protection system was connected up incorrectly during the recommissioning process in the 1980s and nobody noticed for a while. During this interregnum, an aluminum yacht-like vessel came to be moored across the pier. Within a relatively short period the smaller vessel sank, and her hull was found to have rather serious wasting issues. It would seem wise to keep an AL hull away from large steel vessels and structures or at least to have a monitoring system which would instantly alert if some bad things were going on with the hull protection.

 

[Steve DAntonio]

As told to me by the chief engineer of the USS New Jersey:
Somehow or other the active cathodic hull protection system was connected up incorrectly during the recommissioning process in the 1980s and nobody noticed for a while. During this interregnum, an aluminum yacht-like vessel came to be moored across the pier. Within a relatively short period the smaller vessel sank, and her hull was found to have rather serious wasting issues. It would seem wise to keep an AL hull away from large steel vessels and structures or at least to have a monitoring system which would instantly alert if some bad things were going on with the hull protection.

This could be an issue, even if the USS NJ wasn't using an impressed current system, if the NJ, which is steel and cathodic to AL, and the affected AL vessel shared a common shore power ground, which is possible if both were plugged into shore power. The aluminum hull would "protect" the steel by sacrificing itself.

Every aluminum vessel should be equipped with an isolation transformer for exactly this reason, to isolate the vessel from other vessels, as well as from steel bulkheads. It's critically important to achieve this complete isolation from shore ground on metal, Al and steel, vessels, although FRP vessels benefit from it as well.

More on shore power transformers Benefits of shore power transformers - Ocean Navigator - Ocean Voyager 2017

(In Kaohsiung, Taiwan)