Waterline mark / staining on aluminum - Normal?

[Aridhol]

I recently purchased a new boat, 18ft hewescraft aluminum and for the first time I left it moored at a marina for the sidney derby (about 48 hours) and when I pulled it out and went to wash it I noticed some distinct darker coloration's. Just wondering if this is normal and not something I should worry about or if something is off.

http://imgur.com/a/cEgH8

20160509_171102

• Aridhol
• May 9, 2016

20160509_171024

• Aridhol
• May 9, 2016

 

[adrian1991]

Just a stain
Try some toilet bowl cleaner on it or a hull cleaner from your favourite store.

 

[trophywife]

a lil algae most likely.. once your alu tho does get a petina or darker finish, do not remove it. it is a change in the alu that will serve as a barrier. or welcome to the bottom painters club.

 

[Aridhol]

Thanks guys. I spent a fair bit on the boat and am quickly becoming paranoid about corrosion

 

[JAC]

Be very careful with cleaners and chemicals on aluminum. Make sure it safe to use on aluminum before u use. I use dish soap and water now because it's safe. Simple green is not safe on aluminum don't know about towel bowl cleaner but I have my doubts

 

[Aridhol]

I've just been using sunlight and a brush, seems to be working but this was some distinct staining.

 

[Birdsnest]

A big problem with docks is electrolysis. Most docks are pretty "hot" and some are worse than others. About all you can do is make sure your aluminum boat is zinced well and also have your power out of the water and zinced well too. The more stuff you have going on around a dock with electricity the worse it is and draping extension cords in the water and leaving unused extension cords plugged in is a no no. I have heard that at some docks people who do this will find there extension cord cut up into pieces.
At my dock I am occasionally unplugging unused cords and getting power cords out of the water.
In your second photo check those white spots and see if there is a pit under that. If there is there is a big problem. Also if you have a hot boat that can add to the problem if your power is on a lot.

 

[Aridhol]

I've never used shore power or dock power and when I was out of the boat I turned the battery switch to off.
I 99% of the time trailer it out of the water, this was just from ~48 hours of sitting in the water at the marina in sidney.

For the white stuff I will double check for pitting.

 

[JAC]

What is your anode made of?

 

[Aridhol]

It's a double zinc (one on each side of that plate.)

 

[bones]

A big problem with docks is electrolysis. Most docks are pretty "hot" and some are worse than others. About all you can do is make sure your aluminum boat is zinced well and also have your power out of the water and zinced well too. The more stuff you have going on around a dock with electricity the worse it is and draping extension cords in the water and leaving unused extension cords plugged in is a no no. I have heard that at some docks people who do this will find there extension cord cut up into pieces.
At my dock I am occasionally unplugging unused cords and getting power cords out of the water.
In your second photo check those white spots and see if there is a pit under that. If there is there is a big problem. Also if you have a hot boat that can add to the problem if your power is on a lot.

wouldn't a properly bonded hull and secondary battery terminal completely eliminate this? it your hull is not correctly bonded to shore power you have a potential of a hot hull and as much floating current as 240V. bonded secondary would drain current back to source through path of least resistance. bonding the negative side on the battery also solves this issue

my buddys AL jet boat gets cleaned with aluminum tire cleaner, spray on, wait, light scrub and hose off

 

[trophywife]

i added zincs just past miship, one on each side . man they get eaten up quick. no more pitting tho!!

 

[ericl]

As birdsnest alluded to, the problem is not your boat, it is other sources of electricity in the water at the marina you were at. These sources could be other boats and/or the marina wiring. See the referenced URL

http://www.performancemetals.com/anodes/AnodeFAQs.shtml

 

[Aridhol]

As birdsnest alluded to, the problem is not your boat, it is other sources of electricity in the water at the marina you were at. These sources could be other boats and/or the marina wiring. See the referenced URL

http://www.performancemetals.com/anodes/AnodeFAQs.shtml

Thanks for that ericl, I did not clue in that he meant other boats/cords, my mistake.

 

[ericl]

Sure thing bud - It's a complex issue because what is going on with your boat matters as well. Poor electrical bonding on your boat can repel fish as well. trophywife says he added electrodes amidships , which helped him. Never done it, but if you are just mooring for a short time, you could hang a few zinc's over the sides if the boat & just pull them up when you leave the dock.

 

[Rednex3]

Basically, there is a reason that aluminum hulls living in the water are painted below the waterline.

One thing that hasn't been mentioned here yet is steel pilings in the marinas. Add boats with possible electrical issues in addition to other electrical leaks to the water and you have a recipe for disaster. I have seen aluminum hulls literally 'boiling' at the waterline because of this. It's a heartbreaking site!

To much zinc on a hull can be almost as much of a problem as none. Almost like trying to balance on a razors edge!