Is this corrosion?

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I recently bought a 1984 19' Gregor Sea Hawk tin. The boat will be used exclusively in the salt, and I am wondering if I should paint the hull.

There seems to be some white powdery substance on the hull bottom, is this corrosion? What should I do about it?? Thanks for any insight!
 

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Looks like what I've got on my hull. When I take it off with a Scotch Brite pad, or similar, there's no pitting underneath. So, I've been assuming it was salt deposits. I'll be interested on the input from more savvy members on here.
 
Yes it is light corrosion, aluminum has a way of preventing corrosion by coating itself with a layer of light corrosion. However, it will continue to corrode especially in salt use. That doesn’t look abnormal. Look out for areas that might show signs of pitting, that could also be caused by electrolysis, do you leave it in the water? Usually a good rinsing is all you need I have also heard that vinegar is a good way to remove salt and corrosion build up to, also known commercially as Salt Away.
 
That's minor surface corrosion. Neutralize it with ospho, then a rinse of water. If it were me, I'd go ahead and put a coat of aluminum bottom paint on there, provided that everything else on the bottom looks OK. Bottom paint is the ONLY barrier between the salt water and your hull. Without it, electrolysis and bottom growth will destroy your hull.
 
So y'all say it's fairly minor? Would I do major damage to the hull if I were to take it into salt water for a test drive and then do the ospho, paint, etc? This is a trailered boat that's gonna live in my driveway for the most part.

I've been reading about mill scale on the other tin boat forum, and am thinking of having a go at acid-washing. This boat is about a thousand pounds tho - not quite so how I'm gonna get it off the bunks for treatment. This is the first full-sized boat I've owned :-o ..
 
What you are showing in the photos is far from an emergency situation. Mine has been like that for years, with no sign of pitting underneath. Take it out, rinse well w/fresh water when you pull it out and deal with it during the off season.
 
Yes, it is electrolysis. You need to get a zinc anode for your hull and DO NOT ground any electronics to the hull. You need a self contained system meaning use the negative battery terminal for your ground, never the hull.
 
[url=https://forum.tinboats.net/viewtopic.php?p=367206#p367206 said:
smackdaddy53 » Today, 15:05[/url]"]Yes, it is electrolysis. You need to get a zinc anode for your hull and DO NOT ground any electronics to the hull. You need a self contained system meaning use the negative battery terminal for your ground, never the hull.


+1 to that.

Unfortunately, if the engine is an electric start, as soon as you hook it to the battery, it is grounded to the hull. So, it's nearly impossible to avoid putting current through the hull, but most definitely, don't make it worse by grounding any devices to the hull.
 
Make sure you get all of the carpet off of your trailer bunks too. As soon as you dip the trailer one time in saltwater, it will hold salt forever. And it will hold it against the hull of your boat. Thus eating your hull while you sleep and work... 24-7/365. Get some of the Tie-Down Engineering bunk glide-ons. Or a similar product.
 
[url=https://forum.tinboats.net/viewtopic.php?p=367072#p367072 said:
SumDumGuy » 26 Sep 2014, 10:26[/url]"]Appears to be oxidation rather than corrosion. :wink:

And the difference is??
 
[url=https://forum.tinboats.net/viewtopic.php?p=367252#p367252 said:
surfman » 29 Sep 2014, 07:39[/url]"]
[url=https://forum.tinboats.net/viewtopic.php?p=367072#p367072 said:
SumDumGuy » 26 Sep 2014, 10:26[/url]"]Appears to be oxidation rather than corrosion. :wink:

And the difference is??

I think that was the point to the wink...
 
[url=https://forum.tinboats.net/viewtopic.php?p=367252#p367252 said:
surfman » Today, 07:39[/url]"]
[url=https://forum.tinboats.net/viewtopic.php?p=367072#p367072 said:
SumDumGuy » 26 Sep 2014, 10:26[/url]"]Appears to be oxidation rather than corrosion. :wink:

And the difference is??

Oxidation, electrolysis, or corrosion. Whichever word it is, none of them result in happy endings for an aluminum hull.

Having operated aluminum boats in salt water for 30 years, and having welded on them for almost the last 20, I can tell you it's not something to just take lightly or ignore. It's a warning sign of problems to come. Combatting and preventing it requires an aggressive, pro-active maintenance and inspection routine.
 
Ok, so perhaps I'm not as good to go as I thought :-O.

Last week, I stripped the decking off the hull, and the bilge was FILTHY. I found twenty year old beer cans down there! It's hard to tell with all the soot, but the inside seems in good condition, I will know more when I pressure wash this weekend.

I plan to:
1) pressure wash the bilge
2) etch the exterior with phosphoric acid
3) Take her out for a test drive
4) place pvc sliders on the bunk
5) redo the interior decks, electronics, etc.

The motor is electric start ... should I be disconnecting the battery when parked??

Also, I'm not quite sure how to accomplish 4, this boat is heavy fully loaded. Am I gonna have to float it, and install the bunks at water side?

Ok a side note, do you think I should paint the interior/exterior??
 

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Etching is usually a prelude to painting. Not sure why you'd want to etch, then take boat out in salt water for a test run. Take it out, then begin doing whatever you decide to do. Your boat is not going to dissolve during one test run.

Here in San Diego there are lots of boats used exclusively in salt water, 20 or more years old, similar to Gregor (my Bayrunner is like a second cousin). I can only recall seeing one that had the outside of the hull painted. Not saying it's a bad idea, but there's a lot of aluminum skiffs running around here w/o hull paint. Here's my hull (photo). Been that way since I bought it in '85. As I noted before, scour white spots off with a scotch brite pad and there's no pitting underneath.

I did have some corrosion, with pitting, where the hull meets the forward portions of the bunks, which I think is a result of sitting on soggy bunks/carpet during a 20 year dormant period. Nevertheless, this winter I'll be installing those glide sticks to minimize moisture being trapped in the future.

As far as I know, electrolysis won't occur if your boat is on a trailer on dry land. (and not filled with water). Don't see a need to disconnect battery for that reason.

You can raise the boat off the trailer to fiddle with the bunks, using the trailer as a jack and putting supports under the boat. Lots of posts on different sites on how to do this.
 

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The etching is too get rid of mil scale on the hull ... there have been some in depth discussions on the "other" tin boat site covering it. Kmorland over there is a boat builder who claims that removing mil scale with an acid etch is one of the most important things to do in preventing corrosion. Of course, I have no direct experience with any of this (first tin boat!) but I don't think it could hurt 8) .

The disconnecting the battery comment came from the fact I have an electric start mercury which is grounded to the hull by default. I think wet bunk carpets, and a hull at different potential than earth ground could certainly cause galvanic corrosion...

Course, I could just be paranoid cause I plunked a few grand on my first tin boat :shock:
 
sonicwonder2000 said:
The etching is too get rid of mil scale on the hull ... there have been some in depth discussions on the "other" tin boat site covering it. Kmorland over there is a boat builder who claims that removing mil scale with an acid etch is one of the most important things to do in preventing corrosion.

I concur 100% with that assessment. It's a simple and cheap enough procedure, versus what will be involved if you let corrosion start to run its course.
 
sonicwonder2000 said:
The etching is too get rid of mil scale on the hull ... there have been some in depth discussions on the "other" tin boat site covering it. Kmorland over there is a boat builder who claims that removing mil scale with an acid etch is one of the most important things to do in preventing corrosion. Of course, I have no direct experience with any of this (first tin boat!) but I don't think it could hurt 8) .

The disconnecting the battery comment came from the fact I have an electric start mercury which is grounded to the hull by default. I think wet bunk carpets, and a hull at different potential than earth ground could certainly cause galvanic corrosion...

Course, I could just be paranoid cause I plunked a few grand on my first tin boat :shock:

Huh. Learn something new every day (on the etching). Wonder why the builders (like Valco) don't/didn't do that at the factory.

On the electrolysis/battery thing, I'm missing the concept. Electrolysis occurs when two dis-similar metals are in a solution. Not seeing the solution and the dis-similar metals when the boat is on a trailer.

Nothing wrong with being paranoid - it's your boat, and, if you're like me it's worth more than you paid for it :0
 

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