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View Full Version : Is this corrosion or a hit from something underneath



Mark0
14-12-2016, 09:02 PM
I have 4 of these spots on the bottom of the boat that are at the back and are a little rough spots, some look like they are pitted a little bit.

Is this corrosion if so is it from the bottom or top that it's happening ? I can see nor access the top/floor behind my back seat due to a stupid shelf that looks from factory to me.

Do I need to get these spots welded if so ?

Pics are not the best sorry.

http://uploads.tapatalk-cdn.com/20161214/8fee021a90402275628edba748df697e.jpg
http://uploads.tapatalk-cdn.com/20161214/39e0ca19adf83b332782129f2bef0fdf.jpg
http://uploads.tapatalk-cdn.com/20161214/154f9018775f3522192915abffd6f9cc.jpg
http://uploads.tapatalk-cdn.com/20161214/122e134aebc2746d1b1030874a999060.jpg

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robothefisho
14-12-2016, 09:20 PM
Looks like corrosion from sitting wet with salt on it.

Mark0
14-12-2016, 09:26 PM
Nor sure how though I hose it off after each use, is it coming from the bottom ?
Does it need fixing by welding in New aluminium ?

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TheRealAndy
14-12-2016, 10:04 PM
That would be pitting corrosion, and its caused by contamination forming an anode, most likely from some salt granules. Possibly also shitty aluminium too, but there is a hundred things that could cause it. Welding is only a temporary solution because that introduces a whole new bunch of issues. If the holes dont go all the way through, I would clean them up so they look like new aluminium and keep a close eye on it. Make sure you clean all salt off it. I remember using an acid mix to create a poor mans anodising of aluminium in my early uni days, but I I cannot for the life of me recall what acid it was, google might help, but something like that could help longevity.

robothefisho
15-12-2016, 07:26 AM
Etch it with an off the shelf aluminium cleaner and then rub a coat of carnauba wax over the area if the pitting isnt close to breaking through hull. If holes are deep just fill with sikaflex. If they go through hull yes weld up. Corrosion is from where you can see judging by larger face is on surface.

Mark0
15-12-2016, 07:42 AM
Ok I'll have a look, I would like whatever is the best fix as I may sell in the next 6 months want to make sure it's all good for next owner, a bit disappointed it's happened the rest of the boat is in excellent condition.

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shaungonemad
15-12-2016, 09:18 AM
Could also be from a sinker or a swivel stuck in there somewhere.

Mark0
15-12-2016, 09:43 AM
In regards to sinker doing it would the bottom look like it does ? That's why I was wanting to know where the hole is starting from inside or out

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Mark0
15-12-2016, 11:45 AM
I've been told to get an access hole in the shelf at the back so I can open it and give it a really good clean, then use FlowCoat on the bottom, then If I want Flow Coat all of the floor up to the Flare on the inside, then also I can FlowCoat the bottom side of the boat as well up to the Flare, so i might investigate this rather then fix anything with welds.

Although I see Flowcoat is for fibreglass not sure how it would go on ally, Possibly cleaning everything and painting both sides with a 2 pac might also stop it in its tracks, not sure.

myusernam
15-12-2016, 01:08 PM
thats electrolosys. check for sinkers and swivels etc inside the hull, under ribs etc. dont ground anything in your boat. Isolate things like flush mounted VHF etc. disconnect batteries after use. Make sure your anode on the engine is ok. If it is maybe just undo and redo the bolt/ clean it up.

Mark0
15-12-2016, 02:00 PM
Yes i think thats my issue personally, whats under the rear shelf I dont know, I am going to get a 27x37 access port and put in the middle so I can get access, I will clean it up get all the shit out of there, then maybe coat it in something maybe the Flowcoat to just add a barrier on top, I might do the entire inside of it below the flare with that after i gurney it.

Then I might just get the 4 spots welded so they are fixed OR put something over it if welding is not needed at this stage (some are not even a pitting hole just the beginnings of it).

I've been told by my boat mechanic that its a 22 year old hull and it will start to happen at some stage, there is not a lot you can do other then clean it up fix any holes and keep cleaning it after use, he also said this all could have started before I owned the boat (i've had it for about 2-3 years), but the boat should be ok for years to come, just keep fixing it, until I change boats.

As for power the only batter in the boat sits in an old plastic hummingbird GPS case they are 2 x 6 Volt batteries that are connected to my GPS and Nav Lights, I dont disconnect them but its also not earthed anywhere in the boat.

myusernam
15-12-2016, 05:05 PM
led navlights with a heatsink maybe touching boat?

Mark0
15-12-2016, 05:07 PM
Back of nav lights are all plastic wires come through hole and that goes through hole in boat.


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tunaticer
15-12-2016, 05:41 PM
Most likely it is salt corrosion if it is in a hard to wash down area.
Electrolysis is a possibility if you have any current passing through the hull.
My boat now has about 30 alloy peen rivets in the bottom after 21 years and 1.6mm aluminium.
My boat has never been applicable to electrolysis because every electrical connection is isolated from the hull, at no point has it ever been earthed.

TheRealAndy
15-12-2016, 07:44 PM
thats electrolosys. check for sinkers and swivels etc inside the hull, under ribs etc. dont ground anything in your boat. Isolate things like flush mounted VHF etc. disconnect batteries after use. Make sure your anode on the engine is ok. If it is maybe just undo and redo the bolt/ clean it up.

Technically speaking, all corrosion is electrolysis. In this case, its plane old boring corrosion caused by some sort of contaminant, most likely salt. It highly unlikely that its caused by stray current from electrical accessories as its just some isolated pitting..

If you want to see what corrosion caused by stray current is like, take a look at the anode on you outboard, or even better the anode on a boat that is always in the water.

myusernam
15-12-2016, 08:10 PM
The steel hull beside ours it looked like someone had gone nuts with a 3/8 drill bit. I dunno looks pretty localised to me.

Mark0
20-12-2016, 10:14 PM
Still undecided what to do here I have ripped my floor out there is some corrosion but most is ok as it's been painted before me, I am wondering do I pressure wash this then work out what to paint it with to essentially keep any corrosion at bay for as long as I can.
I don't think I want to have to get it soda blasted then apply the appropriate resin or epoxy, I understand this is probably the best treatment not sure if I can justify the cost on my tinny.


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TheRealAndy
20-12-2016, 10:48 PM
Still undecided what to do here I have ripped my floor out there is some corrosion but most is ok as it's been painted before me, I am wondering do I pressure wash this then work out what to paint it with to essentially keep any corrosion at bay for as long as I can.
I don't think I want to have to get it soda blasted then apply the appropriate resin or epoxy, I understand this is probably the best treatment not sure if I can justify the cost on my tinny.


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Has the corrosion made its way though the hull?? If not, clean back the corrosion till its shiny aluminium and keep a very close eye on it.

Mark0
20-12-2016, 11:08 PM
Well much of the inside was painted so I don't know if I can get it all off the paint that is.
I dont have any holes.
How would I clean the corrosion off on the inside ?
I would probably like to clean up any bits where paint flaked off for example and put something on it or paint over the whole floor internally with something so it's protected and looks good.
On the under side of Hull I just have those few pitting marks as per pics on first page.
Tbh it's got me a bit stressed out as I am not experienced in this stuff and cant seem to find a common solution that's recommended.


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TheRealAndy
21-12-2016, 12:02 AM
Well much of the inside was painted so I don't know if I can get it all off the paint that is.
I dont have any holes.
How would I clean the corrosion off on the inside ?
I would probably like to clean up any bits where paint flaked off for example and put something on it or paint over the whole floor internally with something so it's protected and looks good.
On the under side of Hull I just have those few pitting marks as per pics on first page.
Tbh it's got me a bit stressed out as I am not experienced in this stuff and cant seem to find a common solution that's recommended.


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Clean it up with scotchbrite or wet and dry (or both). Dont repaint over it unless you are going to do it properly.

The problem with boats is that any paintjob is typically for show, not for protection. If painted it has to be done correctly. Even when painted correctly you still see corrosion. In the aircraft industry its not uncommon to see new aircraft painted properly show signs of corrosion, and when it happens the engineers will repair/repaint.

If in doubt, use google to search for aviation info. People in the aviation industry are a lot more proactive and concerned about corrosion for a very good reason!

Mark0
21-12-2016, 12:19 AM
Hi Andy thanks for the reply, would you agree pressure washing inside of Hull, then clean up where I can see corrosion with the scotchbright then essentially leave it and monitor ?
I would have thought a cover over the aluminium would have helped, eg paint of flowcoat even if not the greatest job.

Should I also scotchbright the bottom 5 pittings as well and just leave them ?

I think I will get stuck into it tomorrow hense questions and have it all done ready for Xmas break.

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Mark0
21-12-2016, 07:27 AM
Pics of inside floor it's a bit dirty as I am half way through cleaning, some corrosion spots no pitting on inside.

This is where I am going to pressure clean then I will rub back corrosion and either leave which looks crap or paint it.

The other pic is the shelf in my boat that meets the transom, I was planning to cut it and put an access port 277x 360 in it for access, I am worried what I will find but there is no access to this area and anything stray will have ended up there.

It's all a real bitch.

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