Advice for Corrosion

[kmorin]

BCTony,

Reacting to your post- WHATTTT?

I referred the matter to North River who said to me that it looked to be purely saltwater corrosion.

How come the entire boat isn't reacting? What is "purely saltwater corrosion"? Of course I've only been involved with welded aluminum since the 1970's so my experience may be too limited to compare with whoever tried to sell that steaming pile? I've never heard of, seen or experienced saltwater corrosion of marine alloy aluminum - so my malarkey meter just pegged on that phrase.

regarding soap, all that matters is the MSDS, and maybe some patch testing to see how it behaves? The photos of the soap bottle show the main cleaner is ammonium chloride and I'm not aware of that being particularly corrosive to aluminum? But I'm not well informed about the compatibility- I'd still contact the mfg and do a spot test.

As regard the images - although I'd say it was somewhat hard to tell for sure - I see initial corrosion in all of them. Maybe these coloration spots are just water stains of some kind? IT doesn't look like the builder removed the mill scale? and that porous film will promote white flower corrosion cells because it hold ambient moisture to the metal allowing crevice sites to form. This fact is denied by countless major builders- who use phrases like - "normal corrosion" but that is 100% absent from acid etched boats.

There are countless posts here showing many boats with the mill scale intact- and their corrosion while sitting on a trailer-just from the ambient air moisture!

It could be that the only wash-down this fish-box received before its extended trip south was from salt-water.

so did the entire hull, as it ran in salt water to get South- why hasn't that metal act like the fish box?

When I visited North River in August the fuel tank and deck fuel tank pad had been reinstalled so unfortunately I could not see the bilge.

You can get a rental or for a hundred bucks; buy a video bore scope- that will allow you to inspect any place you can feed the camera into.
https://www.amazon.com/video-borescope/ ... 0borescope

I'm kind of stumped by the surface being covered uniformly by bilge water and still pitting in sites something more commonly seen where there is a drying/wetting cycle that concentrates the out of range ph material. However, I've seen that when the water was carrying metal particles or in solution.

Galvanic corrosion is usually a site related event- for example a SS bolt in a hole drilled in the aluminum. If the SS is not passivated and coated with some dielectric paste or thread goop- the corrosion is usually at the nearest points of contact between the metals. However, I have seen examples of extreme pitting in wide areas of a bilge (the main hull area) where a wash down pump that was brass- not bronze- had created a bilge water that was corrosive- the corrosion was galvanic- different metals and wide spread because there were copper ions in the water. The pumps' impeller was not rubber but metal so the rate of transfer of metal particles into the water was apparently high enough to make that bilge copper filled?

So my remarks about galvanic corrosion are not confined to points of contact of different solid metals, there is also a good possibility of bilge water to have a galvanic action due to a metal salt in solution. The term salt here is not limited to sodium chloride salt. http://www.vopelius.com/products/metal-salts

Also a note in reply to the idea of a bilge anode. Anodic protection is based on a couple things- #1 the galvanic scale where any metal more noble (more inert) can be 'protected' by a less noble (relatively more reactive) #2 when there are electrons flowing- current- ie "stray current". Why or how is there any place for current to flow from the hull INTO the bilge water? How is it that bilge water could be a lower potential location for electrons? Why would the current (if there is some stray current) flow into the bilge water instead of off the hull into the water the boat is floating in?

Using a plating tank as an example- meaning to compare a plating tank and current flow model as a means to show corrosion in a bilge- I miss the part where the circuit is completed in the bilge? Plating tanks have two poles to their driving electrical circuit- I can't see them in a boat bilge?

Outside the hull, where the ocean/lake/river is an infinite lower potential that allows any current to dissipate- I can see an anode being able to 'give up' or 'sacrifice' molecules as the site of the current flowing off the hull into the water- but I'm lost finding that model applying to the bilge? Maybe you understand this anode in the bilge idea better than I do, and perhaps I've just not grasped the fundamental idea? But I can't see the bilge being a site where the metal of the boat flowing into the bilge water - and that seems required to make the anode idea applicable??

Not sure I'm much help but we're at least exploring this condition of your boat's fish hold with more than one set of experiences to help solve your problem.

Cheers,
Kevin Morin
Kenai, AK

[BCTony]

Kevin - thank you for your comments which are very much appreciated. I did say I have doubts but I am not confident enough with all matters boat let alone corrosion to argue the toss with boat builders some distance from me. To try and get some help to separate the BS from the useful is why I detailed the whole timeline.

As to wash-down or its lack off, the boat was standing in the NR yard for some weeks waiting its turn. Whether after it left me it did or did not rain at any time I do not know, but if it did everything on the boat would have benefited from a downpour including bilge with the possible exception of the fish boxes which would receive the least rain. But I agree, who in their right mind would buy an aluminium boat if at the slightest oversite with saltwater will result in corrosion?

Since I have had the boats electronic readings checked in connection with the Electro Guard monitor I am inclined to think it is not galvanic corrosion. However, I am having some electronics upgraded shortly by qualified installers and I shall ask that everything is checked. In addition I have commissioned an electrical audit at the slip.

I cannot think of anything that has been put into the fish-box or could have leached in there. Mostly it is kept empty, but, there are times in rainy periods when I have noticed that the bottom of the box does just seem to be covered in a thin film of water.

As to the bilge anode this was suggested to me by NR. I do recall one time at a boat show looking at a Silver Streak boat and noting that it had a small anode in bilge which if remember correctly was also attached to the bilge pump or its fixing. At the time it was suggested by NR, I thought ‘if it is such a good idea why is it not always done?’ Apart from my two bilge pumps in the bilge I do have two stainless steel thru-hull transducers which although isolated from the hull, I suppose could create current if there was sufficient water in the bilge. Plus any other metals that could find its way into the bilge by accident; electrical cable clippings or coins for example. It was put to me that the anode would only be active if there was water in the bilge and something else to create current - and that there was not really any downside.

Certainly the implication to me from NR is that the corrosion is due to lack of care or maintenance on my part and at the moment I am not in any position to argue.

You say that you see initial corrosion in all the photographs. I think mill-scale corrosion is present everywhere that has contacted water – but, certainly nothing like the booring/pitting type of corrosion seen in the fish-box and I think, nothing to worry about too much at the moment. Hopefully I am not in denial! Mill-scale was not removed by the builder and this is something I have learnt about since purchase. I would like to have the outside of the boat acid washed/etched and at least the central part of the bilge but I have not found anyone willing to do the work. It is not something I feel confident or competent to do myself.

As to video bore scope - funnily enough just in the last week I ordered a simple model to attach to my smartphone with a three metre lead for the very purpose of looking in the bilge. This will be a start – although somebody recently did say to me to use and enjoy the boat and not go looking for trouble!

At the moment the fish-box at issue is sanded and looking good. It is dry and at the moment no sign of the puffing-up has returned. It is too cold currently to apply acid or anything else. My intention is acid-etch and then epoxy and see what happens.

I am very grateful for your information and advice.

[jj225]

BC Tony,

I was putting in a buss bar over the weekend and looked at my corner rod holders while on my back. They drain into the bilge but really not much water comes down them since they are covered most of the time. However, water does indeed come down the tube. Anyways, I could clearly see the where salt had dried on the alum. I took some soap and water and wiped the area down. There was no pitting. No nothing really except for oxidation which you would expect. Now this boat is 2 1/2 years old. I know I've never wiped it down up where I did. You figure it's had salt on it for at least 2 years. So bottom line it seems like a bunch of bullshit what NR is telling you about pitting in such a short time. As for my boat I'm going to put some hoses on the rod holders so the water will go directly into the bottom of the bilge. Although 2" hose is not easy to find believe it or not.

[BCTony]

I have been racking my brains and I think I may have figured out what may be the cause of my corrosion. There is nothing leaching into the fish-box and nothing has been placed in the fish-box at any time that should be an issue. But through the fog of memory a light has been beginning to glow.

My boat was bought new almost four years ago and when bottom paint was arranged by the dealer. About two years ago now the boat was in for engine service and I asked the shop to inspect and renew the boat anodes. When I collected the boat the technician advised me that there had been bottom paint underneath the anodes and that the only real connection was the small gauge fixing bolts and that they had cleared the bottom paint and renewed the anodes. At that time I had not noticed anything amiss but now wonder if corrosion could have got started and taken its time to become obvious and noticed.

My boat is moored year-round and usually I leave the outlet valves of the fish box open so there would have been direct water access to the bare aluminium of the fish-box. The tennis-ball-type scupper normally prevent the fish-box flooding when the boat is at rest but not always and whatever water is in the fish-box is flushed out when the boat is cruising. Also when there is water on deck whether from rain or anywhere else some water always ends in the fish-boxes which never remain dry for long. It is also fair to say that I only really noticed the pitting when the fish-box valves were closed (because their scuppers were not operating correctly) and sections of the fish-box were able to dry end of last summer.

It seems to me that anode protection would have been severely compromised and that while the hull may have been protected by barrier paint the bare aluminium fish-box(es) would have been particularly vulnerable. That only one of the fish-boxes appears to have been affected could perhaps be explained by that it is on the side of the boat that is climbed aboard and so is rocked that side and water rises up into the fish-box.

There is certainly nothing amiss with my protection now. Last fall Chaps renewed all bottom paint and anti-foul as well installing his excellent stand-off anode system which exposes both sides of an anode connected to the hull through 3/8th stainless bolts. And I have an ElectroGuard monitor fitted.

What I have done is that I have acid-washed the fish-box twice which smoothed out my sanding and most of the pits. The half a dozen pits up the side walls which were not opened as effectively as those on the bottom I have cleaned with a counter-sink drill. I have then applied six coats of epoxy barrier to the affected area. If sign of corrosion returns I shall have the fish-box bottom cut out and replaced.

Meanwhile I shall continue surveillance for corrosion everywhere else on the boat.

‘You can’t buy experience, but, it always costs you dear’

[BCTony]

I thought I would post some pictures of how I have treated the fish-box. Acid (Muriatic acid diluted 50%) washing was a first and an education! Despite the low temperatures and rain I managed to get the epoxy to harden pretty quickly by jamming a fan heater under the lid with a tarpoulin over (air space for heater created with a bucket). It worked - just hope I have killed the corossion and it does not re-appear or appear elsewhere.

[Chaps]

Nice job there Tony!

[BCTony]

Having an electrical re-fit and some electronics upgrade has enabled me to have look at the bilge in area normally inaccessible under the battery floor. Well ‘look’ by photographs the electrician took and sent to me, one of which is a bit blurred. From what I could see - although I did ask him to check by eye and confirm a couple of points of concern – there is nothing to be too worried about. I shall hire a bore scope to inspect the areas further forward under the fuel tank and fish-tank but I think that the bilge is OK.

Now that I have managed to stop all leaks of water into the bilge – a situation I hope to be able to maintain – I shall be attempting to ‘clean-up’ the bilge. During the winter I did one rinse with vinegar followed by a rinse of ‘baking soda water’ and then copiously flushed with fresh water. I propose to do it again in a few weeks in warm weather and shall leave the vinegar in for a day or so.

Returning to the fish tank corrosion I have not been able to nail-down a reason for the corrosion. It is not as a result of under-anode protection or stray wire or stray electricity from elsewhere I have had all that tested. There is nothing on board my boat leaching into the fish box. It has been suggested that perhaps when my boat has been in a yard or even at the marina that perhaps airborne grind from something being ground somewhere perhaps bronze may have got onto the surface of the fish box which being liable to be wet and/or humid on a regular basis allowed corrosion to get started.

At the moment my treatment with acid and barrier paint seems to be holding up. Whatever it has made me think that with bare aluminium fish boxes of the type I have with a boat in permanent moorage like mine that the fitting of anodes and/or barrier paint is not a bad idea.

Can't seem to post photos - files too large.