Painted Aluminium Rust

[matty_j]

Hi,
I'm just looking at buying a small runabout soon however the boats I've looked at have only been about 4-5 years old with severe rust around screw and pop rivet holes where accessories have been screwed into the hull. The paint has been bubbling around the area and spread quite fast in some areas.

From on what I understand it is because they have used stainless rivets or bolts onto an aluminium hull.

How do you prevent this from happening? Silicone? Sikaflex?

I would have have thought that this would have been done properly in the factory? Or is it the dealers that add the extras and don't care?

I'd be pretty shitty if my $20k plus boat started doing it after a few years. You would nearly have to pull all the screws out and check and do it properly yourself?

Thanks

[perko]

Must use duralac or tefgel under the screws to isolate the different metals.

[myusernam]

But it still happens. I say buy something cheap with it already there and then u won't care.

[wags on the water]

But it still happens. I say buy something cheap with it already there and then u won't care.

Any advice from an informed gentleman like yourself if you shell out $40+k on a brand new boat and corrosion is already there? The dealers/manufacturers couldn't give a flying F and it still happens.

[tunaticer]

You buy alloy, you buy the negatives that come with it too.
Same deal with glass and plastic, each shines in it's own way.

Duralac and Tefgel are the two better products out there to reduce this happening, sorts of a time delay thing because eventually it will occur.

Also worth considering is paint encapsulates the corrosion and forces it spread with the blisters that form. It does not happen anywhere near as badly on unpainted alloy becuase the elements break down the strenght of the corrosion acids and alkalis.

[scottar]

This sort of corrosion (Galvanic) in alloy boats is basically impossible to stop. It can be minimised but the moment you introduce any sort of fastener that is comprised of metals higher in the periodic table it will happen to an extent. It makes it's prescence felt to a greater extent on painted boats but will effect any alloy hull. To minimise the problem, welding fixtures on instead of using fasteners is the ultimate solution but is simply not practicle or cost effective in a lot of situations. Products such as duralac and Tef-gel will slow the process down but wont stop it. Using plastic washers behind any stainless is also helpful. The other thing that helps is to prevent moisture getting between whatever you are attaching and the ally. On a tinnie I once owned I fitted plastic rail mounted rod holders. When I removed them, there was severe corrosion behind the plastic clamping arrangement simply due to the fact the salt had got in there and sat. Using a sealant to prevent the moisture getting there in the first place is a big step in the right direction. Aluminium pop rivets are a useful solution where practicle but still require using other measures to further slow the process(Duralac/Tef-gel). Personally I use a combination of all these methods to try to minimise the issue.

[Aussie123]

There is 2 problems there in your description.
Firstly there is Galvanic corrosion that the other guys mentioned but the rust stains is from 304 grade screws, bolts or fittings.

[tjotter]

re 304 grade stainless steel:

I was buying screws from Masters & they had 304's & 314's,
& a placard that from memory said 314 was more rust resistant than 304.
I think 304 is a bit stronger than 314.

[not talking about Galvanic corrosion here].

[wags on the water]

Stainless steel chart. 304 is cheaper than 316 - hence the reason why it is in most shops.

103586

[matty_j]

It's just very sad and disappointing that these boats have succumb to this when it's such an easy thing for dealers to do. This might sound like a silly question, but how do you know it's been applied? other than the corrosion showing? Are the screws oily or greasy?

I'm just upgrading from a small tinnie and don't want to buy somebody else's problems.
Thanks
Matt

[scottar]

Duralac is easy to see. It is yellow in colour and is the only product that I know of that spreads itself around almost worse than sikaflex. Tef-gel is a lot harder to see as it is white/opaque. You can almost guarantee that a production based vessel will not have had it used unless the accessories have been fitted aftermarket or by the owner. Custom build stuff will depend on the builder. This sort of thing is pretty standard across the industry though right through to some of the well respected players. The big issue with this sort of stuff and silicone sealants under fittings from a manufacturers point is purely the man hours it takes to clean up properly when something has been properly sealed. As with everything today, products are built to a price no matter how much they cost. Not saying it is right but it is what it is.

[Shark Poker]

Sorry fellas but Scottar is entirely correct.
Matty J you obviously haven't spent any time in the fit-out section of a boat factory. Which is commonly where their most inexperienced and zero skilled staff start off.

And its nothing to do with 304 vs 316 stainless, that's petty detail and not the cause of this issue. Anywhere that (untreated) screws or sst canopy fittings touch the paint there will be bubbling within weeks. If you don't believe me just go and have a look at more late model alum boats and you will see.

So yes, pull out all the screws and re apply them. Replace with alum rivets if possible. I use lanolin grease (lanotec) with great success. Lots of nylon washers as well.

[matty_j]

Thanks. I'm sick of looking at great boats with corrosion. I've settled on a new Stacer 429 Seaway. Looks like I'm going to pull it apart and coat the screws and pop rivets with tefgel or lanotec. Any other tips or tricks to prevent corrosion on boat and or trailer? Lanotec grease on wheel nuts etc? Should I apply anything under the floor?

[scottar]

Best way to minimise it is get one that isn't painted. Sure it's not as pretty but they dull off and pretty much look almost the same 10 years later. If you want the pretty one, pull off every fixture that you can, seal under it to stop the water getting in as best possible and reapply fixings with Tef-gel (If you are brave use Duralac but be warned - the sh*t gets everywhere). Anywhere you have a stainless washer against the alloy, put a nylon washer under it and use sealant to keep the moisture out (unless it is a high load area eg: motor bolts. In this case no nylon as it will compress) . Have fun, it will most likely be a messy, time consuming, not so much fun job. Make sure you have rags in abundance and the correct cleaners for the sealants you use. Check with some of the urethane type sealants - if you clean them off with alcohol(metho) it can leave the surface tacky. Also bear in mind that some of the sealants - sika in particular, don't stay white long in the UV. They yellow off and look pretty average. For your floor, especially if carpeted, use Tef-gel. If you get Duralac in the carpet it will leave a stain.

[DM]

Tefgel and aluminium pop rivits are the closest thing to a solution. We have repaired boat not even 6mths old. But alli rivits are the go!

[rodneyk]

Alloy rivets with Alloy stems nylon washers under every fitting plastic tube or hose around engine bolts large lexcen washer under engine bolt washers Starboard between engine and hull that's about all you can do biggest problem is isolating engine from hull . Definitly no stainless rod holders even the ones with gaskets . Dissimilar metals create Galvanic corrosion Isolation is the only ANSWER