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Help - Boat Corrosion at Drain Plug
Posted on 7/20/23 at 9:43 pm
Posted on 7/20/23 at 9:43 pm
My drain plug fixture broke almost in half. Most of that white in the pic is prob 3M 5200 or the like. It is an aluminum boat. Do I need a sacrificial anode other than what is on my outboard?
This post was edited on 7/20/23 at 9:48 pm
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Posted on 7/20/23 at 11:50 pm to CajunSportsman
That looks to be galvanic corrosion (dissimilar metals touching each other). Get one of those orange plastic drain plugs. They are supposedly for emergency use only but I have never had a problem with them. Just replace often.
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Posted on 7/21/23 at 4:36 am to CajunSportsman
Yes, looks like galvanic corrosion from dissimilar metals.
Remove, clean up, and have someone weld in an NPT collar, use an aluminum plug.
If that will take too long, remove and put a stainless steel version of the same type of plug.
Do you have bottom paint on this boat?
Remove, clean up, and have someone weld in an NPT collar, use an aluminum plug.
If that will take too long, remove and put a stainless steel version of the same type of plug.
Do you have bottom paint on this boat?
Posted on 7/21/23 at 5:27 am to ultralite
that type of plug assembly is what I see on fiberglass boats...
Posted on 7/21/23 at 8:04 am to CajunSportsman
Definitely galvanic corrosion. It’s a little concerning that the plug is corroded and broken though. I would expect the hull to corrode to protect the plug so your plug should be almost perfect. Replace with similar metal.
Magnesium Hull anodes wouldn’t hurt either.
Magnesium Hull anodes wouldn’t hurt either.
This post was edited on 7/21/23 at 8:12 am
Posted on 7/21/23 at 9:01 am to skidry
quote:
Definitely galvanic corrosion. It’s a little concerning that the plug is corroded and broken though. I would expect the hull to corrode to protect the plug so your plug should be almost perfect.
Yeah, but what are those screws made of? Brass will act as an anode to protect some stainless steel alloys and given the amount of adhesive/sealant between the brass fitting and aluminum hull, there might not be a good connection between the two, unlike with the screws and fitting.
Posted on 7/21/23 at 9:41 am to CajunSportsman
my aluminum boat had a similar threaded drain plug machine screw like that. if its completely rotted you'll need to drill it out and re-thread the hole for a larger plug. honestly what i would do is what i did...weld up that hole and put in a bilge pump
Posted on 9/5/23 at 10:26 pm to ultralite
Sorry for the late reply, yes, it is a Cajun Special and factory painted hull. Seems to be a brass fixture with a brass plug so I am not understanding the dissimilar metal posts(?)
Posted on 9/5/23 at 10:56 pm to CajunSportsman
quote:
Seems to be a brass fixture with a brass plug so I am not understanding the dissimilar metal posts(?)
But it's not. The sealing ring is one thing, the plug ring is another.
Drill out the rivets or screws. Replace them with quality components and seal with marine epoxy.
I suspect the screws or rivets may also be part of the problem in your case.
Posted on 9/6/23 at 7:31 am to CajunSportsman
It looks like a brass plug, brass plug fixture, stainless screw, and aluminum boat. The issue is probably with the stainless and aluminum.
I’m assuming the boat is stored on a lift or in the water? As in you aren’t removing the plug often?
I’m not sure of the best thing to do with boats stores with the plug in with this situation I’d assume the manufacturer will know? That looks like someone has changed around the factory plug to some degree.
I’m assuming the boat is stored on a lift or in the water? As in you aren’t removing the plug often?
I’m not sure of the best thing to do with boats stores with the plug in with this situation I’d assume the manufacturer will know? That looks like someone has changed around the factory plug to some degree.
Posted on 9/6/23 at 8:11 am to CajunSportsman
Galvanic corrosion, remove, clean & have a piece of Al tubing welded for garboard drain. Using three dissimilar metals wasn’t a smart idea.
Posted on 9/7/23 at 12:08 pm to CajunSportsman
Do you have a battery disconnect switch? You might have stray current running through the hull. You can check with a multi-meter. Put positive on an unpainted part of the boat and the negative on the negative battery post and see if you have any voltage. If so, get a disconnect switch.
Posted on 9/8/23 at 11:14 am to CajunSportsman
As long as you have dissimilar metals, you’ll have galvanic corrosion. I’d go with a traditional/old school expandable rubber plug (or else the threaded plug shown previously). Other option is to keep all your dissimilar metals painted/coated, so the water/electrolyte can’t enable the corrosion.
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Posted on 9/8/23 at 11:42 am to knight4
I’ve used a rubber plug for years without leaks.
I change rubber plugs every five years or so and I keep two spares on the boat.
They are cheap so when I do change the plugs I change the spares as well so 2 out of the 3 plugs get thrown away without ever being used.
I change rubber plugs every five years or so and I keep two spares on the boat.
They are cheap so when I do change the plugs I change the spares as well so 2 out of the 3 plugs get thrown away without ever being used.
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