best way to mount Aluminium to steel underwater

[Jgbrown]

Hmm. What about using a Marelon thru-hull as a spacer?

You could use better lights, such as the Ocean-LED HD series, they have bronze bodies, and stick through enough that you can attach a bonding wire to the backside, this seems to be OK for FG boats, I don't know about steel though, if grouding bronze to the regular zinc would be sufficient.

*Note: We are a registered dealer/installer for Ocean-LED, but I think anything similarly well built should due the trick.

I do agree they are a bit silly, though could be neat for night diving/fishing I've sometimes thought.

[mitiempo]

To attach any other metal (aluminum or bronze) to the hull of a steel boat is asking for trouble. Except for the propeller and shaft keep it to steel only. A spacer wouldn't help much as the salt water connects the light housing and the hull.


The West Marine lights you linked to are NOT aluminum though - they are, as already mentioned, polycarbonate so there would not be any issues with those.

[Alex W]

These seem like a great way to add some underwater drag. Do you really want that? I'm not against needless underwater bling (I don't want it on my boat, but would never suggest that someone wouldn't want it on their's), but needless underwater bling that adds through hulls and drag seems like a pretty bad idea. It's also likely to hurt resale...

[xymotic]

Originally Posted by mitiempo

To attach any other metal (aluminum or bronze) to the hull of a steel boat is asking for trouble. Except for the propeller and shaft keep it to steel only. A spacer wouldn't help much as the salt water connects the light housing and the hull.


The West Marine lights you linked to are NOT aluminum though - they are, as already mentioned, polycarbonate so there would not be any issues with those.

I have one in my hand and it is most certainly milled billet aluminium.
However, it's also not "in" the hull, it's surface mounted. So I'm really only concerned about standing it off of the hull, the light comes with nylon spacer to keep the Stainless screw from contacting the Alum body.

[xymotic]

Originally Posted by Alex W

These seem like a great way to add some underwater drag. Do you really want that? I'm not against needless underwater bling (I don't want it on my boat, but would never suggest that someone wouldn't want it on their's), but needless underwater bling that adds through hulls and drag seems like a pretty bad idea. It's also likely to hurt resale...

At this point I'm unsure whether I will put them on the sides or just at the transom.

But my boat is a 40,000 pund monster with a 20" wide keel and a whole bunch of welded plate that was never faired. Not really sure drag is my top concern.

[xymotic]

Originally Posted by noelex77

There is no danger to the hull. The problem is the light is nice anode for the hull. If the aluminium light housing dissolves, which it will do sooner or later, you are left with a hole in hull underwater

Thanks, That is a concern indeed.

As for the actual hole for the wire, it can be pretty small, less 1/8" or so.

What would be the best way to seal it? Inject epoxy? Or am I over-thinking that as well and just use 5200?

[boatpoker]

noelx77 is correct, done improperly this could sink your boat.

"electrolysis" is not the issue. Electrolysis is the chemical change in a solution or electrolyte due to the passage of electric current.

The potential problem here is "galvanic" corrosion and mixing steel, aluminum and DC current under water could cost you big time if not done properly. I strongly advise you to consult an ABYC certified electrician before proceeding.

[xymotic]

I may rethink this and find an all plastic version instead. Seems safer.

But same question: If I drill & tap the hull, what's the best way to seal the thread and prevent galling? Something like permatex thread sealant, Tef Gel (water tight??) or 5200?

[mitiempo]

I would use 3M 4200 or Sika 291

[Maine Sail]

Xymotic,

PLEASE, please, please before you do anything below water to your metal hull buy and read Everett Collier's book

The Boatowner's Guide to Corrosion: Everett Collier: 9780071550192: Amazon.com: Books

The Boatowner's Guide to Corrosion: Everett Collier: 9780071550192: Amazon.com: Books