best way to mount Aluminium to steel underwater - SailNet Community

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Old 01-05-2013
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best way to mount Aluminium to steel underwater

I'm interested in using these underwater lights:
WEST MARINE Platinum Series Bay Blaze Underwater LED Lights at West Marine

but I'm unsure how to best go about it. The lights themselves come with a nylon spacer to offset the SS screw from the aluminium body.

But the body itself would rest against the hull. (there will be paint and barrier coat but still) there obviously needs to be a hole for the wire, but I'm also not super hot on drilling/tapping the hull and mounting the screws in.

So I'm wondering what you guys think. weld a SS nut onto the hull and then attach the light to that a little offset from hull? A plastic backing material?
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Old 01-05-2013
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Re: best way to mount Aluminium to steel underwater

Why do you need an underwater light?
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Re: best way to mount Aluminium to steel underwater

Quote:
Originally Posted by treilley View Post
Why do you need an underwater light?
Need?? What means this word?
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Old 01-05-2013
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Re: best way to mount Aluminium to steel underwater

xymotic:

I think welding a nut onto your hull is overthinking it a bit.

I'd probably be inclined to treat the light as any other below-the-waterline through hull. Pick your location, drill your main and bolt holes, bed the puppy with a liberal amount good sealant, and through bolt it. Since your hull is steel, lock washers and hex nuts should be sufficient.
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Old 01-06-2013
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Re: best way to mount Aluminium to steel underwater

IMHO if the body of this light is aluminium you cannot use it on a steel hull.
There will be electrical contact between the aluminium and steel via the fastenings.
This will result in rapid galvanic corrosion of the aluminium.

Please don't do it.
I honestly think your boat will sink in about 6 months if you do.
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Old 01-06-2013
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Re: best way to mount Aluminium to steel underwater

Xymo - if you are talking about those pimpin' underwater lights that are being used on big power cruisers and sport fishers I recommend you screw them directly to the hull with no gasket or spacer between the metals - this will ensure a good ground for the electricals. You also don't need to do anything special with the wire connections - they are UNDERWATER lights after all so that's all been taken care of by the manufacturer.
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Re: best way to mount Aluminium to steel underwater

You may need some bedding to prevent electrolysis, but these are holes drilled through your hull with no seacock to shut down a failure. They should be bed in the nastiest, most permanent goop you can possibly conjure up.

The prior owner of our boat had them installed. They make me nervous and boy do they suck up some power when they are on!! In any case, they are completely useless around here. Even in the relatively clear water of Cuttyhunk, I haven't been able to see anything. The grass bed is only 7 or 8 feet below the lights and its indistinguishable. Unless in truly crystal clear water of the Caribbean, they are a waste of money, IMO.

If you just want the "glow" around the boat at the dock, no other sailboat crew is going to speak to you.
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Re: best way to mount Aluminium to steel underwater

Quote:
Originally Posted by PorFin View Post
xymotic:

I think welding a nut onto your hull is overthinking it a bit.

I'd probably be inclined to treat the light as any other below-the-waterline through hull. Pick your location, drill your main and bolt holes, bed the puppy with a liberal amount good sealant, and through bolt it. Since your hull is steel, lock washers and hex nuts should be sufficient.
Thanks, I think I'm gonna 'just do it' like you said and not worry too much about it.

As for electrolysis, I'll just isolate it with some nylon spacers. But worse case it would be the $100 aluminum light that goes, not the hull (right!?) In any case, it'll be in a place where I can inspect the backside easily.

As for power/heat, these are LED and really quite nice little lights. I'm also planning on using some as spreader lights.

As for the pimpin light... can't help it! I am a redneck and grew up in a trailer park. I have about a billion projects for my boat and so where did I start? I bought some Blue LED speaker grills of course!

Yes, I realize how ridiculous that is.

I did do some actual work on it though:

before:
Code:
inline images seem to be broken, and there should not be a space and link in text inside a img or code tag... 

http://www.ontheboat.net/gallery3/var/resizes/Oceana/projects/Ports-and-hatches/Forward-Hatch/20120711-IMG_20120711_142940.jpg


after:

http://www.ontheboat.net/gallery3/var/resizes/Oceana/projects/Ports-and-hatches/Forward-Hatch/IMG_20121019_124319.jpg

http://www.ontheboat.net/gallery3/var/resizes/Oceana/projects/Ports-and-hatches/Forward-Hatch/IMG_4980.jpg

Last edited by xymotic; 01-06-2013 at 06:15 PM.
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Old 01-06-2013
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Re: best way to mount Aluminium to steel underwater

Quote:
Originally Posted by xymotic View Post
I'm interested in using these underwater lights:
WEST MARINE Platinum Series Bay Blaze Underwater LED Lights at West Marine

but I'm unsure how to best go about it. The lights themselves come with a nylon spacer to offset the SS screw from the aluminium body.

But the body itself would rest against the hull. (there will be paint and barrier coat but still) there obviously needs to be a hole for the wire, but I'm also not super hot on drilling/tapping the hull and mounting the screws in.

So I'm wondering what you guys think. weld a SS nut onto the hull and then attach the light to that a little offset from hull? A plastic backing material?
what aluminun it says it is a polycarbonate housing and glass lens. looks to me like they are the cheap type of underwater light made for trailer boats
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Re: best way to mount Aluminium to steel underwater

Quote:
Originally Posted by xymotic View Post
As for electrolysis, I'll just isolate it with some nylon spacers. But worse case it would be the $100 aluminum light that goes, not the hull (right!?) In any case, it'll be in a place where I can inspect the backside easily.
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
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