Interior welding while in water?

I'm installing a watermaker in an aluminum sailboat, recently launched. I'd like to mount the HP pump/motor in the engine compartment. The floor in the area is inside of the hull plating. Ideally I'd like a small platform just a couple of inches off the floor that I could bolt the motor to. This platform will need to sit on a couple of sleepers attached on the floor. I'd prefer these be welded to the floor. The boat is currently in the water.

I'm not a welder, so would hire this out. My question is, can a bit of interior welding like this, on the inside of a hull, be done while the boat is in the water, or must it be hauled out to get a decent weld?
Thanks.

 

I don't know.
Have you asked your welder?

 

Not yet. I thought perhaps there might be some with more knowledge of it than you or I who could weigh in with either an "absolutely not.....a whacky idea", or a "no worries....done all the time".

 

Fair enough.
However, we don't have much info.
No pictures, no sketch, etc.
I would find a marine welder that knows.
And then get two more estimates.

 

The devil is in the details.
Welding Al is a bit tricky.
Floating adds a bit more trickyness.
Welding in a confined space is a lot more tricky.
Explosive fumes in bilge is spectacular

Call your welder. Floating isn't a serious problem.

 

Happy to hear that being afloat (water on the opposite side of the plating from the weld) isn't in and of itself a deal breaker. I'll discuss the details with a welder, thanks

 

I’d be exploring adhesives for that job.
Might be an opportunity to isolate the water maker from the hull with a layer of nonconducting, vibration absorbing material.

 

How far apart are the transverse frames and the longitudinal shell plate stiffeners in your engine room?
Can you post a photo of your chosen location?
As Kapn D says, this is an ideal way of making sure that your water maker is insulated from the hull.
Would it be feasible to build a suitable bracket for supporting the water maker, and then mount it across two frames or stiffeners?
The bracket could be bolted or glued to the frames / stiffeners - preferably with an insulator strip in between.
If using bolts, make sure that the bolts are insulated from the aluminium structure.

 

Don't consider welding anything to the floor plating when it is in the water or you will more than likely blow a hole through the hull plating.
I am assuming that the plating is say less than 1/4 inch

As aluminum conducts heat extremely fast the water pressure on the outside of the hull will just blow through the weld pool

Fab the pieces, get to a hull sling, pull it up, weld them in and you are done. Dry the outside of the boat where the weld beads will be on the inside

 

SVBravo,

Have you consulted a competent marine welder yet?

If so, what did they say?

Please, let us know.

 

If the welding is above the waterline... then yes, it is ok.
If the welding is below the waterline - then no.

 

There you have it Bravo, two no's and a yes.
Now what are you going to do?
Hmmmm, I have an idea...

 

Hi. Barry is correct. Above the waterline, ok. Not above...you weld alu on AC. Blown out weld, dead welder.
I have a TIG onboard and when on AC ...I’m very careful about any water source, diesel fumes, rain, fire...always have my wife at the welder to shut it off because I’m under the hood concentrating. Even near the waterline, a wake can kill you.
Liquid aluminum. Amps. A fire can smolder out of sight long after you finish. Lightning. You are holding AC in your hand.
I’m an old, manatee because I’m a careful manatee.
Mark