Weld on or bolt on to an aluminum hull?

[tmoandj]

I'm going to attach my wind vane self steering soon but still haven't decided whether to bolt it on or weld it on. It's an aluminum hull. I'm not too enthused about putting holes in my hull to bolt it on but welding it will require removing insulation and hauling the boat and probably getting a pro in to weld too. Not sure which way to go. Anyone have experience in this type of thing?
Thanks

[Panope]

I am a huge proponent of welding EVERYTHING to a metal boat. I have done a monumental modification/refit of an older aluminum boat featuring countless items being welded the to outside of the hull and deck.

Removing interior foam is not necessary in many instances as the foam lacks the oxygen to support combustion. A firewatch person is essential, however.

I would recommend welding short tangs to the boat, then bolting the windvane to them. Best to leave the tangs bare metal in the vicinity of the bolts to minimize paint bubbling.

Steve

[Sos]

Just bear in mind that aluminium welds are not as strong as the parent metal unlike with steel welds. Also has to be done well to prevent other problems such as cracking.
Bolted joints would be be better from a structural point of view but not from
eliminating leaks of course.
The lugs are a good idea but I would over spec them and the welds.

[JPA Cate]

Weld on strong lugs, but keep the windvane removable. There will be a time when you want to take it off for repair, or renovation, and replace. We sure did.

Ann

[blueazimuth]

Welding or using mechanical fastenings depends on the job.

Welding would have ruined my paint job, and even if the boat was not painted, I would certainly have used a competent professional welder, with the correct welding equipment - not always easy to find. Aluminium welding requires much more technical expertise than welding steel, and not all welders have that expertise. I suspect that many welders would be reluctant to come out for such a small job - just 4 mounting tabs - and the boat would have to be hauled.

I bolted on my wind vane">Aries wind vane using 3/4" champhered teak backing pads that were 2" larger than the Aries pads. I used 5/16" partial thread SS bolts, penny washers and lock nuts. I caulked between Aries pad and hull and again between hull and backing plate - absolutely no water leaks. It was not necessary to haul the boat. No muss, no fuss.

[tmoandj]

Hi , just wondering: what is the advantage to using the teak backing plates? Is it just for load distribution? I've already made some very strong "tabs" (I'm a moderately competent aluminum welder) that have a fairly large base. Maybe 3"*5" if I remember correctly. Also, what sort of caulk did you use?
I like the idea that seems to be common here that permanently mounted tabs should be coupled with removable gear. I wonder how strong the connection between the two needs to be? Can I just run a bolt through the supports and hope that that doesn't tear the metal eventually?

[Scorpius]

Personally I would ALWAYS weld. The suggested heavy duty tabs on heavy duty backing plates sounds excellent. Thru bolting in aluminum is always risky as any "working" causes the bolts to chew up the aluminum causing more working, leaks, etc.

If you are even a moderately competent aluminum welder, I would think you would know this stuff.

[Kita]

As a welder / mechanic I can't help but wonder why everyone seems to think the boat needs to be hauled to do some aluminum welding. They do have mobile welders that are quite capable at welding aluminum. The only reason I see to have the boat pulled out of the water is if you were going to do something below the waterline. Of course you will have to talk to your welders because a lot of folks don't have that mobile equipment.I know I do.and as far as the aluminum weld not being a strong as the parent material that all depends on what rod they are using. There are different types of aluminum TIG rods,just like steel..but you do need a real aluminum welder both the person and the Machine but they are definitely out there

[Panope]

It really does not matter if the welds are half as strong as the parent metal because it is simple to make the tang/lug twice as long/thick to compensate.

Steve

[Cheechako]

Originally Posted by Panope

It really does not matter if the welds are half as strong as the parent metal because it is simple to make the tang/lug twice as long/thick to compensate.

Steve

Yes, entire aluminum boats are welded.
OP: if you can weld it's better. A lot of seawater action back there to cause issues with Stainless and Aluminum mix. You can devise a scheme with isolating plastic flanged bushings and washers though I suppose if bolting is much easier.

[JeanneP]

We had some SS bolts on our aluminum mast, and galvanic action corroded the mast. It wasn't the hardest fix 'cause it was caught in time. However, I would worry about SS bolts into an aluminum hull for a wind vane.

[Cheechako]

Originally Posted by JeanneP

We had some SS bolts on our aluminum mast, and galvanic action corroded the mast. It wasn't the hardest fix 'cause it was caught in time. However, I would worry about SS bolts into an aluminum hull for a wind vane.

Yes, it can happen very fast. Within a year of a premium mast rebuild and refinish, I had lots of corrosion starting on the bottom 6 ft of the mast above deck. If I did that again I would make it unfinished below the spreaders.

[leftbrainstuff]

Originally Posted by Panope

I am a huge proponent of welding EVERYTHING to a metal boat. I have done a monumental modification/refit of an older aluminum boat featuring countless items being welded the to outside of the hull and deck.

Removing interior foam is not necessary in many instances as the foam lacks the oxygen to support combustion. A firewatch person is essential, however.

I would recommend welding short tangs to the boat, then bolting the windvane to them. Best to leave the tangs bare metal in the vicinity of the bolts to minimize paint bubbling.

Steve

+1

Bolted elements on an alum boat are a pain because you need to use dissimilar metal fasteners. You need to isolate all interfaces either through gaskets or a thin film.

You are going to have to bolt on your vane somewhere. You might bolt on alum pads that you can weld on at next haulout.

Minimize the number and complexity of dissimilar metal interfaces. Ensure those interfaces can be unspected and maintained.

If those interfaces are external then you get to inspect them frequently just by being on the boat.

Ideally your attachments should be to bedding plates rather than directly to the hull or deck. Then you can have a simple flange gasket and lubricated bolts to deal with the dissimilar metal interfaces.

When you weld alum you will anneal the base temper. Some will recover and some will not. This is not an issue with your hull or deck but a little knowledge here will help you understand the corrosion potential.

[Cheechako]

Annealing aluminum will bring it back to 0 temper, dead soft, less strength than the filler area of the weld likely. right?
Annealed 6061 (6061-O temper) has maximum tensile strength no more than 120 MPa (18,000 psi), and maximum yield strength no more than 55 MPa (8,000 psi).

[foufou]

Don't forget one other option which is aluminum bolts. The dissimilar metal problem goes away.I have used these in the past but do not remember the source. Likely aircraft industry. F