welding an aluminum spar

[um saudade]

The weakness has little to do with the weld and much to do with the design. With no gussets on the tang it is an incredibly weak tee joint. One thick piece teed into very thin metal. Piss poor engineering but it worked long enough for the warranty to expire. Once it started to flex, it breaks. Re-welding will not fix this as it was weak in the beginning and you will only make it softer and easier to flex, thus break again.

So it was not bad mig procedures and tig will not solve the problem. Neither will epoxy or pop rivets. A sleeve on the inside may help but is not needed.

To fix it right, start over and do it all on the outside. Grind the tang off cleanly, make a mast profile contour and take it to a good shop and have them match it in 10 gage aluminum. Go at least 6 inches up and down from the tang, so 12 inches minimum length if you can go that far. Make a new tang and weld tang to patch plate with backing to control heat. Gusset the tang. Drill a couple of small holes in the new plate directly above and below where the tang is welded to the plate. Prep the mast and clamp the assembly to the mast. Weld in place. Now weld the holes shut. I would weld with tig or mig, tig is prettier but weld in small segments and the heat from the mig is not that much an issue. Plus there are not that many portable tig welders and tig does not like and wind at all while mig will tolerate a little breeze. A little 110 volt mig in good hands will do the welding on the mast just fine and those are easy to find. Now to find a welding machine that happens to belong to someone who really knows what he is doing is a little trickier. Don’t let the guy down the dock a few slips save you some money, hire a pro to do the welding. All welding will weaken the aluminum but what you have now is big enough and durable enough that it won’t really matter.

Be very careful welding on the mast, consider all the stuff that’s packed on the inside. Makes a real mess when that thermoplastic wire insulation starts to burn and everything fuses together!

Then go sail the boat with confidence, that’s really the end game is it not?

[Cherod]

Or you could just grind it back and weld it up , properly this time , and it will probably last you another 15 yrs , job done.

[UNCIVILIZED]

I'm just thinking aloud here, & some of the below applies to my posts as well. So it's naught personal.

Originally Posted by um saudade

The weakness has little to do with the weld and much to do with the design. With no gussets on the tang it is an incredibly weak tee joint. One thick piece teed into very thin metal. Piss poor engineering but it worked long enough for the warranty to expire. Once it started to flex, it breaks. Re-welding will not fix this as it was weak in the beginning and you will only make it softer and easier to flex, thus break again.

So it was not bad mig procedures and tig will not solve the problem. Neither will epoxy or pop rivets. A sleeve on the inside may help but is not needed.

To fix it right, start over and do it all on the outside. Grind the tang off cleanly, make a mast profile contour and take it to a good shop and have them match it in 10 gage aluminum. Go at least 6 inches up and down from the tang, so 12 inches minimum length if you can go that far. Make a new tang and weld tang to patch plate with backing to control heat. Gusset the tang.
Please further explain/describe what you mean by gusset, with pics if at all possible. And a sketch of the entire assembly you're describing would be even better. Especially for those not well versed in spar design & construction.

Drill a couple of small holes in the new plate directly above and below where the tang is welded to the plate. Prep the mast and clamp the assembly to the mast. Weld in place.
Weld in place how? Around the perimeter of the new assembly, & if so, why? Won't this create an even larger weak spot due to it being an HAZ?

Now weld the holes shut.
What purpose do the holes serve if you're welding the whole assembly in place? Kind of a belt & suspenders approach? And do you really see welding as being superior to mechanically fastening things. Especially given that you have to deal with the heat affecting; mast coatings, wiring, internaal running rigging, internal hydraulics --> CAUTION.
Extreme Fire Hazard due to pressurized flammable liquids.

I would weld with tig or mig, tig is prettier but weld in small segments and the heat from the mig is not that much an issue. Plus there are not that many portable tig welders and tig does not like and wind at all while mig will tolerate a little breeze. A little 110 volt mig in good hands will do the welding on the mast just fine and those are easy to find. Now to find a welding machine that happens to belong to someone who really knows what he is doing is a little trickier. Don’t let the guy down the dock a few slips save you some money, hire a pro to do the welding. All welding will weaken the aluminum but what you have now is big enough and durable enough that it won’t really matter.

Be very careful welding on the mast, consider all the stuff that’s packed on the inside. Makes a real mess when that thermoplastic wire insulation starts to burn and everything fuses together!
This is a KEY tip, & applies to my cautionary note above.

Then go sail the boat with confidence, that’s really the end game is it not?

[estarzinger]

I had a welded tang like that. Fought it for several years, tried pretty much everything discussed above to fix it, still had cracks after ocean passages. The final solution which worked in the end was grind it off, internal sleeve, fabricated bolt on stainless curved plate/tang.

[a64pilot]

To understand the welded holes, look up rosette weld on Google.
It's very common to splice the same size tubes together, slide a tube inside another for reinforcement etc.

However I'd likely rivet on a fish plate myself as opposed to welding.
In reality I'd hire a rigger and let them do the repair.

[Captain Bill]

There sure is a lot of good advice here. I have a marine machine shop guy coming over tomorrow to take a look at it and make a recommendation. He already told me he does not favor re-welding. I'll get more details tomorrow. My electrical conduit runs down the front port side of the mast and the crack is on the rear starboard side so if there's any welding to be done hopefully it will be far enough away. There are no hydraulics in the mast. There is a lot of aerospace industry in this area and I've had a couple of high end welding shops recommended to me. If I end up needing a sleeve I can probably get a good weld job done. I'm tending towards a bolt/rivet on assembly with possibly a sleeve or re-weld. I have now got the name of the company that provided the spar so I'll contact them tomorrow and talk to them about how it should be repaired. This isn't going to be cheap but I need it done right.

[UNCIVILIZED]

Obviously costs go down the more work you do. So one option would be to grind off the old gooseneck, & fabricated the new one out of plywood. Then when you're satisfied with it, cut pieces out of aluminum that match up with the plywood ones in your mockup. Then you just need to pay for welding. And you can attach things to the spar yourself.
You get the idea.

[estarzinger]

Just a little more on our experience . . . . In the end, final solution which worked was for the boom and vang goosenecks to have stainless fabrications made and bolted onto mast. We had sleeve put inside, probably did not need it for this, but it did give more meat for the bolts, and we wanted to stiffen that area for another reason anyway.

For the vang lug on the boom, we put an outside doubler plate wrapped around the bottom of the boom, and then cut a slot thru the bottom and thru top of the boom and put a new tang right thru the boom - welded to the doubler and to the top of the boom.

My experience is that offshore, with the high wave fatigue, aluminum skin/tang weldments for this application are not a super solution. They tend to develop very small cracks right along the edge of the weld. If you show them to an average rigger they will often say 'oh, that's just cosmetic'. But those cracks just continue to get deeper and deeper (I have dug into a couple with a dremel). And this is NOT an issue with shitty design or shitty welding - I have seen the exact same thing happen with the best dutch welding and fabrication and design (Royal Huisman and Rondal). If you must use aluminum, I believe it can be minimized a bit if the part is fabricated offsite and all heat treated - but I have still seen many of those (usually on racing masts) crack.

[Captain Bill]

Originally Posted by estarzinger

Just a little more on our experience . . . . In the end, final solution which worked was for the boom and vang goosenecks to have stainless fabrications made and bolted onto mast. We had sleeve put inside, probably did not need it for this, but it did give more meat for the bolts, and we wanted to stiffen that area for another reason anyway.

For the vang lug on the boom, we put an outside doubler plate wrapped around the bottom of the boom, and then cut a slot thru the bottom and thru top of the boom and put a new tang right thru the boom - welded to the doubler and to the top of the boom.

My experience is that offshore, with the high wave fatigue, aluminum skin/tang weldments for this application are not a super solution. They tend to develop very small cracks right along the edge of the weld. If you show them to an average rigger they will often say 'oh, that's just cosmetic'. But those cracks just continue to get deeper and deeper (I have dug into a couple with a dremel). And this is NOT an issue with shitty design or shitty welding - I have seen the exact same thing happen with the best dutch welding and fabrication and design (Royal Huisman and Rondal). If you must use aluminum, I believe it can be minimized a bit if the part is fabricated offsite and all heat treated - but I have still seen many of those (usually on racing masts) crack.

I am considering having something like this made. https://www.roostersailing.com/pd/Se...ket_106402.htm
This is specifically for a Selden spar but this would be the general idea.

[a64pilot]

Why Stainless? Dissimilar metals corrosion with Stainless
Why bolts? Bolts require an internal nut of some kind, blind rivets do not.

I'd go with aluminum, thick enough so strength is not a concern, and rivet it with countersunk Cherry Max rivets ( you said a lot of aerospace around).
I'd also use some sort of faying compound between the two, I'd use B2 aircraft fuel tank sealer, but 5200 will work

[etterridge]

While any welding on your mast is not a good idea, if you decide to do it then you should enlist the services of one of the companies that make the overhead trussworks that carry signage on all of the interstates. They have very large ovens for post welding stress relief, and there is a shop in most states and provinces.

[Terra Nova]

Originally Posted by estarzinger

...The final solution which worked in the end was grind it off, internal sleeve, fabricated bolt on stainless curved plate/tang.

This is the proper solution.

If made in stainless the fitting can be isolated from the mast to minimize dissimilar metals issues. However the new fitting can be constructed of much heavier gauge aluminum. That fitting can also be heat treated if deemed necessary.

[estarzinger]

Originally Posted by a64pilot

Why Stainless? Dissimilar metals corrosion with Stainless
Why bolts? Bolts require an internal nut of some kind, blind rivets do not.

I'd go with aluminum, thick enough so strength is not a concern, and rivet it with countersunk Cherry Max rivets ( you said a lot of aerospace around).
I'd also use some sort of faying compound between the two, I'd use B2 aircraft fuel tank sealer, but 5200 will work

We tried the 'thick aluminum' solution (10mm base plate, with 25mm tang, with 12mm 'feet/gussets' on the tang). We still got edge of weld cracks. It is not the strength of the aluminum in question, it is the (apparently) vulnerability of the weld edge in this application to fatigue/shock load cracking. As I said above heat treating the part does seem to delay the problem, as does getting as much linear weld loaded as possible - but neither solve/eliminate it - I saw a royal huisman with a HUGE heat treated gooseneck that was being ground off because of this.

I dont know anything about the cherry Max rivets. I do know that experienced riggers use monel rather than aluminum rivets in pretty much any loaded application, and machine screws rather than monel rivets in any reasonably highly loaded application. I know there are a lot of rivets on aircraft skins - but do they really use them to hold high fatigue/shockload parts on - like the engines are they mounted with rivets or with bolts/machine screws?

It is pretty easy to isolate a separate fabricated SS gooseneck from an aluminum mast.

[captlloyd]

Originally Posted by a64pilot

I'd stop drill the crack and have it welded, I'd be very astonished to learn it had any heat treat after welding. Be very difficult to heat treat an entire spar.

X2

[Cheechako]

Originally Posted by captlloyd

X2

X3 and go another 15 years. You could have the welder add some small gussets to make it bullet proof.