SX wings - attachment casting welding to tube?

I have a Hobie 18 with the SX wings. The front main attachment point is a casting that fits inside the alum tubing and is held in with 4 rivets. The front attachment points of both wings on the used boat I bought had some damage. the worst of the two had 2 of the 4 rivets sheared off, the casting pulled out of the tube approx 3/8" and the tubing cracked. I think the combined load of the weight on the wing (tension load on the casting to tube joint) and maybe water impact in a capsize or hitting a dock caused the damage in the first place.

I drilled out the rivets and removed the casting and was planning on welding the tubing back together and then re-riveting the casting in place. However I am considering welding the casting directly to the tube to make this more secure. I have access to some very good aluminum welders and equipment at my work.

My concern is weakening the aluminum by removing the temper with the welding and the fact that once this is done it can't be un-done. I do however think the welding will be stronger than the rivets ever could be and I can even put more rivets in as a back up to the welds. I think the magnum wings may be welded together compared to the rivets in the SX wings.

Another option is to weld/repair the tube and then rivet and JB weld (very strong adhesive) the casting in place.

Has anyone else ever dealt with this type of damage and how did you repair it? Has anyone welded these castings to the tube?

Any feedback on this would be helpfull. I am going to do something soon either way.

Aluminum castings are very difficult to weld (if at all possible). Welding them to an extruded tube of a different alloy would be nigh on impossible.

It might look good initially, but it will not be structurally sound.

Pictures would help here.

I fixed my friends 18 wing problem by having a machine shop fabricate a heavy duty alum. insert that fitted inside the cast pc. and than stepped sized to fit inside the tube and extend into tube by 6".I had to sand it to fit the taper to the inside of the cast pc.I used an aircraft approved epoxy to glue into place along with new rivets in new hole locations and used the remaining epoxy to replace missing and or cracked alum.tubing.Although this is not removable it is as strong as I could come up with.Once the epoxy dried,I sanded it smooth with the tubing.The epoxy is a black colored product and looks real good too.
Do not weld your alum. tubing or the cast pc.
Good Luck Bill 404 21 SE

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Bill 404 21SE

Sleeving it would be the easiest way to do it. It could be welded and re-heat treated but that isn't cheap and may adversely effect the anodizing. Drill thru the sleeve and rivet it all together.

Well I welded it up against the recomendations I got here. I think it will work well but only time on the water will tell. I will touch back after I get the boat in the water this spring.

Just be aware that when it goes it will be quick, it won't bend it will snap off. That will leave a jagged tube capable of taking a core sample out of whomever hits it. If possible have it annealed and heat-treated for safety.

Based on the research I have done on welding aluminum the drawback is that the material was originally 6061 T6 temper which is a heat treatment that makes it much stronger than annealed 6061. The welding of the aluminum partially anneals the material due to the heat added and will make it softer than the original. In other words it will have a lower yield strength that the original. How much softer is a unknown variable because full annealing would take many hours at a certain temperature and it was not worm for that long.

I believe the failure mode would be that the tube bends more easily than the original (lower yield strength) not a brittle fracture.

I do have an engineering degree and have worked with welding and aluminum throughout my career. I have not worked on this specific application but I did a fair amount of research.

If I believed it would be dangerous, I would not do it, I am a very careful person.