In my perpetual list of things to fix on my boat, I need to repair my punctured mast from last season. I have found an aluminum welder in the area that said he could fix it, however, he needs to know the type of alloy used in the mast extrusion so he can make sure he has something that will not only bend around the curve of the mast, but something that will mate with it and not crack when cooling down.
Anyone know off the top of their heads.. or will I have to give Alter a ring?
I don't know the alloy, but was thinking that if you could get a piece of a broken hobie mast to use as the patch pannel the alloy should be the same. I don't know if the alloy would be needed to select the filler rod though.
I think I still have a section of a broken mast if you need a piece.
I has been a long time, I believe Hobie uses 6061 T6
Before you weld it you might want to talk to one of you local rigging shops. Most aluminum alloys goes through a heat treatment or work hardening process to increase the strength. The heat from welding will soften the aluminum significantly. 6061 will have about 3 times the strength in the 6T condition as it will in the soft state. It might be better to rivet a plate over the damaged area with some bonding agent between them.
I was thinking about riveting the plate, but the damage is right near the bottom of the mast, below the sail track, where, I'm assuming, compression loads are high. I don't know if I'd want to trust rivets for that.
Thanks for the response though on the 6061, I had thought I'd seen 5051 on one of the H14 parts diagrams, but I guess I'm wrong.
assume 6061-in a t4 condition.
the welded area will be as stiff, but not as strong.
in general, 6063 is a lower cost extrusion alloy with less strength, but same stiffness and better finish/corrosion resistance.
Hobie is in Oceanside California. You could call them.
Do you think it will be strong enough to handle the loads placed near the base of the mast on a H17 (sometimes with jib)
That looks good, and a lot better than the $150 I was quoted from the aluminum welder!
Yeah - but that's simply brazing a joint just like with copper plumbing...I ~might~ believe their claim to "be stronger than the metal" in a tight tolerance bonding situation but I really doubt it will be in a gap filling scenario.
well I'm not going to fill the gap, I'm going to weld a bracing plate overtop the puncture with the same profile as the mast so it fits flush.
i have used those brazing rods before. as i recall, the brazing material is rather brittle and will most likely crack under the stress
alright.
Well this is turning out to be more of a headache than I anticipated.
If you're going to do a job that's worth doing, it's worth doing right (man, I sound like my father).
Seriously though - if you call Hobie, they will advise you against welding on the mast because of the liability. The heat treating process on aluminum is particular and the material properties will be changed for the worse by welding. If you MUST - you should really consider cutting the damage off and riveting a sleeved section back on.
If you are going to effectively use a sleeve why not glue and rivet it on,
If it works for aluminium sports cars!
I saw a neat trick for reinforcing aircraft structure. This might apply.
1) wrap the spar with release film (wax paper, 2-3 layers)
2) right on spar build up your reinforcing sleeve from carbon/epoxy. Use an undamaged part of the spar for the mold Either vacuum bag it or squeeze out the excess epoxy. For a mast the sleeve would go a couple of inches above and below the damaged area and 3/4 around the mast. You would need 5-8 layers 5 oz cloth. You could probably use 10-layers of fiberglass
3) when hard, slide it off, square the edges and clear coat it.
4) Apply glue to the mast, slide the sleeve on and tape it down to dry. I would probably use a 1 part polyurethane glue (Gorilla Glue) I found this works best for carbon/Al bonds
This is for reinforcing, distributing a load, or just sealing a hole.
I'd probably rivet it on as well, just to be safe.
Thanks for all the suggestions guys. When it comes down to it, I've got two masts. One is this punctured one. The other one is the one I use, its got a slight dent and bend just below the tang. It straightens out under shroud tension, but if I can repair the damaged punctured one, I'd rather do that, because its straighter.
Again, thanks for the suggestions. When I called hobie, they wanted to sell me a new mast. 
Well, I'm surprised no one's mentioned it yet but it's quite common to have tapered Aluminum masts that are purposely cut and welded back to provide the taper. Admittedly this is common at the top of the mast (like on the 30' Sori wingmast I have on my old woodie A-cat from the 80's) where the loads may be lower but that also needs to be the most flexible and still be strong. Don't know where you are but you might try looking for a welder familiar with that technique (there are also some good marine grade welders who fabricate the fishing towers for powerboats or aluminum frames for tops, also some good welders who fabricate/repair the expensive bikes- I know, they are all CF now but the skills should still be around) - Just a thought-
Kirt
I've already inquired at an aircraft welder. He said he'd charge no more than $150 for it, and that'd be including the material he would use to patch it.
If he's a certified aircraft welder, and they trust those welds in airplanes- Don't you think they'd be adequate on a sailboat where if the weld fails you might get hurt or your day would be ruined (vs if they fail in a plane more than the rest of your day will likely be ruined!).
Kirt
In general, when you weld aluminum, you either heat treat it after you weld it or use a non heat treatable Al. 6061 is a heat treatable alloy. Assuming It starts at heat treat 6 (T6) welding 6061 T6 changes it's yield strength from 95,000 Lb/in2 to something between 95,000 lb/in2 and 30,000 lb/in2 around the wield. Probably a lot closer to the bottom of the range than the top.
When people say welding heat treated aluminum is not a good idea, we are mostly reading it right out of engineering or aircraft repair handbooks.
Assuming the fact that I don't know a thing about the loads placed on that part of the mast, would it be of your opinion that this is a futile endevour?
Could you send in a photo of the damage, or at least describe it's size and location on the mast? I saw someone sailing with a large dent near the base of his mast. When I asked about it, he said that it had been there when he bought the boat 10 years before, and hadn't caused any problems. Maybe welding it would make it weaker more than help?? A photo or description would help some of the experts on the list answer your question in a more informed way.
Is your trip to Key Largo still happening?
Jack Hoying
Fort Loramie, Ohio
Prindle 18 #1645
http:/
"Assuming the fact that I don't know a thing about the loads placed on that part of the mast, would it be of your opinion that this is a futile endevour?"
This reminds me of a photo that I saw once. I think it was of Dan Berger using an old Hobie 16 mast to remove some concrete sidewalks on his property. It was like having a 26' prybar. Imagine the leverage you can get with a couple guys hanging on one end. As I recall, the mast was not harmed.
Jack
I'll work on the picture... Don't have a digi cam down here in Raleigh, but maybe a friend will let me barrow it for the day.