Earlier in another post, I removed my posts regarding this issue but I will take a firm stand contrary to others.
I grew up around the original astronauts, Von Braun and gang, and knew many of the earlier test pilots as my dad was the Army's top pilot of his time and learned a lot about planes and rockets. In an addition, I was an insurance investigator handling my own litigation unit successfully. No I am not an engineer but learned a lot from listening, asking questions, repairing masts and so on. I was a sailboat dealer for many years involved with designs, suggestions and so forth. I am not bragging but setting the stage for knowledge and experience.
First, planes use a stronger metallurgy in aluminum and there is structural integrity with framing. The smaller sailboat masts are not as strong and simply a tube without a frame support. There are may forces exerted particularly in the center of the mast. Although some say weld, I advise against it.
when this first came up in my early years by a customer, I first advised you cannot under any circumstances use a back yard welder to begin with. Then my investigative skills told me to contact the mast manufacturers. All said not to weld any mast due to safety of the customers, not trying to sell additional masts for profit.. Then of course they said they would advise against it due to liability. Then some will say it can be done in the aviation field but I go back to the fact there is a frame system and stronger metallurgy vs. a sailboat mast that is a tube only.
I went up two masts without knowing it that had been welded and failed on me with one incident could have nearly killed me. As for one respondent who said there are cut outs for some spreader brackets that go thru the mast and then the attachment of the lower shrouds, this was taken into account by the mast manufacturers but one mast that the owner had drilled too many holes below the spreaders without telling me, it collapsed and I fell several slips over. By the Grace of God, I was spared but to this day I feel that in my back. Then many fail to forget forces exerted on small mast mostly in the center who do not take that into account.
Some have suggested sleeving a mast that has broken. Unless that sleeve is specifically made to be inserted into the mast, that is a very dumb idea when sleeving small masts. I do not know of any sleeves made to fit specifically to any small mast anyway.
In essence, I will never suggest welding any mast particularly in the center as I believe in the safety of the sailors to include children and pets as well from what I was told, asking questions, repairing sailboats as a dealer to include masts. You will never change my mind on that and if welding is being considered, that is a personal decision by the owner.
Now for the soothsayers on this one.