Fixing Broken Masts
From the e-mail list

Rick and Gary in Ottawa ask:

At the end of last season, the clevis pin on the windward side shroud let go (broke?, fell out?). The rig was quite heavily tensioned and needless to say the mast snapped at deck level. The break is fairly clean, but there is a slight bow in the mast.

Has anyone ever had a mast welded back together when it has completely snapped? I talked to a local aluminum welder and he says he has done it before as long as the break is below the sail feed (which is the case with my situation). Can the mast be straightened?

If none of this is recommended, does anyone have a used mast for sale?

Rick Cuthill
Gary Nicholl
CAN 6088

I've never tried to fix a mast that was entirely broken, but I don't think it's any different structurally than with a partial break, and I've had no problems with masts welded after a partial.

1. Straightening out a bend is perhaps the trickiest part. A diagram I once saw in a Proctor book suggested using the ground and a convenient automobile to fulcrum the mast straight. If you do this (or some equivalent), use blocks of wood to spread the load at the fulcrums. The hard part is to keep the walls from dimpling near the fulcrums. If the bend is long enough, this should be possible. If the wall dimples, my understanding is that it's fatal -- the indent area can't be brought back out without losing strength.

2. With a partial fracture, I always drill out all crack tips (generally to around 3/16") for stress relief. Remember that the microcracks may lead the part you can see visibly, so err in this direction. With a full fracture, the loads may be different after reassembly, so you might want to modify this to clean up torn edges. Consult you welder on this, because you will want him to replace any material you remove with weld-metal.

3. Sleeve the mast before welding it. In a Proctor D, the top section from a Laser mast makes a perfect sleeve.

Ed. so does a piece of "C" section with the sail track cut off

Just remove the heel plug from your Proctor D (and any fitting attachments that might get in the way), and jam the Laser top section in from the bottom. You need to span the area of the crack by a foot or more on each side (so the load transfer is gradual), and it is perfectly reasonable with a partner-area break to sleeve from the heel plug to above the gooseneck.

4. Weld, using standard aluminum techniques (inert gas, etc.). I'm not sure that you can avoid heating the sleeve directly beneath where you are welding, and I expect that we've usually wound up with the weld attaching to it as well as to the original section. It doesn't seem to have mattered, though, since the result has been strong enough to last. I usually leave the entire weld bead intact, unless there is a clearance problem, or, if it would be part of a contact surface (for example, directly in the partner).

5. After welding, pop-rivet the sleeve above and below the joint. I usually use steel rivets, perhaps 2 vertically, at the sides of the mast, about 3" and 6" above and below the repair. If fitting attachments in the same areas can substitute for the locating rivets, you can probably leave some of them out. The rivets are giving permanent location to the sleeve and helping to transfer vertical loads in the sidewall (i.e., sidebend loads) into the sleeve (which is why I use stainless steel rivets).

6. Drill the sleeve for your fittings and lines, and away you go.

I've had masts (and booms) repaired in this way last for years. Good luck and good sailing.

Dave Cahn


On my old boat, 8049, when I bought it, it had an ex-Fireball mast (M7) which was lengthen. To make it a 505 mast, at the butt end, 15 inches of new section was welded onto it. I sailed with that mast for about a year, also in heavy breeze, and it was fine. I changed because i wanted a Proctor-D....NOT because the welding job was bad on the M7 mast.

You probably should buy an internal sleeve section. Let it go from the mast foot and at least two feet into the mast above the point where the mast gets welded together at deck level. Put in the sleeve section before welding the two pieces together, and it will take care of getting the mast straight too. This plus a mast collar, it think you will get a strong enough mast to continue sailing without having to worry.

Johan Backsin SWE-8593

Rick & Gary:

Some thoughts to keep you up at night....

Welding the aluminum can be done, but the heat affected area will not have the same temper as the rest of the mast, and will be considerably weaker. I think Proctor (I assume you have a D) uses a 6061-T6 aluminum which has yield and ultimate strengths of 40,000 and 45,000 psi. The same alloy in the "T zero" condition will have yield and ultimate strengths of 8,000 and 18,000 psi, a considerable difference.

Barney Harris

Before any one gets upset about bending aluminum masts, all should note that when the mast comes out of the extrusion press at the Mill it is always bent.

To get a T6 temper the extrusion is first stretched, then heat treated, then perhaps stretched again, then artificially aged.

If a piece is still bent, the Mill will attempt to straighten the piece by running it through shaped rollers. This is a hand operation and takes judgment, but it is not unlike bending the mast over padded mandrels ( like a car, sawhorse, or tire).

Don't worry; if it's already bent, go ahead and try to fix it.

Pete Mohler
USA 1114

Re straightening bent mast Using a car tyre as the fulcrum works well and helps avoid the complication of dimpling.


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