Mast hole repair

I have a small, trimaran with mast sections used to connect the hulls. The previous owner drilled holes approximately ~7/16 inches in diameter, clear through the spar, in some high stress areas. Although I see no evidence of impending failure, thoughts of a weakened area is giving me nightmares. These mast profiles are no longer available. I am not too keen on the idea of internally sleeving this area as I have strong doubts about my ability to remove castings attached to the end of the spar without damaging it. Finding a suitable internal sleave would be another problem.

I understand that the heat generated during welding can weaken the spar. I am not overly concerned about the appearance of the repair / strengthening. An external patch would be fine. Can a strengthening patch be applied to seal the holes and reinforce the spar, or will the act of welding / brazing / soldering weaken the spar?

Any advice would be appreciated.

As an old weldor I can tell you that welding tempered aluminum will ggreatly weaken it. It is like annealing high carbon steel. it gets all soft and bendy. If looks are not an issue then an external sleeve will work. I did this for the mast on my boat because it was broken in two at the spreaders. I found a section of larger mast that would fit over the existing mast once the sail slot was cut out. then I drilled in several places and riveted it to the outside. Use SS rivets and tef gel. HTH

What is TEF gel?

[Renoir]

You could probably drill a lot of 7/16" holes in an aluminum mast before being too concerned, depending upon the safety factor of the designed application. What is the width and length of the cross-section as well as the thickness of aluminum?

The boat is about 45 minutes from my home, so I don't have easy access for measurements. The mast section supporting the "pontoons" is quite light . All stayed-up it is quite a flexible "springy" setup. I have not had a failure. No cracks, but the holes makes me nervous. They should not have been drilled in the first place, especially at the point of maximum foil width. If I could reinforce this area, I would enjoy the boat more.

[Ian McColgin]

I second the notion that it takes lots of holes to make a problem, holes you'll be adding if you to a rivited external reinforcement.

I am no engineer and am far more sensitive to wood than metal but hollow wooden spars can be ruined by a repair that creates a hard spot. Depending on the designed flex in the spar, you could make a hard spot that establishes a failure point just beyond it, though usually tri spars are compression loaded and should not bend as a mast does.

An exception is the radical Gougeon Bros racing tri's that have the motto "Free the amas" with laminated spars designed as huge wooden springs. Perhaps your rig somehow does that with aluminum under compression and some flex from the guying design ??

Anyway, I'd be inclined to use some epoxy paste to plug the hole and otherwise just watch it a while longer.

G'luck

Ian

I value everyone's opinions. Thank you all for your responses. I will continue to monitor this thread should other people have good ideas.