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post #11 of 14 Old 12-02-2015
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Re: Structural question for you engineering types

In all probability you are ok. However, for peace of mind, you might take some aluminum flat plate of at least same thickness as mast aluminum or even thicker, cut it to the round shape of the winch pad/winch base, and drill it to match the new holes for new winches. Then install a plate under each winch using the winch mounting fasteners (might need longer ones to be sure these are securely through the mast). I wouldn't worry about the old holes. This will provide some stiffening in this area. Use anodized plate aluminum if you can. Of course, the winch itself adds stiffness in this area. Personally, I would not do any welding on the mast without making sure that the welding wire/rod were compatible with the mast metal and that the heat wouldn't have any adverse effect.
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post #12 of 14 Old 12-02-2015
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Re: Structural question for you engineering types

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Originally Posted by hellosailor View Post
Pearson masts tend to be tree trunks, not bendy frail things. So the odds are it was robust to start with. Then again, the winch "pads", which presumably are taking side load from the winch mounting screws as well, are probably also acting to reinforce the mast almost the same way that sleeving it would do.

At this point if you really wanted to go bullet-proof, you could call in a welder and have the pads welded to the mast, which would absolutely make them into reinforcement for it. Of course, aluminum welding means finding someone who can do a professional job and do it right.
and this

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Filing the holes probably makes no difference. The holes can be tig welded by anyone. Spars are full of holes and they seem to hold up.

I wouldn't worry about it
basically what I would have said. If it were one of today's boats I might be worried, but heck back then they did not understand how strong Aluminum was, and it was cheap, so they just used a lot of it (OK so this does not work as well as it does for fiberglass and old boats does it?!?!? ) But since it is a mast head rig, with a fairly stiff and heavy mast you should be OK. If you had a fractional rigged boat it would concern me. At some point if you are doing other work on the mast you might want to have the holes welded, but otherwise it should be fine.

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post #13 of 14 Old 12-04-2015
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Re: Structural question for you engineering types

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Originally Posted by BubbleheadMd View Post
I probably should have kept the pads bolted to the mast with countersunk screws in the original pattern and drilled the new pattern into the pad and tapped the holes and bolted the new winches to the pads *only*.
I think I might use the old pattern with countersunk screws from the pads to the mast (as you describe), if just to keep out water. The additional strength couldn't hurt either....
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post #14 of 14 Old 12-05-2015
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Re: Structural question for you engineering types

The mast is primarily in compression at any location that you can reach. So the holes will be no problem provided they don't give the impression of your run-of-the-mill cheese grater. And, whenever possible/practical, don't weld aluminum for strength. Aluminum actually looses up to 50% of it's strength within 1" of the heat affected zone. I say "up to" because engineers can slant things when calculating stresses (that's why they call it "justifying") so that number can go from 25 to 50. Some alloys that I am not familiar with may have different results but 6061-T6 (and 6063-T...) fall into the category. So don't weld the holes. Steel, on the other hand, often increases in strength at the joint, usually due to the filler rod being 50 ksi material of better. That's why most people consider welding a benefit. If you see an aluminum something with welded joints, it probably isn't structural in nature, more assembly oriented, like building a chair or a work bench frame. If it is structural, a car frame or trailer frame, it will either be an engineered joint or bolted assembly at key stress areas.
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