DSII Replacement Masthead Doesn't Fit Holes in Mast

[danamags]

I've purchased and received the replacement masthead from D&R for my 1977 DSII, however upon pulling the old one off (think war against old rivets) and trying to fit the new on in (which took some rubber mallet work) - I've realized that the holes in the mast actually fall below the lip of the masthead on the new masthead. They fit the old one but it's in rough shape. Also, the old masthead is a more square shape - perhaps this was the design at the time - but does anyone have any suggestions on how to affix the new masthead to the mast? I would not be too keen on drilling more holes because it may further weaken the alumnium - or would that be an issue that close to the top? Thoughts? Advice? I've put pictures of the hardware up here:

https://picasaweb.google.com/1007155499 ... NCvquzmDg#

[dbk0630]

One option to replacing the entire masthead, is to install a new set of sheaves in the old masthead. Following a suggestion in a thread last year, I changed mine out last fall by drilling out the rivets and installing the new sheaves using 1" cleavis pins and rings instead of rivets.

[seandwyer]

I did the same thing - just replaced the sheaves and used clevis pins instead of rivets. It was easy and without rivets it'll be even easier the next time.

[talbot]

I suspect the extra holes are not a serious issue in terms of strength. But make the new holes offset from the old ones far enough that you don't crack the aluminum between them, and fill the old holes with epoxy.

If you are really concerned, you can take an old section of a junked spar, just a couple of inches long, and split it on either side of the sail track. It will flex enough to fit tightly inside your mast. Daub this collar with epoxy and push it down with the new masthead so that it covers the old holes from the inside. Then you can either rivet the collar in place using the old holes, or just putty the holes over. The mast will be double-think just below the new masthead. One year I had to replace a broken boom, and I used this technique to salvage a badly corroded spar I found in a junk yard.

--Talbot

[danamags]

talbot - thank you for this idea - i like the idea of actually drilling new holes, but my biggest concern was weakening the mast - but filling the old ones and reinforcing from inside will be a great solution. i'll add it to my rapidly growing list of boat tasks that i hope to accomplish this weekend.

dm

[Alan]

Pssst, danamags. Don't encourage those lists. The more you add to them, the more they grow.

[Peterw11]

You've got 3 options:

Ignore the holes and just drill 2 more. That's what I'd do.

Given the wall thickness of the mast, and the way force is applied in this case (in compression), I doubt it'd make much difference.

or:

Have a welding shop close up the original holes, and then redrill.

or:

Lop of the top inch with a Sawzall, immediately below the original holes and drill new ones (assuming you don't mind giving up an inch of height).

And you can always call Rudy at D&R for his advice.

[GreenLake]

Just drill new holes.

The overall strength of the mast is not an issue at this location. As Peter wrote, the mast is loaded in compression mode - the rivets don't actually do much load bearing, that's done by the lip of the masthead resting on the profile. That's why it shouldn't matter much where you drill your new holes, the don't have to be in any particular place (other than far enough away from the old ones).

In the middle of the mast, you'd worry about affecting the buckling strength of the spar - there are some configuration of holes that could indeed weaken a mast there. However, this is not a an issue near the end.

As long as you don't drill so many holes that the mast profile will split under pressure from the halyard, you should be fine. That's why you give a bit of a distance, say 1", to the old holes.

The sleeve trick etc. are useful if you have a spar with damaged ends, where it might split under load, or for a boom cap, where there are some loads sideways to the spar.

Filling the holes should be something you do in order to keep water out of the mast, not for strength. Before you put in the new masthead, check the bottom of it, and if there are openings, cover them. And bed your new fitting in caulk. Having a mast that cannot take water when capsized is a good thing. (To get the full benefit you may have to check that there aren't any other openings).

[danamags]

ok, so i went ahead and just drilled new holes and it seems that this worked nicely without making the mast look too much like swiss cheese. im going to rivet it on later this week and go from there. it was a good chance, too, to actually clean out the mast which was full of junk at this point.

thanks to all for the guidance and advice.

DM