From double to triple clutch: hole centre strength?

Tim Good

Tim Good

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This is my mast. It’s a thick one piece proctor mast. There is a double clutch mounted on an alloy fitting plate. I want to add a triple clutch.

If I remove the double and add the triple, I would need to drill 6 new holes. Between which the old holes would be.

The old holes have around 21mm separation. If I drill 6 new holes, there will only be around 7mm separation. See diagram. Grey circles are the old holes.

My questions:

- Will 7mm spacing be sufficient for the new holes?

- If not could I fill the old holes with JB weld or something to help support. Or maybe screw in a helicoil to help support the hole?

- The alternative is that I mount another single clutch on the mast directly next to the double. I have a spare single. Maybe not as neat but perhaps simpler.

Any other advice appreciated.

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If it were me, I’d either,

A) Make a pad which attaches to the mast using the existing holes and to which you can bolt the new clutch to. 5mm stainless plate would likely be fine for the pad.

B) mount the single clutch - perhaps slightly above and to the side of the existing clutches.

rationale is that area of the mast is under most dynamic forces near the gooseneck so I wouldn’t want to do anything the weaken that area any more. Of which your old / new holes closely spaced would induce.
 
Can't you mount it offset to the left, so the four existing holes are re-used on the right and middle, and just 2 new made for the left?

Any which way I'd mould a pad to fill the curved mast/flat base interface.
 
KevinV said:
Can't you mount it offset to the left, so the four existing holes are re-used on the right and middle, and just 2 new made for the left?

Any which way I'd mould a pad to fill the curved mast/flat base interface.
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Yes sorry I should have been more clear. There is an allow pad already. You can see it behind the double clutch. Could I mount it offset on that pad… hmm not sure
 
Tim Good said:
Yes sorry I should have been more clear. There is an allow pad already. You can see it behind the double clutch. Could I mount it offset on that pad… hmm not sure
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Make a new pad for the triple - easy peasy with epoxy putty and some cling film
 
KevinV said:
Make a new pad for the triple - easy peasy with epoxy putty and some cling film
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Well the existing allow pad or bracket is already riveted to the mast. 4 holes. If I take it off and add the triple clutch, I then have 8 holes in the mast in total, if you include the 4 from the old mounting pad / bracket. I don’t like that idea really.

I’ve added two more photos of the bracket / plate to the original post but here also:

IMG_9907.jpeg
 
Would the triple mount on the existing pad or failing that I would just mount the single along side on the mast, or could the double be moved over leaving room for the single alongside on the pad.
 
Tim Good said:
Well the existing allow pad or bracket is already riveted to the mast. 4 holes. If I take it off and add the triple clutch, I then have 8 holes in the mast in total, if you include the 4 from the old mounting pad / bracket. I don’t like that idea really.

I’ve added two more photos of the bracket / plate to the original post but here also:

View attachment 202242
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I think the suggestion is that you rivet/bolt the clutch only to the pad, and then the pad to the mast.. no more additional holes required..
 
Tim Good said:
Well the existing allow pad or bracket is already riveted to the mast. 4 holes. If I take it off and add the triple clutch, I then have 8 holes in the mast in total, if you include the 4 from the old mounting pad / bracket. I don’t like that idea really.

I’ve added two more photos of the bracket / plate to the original post but here also:

View attachment 202242
Click to expand...
Ah, not what I'd envisaged at all - are you certain the clutch is screwed through the mast? That base looks thick enough that it may not be (ie clutch screwed to base, base riveted to mast) . I think I'd start by drilling the 6 rivets out and having a look see
 
KevinV said:
Ah, not what I'd envisaged at all - are you certain the clutch is screwed through the mast? That base looks thick enough that it may not be (ie clutch screwed to base, base riveted to mast) . I think I'd start by drilling the 6 rivets out and having a look see
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No it’s deffo not screwed to the mast.

Sorry I think I should have made a better initial post. The pad is riveted to the mast and the clutch is screwed to the plate. My question is that if I drill 6 new holes into the plate, will it weaken it sufficiently to be dodgy, assuming the 4 old holes remain. Thats my diagram. It’s a sketch of what the Selden aluminium alloy plate would be afterwards, with only 7mm clearance between new and old holes. The plate is large enough to accommodate a triple.
 
Tim Good said:
No it’s deffo not screwed to the mast.

Sorry I think I should have made a better initial post. The pad is riveted to the mast and the clutch is screwed to the plate. My question is that if I drill 6 new holes into the plate, will it weaken it sufficiently to be dodgy, assuming the 4 old holes remain. Thats my diagram. It’s a sketch of what the Selden aluminium alloy plate would be afterwards, with only 7mm clearance between new and old holes. The plate is large enough to accommodate a triple.
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Well that changes it entirely then - I thought we were talking about a load of new holes in the actual mast at the gooseneck.

I’d go with it myself in that case. You’ve moved the worst case scenario from a broken mast to a cracked pad! That you can deal with should it happen, by keeping the halyard on the winch and to a clear.
 
Minerva said:
Well that changes it entirely then - I thought we were talking about a load of new holes in the actual mast at the gooseneck.

I’d go with it myself in that case. You’ve moved the worst case scenario from a broken mast to a cracked pad! That you can deal with should it happen, by keeping the halyard on the winch and to a clear.
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True. And filling the old holes with something perhaps. A bolt with the top ground off might perhaps give some stability to the old holes. 🤔
 
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