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Old 20-04-2021, 09:40   #1
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How to sleeve a mast

Hello All:

I have a splice in the mast of my race boat. it is a 1939 design called a Mercury. There was a splice below the deck and the other day I heard a loud crack. Didn't see any problem. Continued sailing. When I got to the dock I found that the interior sleeve in the mast had broken. The interior sleeve had a wall thickness that was about half of that of the mast section.

Luckily I was able to find a mast section that matches my boat in the boneyard. I just don't know how long a sleeve that I should put inside the mast to sleeve the two sections together. I plan on either using monel rivets or to tap the mast and use SS screws.

Can anyone make a suggestion as to the length of the sleeve or the number of fasteners to use?
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Old 20-04-2021, 14:05   #2
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Re: How to sleeve a mast

Charlie, I don't have experience in such matters, but in your place I'd have a look around for a mast on a larger yacht that came with a sleeved splice from the builder. You should be able to estimate the length of the sleeve relative to the diameter of the spar and count the number of fasteners and extrapolate to the size of your mast.

Alternatively, you could call one of firms that build big masts and ask them for advice. They might be helpful.

Good luck, and good onya for preserving a classic racing dink!

Jim
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Old 21-04-2021, 04:48   #3
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Re: How to sleeve a mast

A rule of thumb would be 3 times the diameter in each direction.

Apparently this mast section is not just in compression. I recommend that you examine the standing rigging for a source of the fracture, so it doesn't happen again.

How was the present sleeve attached? That's a clue. However, if the insert is thick enough to hold 2 1/2 threads, I'd recommend screws rather than rivets. If rivets, go with aircraft grade and make sure the holes fit really well.
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Old 21-04-2021, 10:15   #4
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Re: How to sleeve a mast

CherryMax rivets are my go-to for structural blind rivets. Not a bad idea to shoot them wet, either.
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Old 22-04-2021, 08:12   #5
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Re: How to sleeve a mast

Definitely go for monel as it is inert to corrosion- Stainless steel and aluminium are not.
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Old 22-04-2021, 08:29   #6
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Re: How to sleeve a mast

Quote:
Originally Posted by Charlie View Post
Hello All:

I have a splice in the mast of my race boat. it is a 1939 design called a Mercury. There was a splice below the deck and the other day I heard a loud crack. Didn't see any problem. Continued sailing. When I got to the dock I found that the interior sleeve in the mast had broken. The interior sleeve had a wall thickness that was about half of that of the mast section.

Luckily I was able to find a mast section that matches my boat in the boneyard. I just don't know how long a sleeve that I should put inside the mast to sleeve the two sections together. I plan on either using monel rivets or to tap the mast and use SS screws.

Can anyone make a suggestion as to the length of the sleeve or the number of fasteners to use?
Wow, it cracked below deck? I would not have thought it would down there.
I had a mast pro sleeved once. The sleeve was fairly long... at least 3 feet on a 47 foot boat. It was put inside the mast with structural epoxy that was more like sealant consistancy (the sleeve never fits perfectly) and riveted about every 2" all over near the joint and wider spaced away from the joint. Special rivets were used, not pop rivets.
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Old 22-04-2021, 08:32   #7
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Re: How to sleeve a mast

The old sleeve would be the best guide as to the length and also to the number of fasteners.
If the section you have found is same size as current mast you need to take some action to fit it inside, either by cutting out a strip and then bending the remaining section and push it inside. Another method is to cut the section vertically/diagonally at two opposite sides of section, than slide one of the pieces up against the other until you'll get required dimension.
Fasteners:
Be careful of galvanic action between the fasteners and mast. Best will be identical material, i.e. if your mast is aluminium, use aluminium rivets - the role of the fasteners in your case is only to keep the internal section in place, so no real stress if the rig is positioned properly.
S/S or Monel rivets are difficult to install, and as your sleeve is below deck it is in danger of being in contact with salt water - the combination of S/S salt water and aluminium is not very happy one.
Ensure that the internal end of any fastener you use is not sharp (very important) and does not protrude too much - lines and cables should pass unhindered (do you have a conduit?).
Bolts are problematic - first of all it is difficult to close the nuts inside mast profile. Second problem is to ensure the nuts remain in place as the mast 'works' - you should use some peening/punching on the bolt end or Locktite. Pop rivets will be better and if you are worried add more rivets.
If you are going to use existing holes for new fasteners, check that the size fits exactly and that the holes are perfectly round (the tend get elongated when working).
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Old 22-04-2021, 08:42   #8
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Re: How to sleeve a mast

seems like people think masts are just in compression. If that was true, they wouldn't bend and racing boats often induce significant bend. Often that puts a load pushing forward at the deck/partner, and rear ward at the keel/step. High bending loads in the section between the deck and keel.


I attached a pic of my splice for review. This is a 1975 Tartan 41.
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Old 22-04-2021, 09:26   #9
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Re: How to sleeve a mast

The sleeve in my mast was drilled with dozens of holes and each hole somehow drip welded. I never knew how it was joined until I drilled a hole through it for a radar cable with a hole saw and the plug I removed had one of the welds in it. Years later when I had the mast painted it was stripped to bare metal and I could see all of the welds.

I don't know how long the splice is. It is at the lower spreaders.
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Old 22-04-2021, 09:38   #10
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Re: How to sleeve a mast

I have sleeved several masts and using an identical section as the mast worked well. I cut the track part off using a table saw and squeezed the section with a c clamp and hammered it in. Then rivets as Meirriba suggested. If the original thin sleeve worked awhile, the thicker one should be fine. And if you end up using stainless rivets use plenty of tefgel or other anti corrosion product. good luck
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Old 22-04-2021, 09:45   #11
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Re: How to sleeve a mast

Thanks for the replies. I will post pictures of my project later. I decided to match the existing sleeve length. It was ~4' long. This is probably excessive. The sleeve that broke had a wall thickness that was half the size of the mast section. The new sleeve is a bit larger than the existing section. A rigger I spoke with said that this could potentially create a hard spot in the mast but given that it was below deck and not a place where the sail was held it would "probably" be okay.

I decided to match the existing rivet holes and to use SS rivets. My reasoning was: a) The existing rivets and mast showed no sign of corrosion, b) The rivets were not the cause of the failure. The sleeve broke. c) I need to fix the mast prior to my next race on May 1st. and d) I didn't want to add more holes to the mast.
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