Sheaves at the mast top

I have my mast from my E34 at the local boat yard to have the standing rigging replaced. I want to inspect the sheaves at the top of the mast since I have a lot of friction when raising the mainsail. The only access to the sheaves appear to be a few small inspection ports around the circumference. The plate which forms the top of the mast appears welded in place. How do you actually replace the sheaves?

If your masthead is like mine (original E32 / Kenyon spar) there will be pins that go through the masthead from one side. the pins are held in place by an oval-shaped flange that holds them in place.



Unscrew the screw that holds the flange to the side of the mast, and you can pull the pin out.

What worked for me (before pulling any pins) was to work a length of tagline or small cord around the sheave and pull it tight so you have sort of a "leash" to hold onto the sheave, because once the pin is out the sheave is free to move and can fall farther into the masthead. That's a headache you want to avoid. I put a "leash" like that on each of the four sheaves before pulling any of the pins, and used it to guide each sheave in turn out of the front of the sheave-box. If there is a halyard-guard bolted to the front of the masthead, you'll have to remove it to get the sheaves out.

That "leash" is super-helpful for maneuvering the sheaves back into place when it is time to put the pins back in.

On my masthead there were three pins: one for the main-halyard sheave, one for the jib/centerline halyard, and then one that is shared by the two spinnaker/wing halyards.



Hope that helps
Bruce

Replace existing sheaves with some by Zephyrwerks www.zephyrwerks.com (no financial interest just a satisfied customer- I have one for current boat on order now). They are super smooth.

bigd14 said:

Replace existing sheaves with some by Zephyrwerks.

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+100 on zephyrwerks. I replaced all 4 when I had the rig out. They're gorgeous, they run smooth as silk, and he was easy to work with.

thanks to all, great information. I think my high friction problem may also be related to the width of the existing sheaves. The jib halyard presently is wire to rope and I plan to change to all rope. The main halyard was already all rope when I got the boat 4 years ago and was ratty so I changed to. I put in 7/16 low stretch line because it was easy on the "hand" but now that I can see the fit, the line looks a bit too wide for the sheave and that may be part of my friction problem.

I could switch the line to more expensive dyeema type line and down size to 3/8 but I do like the 7/16 for ease of handling. So the other alternative is to put wider sheaves, has anyone done that?

HerbertFriedman said:

thanks to all, great information. I think my high friction problem may also be related to the width of the existing sheaves. The jib halyard presently is wire to rope and I plan to change to all rope. The main halyard was already all rope when I got the boat 4 years ago and was ratty so I changed to. I put in 7/16 low stretch line because it was easy on the "hand" but now that I can see the fit, the line looks a bit too wide for the sheave and that may be part of my friction problem.

I could switch the line to more expensive dyeema type line and down size to 3/8 but I do like the 7/16 for ease of handling. So the other alternative is to put wider sheaves, has anyone done that?

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Our spar and sheave system is very much like yours.
When changing from wire to all-rope halyards the new 3/8 would chafe a bit in the sheave sides at the mast head. I then went with ultra-low-stretch 5/16 line (T-900). I have not noticed an real difference in handling compared to the old 'fat' halyard tail line.

Of course..... YMMV.....

HerbertFriedman said:

...high friction problem may also be related to the width of the existing sheaves.

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It could be a number of things; as you note, it might be simply that the line is fatter than the sheave-box and is rubbing. It could also be that the stainless pins have worn out the holes in the aluminum sheaves, and they're wobbling/tilting/binding. Or it's possible that the sheave box itself is not square, and the sheaves themselves are binding on the walls of the masthead. It happens.

When I talked to Zephyrwerks, it wasn't just about the sheaves ("I need 4 sheaves, 2-1/2" diameter, 1/2" wide, cut for 3/8" line, with bushings for 3/8" pins..."). He had me take a bunch of measurements of the masthead itself so that he could be sure the new sheaves wouldn't bind on the pins or rub against the walls of the masthead.

Edited to add: if you really want to stay with 7/16" halyards, I think the masthead has the room, but you'd probably want to get sheaves sized for that line. the original sheaves were sized for 3/8".

Loren Beach said:

... ultra-low-stretch 5/16 line (T-900).

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I did the same thing (New England VPC in my case). the 5/16" line runs very smoothly through the mast, and is easy on the hands. It's also stronger (IIRC) than the 3/8" Samson XLS it replaced.

Bruce