Install Oversize Masthead Sheaves for More Halyard Choices

When planning the replacement of my wire/rope halyards with all line halyards so that I could lead them aft to the cockpit, I decided to use all 8mm (.314″) rope. Along with cockpit convenience for single-handing, I wanted easier line handling and less stretch, especially for hardening the luffs since I don’t have halyard winches. The cost is not much more than the standard 1/4″.

Eight millimeters is larger than the standard equipment 1/4″ rope that is used for external halyards on first generation C-22s. If you have internal halyards, they are probably 5/16″ (.3125″). With internal halyards, there are only two sheaves in the masthead, one forward (headsail) and one aft (mainsail). They each take up the entire width of the sheave slot. Each of the two pairs of external halyard sheaves must sit side by side in that same slot along with a spacer between them to keep the lines from jamming in the masthead.

Some of you might be thinking, “But wait a minute, 8mm is too big for the 1/4″ masthead sheaves,” and you’d be right. Even if I switched the four masthead sheaves for the external all line halyard sheaves from a certain Catalina parts dealership, those too can only accommodate 1/4″ halyards and would be too narrow for 8mm lines. CD states that theirs are the only sheaves that will fit in the masthead. That might have been true when they first started selling them, but it’s not so true today.

Getting a big head at the masthead

Ronstan RF251 sheaves are the same inside and outside diameters as the original equipment sheaves but wide enough for 8mm or 5/16″ lines. This means that they are slightly wider than 1/4″ sheaves. Two pairs of them will fit in the masthead with no modification other than a thinner spacer between them. The stock spacer is 2.5 mm thick. I fabricated one out of 1.75 mm aluminum and it fits in the masthead along with the new sheaves and room for them to turn freely.


Instead of making a new spacer, you could sand down the original spacer using a reverse sanding block technique. Afix the spacer to a the bottom of a hand-size scrap of wood with carpet tape and hold it against a belt sander or a piece of coarse sandpaper on a flat surface. Move the block over the sandpaper instead of vice versa. You’ll have much more control and a flatter spacer than if you try to sand the spacer by holding the sandpaper in your hands, even on a sanding block. If your spacer has grooves worn in it from the sheaves like mine did, sand one side halfway, flip the spacer over on the block, and sand the other side halfway.

Oversize sheaves (white) next to the stock sheaves (black) and spacer.
The new, wider sheaves next to the stock (black) sheaves and spacer. Notice the oblong center hole.

To remove the old sheaves, unstep the mast, remove the cotter pins from the sheave pins and tap out the pins. The spacer will come out with the forward sheave pair. The aft pin doesn’t go through the spacer. Note the orientation of the spacer in the masthead. It can be accidentally reassembled upside down (don’t ask me how I know this). If the pins don’t come out easily, see my post on galvanic corrosion for some tips and warnings.

To install the new sheaves, first mount the aft pair of sheaves in the masthead without the spacer using a new cotter pin or ring in the sheave pin. Then slide the end of the spacer that does not have a hole in it between the top halves of the two aft sheaves. The angled edge of this end should be facing up. Rotate the front of the spacer down into place between the two forward sheaves where you can pin it together with the sheaves. Reave the halyards through the masthead while you have the mast down. This would be a good time to also inspect the backstay and forestay terminations and fasteners, the masthead attachment, and any masthead accessories such as your anchor light and Windex.

The Bottom Line

Suggested price: $46.88
$tingy Sailor cost: $18.96
Savings: $27.92


8 Comments Add yours

  1. devarah says:

    Hi there, I just did this project today, wanted to say thank you for all the great advice, part numbers and step by step instructions! It’s going to make raising and lowering my sails so much smoother.
    Fair winds – Deb in NH

    1. Really glad it helped! Thanks for your comment.

  2. Ken says:

    If converting to internal, is it advisable to run four halyards, adding one for the spinnaker and one for a topping lift? If so what would you recommend for exit blocks?

    1. Hello, Ken

      I wouldn’t recommend 4 internal halyards for a C-22 for the following reasons:

      • The mast doesn’t have much room left inside if you consider electrical conduit for a steaming light or anchor light.
      • All the tapping screws inside the mast for jam cleats and other external hardware that can shred the halyards and would have to be replaced or modified.
      • Running the topping lift down the mast would add too much friction and cost for nearly zero convenience. I almost never use it while under sail, so having it on the boom works fine and reduces weight aloft.
      • The masthead exit location is poor for a spinnaker halyard. It should be higher and as far forward as possible from the jib halyard and forestay. That’s why you see spinnaker “cranes” to provide a better position.

      So the only lines that make sense to run internal are the mainsail and headsail halyards. You can do it with two of your existing 4 external halyard masthead sheaves or convert the masthead to 2 centered sheaves.

      I’d recommend exit blocks at the base of the mast like the Harken #131. The halyards can lead directly from those to your deck organizers so you don’t need a mast step plate with turning blocks if you don’t already have them. Makes for a cleaner, simpler installation.

      Harken #131

  3. Doug says:

    Hello, thank you for all the information! I was wondering if it is possible to switch to all rope halyards without changing out the sheaves? Is there a certain diameter of halyard that would be strong enough but a small enough diameter for this? Thanks for your time!

    1. Hi, Doug

      1/8″ Dyneema would probably fit the sheaves but it would be painful on the hands and more difficult to handle. That is, unless you spliced a length of larger (5/16″+) onto the working end similar to your current combination rope/wire halyards. But with that much of a difference in diameters and considering how low friction Dyneema is, I doubt a standard, tapered splice would work well.

      Thanks for your question,

  4. Scott Reynolds says:

    I managed the replacement of sheaves with the suggested Ronstan sheaves, and “machined” spacer (aka did a LOT of sanding) down to the necessary thickness. After re-assembly the new and slightly larger sheaves moves freely and I’m ready to install 5/16 halyards. As always, I greatly appreciate your clear and comprehensive information and directions!

  5. Leslie says:

    Very nice blog you have here

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