changing sheaves on masthead problem - SailNet Community
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post #1 of Old 07-24-2008 Thread Starter
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changing sheaves on masthead problem

I've just lowered my mast to change the halyards from wire to rope and have found a problem. There doesn't seem to be enough room within the mast head to change the wire sheaves to rope sheaves and the mast head is welded to the mast and cannot be changed. Is there anyway to work around this problem to allow me to change sheaves to rope size? Here are some pictures of the mast head. I didn't measure the sheave size and space available, but I would guess the size total inside that area to me no more than 1/2" max, and maybe even 3/8" which would mean a serious alteration.
thanks again for any help.
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post #2 of Old 07-24-2008
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You need to consult a rigger. But it looks very much to me like if you're really intent on replacing the wire halyards with rope, you're gonna have to have a new fitting built to replace the old one. Counting materials, fabrication, welding, etc., that's likely to be very costly.

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post #3 of Old 07-24-2008 Thread Starter
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thanks Bill. Looks like I'm sticking with wire halyards. Now I need to figure out how to prevent them from destroying my mast around the head area while it's sailing. Any suggestions?
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post #4 of Old 07-24-2008
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So whats your reason for wanting to change it?

My Mizzen is still a wire to rope spliced halyard and I have no intentions of changing it cause it works just fine...rope for your hands and winch and wire beyond...even if you replaced your halyard every other year which you dont need to do..the cost is minimal... Less wind-age aloft and not that much heavier either.
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post #5 of Old 07-24-2008
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Replacing the sheaves on that masthead should be rather simple, provided the mast head sheave slots are wide enough for the replacement sheaves. The two shafts with the cotter pins are sheave axles, and if you remove them, the sheaves should drop out.

You don't say what kind of boat it is, but if it is less than 40' you can probably get away with 8-10mm t-900 line for the halyards.

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I was happy with half wire halyards too until they stretched out and started wrapping around the winches and chewing them up. After climbing the halyards they stretched out even further so i cut them back (too much) and now they need to be replaced, which is fine with me. Have you checked your mast for damage on top lately? I wonder why mine is getting so chewed up? Something is wrong and I need to stop the destruction before it wears a hole into the mast or worse yet the mast breaks off at the top.
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post #7 of Old 07-24-2008
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Dan:

Yes I just Striped and repainted my masts...there was zero dammage you refer to....Something looks screwy in your picture...I have added a diagram...It looks as if by the way your shives are positioned that they were designed to be internally lead but appear to be externally lead???? ( two lines at red arrows ) if they are they are taking one heck of a turn at the mast head and no wonder your getting dammage.
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I don't see why you can't change out the masthead sheaves for ones that can accommodate rope. Without a better photo that gives some idea of size, it certainly looks like the sheaves could be swapped out by pulling the axle pins, which are clearly seen in the third photo. The slots look to be at least 1/2" wide. 10mm T-900 would fit on a sheave that fit in that slot, and has a breaking load of 11,600 lbs or so—more than strong enough for any halyard you'd need more likely than not.

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Those don't appear to be the pins for the sheaves that Rainy has circled and Dog refers to. From the first photo it appears that the sheaves are much larger diameter, there is one per halyard, and their pins are captured inside the mast. Cutting torch job, and that's the easy part!

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yes they are externally lead halyards that run from the front to the back and vise versa for the other. And I doubt there is enough room to fit rope sheaves inside there. I'll give it a try though it will have to be pretty thin rope. It's only a 30' sailboat, so it shouldn't take too thick of rope, but considering the size I think I'm in trouble. Tommarrow I state the exact space available and what my options are.
thanks again to all
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