Replacing Sheaves At The Mast Head

[Mark Sutherland]

I'm having my halyards replaced, and some other above deck routine maintenance done by a rigger this week.  I asked my contact at the rigging company to replace the sheaves at the mast head while he was up there.  They said they could only do that while the mast was down.  Is that correct and why? Thanks.

[waterdog]

I think they are correct.    The sheaves are mounted in the cap assembly that you need to pull off the top of the mast.    It is held down by stays.    No real access without pulling the stick.  Or you need a more adventurous rigger...

[Clay Greene]

Because you have to take the top of the mast assembly off and that is how the forestay and backstay are attached to the mast.  I remember seeing photos on this site of how someone managed to do it with the mast up but it struck me as a lot of work with a fair amount of risk for not much benefit.  Do a search and I am sure you will find it.  IMHO, think taking the mast down every few years is a good safety exercise to inspect all of the rigging and fittings for corrosion plus you can do things like replace the sheaves and lights, etc.   

Garhauer is a good source for the replacement sheaves that are aluminum running on ball bearings instead of the cracked plastic originals.  Mark Felgenhauer will know the right sheaves for your C34. 

[KWKloeber]

If the mast truck has an open top (like C30) then you can do it with not "TOO MUCH" trouble, though tricky.   If the top of the truck is closed (as I have seen on at least some C34s) then it's nearly impossible to get at the sheaves, get and restrain the halyards and sheaves while replacing, etc.   Couple that with possibly a seized clevis pin, and it gets "interesting."

kk

[Stu Jackson]

One might choose to actually look at the MANUAL to see how it's built.

[Ken Juul]

about the only way to do it safely is with a bucket truck.  disconnect the fore an aft stays, unbolt the cap, pull it up enough to change the sheaves.

[Dave Spencer]

I replaced my sheave a few years ago while I was repairing the loose conduit in the mast.  Reply #28 here  http://c34.org/bbs/index.php/topic,7170.msg48681.html#msg48681

Here are a few more pictures showing the details at the mast head.  It's good to know what you can expect to be looking at when you take on the job.  I take my mast down every year so it's fairly easy to do while it's down.  The new Garhauer ball bearing sheave's sleeve was slightly undersize and I had to ream it out a bit to get the pin to go through.

I would think this would be difficult to do 50 feet in the air with a bucket truck but it sounds like some may have done that.