Replacing Sheaves At The Mast Head

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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.
Dunrobin II, 1986 C34 MK1 #170

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...
Steve Dolling
Former 1988 #804, BlackDragon - Vancouver BC
Now 1999 Manta 40 cat

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. 
1989, Hull #873, "Serendipity," M25XP, Milwaukee, Wisconsin

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
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Stu Jackson

One might choose to actually look at the MANUAL to see how it's built.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."

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.
Ken & Vicki Juul
Luna Loca #1090
Chesapeake Bay
Past Commodore C34IA

Dave Spencer

#6
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.
Dave Spencer
C34 #1279  "Good Idea"
Mk 1.5, Std Rig, Wing Keel, M35A Engine
Boat - Midland, Ontario (formerly Lion's Head)
People - London, Ontario