When I switched from wire/rope halyards to all rope I removed the sheaves and machined them from a V groove to a U groove. At the same time I replaced the bearings with new oilite bronze. After two years I pulled the sheaves again and the bearings were noticeably worn with cracks at the edges. Replaced them again. Two years later it was the same story so I replaced them with Isomat Acetyl sheaves that run on a matching Acetyl bearing. The bearing was drilled out to be a press fit over the SS shaft. The last part was adding custom cut sheets of delrin on both sides of the sheaves and in between to act as thrust bearings.
I suspect that a process was occurring that added significant friction and wear with the previous aluminum sheaves and oilite bearings. The bearings were crushing down enough even over one racing season to allow some slop, which translates into the sheave twisting in the mast head. The side of the sheave would then rub on some part and cause friction as the halyard tensioned. The original setup used two sheets of aluminum to separate the sheaves, both were heavily scored. At some point a previous owner swapped the plates around to get a clean surface again. There is not that many rotations of the sheave under load so judging by the depth of the gouges on the material I would say the twisting force would have to be pretty high. The bearing diameter on the acetyl sheaves is larger, and the plastic to plastic slipperiness presents lower friction than the oilite on SS did. I have not pulled the mast apart to do a thorough examination but a check when I unstepped the mast for the season looked like there was no wear. I did head sail changes during the Lake Ontario 300 in 20 to 30+ kts true. Usually an outside hoist would require hard winching most of the way up, with the new setup it was much easier. The sheaves on a 30-1 are 3.5" OD and 0.5" width, 7/16" ID on the bearing. A reasonable fit was the Isomat 85mm x 15mm ( 3 3/8" x 5/8" ) using a 22mm ( 7/8" ) ID and a matching acetyl bearing. http://www.rig-rite.com/Spars/Isomat_Spars/isomat_sheaves.html The acetyl is rated for handling wire halyards. Michael Brown Windburn C&C 30-1 Date: Sat, 6 Dec 2014 09:12:25 -0500 From: "Jake Brodersen" <captain_j...@cox.net> To: "'davidrisch75'" <davidrisc...@msn.com>, <cnc-list@cnc-list.com> Subject: Re: Stus-List Masthead sheaves replacement Message-ID: <091a01d0115e$a9637550$fc2a5ff0$@cox.net> Content-Type: text/plain; charset="utf-8" David, I replaced several of my sheaves many years ago. The groove for the wire is not that deep. All rope halyards run over them pretty easily without any additional drag. I replaced mine because the plain bearing material had worn away. The original stainless steel shafts were easy to clean up with emery paper. Jake Jake Brodersen ?Midnight Mistress? C&C 35 Mk-III Hampton VA
_______________________________________________ This List is provided by the C&C Photo Album Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
