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Masthead Sheave (Read 361 times)
Jonathan
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Masthead Sheave
21.06.2020 at 14:05:02
 
I was so pleased that my club decided it was OK to launch our boats for the season with some easing of the Covid regulations only to find once afloat that there is something wrong at the masthead. Only by maximum effort with longest winch handle can I raise the main. Clearly nothing to do with the luff as it comes down easy enough and pulling on the fall both sides it seems the sheave is rotating but feels more like a flat tyre going bump bump. I am going to get alongside the club jetty where I can dry out for a day and lower the mast not in the heatwave and when wind fairly light.

Hopefully I will be able to remove the sheave without too much trouble. The mast, now 40 years, old is the original I think by Procter and from memory there was a stainless plate held by two self tappers and this carried the spindle. I have not been there for 25 years on the if it ain't broke don't fix it principle so hoping it will come out OK - I see an earlier post of an owner having difficulty with this. It looks to me as though the sources for a new sheave will be Selden who took over Proter I think, Barton who are local at Whitstable or Allen. Between them they seem to have a range of sizes but I have no idea yet what size I need. Width and bore seem to be critical though I guess I could drill out a smaller bore if the width is right.

A lot of the sheaves available are Acetal but I am sure the original is metal. Is it OK to use Acetal for the masthead main halyard? I have replaced most of the deck organiser and mast foot organiser sheaves some with metal and others with Acetal and those seem to be OK but would be easy to replace. This masthead sheave has 4mm wire running over it at all times. Will Acetal put up with that?

I will be grateful for any experiences or possibly suggestions of other sheave makers I have missed.  
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Paul
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Re: Masthead Sheave
Reply #1 - 03.07.2020 at 09:00:48
 
Hi Jonathan,
Your diagnosis of worm out sheave seems logical. I recall my old Proctor mast used a fairly small metal sheave. If you are retaining a wire halliard section I would not use Acetal as its resistance to any fretting movement due to mast moving however slight will be inferior to metal. On Nautibuoy I transferred old Dyneema halliards from original mast into new Z Spars unit.This has a metal sheave I think. The Dyneema is 16 years old and appears good as new. Of course either material for sheave would be fine with Dyneema.

Dell Quay decided on launch early june. With restrictions on who could assist (family members ) and same for sailing about half the boats including

myself decided to sit the season out on the Quay. Might have worked out better early July but fairly short season!

Had thought that earlier prep in March for launch would mean boat all set for 2021 launch but recent visit shows new antifoul is 'washed out ' from vivid to pale blue by rain water.
Does anyone know if this would still be effective ( I suspect not!!!) And whether a pressure wash next March and further coatis the way to go?

Anyhow to those able to sail, enjoy the season, with the hopeful expectation that next year will be much better.

Cheers
Paul
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Jonathan
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Re: Masthead Sheave
Reply #2 - 03.07.2020 at 19:41:18
 
I now have the mast down and the sheave out. The wear and tear or corrosion damage is so severe I wonder it had not failed me some time back. It looks as if the sheave was originally 10mm wide with a groove for 4mm wire and 36mm diameter. That rules out all of the off the shelf sheaves I can find so the options look like either going for 8mm and inserting some form of sleeve or bush as they all seem to have 8mm bore at smallest and the axle looks to me to be pre-metric 0.25" or I could get a 10mm selden sheave (nylon) and drill out the bore as it comes as 6mm  but it is only 23mm diameter whereas the one I have taken out is 36mm.

With Allen and 8mm width I have a choice of Acetal or Aluminium. Not sure about resistance of aluminium to electrolysis and corrosion but may last a few years and maybe dyneema is the way to go. If I had not been launched I would not have found the problem but now beginning to think by the time I have solved this there will not be a lot of season left.

Most tins of antifoul say something about a time limit before launching. I am not sure precisely why so assume it does lose its effectiveness. I was not sure if mine was already past a critical date as I applied it well before Covid - we will see come lift out.
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Paul
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Re: Masthead Sheave
Reply #3 - 04.07.2020 at 11:14:01
 
Hadn't realised the sheave was that diameter.
Try looking at Barton Brass sheaves  which are for heavy duty  use with wire or  rope.
I have one on the backstay adjustment and its standing up well to the wire.and exposed conditions
I think there are two sizes, one at 35mm?
Paul
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Foddubh
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Re: Masthead Sheave
Reply #4 - 10.07.2020 at 16:47:16
 
Jonathan

I replaced this last year but used the original pin which is off centre . I thought it was bent at first. I replaced wire with 8mm rope and is working fine on metal sheave with bearings.. I was able to use the original pin with new sheave which just about fitted back onto to the old pin.
I didn't think the 8mm would work but it just about made it .

I cannot send images as I have not made more than 6 posts but you can perhaps PM me if you need more info.
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Jonathan
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Re: Masthead Sheave
Reply #5 - 19.07.2020 at 16:30:55
 
Thankfully I now have a replacement sheave installed, the mast back up and have managed to get a first sail for this season. Many thanks to Paul for his advice a while back about using a halyard to hoist preventer lines to stop the mast swinging sideways whilst half way. (Much easier and safer than a ladder) I used the Spinnaker halyard to leave the main free for dealing with the sheave.

I am most interested in the comment "original pin which is off centre". I am assuming the plates carrying the pin are all the same on the Proctor masts. I did not have enough of the old sheave left for an accurate measurement of width and put my gauge as far as it would go into the slot and appeared to find 10mm, so used an 8mm sheave with a 1.5mm penny washer of similar diameter. It was fiddly enough to introduce both sheave and washer and line the holes up but though I could slide the pin through both I was quite unable to locate it in the mast the other side. With the spacer washer the sheave seemed very tight so I did away with the washer and hey presto all went together easily. The fit looks snug enough so I am not bothered about the wire jumping off the sheave. Maybe there is some peculiarity about the pin I had not noticed or my initial measurement was wrong.

Having done all this I have found somebody in my club who says he could turn up a sheave on a lathe to precise size needed. I will probably take him up on this in the winter as I notice one of the forestay sheaves has started to wear.

What I took to be the original sheave may not have been. The self tappers holding the pin and its mounting plate are different sizes suggesting someone has been here before and the remains of the sheave I took out had a plastic bush at centre with a bore 8.75mm. How much was wear I cannot say but my pin is only 6.3mm so it was a pretty sloppy fit. My replacement sheave was an 8mm aluminium one for Allen with a bore I drilled out to 12.5mm to take a nylon bush with a 6.4mm bore obtained via Ebay. The main is now easier to hoist than it has been for years and I thought it was me getting weaker.
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