Masthead sheaves

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chwarae

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Hi,
Just lowered the mast to fit a wind instrument and a general examination. Noticed that one aluminium sheeve at the mast head is jammed and the others look worn but still turning.
On side of mast appears a stainless bar held in with two stainless machine screws or self tappers. Similar arrangement on both sides of mast. Any help with information to remove the sheaves and possibly replace with nylon/plastic would be appreciated.

Thanks
Harry.
 
I was quoted £25 per sheave by Hamble Yacht Services when I asked to replace them as there are unlikely to be any correct spares in existence.

Undo the screws and pull the stainless bar away from the mast wall , in line with the centres of the sheaves.

On my Proctor mast this 'bar' is a flat elliptical stainless steel plate welded on the end of a pin going through the sheaves. The screws stop it falling out. Dont forget that the sheaves will then fall out in whichever direction they want to when the pin through the sheaves is gone.

I replaced the sheave by going to a the Hamble Chandlery Barge (static boat jumble/pile of scraps), and buying sheaves of about the right diameter but too wide and with a hole in the centre that was too small, and then filing and drilling until they fitted.

In terms of effort getting some turned by an engineering shop is more time saving but at the time I thought I needed to get the mast ready in one day, little did I know the riggers would not obtain the correct terminals for the shrouds for nearly 2 weeks.
 
Unless your using wire halyards I don't think you need aluminium sheaves. Nylon is OK most of the time, but a bit soft if you put a lot of tension in the halyard, I'd use Delrin which is a commonly used engineering plastic and harder than nylon if you are going to winch up the halyards so you can play middle "C" on them. Ask a local rigger, they have a tame engineering shop who will make some up for you. I've just replaced a Genoa sheave with Delrin, the nylon was wearing very quickly.
 
Can I ask those with an interest in this subject would it not be desirable to fit a ball bearing sheave rather than, say, solid delrin to facilitate raising and lowering the mainsail?
 
Friction?

srah1953 said:
Can I ask those with an interest in this subject would it not be desirable to fit a ball bearing sheave rather than, say, solid delrin to facilitate raising and lowering the mainsail?
Click to expand...

My guess is that the resistance of the sail or slugs in the mast groove by far the largest source of friction when raising the mainsail and that ball bearing sheaves would not help much. But its just that - a guess.

If you suspect your masthead sheaves are a source of friction...could you test them by lifting a known weight up off the deck attached to the halyard by hauling down on the other end with a spring balance? If the weight registered on the spring balance was significantly more than the known weight you presumably have friction somewhere in the halyard set up.
 
sheaves

If you're not sorted you can get a good range of spare sheaves for all rope dias.from the catalogues of Wichard.com Allenbrothers.co.uk Bartonmarine.com
 
Hopefully sorted,new sheaves arriving in next day or so.
Old aluminium sheaves removed,amazed at wear and corrosion.
Hope relacement sheaves go back in as easily as originals came out.

Thanks for everyone's input.
H.
 
Remember to pass a length of line round the sheaves before you remove the pin, so you don't lose them in the mast.
 
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