[Public-list] Public-list Digest, Vol 741, Issue 3

[Cole, Andrew L]

George,

I spoke with one person who measured his sheave at 6.5", but it was
possible that the diameter had been reduced slightly by wear on that
one.  Otherwise, 6.75 seems to be the unanimous consensus on diameter.
Where the tightness comes is from the aluminum plates screwed onto the
fore and aft faces of the mast just above the sheave.  These were
intended to keep the wire on the sheave, and fit fairly tightly to the
sheave to prevent the wire from jumping.  If you are staying with wire,
the sheave should drop straight in with no modification to the plates.
If you are switching to rope, it is very likely that both of these
plates will need to be slightly filed down to permit the additional
diameter of the rope (the rope in the old system never went over the
sheave).  I would worry that if the sheave diameter were any smaller,
the rope would chafe on the mast extrusion fore and aft just below the
sheave.  As it is, with the 6.75" sheave the wire hits the aft face of
my mast and has over time worn a very slight groove in the extrusion.
It may be that when we see how everything fits, that the plates are no
longer necessary with rope, or can be substantially cut down to be well
out of the way of the rope and splice.

We will have a chance to install two test sheaves before doing the
entire run, one in Lanny's boat and one in mine (152 and 562), hopefully
these two will provide a good diverse sample and we can correct any
issues before making 25 coasters.  I will try to get lots of photos of
the installs so that everyone can see exactly what it is we are
purchasing, and how it fits in the mast.

Andrew  

>The measurements at
http://alberg30.org/maintenance/SparsSailsRigging/MainSheave/ are 
>actual.  Note that it's bushed to 5/8".  Jay subsequently said that the

>6.75" diameter was too tight, once the shackle was spliced into the 
>halyard.  I believe he reduced the diameter slightly from this so the 
>splice wouldn't jam.

>  - George  

Cole, Andrew L
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