All line mfgs have a specification for minimum turning diameter for their
line, as do block mfgs for what type of line they will take.

Also. the sheaves (wheels inside the blocks) that have been carrying wire
may burs or other unusual wear that may cause increased abrasion or tearing
on line. This aspects should be looked at and fixed.

You say that you are looking at Spectra - (or similar)
These types of lines are interesting. Usually the sizing becomes finding
the minimum size that is suitable for human handling then checking to make
sure that it is exceeds the requirements of the load.
The line is not inexpensive, but then BOAT stands for "Bring Out Another
Thousand"

You will likely find that the existing sheaves with double grooves for wire
and rope are going to be fine for Spectra with a diameter that exceeds the
load requirements you need, but you may find that this diameter of line is
too thin to work with!

I think that wire/rope sheaves do cause increased wear on line when under
load as the line is pulled down into the wire groove, thus it would be best
to replace the blocks to suite the new line where the line diameter is
greater than the wire groove.

There are a number of lines like spectra that have an optional outer core
that can be removed where it will not be handled by people - thereby
reducing the diameter from say the gooseneck to just beyond the masthead
block, but bulks up the line where it is handled.

If you do high performance racing, then you can get a good idea of what is
done by looking at your competition. If you don't race, and thus don't need
to go for the minimum weight/drag line types, you have more choices
available.

On a 22, you should be able to unstep the mast by hand with a few friends,
so it shouldn't be a major task to bring it down for inspection / refit

Check out the detail for this type of line
http://www.samsonrope.com/home/newindex.cfm

Hope this helps

Matt




So you should get this info
"Tim" wrote in message
om...
Hello,
I recently bought a Space Sailer 22 (22 foot keelboat). At the moment
the main and jib halyards are wire with rope tails. The wire seems to
be in ok condition but the rope tails are really bad (destroyed by
sunlight and moisture). I am considering replacing these halyards with
Spectra.

My question is - If I replace these halyards with spectra will I need
to replace the blocks at the top of the mast?? Being an older boat it
may not be a bad idea to lower the mast and check it out but if it can
be avoided it would be good.

I am of the understanding that there are different types of block
(with grooves etc and made of different materials) that are used
depending of whether you are running wire or rope. Would it really
matter if I use a spectra halyard if the block was originally meant to
run wire?? or would it jam or wear too much?

Thanks,
Tim