Dick Locke wrote:
On Mon, 09 Aug 2004 05:50:52 GMT, "William Graves"
wrote:


I have several similarly rigged blocks for lifting my dinghy and its motor.
Top and bottom blocks have two sheaves. The top block has a place to
dead-end the beginning of the line (I forgetwhatthat'scalled!.Anyway
the line goes down, around the first sheave, up to the same side sheave,
then down and outboard to the next sheave, up to the final sheave and then
to my hand for pulling.

I use good quality woven line and the line develops twist whenever there is
a load being lifted. Not much twist develops without a load. I can remove
the line and clear out all the twist. When I re-rig and then load, the
twists start coming back.

I believe something about this setup forces a twist in the line WHEN LOADED.
I am thinking that the line that crosses over from one vertical plane of
sheaves to the other must ride on the edge of the sheave as it enters and
then gradually gets "rolled" as it finally meets the groove in the sheave.

Anyone know what is happening?
Is there a way to rig this kind of purchase without getting a twist?
-- - - - - - - - - - - - - - - - -
Bill Graves RKBA!




You can get blocks that won't swivel. I had that problem in my
mainsheet and a new block fixed it.

I lashed one built in swivel on a block using string to prevent it
from turning more than about 1/2 turn. In another case with multi
blocks, re reeving the lines, essentially reversing the direction
the line went through one of the blocks seemed to stop it, but the
lines tended to rub against each other which while stopping the
twisting, made the tackle a little slow to run out unless under a
reasonable strain.

Some lines seem more likely to twist up under load. Perhaps a badly
balanced lay up by the mfgr?

Terry K