pic: Telescoping Arm Warning

[Tom Line]

Thanks for the pic. Your post brings up a good point. Not only do you have to be wary of mechanical advantage. Putting a knot in a line ('rope' for you non-sailors) will lower the breaking strength by nearly 40%! The 'correct' way once you know your required line lengths would be to use a thimble (not the sewing kind) and have the line spliced, or you can mearly account for the reduction in strength due to the knot and use larger line.

[gblake]

Originally Posted by Tom Line

Thanks for the pic. Your post brings up a good point. Not only do you have to be wary of mechanical advantage. Putting a knot in a line ('rope' for you non-sailors) will lower the breaking strength by nearly 40%! The 'correct' way once you know your required line lengths would be to use a thimble (not the sewing kind) and have the line spliced, or you can mearly account for the reduction in strength due to the knot and use larger line.

This is an asterisk on Tom's good advice:

Anything (including a thimble) that puts a curve into the line lowers the force it can survive without breaking. The fibers on the inside of the curve go slack a little bit and contribute less to the strength of the total line; and consequently the fibers on the outside (that are now carrying more load) break under less load than a straight line could survive. Each individual fiber is as strong as as ever, but fewer of them are sharing the total load.

Using a thimble's "gentle" curve reduces the breaking point less than an ordinary knot with a severe (small radius) initial curve; but I wouldn't want anyone to think that using a thimble allowed you to avoid the strength reduction entirely. Even with a thimble you have to account for some loss of load-carrying ability.

Blake

[travis]

Some people will tell you that there is no rope on a sailboat, but this only holds true for an ill-prepared one. Even fancy pants spinneret-ed high tech fiber used for holding stuff together on an america's cup boat is called rope when it is on the spool, as "rope" is the term for the raw material. A line is a usefully knotted/spliced/whatever amount of rope. So next time "captain" Bill castigates you with the old chestnut, tell him to wait while you go get some, cause how else are you getting home if the halyard snaps?