I broke my jib
sheet and need to deal with it. Following the break I am now using an old, previously retired sheet.
I have a 20mm diameter braid on braid polyester jib
sheet tied with a bowline to the clew of the yankee and running through a 65mm diameter sheave on the genoa
car to a large cheek block, then to the winch
. The angle from deck
to the clew at the sheave on the car was about 60 deg, so quite steep. Whilst beating under full sail in barely moderate conditions and with a steady wind
of 16kt the sheet snapped at the jib car sheave.
are about 6 years old and spend most of their life in the Caribbean
sun, but show no significant sign of wear or aging. Mileage is not large. The sheet loads should have been somewhere around 700kg from the Harken
calculator and the sheet breaking strength should be somewhere over 8000kg. I am not sure of the brand of my sheets
, so am assuming a low strength figure there.
I am surprised it broke. I can't work out why. I would have expected the sheet to go at the bowline as that ought to be the weakest spot.
I wonder if the repeated running over the tight bend at the sheave on the car weakened the rope
, plus of course there would be some UV damage. But all combined, surely not to weaken it to less than a tenth of its rating?
So, I am wondering what to do. If the breakage is due to a fatigue failure over the jib car I could just shorten the rope
to work a different area. I do end-to-end it already, so any fatigue will be less than it otherwise would be.
I know it is a good idea to have a large diameter sheave in relation to the rope diameter, so I could go for a dyneema
sheet, where I could have the same strength with 14mm instead of 20mm and get a 4.6x ratio over the sheave instead of the 3.25 that I have now. Plus lighter weight and easier handling. Or maybe a larger size for reserve strength. On the other hand would a thin rope work OK on the winch
? Would more wraps deal with it OK? Would it be too inelastic and transmit heavy loads to the boat? My sails
are already stiff string sails
, so there will be little shock absorption in the system.
Any suggestions as to what happened and what to do about it?