Pulling Power

[kermwood]

Hi again to all in EC 12 World
I am playing around with different ways of mounting the front pulley block and could really do with knowing what sort of strain the block would be put under.So does anybody know or are there any figures around on the amount of pulling power the mainsail can put on the main sheet to the front pulley block.(Bearing in mind it can blow a bit in my part of the world!)
Thanks Woody

[Larry Ludwig]

I have never ripped out a block from a mounting although I did manage to pull apart a Pekabe single block on a J boat 2 weeks ago... that was a shock... but just common sense will guide you through this. If it feels like it will fail.. it probably will.

Something to consider is making it easy to thread the darn thing once it is installed, and allow for that... and to replace it when the time comes. Yes, they can wear out, I have boats around here 25+ years old and things will wear out before the operator does.

[PegLeg]

Not to worry so much about the sail pressure on the pulley as to consider the winch output as the determining factor. I have pulled a brass screw eye straight. Since then I use a carbon fibre rod with a shaped block and mount the pulley to that, Now I can fix and fiddle without worry.

[Philip Whitley]

I would agree that the amount of weight in any part of the winch system would be the release weight of the winch eg: 10kg [:0] or the breaking strain of the winch line.

Phil

[Paul Fixx]

The line holding my bow block broke this weekend just before the regatta in Newport when the main sheet wrapped around a cleat on my cradle. The line holding the block was 90 pound spiderwire. I use a 26mm spiral step down drum on a Smartwinch 280DL. The sheet was out on the 26mm section of the drum so I figure the winch could exert up to about 24 pounds of force. There was a 180 degree bend in the line through an eye made of very smooth, 3mm stainless steel and it had been in the boat about a year, so there was certianly some wear. I figure the bend reduced the line's strength by about half and the wear by maybe another half so 22 or so pounds of force to break it is probably about right.

I was thinking about replacing the line holding the bow block with something stronger, but I got to thinking what that would mean. As it was a 2 gram block went bouncing around in the hull. If that line hadn't broken, there are a lot worse things that might have. I figure what I used was about right.

By the way, I've removed everything on my cradle that could snag a sheet in the future.

-Paul Fixx

[Jim Hale]

Here is a technical point, that some of you may not understand. If the load on the sheet is 10kg, then the load on the winch is 10kg, but the load on the block is 20kg. I'm an engineer, I get paid to figure these things out.

Jim Hale