Load on mainsheet blocks & winch

[NoExit]

Hello savvy sailors,

If the load on the sail/boom in this set-up is ~1,500 lbs, what is the load on each block and the winch in this system? I'm trying to determine the specs of blocks I need for this set-up on a 2007 Hunter 31. Thanks.

 

[JoeWhite]

500 ib

 

[Davidasailor26]

If the 1500 lb measurement is meant to be what’s carried by the mainsheet (ignoring the gooseneck and the torque from the mainsheet being mid-boom and not at the end) -

You can approximate that the 1500 lbs is distributed equally by (5) and (7), so they must carry 750 lbs each. (6) will carry the full 1500. Tension on the line will be 1500/4 =375 lbs. Blocks 3 and 4 are each 90 degree turns in a line carrying 375 lbs, so they each experience 375*1.4 =525 lbs. Block 2 has a gentler 45 degree turn, so that one’s about 375*0.76=285 lbs. The winch experiences the sheet load of 375 lbs.

I would not be surprised if shock loads in a gybe were much higher.

 

[NoExit]

500 ib

Thank you. Forgive me, as math/physics were not my strongest in school. Does this mean it's a 3:1 purchase system?

 

[NoExit]

If the 1500 lb measurement is meant to be what’s carried by the mainsheet (ignoring the gooseneck and the torque from the mainsheet being mid-boom and not at the end) -

You can approximate that the 1500 lbs is distributed equally by (5) and (7), so they must carry 750 lbs each. (6) will carry the full 1500. Tension on the line will be 1500/4 =375 lbs. Blocks 3 and 4 are each 90 degree turns in a line carrying 375 lbs, so they each experience 375*1.4 =525 lbs. Block 2 has a gentler 45 degree turn, so that one’s about 375*0.76=285 lbs. The winch experiences the sheet load of 375 lbs.

I would not be surprised if shock loads in a gybe were much higher.

Thank you. I think I follow the logic here, but math/physics were not my best subjects in school. Does this mean this is a 4:1 purchase system? I'm looking to move to the system in the diagram in my original post above, from this below, which I think is 2:1, but I'm not confident in that, and wonder if it's only 1:1.

 

[Project_Mayhem]

That's probably a 7:1 purchase as there's a double block and one with a beckett. I'd imagine the math would be 1500/7=214lbs per point? if this is correct, would the double block or beckett block need to have double the load capacity?

 

[thinwater]

David got it. Also, you have not given enough information.

It is a 4:1 system, but load is not boom-end, which reduces efficiency. Neglecting friction, the red line is 375 pounds everywhere. Also ignoring small corrections for the exact angles.

• 7 is double = 750 pounds.
• 6 is quad = 1500 pounds.
• 2 and 4 are 90 degree deflections. About 525 pounds.
• 5 is an oddball. About 840 pounds.

However, load is not boom-end, which reduces efficiency. The actual load is probably about twice this (ratio of lengths--also, you did not give the block spacings).

And like he said, the jibe load will be greater, about double with polyester sails, polyester sheet and traveler, and reasonable control. If any of this is Dyneema the numbers go up (shock). Yes, I have measure some jibe loads--obviously, they are extremely variable.