Sheet Load Engineering

[Mark Johnson]

Jim, this will not help out your "inner engineer", and I eventually dropped out of mechanical engineering, but...

With larger boats this is a valid point to try to figure out. With your 31'er however, assuming you avoid chafe, if you go with say... NER 7/16" Sta Set, (the smallest size that I like the feel of), the rope is NOT the weak link! Either the blocks, traveler car, boom, or clew of the mainsail is...
You still have to avoid an out of control, crash slam, accidental gybe! I have always been a multihuller, and in my youth, did one of these on my cat, not realizing that the (2 X oversized) traveler was somehow not cleated. It crashed across the 12' track with such speed that the huge traveler car EXPLODED! The 3/8" double braid polyester line was fine. It is hard to engineer a boat for doing something stupid like I did!

A 7/16" mainsheet is big enough for a 31' monohull, even with mid boom sheeting...
Mark

[Brion Toss]

Hi again,
Great traveler story. I once saw a winch explode, one of the gears blowing a hole in the wall. At least I think it was a gear, but we never found it. So yeah, we are dealing with forces that matter, which is one reason to run those numbers.
As you move on to block selection, remember that the angle of the line on the block determines block load, and that you do not scale the block to the selected rope size, but to load and angle.
Fair leads,
Brion Toss

[lavery]

Thank you Mark and Brion,

Mark,
Wow! Yes, operator error trumps good engineering – all part of the sailing adventure. On my 26’ S2 sloop I used a 3-strand nylon (16% stretch) mainsheet to back up my operator errors. I liked the cushioning, but may have degraded performance.

Thank you for your rope recommendation, and too for sharing the diameter that works for your hand. That is another variable for me to consider.

Jim


Brion,
I’ve seen your tratment of angles in “Rigger’s Apprentice.” Good stuff. I look forward to applying it. Thank you for pulling that book together. It has been a big help.

Jim

[lavery]

Thank you Mark and Brion,

Mark,
Wow! Yes, operator error trumps good engineering – all part of the sailing adventure. On my 26’ S2 sloop I used a 3-strand nylon (16% stretch) mainsheet to back up my operator errors. I liked the cushioning, but may have degraded performance.

Thank you for your rope recommendation, and too for sharing the diameter that works for your hand. That is another variable for me to consider.

Jim


Brion,
I’ve seen your tratment of angles in “Rigger’s Apprentice.” Good stuff. I look forward to applying it. Thank you for pulling that book together. It has been a big help.

Jim