Line Load Litigation

[lavery]

Riggers,
It appears that neither New England Ropes nor West Marine want to venture recommendations for sailboat running rigging applications. Fair enough. They may prefer to avoid ever seeing a lawyer show up at their door as a result of their recommendations.

So I am grateful for Brion’s “Rigger’s Apprentice” (the textbook for this note) for providing charts, graphs, formulas, techniques, material descriptions, and product reviews to guide me toward my rope purchase decisions. (..end of testimonial..)

(..intro to question..) Using Harken and Lewmar formulas and chart, and rounding up to the nearest 500 pounds, I landed at 2,000 pounds of force for mainsheet loads. New England Ropes wants me to multiply by a safety factor of 5.

(..the question(s)..)
*What is the range of mainsheet diameters that feels comfortable to your hand?

* I want to use 3-Strand Nylon for the mainsheet for its shock absorbing ability. Would anyone hesitate to use a 7,500 pound nylon mainsheet (1/2” in chart below) to manage nominal 2,000 pound mainsheet loads?

*Finally, for halyards, my sense is that they are subject to far lower shock loads than sheets. My halyards calculate to 1,500 pounds (per Lewmar). What safety factor would you apply to halyards?

Happy sails to you,

Jim Lavery
s/v Hoku Ke’a
Southern Cross 31 cruiser, displacement 13,500 lbs.

New England Ropes 3/8" 1/2" 5/8" Stretch @ 30%:
3-Strand Polyester 7,500 11,700 n/a n/a
3-Strand Nylon 4,400 7,500 12,200 13.0%
12-Strand Single Braid Poly 4,500 7,500 11,000 4.5%
Double Braid 4,400 8,500 14,400 3.5%
Double Braid Parallel Core n/a 5,500 9,600 2.8%

[allene]

I am no rigger but why on earth would you want to use 3 strand or nylon? That is dock line. If you are concerned about shock loads, don't use HM line like Warpspeed.

Use some 7/16 Sta-set or XLS. Your boat isn't that big, is modern, etc. I mean, you probably have an aluminum rig. Mine is wood, my sails are bigger than yours, and I use 7/16 XLS for the mainsheet. Works great. You really don't want that much stretch and 3 strand just won't run nice.

As for the 2000 pound load on a main, if you have 4:1 blocks on there that means you are pulling with 500 pounds, which is 10x what you can pull.

Allen

[Ian McColgin]

Second that on nylon with what I hope is a wake up call rather than is taken as an insult. After all, the only really stupid question is the one you didn't ask.

Have you ever sailed? How could you possibly want stretchy line for sail control?

Your concern about "shock loading" the halyard is so far beyond reality that I'm at a loss as to how you think you might correctly rig any boat.

It is true that some classic fleets suffered spar breakage when there was a mass conversion from natural fibre to dacron sheets but I can't imagine that you're old enough to remember that because if you were, you'd already know the answer.

The question displays such profound lack of understanding of the basics of sail control that I'd rather not answer your questions directly without some insight into your experience. It's possible, for example, that you've been an AB on a tug or ferry or something and, while used to line handling, don't know about sail control. It's even possible that you've been a crew on some boat somewhere but did not learn the why's of what you were doing.

When you set a sail, you want to adjust it for the conditions and then not require constant readjustment. Assume for the moment that you're looking at how to set up a marconi (triangular and attached to the mast and most often boom) sail. You may sail enough to get the idea how in heavier weather flattening the sail out by increased luff and foot tension. If the halyard and/or outhaul creep, you'll just have the sail bagging off depowered and in a poor shape. So, you use dacron or perhaps even more modern really no stretch exotics) to put AND KEEP the pounds of force you want.

Same with the sheet. You want to haul on the mainsheet such that the sail is where you want it and stays there. If you need to ease or trim the sail due to wind shift or a little gust or whatever, you want to control that rather than have the accidents of stretch for a given line diameter as modified by the mechanical advantage of the sheeting tackle.

There is such a thing as shock-loading a sheet if you don't handle it correctly during a gybe. Rather than rely on sheet stretch that destroys your ability to trim the sail correctly, learning elementary line handling does the trick.

Please give an indication of the boat and her rerigging needs. There are general standards for suitable sizes for a given sail area. But more than this, please give a hint as to what sail-knowledge resourses you have at hand - books, mentors, wise old fellow with pipe and cool hat, whatever - so that people here can give you a notion of where to look for further guidance.

G'luck

Ian

[lavery]

Allen & Ian,
Thank you both for your informative and very entertaining replies. Now that I have finished crunching numbers, a conversation with experienced opinionated sailors is exactly what I need to balance my results.

Allen,
Thank you for your recommendation of 7/16 Sta-Set or XLS. That is certainly in the calculation ballpark. Also your comments about line feel and running are just what I was hoping to get from this conversation.

The 2,000 pound mainsheet load is the result of heavy-handed (some might call it "conservative") use of Harken's Main Sheet Load calculation at:
http://harken.com/calculators/MainsheetLoading.aspx
Try it out. V is relative wind speed. Let me know what you get for your mainsheet load, and what you used for wind speed.

Using a simple Lewmar chart for my 31' boat, I get 1,100 pounds. At 4:1 that is still, by your estimate, 5x more than I can pull. So here so far we do not have convergence.

Thanks,

Jim



Ian,
Wake up calls are most appreciated. I'd rather figure out the errors of my ways while sitting in front of a computer than....

First, my question on halyard was misleading. I failed to specify that I want Sta-Set-X (or equiv.) for halyards. My sense is that once set, halyard loads will not change very much, unlike sheets. So my question is: Are halyards subject to shock loads? If so, then I must take that into consideration.

I may be thinking about shock loading incorrectly. In sizing my lines, I am looking for any event that may impact halyard load significantly beyond normal setting tension. If it exists, I want to quantify halyard shock load in pounds added to normal tension.

Also, I have no doubt that you are right about a stretchy mainsheet not getting the best performance.

Thank you for wanting to asses my experience. That is important. I have sailed a 26' S2 7.9 for 12 years in Prince William Sound in Alaska. Sounds good until I add that the boat was 300 miles away from where I lived and worked a day job, so boat outings were limited to occasions where I could get away 4 or 5 days in a row. Oh, and the practical boating season is only about 5 months. So I would guess that all boils down to maybe a year's worth of good hands-on mostly solo sailing. Still, I got out, met some challenges, and lived to tell about it.

After about 4 seasons I replaced the running rigging on the S2. I used 3-strand nylon for the mainsheet as an experiment. Having experienced a few boom-slams, I wanted to try stretchiness to back me up when I was distracted or behind the curve. I was very happy with the results. Not being a racer, I never noticed a performance loss though I did not pay much attention. I spent a lot of time in the Valdez Narrows (about a mile across) sheeted in hard, having too much fun beating my way uphill, tacking, and not getting run over by tankers.

The boat that I am rigging is a Southern Cross 31 with ~240 sqft of mainsail. The textbook for my questions is Brion's "Rigger's Apprentice" from which I got most of the rope information, and all of the formulas and charts that I used to arrive at my initial plan.

I am now seeking from you and all a peer review. I appreciate your feedback.

Rigging needs are halyards and sheets for jib, staysail and mainsail. I have books and internet, and you and Allen are my wise old mentors with pipe and cool hat.

My questions remain:
What is the range of mainsheet diameters that feels comfortable to your hand? (subjective - no engineering required)

What load is your mainsheet designed to carry? Allen questions my 2,000 pound figure so this is a good challenge to work through first. We can deal with line material elsewhere.

For halyards (with Sta-Set-X for example), are shock loads significant as they are with sheets? My definition of shock loads includes any event that might add load above set tension.

Lastly, Ian, what is an AB? (I'm guessing Assistant Bos'n)

Thanks,

Jim

[Ian McColgin]

Ahoy Jim,

AB is short for able bodied seaman, the step up from wiper. (Don't ask, but that was my first z card.)

Shock loading on halyards is most rare but a gaff peak halyard can get quite a strain during a gybe. When one local fleet finally moved from manila to dacron, they had the halyards set by feel like they had with the manila. In a good wind the loads up there are impressive and you'd see bending gaffs commonly, sometimes breaking just under sail. Setting the peak that hard with manila worked well enough since in a gybe the line would gather back some of the stretch and let it out the other side. Dacron was just enough less stretchy that people had to learn to trim the peak halyard a little less belligerantly.

Good sailors can spot folk with nylon sheets a mile off and it's painful. You really will have so much more fun with your boat if you do her the honor of letting her sail right. A gybe is the only time the shock on the sheet matters much and the risks are way over-rated compared to everything else that can go wrong. For example, when the wind gets on the other side of the sail, the boom naturally lifts. Absent a heavy boom or a vang, it can easily lift high enough to foul the backstay on the way across. No there's some shock loading but it's not on the sheet.

Many contemporary sloops have the main ending with a cam cleat mounted on the exit tackle, which is often on a track. The cam cleat needs to be angled such that when you're hauling in the sail at the start of your gybe you're not hauling through the cleat. Once the sail's coming across you want it running freely. With a little practice and maybe some gloves if you don't harden your hands with rowing or rope climbing or something, you should be able to haul in fast and when the sail crosses do NOT hold the sheet to then let out. Rather, have your palms open so the sheet can run and you grip it only when it's moving. That way the only shock is overcoming the sheet tackle's initial inertial resistance.

There are various boom tamers on the market but it's worth just learning how to handle and surge the line.

It's also useful to remember the the shock is rarely that big a deal. The boat will roll with it and modern dacron in the sheets and sails are incredibly strong.

Line size - you don't want it too big for the boat but most main sheets are fantasticly stronger than the job requires since the hand grip comfort is paramount. I find line smaller that 1/2" annoying. For a genny sheet, 5/8" is hardly too small.

G'luck

[lavery]

Ian,
Yes, the mainsheet on my S2 sloop was set up as you described: "cam cleat mounted on the exit tackle, which is ... on a track." The cleat was on an angle clear of the sheet until I purposely locked it in. It worked very well.

Based on your comments I will let go any concerns about halyard shock load.

Also, your comments about stretchy mainsheets are very well taken. In the direction in which I am moving I see the opportunity to spend more time on the boat refining techniques. As a result of our conversation I am leaning now toward a more conventional single braid polyester mainsheet (such as New England Regatta).

Thank you also for your reference to line diameter comfort in hand, which for you is at least 1/2" - very helpful.

Thanks and good sailing,

Jim