J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Halyard Loads

Bob posted the following in another thread. I thought I'd move the discussion to an appropriate thread and ask a more direct question.

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Checking Harken.com's Compuspec "load report", the sheet load on the Genoa in 20 knots is 507 lb and 1355lb on the #3 in 40 knots, with an end boom load of 1818lb. That's 1/7, 1/3 and 1/2 respectively of the 3800 lb tensile strength of 3/16" Spectron 12. Figuring 100 feet from Layline, Spectra is $55, Technora $70 and Vectran $83, it's hard to justify the additional cost for the extra performance. Spectra is a bit lighter and there is no concern about UV. Creep, the supposed Achilles' heel of Spectra, has not been a problem, though we do regularly adjust halyard tension when racing. We've had the same jib and main halyards for over four years and they were pulled only for one winter. Ours are covered only at the clutch; before you locate the covers, be sure to consider that the luff of the #3 is 2'3" shorter than the #1 and you might reef the main! We use covered Spectra for the spin halyard and sheets for ease of handling.

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Good information. Does anyone know what the actual design loads are for the halyards? Or, just as good, does anyone know how to calculate the actual loads? I'd like to pick the right size lines based on actual design loads for the halyards rather than use loads from Harken that are for sheets and blocks.

Alan Grim
J30 #359 JayHawk

Alan,
When a triangular sail is sheeted in (as in going to weather) the loads on each of the three corners are just about equal; therefore: sheet load = halyard load = tack fitting load.
Safe working loads depends on application and your acceptance of risk. I use a safety factor of 200% for noncritical loads such as sails and 1000% for critical loads such as hoisting a person to the top of the mast. Using Bob's 3800-lb breaking strength for 3/16 Spectra, I would be "happy" using it for halyard loads up to 1900 lb and for hoisting a person up to 380-lb. (Although I hope I never have that much sail up in that much wind or have to hoist someone that big to the top of the mast.)
Another factor to consider is that for some of the wonder fibers the %elongation is nonlinear and becomes a lesser percentage as the load increases.

Alan,

The equations you are looking for are in the Harken Catalog at http://sailingsource.com/harken/pr_lod-e.pdf

The equations for jib and mainsail show the load increasing as the square of the wind velocity but do not account for the reduced sail area exposed as the boat heels. The equations are therefore conservative. The mainsail equation accounts for the fact that the mainsheet attachment is not quite at the end of the boom. (E=13.0, X=0.75 on my J/30).
If you want the main halyard load, which is a little less than the mainsheet load, set X=0.0.

Jim Ingles
Rosebud, Hull 201