High-Modulus Upgrade

Ben Cantor of New Bedford, Massachusetts, asks:

"I’ve been cruising on a 1973 Pearson 36 for the past 10 years, and this year I plan to splurge and buy all new sails and running rigging. I expect I will order high-quality Dacron sails. I’ve read a lot about high-modulus line and would like to try it out, but I wonder if it is worthwhile using it on a cruising boat. I like to sail my boat well, but can’t afford to spend a fortune. Does it make sense to use high-mod line for some lines but not others? What sort of rope would you recommend? And do I have to learn to splice?"

Win Fowler replies:

You’ll find it worthwhile fitting high-modulus halyards on your boat, especially the genoa halyard. Luff tension is a critical sail-shape control, and the genoa halyard is the only way to control genoa luff tension. A polyester doublebraid genoa halyard can stretch as much as 6 to 7 inches under typical loads on your boat, while a high-modulus line will stretch perhaps 1.5 inches under the same load. Luff tension is equally important on the mainsail. You can control this with a cunningham, but I suggest you also install a high-modulus main halyard.

You won’t gain much on your boat using high-modulus rope in other applications. Sheets are shorter (stretch is a function of both load and length), are adjusted more frequently and your polyester sails will stretch a bit anyway. So I think high-modulus sheets would be overkill.

For your new halyards, I recommend using a braid-on-braid rope with a Dyneema SK75 or SK78 core and a polyester cover. As for splicing, there’s no need to learn unless you want to. You can buy pre-spliced halyards cut to length from a rigger or sailmaker. Professional splices will likely be much stronger than the first few you attempt yourself.

Finally, check the sheaves at your masthead. Many boats of your vintage were fitted with sheaves designed for wire-to-rope halyards. High-modulus rope won’t perform as well and will wear out prematurely running over this type of sheave.

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