Short answer

Choose halyard rope by matching low-stretch core fibre to the load, then sizing for the hardware and hands that will use it rather than for strength alone. Most cruising halyards are oversized for grip and clutch compatibility, not because the load requires it. Confirm the rope suits your clutches and sheaves before buying.

Halyards are chosen for stretch before strength. A halyard that creeps under load lets the sail luff sag and the shape go, so a low-stretch core — typically a high-modulus fibre — matters more than a big breaking load.

Size for the system, not the spreadsheet. The load on a cruising halyard is usually well within a small-diameter high-modulus line, but that line may slip in your clutches, chew through undersized sheaves and be unpleasant to hold. Diameter is usually set by hardware and hands.

Cover and core do different jobs. The core carries the load; the cover provides grip, abrasion resistance and UV protection. Halyards commonly fail at the cover first, in the sections that sit in a clutch or over a sheave.

Check clutch compatibility explicitly. Clutch jaws are designed for particular cover constructions and diameters, and a mismatched rope will either slip under load or be damaged by the jaws. The running rigging guide covers rope selection in detail.

Key facts

First priority
Low stretch under load, not maximum breaking strength
What sets diameter
Clutches, sheaves and handling — rarely the load
Core vs cover
Core carries load; cover provides grip, abrasion and UV protection
Usual failure point
Cover damage where the rope sits in a clutch or over a sheave

Full background: read the guide