Part II - Crew Control and Boat Handling
Build 27 · 20 September 2026 · not yet reviewed
5Crew Kinetics and Balance
Sections in this chapter
This chapter covers the mechanics by which the crew's bodies keep the 49er's sail plan upright and driving: the righting moment as the product of weight and horizontal lever, the extension of that lever by the wings and the twin trapeze, and the way trapeze height, wire tension and body angle turn a fixed mass budget into a moment held steadily through gusts, waves and manoeuvres. At the crew's request the chapter has been reduced to a single section, 5.2, and the original numbering is retained. The section connects three quantities the crew otherwise manages separately: the mass budget as stated by the class rules, the class association and the builders; the lever geometry that decides how much of that mass acts against the heeling moment; and the trapeze technique that decides how constant the lever is when the boat rolls or re-accelerates. The rest of the book treats the righting moment described here as the fixed quantity that sail power is trimmed to match, and rig set-up takes over where the lever has reached its maximum.
5.2Righting moment, trapeze geometry, and wire tension
Righting moment is the weight carried multiplied by the horizontal distance of that weight from the axis about which the hull heels, and in steady sailing it must equal the heeling moment of the rig S19. Hughes gives the crew's version: righting moment is crew weight applied over the S25. Mass is fixed for the day, so the crew controls only the lever: its length and how steadily it is held.
The class and the builders fix the mass budget: a including wings of 94.0 kg under class rule C.7.3 S3, a mast that "can support a combined crew weight of up to 165kg from its dual trapeze" S9, an optimum crew weight of 145 to 165 kg from Mackay W1 and an ideal racing weight of 150 to 170 kg from Ovington W2. The crew is therefore the larger part of the sailing mass and the only part on a lever, since hull mass sits near the centreline. The wings carry the feet out to the boat's 2.9 m beam S9S11, and the twin trapeze extends it again by holding each body on a wire from the hounds with its centre of mass well outboard of the feet. The crew's combined mass is crew value.
Trapeze height sets body angle, and body angle sets the lever. The lever is longest when the body lies perpendicular to the mast; Hughes' instruction is to get as close to that line as possible without going below it W3, since below it the lever shortens and the body meets the water at speed. The wire carries the weight and the feet the horizontal reaction, so a straight body on a low hook hangs its whole mass on the wire, and harness load is the evidence of a deployed lever: "The goal is to always have consistent weight on the wire" W3. Bending at the knees or waist during clip-in moves the mass inboard onto the legs and collapses the lever as the boat re-accelerates W3. A low body also : a mass above the heel axis moves outboard in a windward roll and inboard in a leeward one, so its moment feeds the roll, whereas a mass near the axis keeps almost the same lever through small roll angles. Low trapezing therefore dampens roll and keeps the sail plan upright for a higher percentage of the time S25 W3.
The lever is used up before the rig is depowered. As pressure builds the crew move outboard and lower while heel is held within the skiff coaching standard, "Flat is FLAT, +/- 5 degrees is acceptable, +/- 10 degrees is only just tolerable" S36. Once both bodies are straight and perpendicular to the mast, further heeling moment is removed at the rig, where the class tuning guide takes the cap shrouds progressively tighter above about 11 to 12 knots S13. Downwind the lever sets heel rather than opposing it, since the manual requires the boat "heeled to windward with the windward chine in the water" S12. An observer would see both bodies straight and near perpendicular to the mast whenever the boat is powered, harness loads that never slacken, and heel within 5 degrees S36 of target above the wind speed of first full extension, crew value.