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Headsail

Headsail Measurement Guide

Section titled “Headsail Measurement Guide”

Follow the 4-Layer protocol for a systematic headsail measurement.

L1 — Geometry (Foretriangle Dimensions)

Section titled “L1 — Geometry (Foretriangle Dimensions)”

Goal: Determine maximum foretriangle dimensions (I & J).

  1. I (Foretriangle Height):

    • Definition: Vertical distance from the upper edge of the forestay sheave on the mast to the foredeck (or boom height datum).
    • Note: The headsail may not always be hoisted to the absolute maximum (especially to clear spreaders), but we need to know the physical upper limit.

  2. J (Foretriangle Base):

    • Definition: Horizontal distance from the stemhead forestay pin center to the mast’s forward face.
    • Note: This must be a horizontal measurement, not along the deck.

  3. LPG (Luff Perpendicular — Geometric):

    • Definition: The perpendicular from the clew to the luff line. Determines the headsail’s overlap percentage.

L2 — Physical Constraints

Section titled “L2 — Physical Constraints”

Goal: Establish overlap limits and clearance.

  1. Spreaders:

    • Width: If the headsail is 135% or 150% genoa, the spreaders will likely contact the sail.
    • Position: Height above deck for each spreader level.

  2. Shrouds (Standing Rigging):

    • Position: Upper and lower shroud chainplate positions.
    • Self-tacking jib: If the headsail is self-tacking, the shroud position is the absolute limit for the leech — this is critical.

  3. Furler Drum Height:

    • Measure: Distance from the deck to the top of the furler drum.
    • Why it matters: This directly reduces the effective luff length. The sail’s tack starts above the drum, not at the deck.

L3 — Hardware Interfaces

Section titled “L3 — Hardware Interfaces”

Goal: Confirm all hardware connections.

  1. Luff System:

    • Furler: Brand? (Harken / Facnor / Profurl / Seldén) Model?
    • Groove diameter: 5mm, 6mm, 7mm? This is the most common measurement error. If dual-groove, note it.
    • Non-furling options:
      • Hank-on → Piston snaps or bronze snaps?
      • Tuff Luff (dual-groove racing foil)?

  2. Tack (Lower Forward Corner):

    • Cutback: Many furler drums offset the tack ring from the forestay centerline. Measure the offset.
    • Fitting type: Webbing loop or D-ring?

  3. Clew (Lower Aft Corner):

    • LP (Luff Perpendicular): What size headsail? (100% / 105% / 135% / 150%)
    • Fitting type: Pressed cringle or webbing loop?
    • Clew Height: Desired clew position — deck-sweeper (low) or high-cut?

  4. Head (Top Corner):

    • Head Swivel: How high can the furler’s top swivel go? This is often the bottleneck limiting maximum luff length.

L4 — Protection & Accessories

Section titled “L4 — Protection & Accessories”

Goal: Identify wear points and protection needs.

  1. Stanchions & Pulpit:

    • Position: Identify all foredeck obstructions (pulpit, stanchions, anchor rollers).
    • Patches: Deck-sweeper genoas need foot patches and leech patches at stanchion contact points.

  2. UV Cover:

    • Color: If UV strip is needed, specify the Sunbrella / WeatherMax color code.
    • Furling direction: Does the sail furl to starboard or port? The UV strip goes on the exposed side.

For the measurement philosophy behind this protocol, see 01 — Measurement Philosophy.