GP14 Rig Tuning Guide: Chainplate Adjusters & Mast Gate Chocks

1. Core Principles

Your two main geometric controls:

Control	Function
Vertical chainplate adjusters (shroud pins/channels)	Set mast rake and baseline rig tension. Moving pins up makes the mast more upright (less rake, tighter forestay, flatter sails). Moving pins down increases rake (softer forestay, more power).
Mast-gate chocks	Fine-tune mast bend at deck level. Adding or removing them changes how freely the mast can bend under load, which directly affects mainsail depth and leech tension.

The adjusters provide the coarse tuning; chocks provide the fine control.

2. Interaction Summary

Adjustment	Mast Rake	Forestay	Mast Bend	Sail Shape	Typical Use
Pins down (lower hole)	More rake aft	Softer	More bend	Fuller	Light winds (power)
Pins up (higher hole)	More upright	Tighter	Less bend	Flatter	Strong winds (control)
Add front chocks	Mast straighter	Tighter	Less bend	Deeper main, tighter leech	Add power
Remove front chocks	Mast free to bend	Looser	More bend	Flatter main, open leech	Depower
Add behind-mast chock	Pushes mast forward	Slightly tighter	More prebend	Flattens main further	Max depower

3. Recommended Starting Settings

(Assuming Selden or Superspars mast; measure mast rake from top of mast to top of transom deck)

Wind Strength	Shroud Pin Hole (count from top)	Mast Rake	Front-of-Mast Chocks	Behind-Mast Chocks	Rig Tension (Loos Gauge)	Performance Aim
Light (< 8 kt)	4 – 5 (lower down)	~6900 mm	2 thin (≈ 10 mm total)	None	18 – 20 (~300-350 lb)	Maximum drive and height in lulls
Medium (8–14 kt)	3 – 4	~6875–6885 mm	1 thin (≈ 5 mm)	None	22 – 24 (~400 lb)	Balanced height vs speed
Fresh (14–18 kt)	2 – 3	~6860–6870 mm	None	Optional 1 thin	24 – 26 (~420-440 lb)	Depowered but still responsive
Heavy (> 18 kt)	1 – 2 (top)	~6850–6860 mm	None	1–2 thin	26 + (~440-450 lb)	Maximum control and flat sails

4. Step-by-Step Tuning Routine

1. Set chainplate pins for expected wind.

Lower for light; higher for heavy.

2. Step mast, attach shrouds, and tension jib halyard to sailing load.

3. Insert chocks in mast gate according to wind:

• Light → more front chocks (stiffen).
• Breeze → remove front chocks (let bend).

4. Check rake using main halyard to transom.

5. Sight up mast for smooth continuous curve—no sharp kink at deck.

6. Sail test:

• If over-powered → remove one front chock.
• If under-powered → add one front chock.

5. Diagnostic Guide (On-Water Feel → Adjustment)

Observation	Cause	Remedy
Boat feels heavy, heeling early	Mast too straight, leech tight	Remove front chock
Boat lacks drive, slow after tacks	Mast too bent, sails flat	Add front chock
Poor pointing, jib luff sagging	Forestay too soft	Add front chock or raise pins
Excess weather helm	Too much rake	Raise pins one hole
Boat lifeless / lee helm	Mast too upright	Lower pins one hole
Still over-powered after chock removal	Main too full	Add thin chock behind mast to induce extra prebend

6. Complementary Controls

Control	Adjustment	Purpose
Vang / Kicker	Increase to flatten main & control twist in breeze	Major depowering tool once chocks set
Cunningham	Use in breeze to flatten luff	Maintain shape as mast bends
Outhaul	Tighten as wind builds	Flatten foot of main
Jib Halyard / Rig Tension	Adjust before sailing	Sets base forestay tension
Jib Cars	Move aft in breeze, forward in lulls	Controls jib leech twist & slot width

7. Key Takeaways

Chainplate pins = rake & tension (coarse tuning).

Chocks = mast bend & leech control (fine tuning).

As wind increases → raise pins and remove front chocks.

In extreme breeze → add a thin behind-mast chock to promote prebend and flatten main.

Always measure and log your own rake/tension/chock combinations for repeatability.

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