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GP14 Spreader Tuning Guide
For Selden & Superspars Masts - Applicable to Most GP14s
1. Purpose of Spreaders
Spreaders control how much your mast bends and how tight your forestay stays as rig tension and kicker loads increase. They define your mast's pre-bend, affecting both power and depower range in the sails.
In short:
- Spreader length and deflection set your rig stiffness
- Heavier crews = stiffer setup; lighter crews = more bend
2. Key Measurements
| Measurement | Symbol | Description |
|---|---|---|
| Length | A | From the side of the mast (at spreader root) to the centre of the shroud at the spreader tip |
| Deflection | B | The distance from a straight line drawn between the shrouds (at spreader roots) to the aft tip of the spreader |
Tip: Use a string line between shrouds to measure deflection.
3. The Relationship
| Change | Mast Bend | Forestay | Sail Shape | When to Use |
|---|---|---|---|---|
| Longer spreaders | Straighter | Tighter | Fuller | Light wind / heavy crew |
| Shorter spreaders | More bend | Softer | Flatter | Strong wind / light crew |
| More deflection (tips aft) | More pre-bend | Looser | Flatter high-up | Depower setup |
| Less deflection (tips forward) | Straighter | Tighter | Deeper main | Power setup |
4. Baseline GP14 Spreader Settings
| Mast Type | A: Length (mm) | B: Deflection (mm) | Crew Weight | Rig Feel | Notes |
|---|---|---|---|---|---|
| Selden / Superspars Standard (medium section) | 380 | 150 | 24–28 st (150–180 kg) | Balanced | Class average setup |
| Selden Epsilon (softer) | 360 | 155 | < 24 st (150 kg) | Softer | Adds bend for lighter teams |
| Superspars M2 or Zeta (stiff) | 390 | 140–145 | > 28 st (180 kg +) | Stiff | Holds forestay tight in breeze |
5. Adjusting for Crew Weight
| Crew Weight | Length | Deflection | Effect | Purpose |
|---|---|---|---|---|
| Light (< 23 st / 145 kg) | 370–375 mm | 155–160 mm | Softer, more bend | Easier depower, flatter sails |
| Medium (23–28 st / 145–180 kg) | 380 mm | 150 mm | Balanced | Standard baseline |
| Heavy (> 28 st / 180 kg) | 385–390 mm | 140–145 mm | Stiffer | Maintains forestay tension, power |
6. How to Measure Step-by-Step
1. Step mast and tension rig normally
2. Mark the spreader root pivot pins both sides
3. Run a string line between shrouds touching the spreader roots
4. Measure from string line to the aft tip of one spreader → B (deflection)
5. Measure from mast wall to centre of shroud at spreader tip → A (length)
6. Ensure both sides match within ±2 mm
Tip: Record these values on a waterproof card or mast sticker for easy reference.
7. Interaction With Rig Controls
| Control | Effect on Spreader Function | Tuning Tip |
|---|---|---|
| Chocks (at mast gate) | More chocks → straighter mast → may require more deflection to maintain bend | Adjust both together |
| Chainplate Adjusters | Changes rake & shroud tension, altering spreader load | Always re-check spreader symmetry after changing rake |
| Kicker (vang) | Loads mast down and aft, testing spreader deflection | If mast over-bends under kicker → reduce deflection or lengthen spreaders |
8. On-Water Indicators
| Observation | Diagnosis | Adjustment |
|---|---|---|
| Main too flat in medium wind | Too much deflection (mast over-bending) | Reduce deflection by 5–10 mm |
| Main too full / leech too tight | Not enough deflection (mast too straight) | Increase deflection slightly |
| Excess forestay sag | Spreaders too short or too much deflection | Lengthen or reduce deflection |
| Hard to depower / kicker ineffective | Spreaders too long or too little deflection | Shorten or increase deflection |
9. Example Tuning Scenarios
Light Crew (140 kg) – Breezy Conditions (15–18 kt)
- A: 370 mm
- B: 160 mm
- Result: Softer, more bend → flattens main → easy control.
Medium Crew (165 kg) – Mixed Conditions (10–15 kt)
- A: 380 mm
- B: 150 mm
- Result: Balanced shape and slot → general purpose race setup.
Heavy Crew (185 kg +) – Moderate Wind (10–14 kt)
- A: 390 mm
- B: 140 mm
- Result: Straighter mast, tighter forestay → maximum pointing power.
10. Testing and Logging
After each session:
- Record: wind strength, chock setup, rake, spreader A & B, performance notes
- Compare mast bend sightline (base to hounds)
- Adjust spreaders in 5 mm increments only — small changes make big differences
Over time, you'll build a custom tuning log suited to your boat, mast, sails, and crew.
11. Key Takeaways
Length = Power, Deflection = Bend
Lighter crew → shorter & more deflected
Heavier crew → longer & less deflected
Always match spreaders side-to-side within 2 mm
Re-check after altering rake or replacing shrouds
Small, measured adjustments win races — not big guesses