GP14 Rig Tuning Guide — How to Use a Loos Gauge
Accurate Rig Tension Measurement for Consistent Performance
1. What a Loos Gauge Does
A Loos tension gauge measures the tension in your wire shrouds or forestay (in pounds or kilograms).
It helps you:
- Reproduce your exact rig setup every time
- Check both shrouds are even
- Confirm mast rake and chock setup are correct for the conditions
2. Which Gauge You Need
For a GP14, the shrouds and forestay are typically 2.5 mm or 3 mm 1x19 stainless wire.
So you'll need:
- Loos PT-1M (metric) or Loos Model A tension gauge (imperial)
- Range: ~5–25 on dial (which corresponds to 150–450 lbs)
- Suitable for 2.5–3 mm wire
Tip: Mark your gauge so you always use it on the same side and same shroud position to ensure consistent readings.
3. How to Use the Gauge (Step-by-Step)
Step 1 — Step and set up the rig
- • Step the mast
- • Attach shrouds, forestay, and jib halyard
- • Tension jib halyard to sailing load (not just slack setup tension)
Step 2 — Choose a shroud to measure
- • Use the leeward shroud when the boat is static ashore (both sides even)
- • Or the windward shroud afloat (approximate, if mast centered)
Step 3 — Attach the gauge
- • Hook the Loos gauge's lower hook around the wire
- • Pull the slider arm until it sits on the wire under moderate pressure
- • Ensure the wire sits in the correct groove on the gauge (for your wire diameter)
Step 4 — Take the reading
- • Read the number from the scale on the sliding arm
- • Convert that to tension (lbs or kg) using the printed conversion chart on the gauge body
- • Note that number (e.g. reading = 22 → 420 lbs)
Step 5 — Compare sides
- • Check both shrouds read the same (within ±10 lbs)
- • If not, adjust chainplate pins or rig tension until equal
4. Typical GP14 Tension Readings
| Wind Strength | Rig Tension (Loos Reading) | Approx. Load (lbs) | Use |
|---|---|---|---|
| Light (<8 kt) | 18–20 | ~300–350 lbs | Softer rig, forestay sag for power |
| Medium (8–14 kt) | 22–24 | ~380–420 lbs | Balanced rake and power |
| Fresh (14–18 kt) | 24–26 | ~420–440 lbs | Tight forestay, flatter jib |
| Heavy (>18 kt) | 26–28 | ~440–460 lbs | Max control and pointing |
Tip: Record the gauge reading together with your mast rake (halyard-to-transom measurement). This pairing is your "rig fingerprint" for each condition.
5. How to Adjust Rig Tension
On a GP14, tension is mainly set by the jib halyard system, not by the shroud pins directly.
| Method | Purpose | Effect |
|---|---|---|
| Pull on jib halyard | Increases rig tension | Tightens forestay, reduces rake slightly |
| Ease jib halyard | Reduces tension | Adds rake, increases power |
| Move shroud pins up | Straightens mast slightly | Adds forestay tension, reduces rake |
| Move shroud pins down | More rake aft | Looser rig, adds power |
Once tension is correct, you fine-tune mast bend using chocks at the mast gate.
6. Using Gauge for Consistency
Mark and log your setups:
Create a simple table like this:
| Wind | Chainplate Hole | Chocks | Mast Rake (mm) | Loos Reading | Notes |
|---|---|---|---|---|---|
| Light | 4 | 2 thin front | 6900 | 19 | Good drive in chop |
| Medium | 3 | 1 front | 6880 | 23 | Perfect balance |
| Heavy | 1 | none | 6860 | 26 | Flat, high pointing |
Every time you find a fast setup, write down the Loos number — this gives you repeatable precision.
7. Common Mistakes
| Mistake | Result | Fix |
|---|---|---|
| Measuring with rig slack | False low reading | Always tension jib halyard to sailing load |
| Measuring on both sides unevenly | Inconsistent data | Always measure same side, same point |
| Pulling gauge too hard or wrong groove | Skewed reading | Use correct groove for wire size |
| Ignoring temperature/humidity | Minor, but real | Measure in stable conditions if possible |
8. Pro Tips
- Check rig tension before every race day — wires stretch slightly over time.
- Mark the halyard purchase line so you can re-tension exactly to your target Loos reading without the gauge.
- Occasionally calibrate your gauge using a known weight or tension (Loos provides charts online).
- Store gauge dry — moisture or grit can cause false readings.
9. Summary Reference Chart
| Condition | Target Loos Reading | Approx Load | Mast Rake | Notes |
|---|---|---|---|---|
| Light | 18–20 | 300–350 lbs | 6900 mm | Power & drive |
| Medium | 22–24 | 380–420 lbs | 6875–6885 mm | Balanced |
| Fresh | 24–26 | 420–440 lbs | 6860–6870 mm | Control & height |
| Heavy | 26–28 | 440–460 lbs | 6850–6860 mm | Max depower |