A rig tension gauge measures the tension in a sailboat's shrouds and stays by reading how far a calibrated spring deflects the wire, giving a repeatable scale number you convert to pounds—or a percentage of the wire's breaking strength—using the manufacturer's equivalence chart. This guide explains how to read Loos Standard (Model A/B) and PRO (PT-series) gauges, how to interpret the equivalence and conversion charts, and how modern digital sensors fit in.
Rig tension gauge types at a glance
| Gauge family | Example models | Wire range | How it reads |
|---|---|---|---|
| Loos Standard | Model A / A-Metric, Model B / B-Metric | 2.5 mm – 7 mm (3/32" – 9/32") | Hook-and-lanyard, single spring, direct scale read |
| Loos PRO (PT series) | PT-1/1M, PT-2/2M, PT-3/3M | 2.5 mm – 10 mm (3/32" – 3/8") | Two-spool slider, hands-free, calibration-table lookup |
| Digital / smart sensors | Spinlock Rig-Sense, Cyclops Smarttune | Model-specific (e.g. 5–6 mm) | Direct load/tension display, no chart needed |
What does a rig tension gauge measure?
A mechanical rig tension gauge measures how much a calibrated spring is deflected when it pulls against a wire under load. You hook the gauge on the shroud or stay, pull a lanyard to a fixed reference, and read a number off a scale. That scale number is not pounds directly—it is an index you translate into actual cable load using the gauge's equivalence chart. Consistent, numerical readings are what let racers tune the same way every time and repeat a fast setup across regattas.
These gauges are calibrated for 302/304 1x19 stainless steel wire in the appropriate sizes. If you use one on a different cable type, size, or construction, the readings will still be repeatable, but the pound values printed on the label will no longer be accurate for your wire.
How do I measure with the Standard (Model A/B) series?
The Standard series uses a single hook and lanyard:
- Hook the gauge on the cable, then pull the lanyard until the pointer lines up with the black calibration mark.
- Read the scale at the exact point where the middle of the cable touches it. For best accuracy, hold the gauge so the scale barely touches the wire, which eliminates friction.
- Do not over-pull. Pulling the pointer past the calibration mark can permanently bend the spring and damage the gauge.
Model A and Model A-Metric cover 3/32"–5/32" (2.5–4 mm); Model B and Model B-Metric cover 3/16"–9/32" (5–7 mm).
How do I measure with the PRO (PT) series?
The PRO gauges use two nylon spools and a sliding hook, which lets them stay on the wire hands-free while you adjust:
- Hold the gauge in one hand and place the cable between the two nylon spools.
- With the other hand, pull the lanyard to extend the spring until the hook on the nylon slider can be latched onto the cable.
- Release the lanyard and read the needle on the scale, then use the calibration table to convert that reading to cable tension. The gauge can stay on the wire for hands-free adjusting.
- Keep readings accurate by making sure the slider moves freely and does not bind, and lubricate the slider slot regularly with silicone lubricant.
Tip: wiggle the gauge slightly and let the slider settle into the middle position before taking the reading. PT-1/1M cover the small wires, PT-2/2M the mid range, and PT-3/3M reach up to 10 mm (3/8").
How do I read the equivalence charts?
Equivalence charts turn a scale reading into a real cable load and a percentage of breaking strength. Take a worked example on a Hobie 33 upper shroud measured with 3/16" wire:
- The first reading on the scale is 21.
- The target is at least 26% of the wire's breaking strength.
On the equivalence table, find the scale number (21) in the left column, then move right to the column for 3/16" wire. Each cell holds two figures: a black number for pounds of tension and a red number for the percentage of breaking strength. Here the black number reads 640 lbs and the red number reads 14%.
Since 14% is well below the 26% target, the shroud is too loose. Tighten the turnbuckles until you reach 26% of breaking strength, which corresponds to a scale reading of 28. The same logic applies to any Loos gauge—just remember the target tension varies by wire size, and optimum rig tension is ultimately a function of the boat design, the rig type (masthead or fractional, single or multiple spreaders), and even the cut of the sails.
Can I convert Standard readings to a PRO gauge?
Yes. If you upgrade from a Model A or B to a PRO gauge (PT-1, PT-2, or PT-3), a conversion chart lets you reach the same recommended tension you used before. Match your old Model A/B scale number to the corresponding PT reading for your wire size. This conversion approach was documented by L-36 so sailors moving up to the professional gauges keep their proven tuning numbers.
| Model A scale | PT-1 (3/32") | PT-1 (1/8") | PT-1 (5/32") | Model B scale | PT-2 (3/16") | PT-2 (7/32") | PT-2 (1/4") |
|---|---|---|---|---|---|---|---|
| 5 | 6 | – | – | 10 | 11 | – | – |
| 10 | 9 | – | – | 15 | 13 | – | – |
| 15 | 12 | 14 | – | 18 | 15 | – | – |
| 20 | 16 | 16 | – | 20 | 16 | 18 | – |
| 25 | 20 | 19 | – | 22 | 18 | 20 | – |
| 28 | 23 | 21 | – | 24 | 19 | 22 | – |
| 30 | – | 22 | – | 26 | 21 | 24 | – |
| 35 | – | 27 | 25 | 28 | 23 | 25 | – |
| 38 | – | 30 | 28 | 30 | 25 | 27 | 25 |
| 40 | – | 33 | 30 | 32 | 27 | 29 | 27 |
| 42 | – | – | 33 | 34 | 29 | 31 | 29 |
| 44 | – | – | 36 | 36 | – | 33 | 31 |
| 45 | – | – | 38 | 38 | – | 36 | 33 |
Frequently asked questions
What wire is a Loos tension gauge calibrated for?
Loos gauges are calibrated for 302/304 1x19 stainless steel wire in the matching size. On other cable types or constructions the readings stay repeatable, but the labeled pound values will not be correct.
What is the difference between the black and red numbers on the chart?
In each equivalence-table cell, the black number is the cable tension in pounds and the red number is that tension as a percentage of the wire's breaking strength.
Can I damage a Standard gauge by pulling too hard?
Yes. Pulling the pointer past the black calibration mark can permanently bend the spring and ruin the gauge, so pull only to the reference mark.
Which gauge covers larger wire up to 10 mm?
The PRO PT-3 and PT-3M cover the largest wire, reaching up to 3/8" (10 mm), while Standard Model A/B top out around 9/32" (7 mm).
Do I still need a chart with a digital or smart sensor?
No. Tools like the Spinlock Rig-Sense and Cyclops Smarttune display tension or load directly, so you skip the scale-to-pounds conversion entirely.
What determines the right rig tension for my boat?
There is no single number: optimum tension depends on the wire size, the boat's design, the rig type (masthead or fractional, one or more spreaders), and even the cut of the sails—use the chart target as a starting point and refine on the water.
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