How to Tune a Sailboat Rig
Welcome to Sun Love Sailing! Thanks for tuning in. Today we're going to start tuning the rig on Bella Sera, and I'm pretty stoked about that. We'll be using a Loos tensioning gauge for this project, and I'll go over this tool in detail throughout the video.
Tuning the rig is a two-step project. In this post, we're only going to cover the first part: tensioning the rig in the slip. The second part—fine-tuning—is done under sail, and we'll catch up with that in a later post.
Safety First: A Voyager's Perspective on Rig Tuning
Many instructional tutorials I've seen focus on tuning a rig for performance, generally in terms of getting around the buoys faster or… racing. But from a voyager's perspective, I feel that to perform at one's best, safety must be secured and tuned first. We need to feel confident in our boat's ability and preparedness to proceed confidently as the skipper.
The old adage "safety first" is an ongoing theme that runs through all my videos on fitting out yachts, and it's the basis behind most of my protocols for fit-out. In other words, it's not about performing—it's about having a seriously strong, robust yacht that you're confident in and know you can count on under any conditions.
Racing vs. Cruising Philosophy
In racing, boats sail at the very edge of their gear's strength. They're always pushing to the limit all the parameters of the yacht, including the rig. For serious ocean racers, they often push right up to and beyond their breaking point.
But for voyagers, we want headroom. We want a safety margin. We want to be overbuilt and strive to be overprepared for anything the ocean can throw at us. We don't want to push our boats and gear to their limits. That's what we're going for when we fit out our yachts for ocean voyaging, and that's what we're going for here at Sun Love Sailing in all aspects of our refit on Bella Sera.
Why Proper Rig Tuning Is Critical
Back to the safety aspect of tuning a rig: A poorly tuned rig can lead to catastrophic failure. This is a much more pertinent reason for a properly tuned rig than getting from point A to point B quickly or first. We want to get from point A to point B safely—that's the idea behind a voyaging yacht and the most important thing when we talk about fitting out for voyaging.
Tuning the rig isn't just about ensuring proper specifications are met in terms of correct tensioning of cables proportionate to their working load or breaking strength, or for the loads on chainplates, terminal connections, and specs for the specific yacht design. Because remember, all yachts are specifically designed to sail under the exact parameters of their gear—it's a package that all works together. Exceeding or undervaluing these specifications can lead to catastrophic failure.
The Inspection Component of Rig Tuning
As much as the above technical aspects are important, when tuning the rig, you also need to carefully and continually inspect it. To me, this is also part of tuning the rig.
We must always be taking note of the rig's appearance and condition, even keeping notes in your log of your observations. Here's what to check:
Terminal Connections
Check around all terminal connections (swage fittings, Norseman, Sta-Lok terminals)
Look for rust where cables enter fittings
Check for hairline cracks in cables or fittings
Use a jeweler's loupe or powerful magnifying glass (I have one with a 10x magnifier in the middle)
Connection Points
Examine the eyes of terminals where clevis pins pass through toggles
Check for wear in holes to ensure oblong holes aren't being worn
Note: You can only see these connections when stays are unattached, so take advantage if you're changing out a stay
Hardware Inspection
Inspect turnbuckle threads for wear
Check all clevis pins for rust, corrosion, and cracks
Check all cotter pins and split rings for wear or metal fatigue (these often get overlooked)
Inspect chainplates for cracks, corrosion, and rust
Cable Condition
Check all cables for fish hooks and cracks in wires
Look for corrosion throughout
Keeping notes of all observations is key to knowing the progression of wear on your rig.
The Loos Tensioning Gauge
Let's look at the tool we're using for this project. The Loos tensioning gauge comes in several models—some that are not necessarily professional-rated, and then a series of professional-rated ones: PT1, PT2, PT3. These are available in either metric or imperial measuring systems. This one is imperial because this boat was rigged in the United States, though I am in Mexico 😁!
The gauge has a scale for measuring cable diameter and is specifically designed to measure the tension of 1x19 stainless steel cable. You bend the cable between the two knobs, pull back the spring-loaded grip, and the tool measures the deflection or resistance of the cable. The tension value is denoted on a scale at the top.
Each numeric value on the scale has a correlating value for pounds of tension (denoted in black) and a percentage of breaking strength (denoted in red). There's a graph for each corresponding cable dimension.
Practical Rig Tuning Process
Starting the Tune
Most of the tuning on Bella Sera has been done, but I'm still doing some fine "in the slip" tuning. My series of procedure is to start with the cap shrouds first, then put some tension on the lowers to stabilise the middle section of the mast, then tighten the backstay/s. All the while keeping a sight up the mast, both fore and aft, and athwart ships, to make sure it’s staying in column, and adjusting as necessary. Here I’m starting with the lower aft shroud because I had tensioned the backstays and introduced a little aft curve at the top of the mast. Since the lower aft shrouds were still loose, I wanted to see if I could remove some of that curve and get the mast back straight into column by adding tension to these shrouds.
Turnbuckle Technique
When adjusting turnbuckles, count the number of turns you make—usually half turns, depending on how far you can spin the wrench. The best way to turn a turnbuckle is with a wrench that's the size of the turnbuckle, turning it right in the middle where it's strongest.
You must also hold the top of the turnbuckle at the toggle; otherwise, the whole thing might turn, and when you let go, it unravels due to the cable wrapping.
After making adjustments (I ended up doing about six half turns or three full turns), I got the tension up to around 13 on the scale, putting us at about 14-15% of the breaking strength of the quarter-inch 1x19 cable. This is right where we want to be for the preload on the rigging.
Centering the Mast
Over the years, I've seen various ways to center the mast when first stepping or tuning rigging. The goal is to get the mast dead center with the plane from stem to stern, straight up. If in the design of your yacht, there’s supposed to be a rake in the mast, then sighting up the mast fore and aft, and making the appropriate adjustments is how that is accomplished.
Common Methods
Halyard Method: The most well-known way is using your halyard, making a mark on it, and pulling it to a stanchion base on one side, then the other, to see how the mark lines up. Use any fixed point that's the same on either side of the boat.
Weight Method: Some people hang a weight from the halyard to show which way the mast is leaning. The problem is your boat has to be perfectly level, which is impossible—even the slightest list from the top of a mast to the boom will creates a large difference.
Cable Method: If I had the ability, I'd use a piece of Dynema or cable that doesn't stretch for a more exact measurement side to side.
My Preferred Method
I use the tried-and-true halyard method, making a mark and running it down to stanchion bases on either side, using my eye as well. We're getting really close with this technique—certainly close enough for a cruising yacht. Probably within a centimeter or two, which is pretty darn close.
I use the jib halyard, which runs through the center sheave on top of my mast, so I'm dead centered coming down.
Understanding Headstay and Rake
The headstay on a sailboat controls the rake of the mast. It's a predetermined length from pin to pin—from the tang on top of the mast to the pin on the turnbuckle at the stem. This predetermined length controls the mast rake and is set before installation to the specific length for that design. If some adjustment is needed, it is possible to get in between the forks of the roller furling, and woory that turnbuckle, but it’s not an easy task.
You attach the backstays and tension them to their proper adjustments, which sets the tension for the headstay.
Critical Safety Point: Always ensure the mast has no forward rake or forward curve—this is a very dangerous position for a mast.
Understanding Mast as a Column Under Compression
Your mast is a column under compression—either being pulled down or pushed down. When a column under compression has a buckle introduced, you'll have a failure point. Some masts are raked but supported in ways that prevent buckling. Some racing masts actually have curves built in, but they're specifically designed and supported for this usage.
Lower Shroud Tuning Process
When first doing preliminary tension on shrouds, bring them all to a hand-tight position. The lower shrouds control the curve or support of the middle of the mast in its height.
As you tension the lower shrouds, continually sight up the mast to ensure you're not coming out of column. The fine-tune will determine the final tension amount on all the shrouds and stays. Often, forward lowers will be slightly more tensioned than aft lowers because of the stress from the “center of effort” of the mainsail.
Much of the stress from the mainsail is carried in the center of the mast up and down, and those forward lower shrouds support the center of the mast against being pulled aft under the strain from the mainsail.
Final Tuning Under Sail
All fine-tuning will be done under sail. We'll continue sighting up the mast to ensure things stay in column—not just forward and aft, but athwartship as well (port and starboard). We want to ensure the mast isn't leaning in any direction and certainly not forward.
Complete Rig Replacement Notes
If doing a complete rig replacement, everything should be replaced pin to pin—from the clevis pin passing through the toggle at the bottom turnbuckle into the chainplate, all the way to the pin at the terminal fitting through the tang on the mast.
Conclusion
We've completed a preliminary tune, and I feel pretty good about it. There's still that slight aft curve in the top of the mast, which I'll work on next time by adjusting the lower aft shrouds further. Then we'll do the final fine-tuning under sail.
Remember, this approach prioritizes safety and reliability over performance—exactly what we want for ocean voyaging. A properly tuned rig isn't just about going fast; it's about getting there safely with complete confidence in your boat's systems.
