Back to the Basics


Sail your boat better with the right instruments  (published June 2013)

Like any art, sailing requires no specific instruments or devices aboard ship in order to enjoy. But like any science, sport, or hobby, the addition of useful, timely and well-presented data can significantly enhance and supplement finely honed instincts. And that data can also help you learn to be a better sailor by knowing when to take in a reef, or just plain give you the confidence to fly that sail you’ve wanted to but were never sure if the conditions were right. In short, good instruments and knowing when and how to use them can make your sailing experience more enjoyable and bring a sprightly heel to any boat.

Ah, the old timers will wag their heads and cluck their tongues. “We sailed without instruments for decades!” Not so fast my well-salted friends. The venerable telltale is itself an instrument; as is the log, the glass, the lead and the list goes on. Instrumentation to assist and enhance the sailing performance of a vessel has been included since the first days of commercial sailing—when commerce itself was very nearly equal to competition. Nowadays, hardly a yacht leaves the factory floor without a dizzying array of instrumentation, most of which is electronic. The average helm approximates a small airliner’s cockpit, festooned with data. The main issue these days isn’t getting the data, the issue is knowing what data matters when, and making sure it is not lost in a sea of confusing numbers.

So, as blue water sailors, here’s a quick and slightly non-traditional guide to some overlooked instruments and data sources that can help make sailing more enjoyable, maybe add a few points to your speed and possibly even increase your margin of safety on the water without sacrificing performance.

IS20_Rudder_Analogue_Instrument_2686    One of my favorite instruments is actually the simplest—the clinometer. A gravity-operated device, the clinometer does exactly one thing with great precision: it indicates your exact angle of heel. This is tremendously useful for a couple reasons. It is a very handy guide to know if you’re sailing your boat in the “sweet spot”, balancing maximum speed, crew comfort and a margin of safety. It is also a great, quick indicator of over-sheeting or flying excessive canvas if you’re in doubt. The correct angle of heel is different for every boat and her design, but knowing it and not exceeding it is important for a variety of reasons, especially when in heavier sea conditions. Most importantly on monohulls, it keeps the rudder efficient and maximizes the lift of the keel. On catamarans it can be very handy to indicate when the windward hull is about to lift out of the water if you cannot easily see it (e.g. at night).
I find that while a general idea of how far a boat is heeling can be directly sensed, depending on wind and water conditions, this can also be very inaccurate. The amount of freeboard remaining on the lee side is not proof of a certain angle of heel when one is beam-on to a large wave train and higher winds seem to cause people to overestimate the heel of a boat, or to err the opposite way and allow the boat to heel too much, losing rudder control.

The clinometer is also a great way to help gauge when to throw that reef in as the wind picks up. If you’re holding your course and your sails are properly trimmed, as the wind increases the boat naturally heels more. If you exceed your optimum heel angle and need to feather the sails to keep the boat “up”, a reef can actually make you faster and more in control at the same time, but when looking at speed alone this is hard to gauge accurately. The clinometer can make the difference between guessing and knowing.

I strongly dislike beating to weather on my offshore passages, but it is nearly a fact of any longish non-trade-wind voyage. During those times, it may be hard to tell if the boat is pinching. Race boats with nice large telltale windows and the budgets to replace them every season can constantly keep an eye on the jib luff telltales for some indications, and if you’ve added some telltales on the main leech and a few intermediate points (and know how to read them) you probably have better data on that than most cruisers. But for the majority of us, a very useful indicator is a simple wind angle vane either atop the mast or a few bits of thread on the shrouds near eye level. I’m not a big fan of the windex type indicator. Apart from the neck pain and difficulty to read at night, the location does not lend itself to habitual consultation when one needs to be paying more attention to the horizon.

However, a lot of times with dodgers, biminis, arches and other structure in the way even the lower telltale location is not ideal. This is where our modern electronics can really help. A masthead wind angle sensor (a.k.a. “bird perch” as many owners ruefully acknowledge) can link to a display both at the helm and belowdecks in the nav station. I find this second, less obvious, location to be of particular usefulness on a blue water boat, as the skipper and/or navigator will not be helming all the time and may have the boat under wind pilot or other automatic control. If the boat is under windvane or autopilot, the wind angle at the location of the vane or helm may be shifted a bit from what the sails are seeing, and getting the best angle both maximizes speed and can minimize discomfort and pounding caused by excessive pinching.

So this extra data point can come in handy when trying to judge the wind at surface level, particularly when the waves get up. If the wind strength changes significantly and the boat becomes unbalanced, forcing the wind vane to work harder, this often reflects in a relative wind shift—as well as slowing down with the extra rudder drag—when hard on the wind, which can help indicate to those belowdecks that the vane and sail trim might need some attention.

Some manner of displaying the rudder angle is necessary, particularly on boats with wheels as opposed to tillers. One of the tremendous advantages of tillers is that they directly give force feedback and immediately and accurately display the rudder angle, with zero ambiguity. This is essential for knowing whether the sails are properly balanced.
At the risk of repeating basic sailing principles, if your sails aren’t properly balanced you end up needing greater rudder angles to hold the boat on course, which means the rudder is dragging and not only slows you down but also reduces your ability to control rudder force in one direction. To hold course upwind, a rudder should never be more than five degrees off center, and optimum is considered to be two to three degrees for most boats.

I can count on one hand the number of boats with wheels that I have sailed that had rudder angle sensors easily displayed and observed from the cockpit (and not hidden in a submenu of the autopilot control). This is one bit of data that, in my opinion, should be shared with the entire crew and not just the helm, as those responsible for trimming and reefing need to be aware of the steering effort as well. Thus, it’s a good candidate for mounting next to the clinometer on a bridge display over the companionway or on the forward cockpit bulkhead.

Another instrument going the way of the dodo in this GPS generation is the humble speed log. Paddlewheel sensors aren’t the most accurate and enjoy accumulating crustaceans at an alarming rate—I know mine certainly does. Most boats don’t yet have the easier-to-clean ultrasonic sensors, and hardly anybody has a walker log or similar taffrail log anymore. But I cannot think of another instrument whose indications are more useful in determining whether any single change helped or hurt a boat’s speed.

GPS is nearly useless in this regard since currents, even in open water, can be significantly variable and are included in your speed over ground. Having an accurate and functioning speed log is extremely useful to learning and improving your sailing performance. There is really no other way to accurately know if shaking that reef out and taking the extra heel was worth it. You might have just run into a favorable current or out of an unfavorable one. But if your speed through the water changes, you know you have something. Thus, it is a great way to tell whether you are in or out of a current: if your GPS speed goes up, was it the wind shift or did you just enter the Gulf Stream?

Speed through the water may be most useful on deck to aid crew when handling sails. But having it available belowdecks for the navigator to identify and compensate for currents is also vital for longer passages or tricky situations. Because of this, it is a good candidate for displaying in a software menu such as on a chartplotter or in a multi-function display belowdecks and having a dedicated instrument, if space and budget allows, on deck. Whatever speed log you have, clean it regularly and store the sensor out of the water when at anchor or moored for extended periods of time to prevent marine growth from clogging it up.

The art of sailing involves a lot of learning on each individual boat, and many more instruments have useful places aboard ship than just the ones covered here. What is perhaps more important than just having instruments is knowing how to use them, what they mean for your particular boat and what practical actions should be taken as a result. This takes time, patience and a willingness to experiment. Even if you don’t race and have no intention of racing your boat or another, you can learn a lot about accurate use of instruments and their data from local racers or some of the classic racing books—just skip the parts about tactics.

Also, the instruments mentioned here can be retrofitted to nearly any vessel and all of them are easily learned, though just like sailing itself, may take a lifetime to master. The speed freaks among us know that if you have the right data and are able to apply it you can get even the slowest, least-weatherly vessel to make that next passage a bit faster and more comfortable.

Daniel Collins, an ASA certified sailing and navigation instructor, amateur extra class radio operator and small boat racer, enjoys experimenting with marine electronics. He is also actively involved in community-driven social change. Email him at, or read his blog at He owns Aletheia, an Allied Princess.

Author: Daniel Collins