Autopilots: Understanding Performance Functions

How your autopilot could get you back on the water and give you the edge when the racing resumes – Part 3

Most people know how to turn their pilot on and off and adjust headings either using the 10 degree or 1 degree increment buttons. Some may switch between compass and wind direction, but in most cases it will be compass heading that is used.

Yet today’s autopilots are capable of steering as well or, in some conditions better than a human. But to achieve this means understanding the next level of controls, how they work along with when and why you might want to adjust them.

To do this requires a bit more time in setup but it is time well spent, especially if you are sailing shorthanded and/or offshore.

“In broad terms the amount of angle and the way in which it is delivered to the autopilot ram is calculated from the sum of three key factors known as; ‘Proportional’, ‘Integral’ and ‘Derivative’ feedback control, better known as PID,” explains B&G Product Director Matt Eeles. “On board the boat these three factors can be adjusted by the helmsman using three functions.”

Rudder Gain

Rudder Gain – (P) This changes the amount of rudder angle used to get back onto course and how quickly it is applied. Turning the gain up means that the autopilot responds rapidly and aggressively to any request. This is the main function that is used to make sure that the autopilot is responding in a suitable way for the current conditions

“It’s not unusual for people to think that high gain is what they want in all cases, but the reality is not as simple. If you compare this to the steering of a car, if you’re going fast you may want a smaller amount of angle on the wheels applied gently to make a change of direction than when you’re going slowly. The amount of gain you may want varies.”

Auto Trim

Auto Trim – (I) This function learns how much weather helm to apply to achieve a steady heading. Changing this setting adjusts the speed with which the autopilot learns to cope with weather helm.

“To assess and set up Auto Trim, with the autopilot off, set the boat up on a reach and steer by hand until you are happy with the feel on the helm. Switch the autopilot on and wait to see that the heading remains the same. Now introduce some weather helm by say over sheeting the mainsail.

“If the autopilot doesn’t compensate fast enough you need to wind down Auto Trim to allow it to learn faster.”

Counter Rudder

Counter Rudder (D) – Counter rudder is the function that applies rudder in the opposite direction to stop it overshooting the required heading.

 “To check this function, set up the boat under engine and note the angle at which you have started and where you want the pilot to steer. Then put in some large course changes of say 20-30 degrees at a time. From this you will be able to see whether the pilot is over or under shooting.

“If it overshoots – increase Counter Rudder.”

“If it undershoots – decrease Counter Rudder.”

 

Easy ways to remember the significance of the three key controls and the significance of getting the pilot to steer how you want it to.

  • Rudder Gain –Adjust this to make the autopilot steer as well as you. 80% of the time it is this setting that you will tweak.
  • Auto Trim – Adjust this to make the autopilot steer better than you
  • Counter Rudder - Adjust this to make the autopilot steer better than you

Matt’s Top Tips

  • The wireless remote (WR10) is an important, if not essential piece of kit allowing you to control the pilot from wherever you are on the boat.
  • Unless you’re about to wipe out, or there is a risk of collision, resist the temptation to take over when the pilot doesn’t behave as you expected or wanted.
  • Instead, watch to see what happens. You’ll have a better idea of what to change to improve things if you can understand what the pilot is trying to do and why.
  • Know how long it takes for the compass to catch up when you bear away around a mark, especially if you’re about to hoist a kite. It’s easy to go too soon with the hoist and result in you ending up on your ear.
  • If you’ve tried calibrating and are still having problems, or your instruments have mysteriously gone out of calibration, check that there isn’t any metal near the compass. For example, has a tool box or an anchor been placed there, or maybe something else metal has fallen down and is now close to and interfering with the compass?
  • Don’t expect too much too soon from your pilot. Don’t switch it on for the first time as you go around the top mark.
  • And do expect to get it wrong. It takes time to get the settings right and time to build confidence.

Biog

Matt Eeles

Matt joined Brookes & Gatehouse in 2003 after previously working as a software engineer and completing a full-time Olympic campaign in the Tornado multihull class. After some time world cruising his role at B&G started in R&D before then moving on to become product Director in 2020.

 

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