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Relatively new to sailing, and have a basic question about autopilots.
Do they just control the rudder? Or can you get more sophisticated? From sailing my little sloop, it seems that just like in a plane, you can't change one control without adjusting and compensating the others. If all they do is hold rudder, what is the big advantage of a modern expensive model, over Josh Slocum's rope lashing the tiller?
Modern autopilots control the helm—whether it is a wheel or a tiller, and not much more.
Main advantage over Slocum's lashing a tiller, is that a modern autopilot can hold a compass course, which a lashed tiller could not. They can also be used to sail to an apparent wind angle if they're connected to a wind instrument.
Mine is a fairly basic ST1000. Holds a magnetic compass course so a Little better that lashing the rudder.
It has a input marked vane so I presume it can interact with wind direction but as it came with the boat I,m not sure.
Have sailed on other boats with more modern versions but they also seemed to only hold a compass course.
I switch mine off for long periods when the course has settled to save juice and the play the sails between times when not busy elsewhere. The auto pilot acts as a lashing and hold the rudder steady at this point. Sail mostly single handed so often rely on "Auto" to make life easy.
Safe sailing
As SD says, the AP will continue to correct the helm to put you back on course as waves, etc push you off. They work well and this is very helpful when coastal cruising or navigating in congested waters. However, if the winds shift, your sails will be out of trim. This is to be expected. It is usually corrected by adding or subtracting a few degrees from the AP heading, with the simple tap on a "+" or "-" button. You would retrim if the winds change significantly or the corrected heading is undesirable.
While technically available, I have not seen an autopilot do very well when trying to hold an apparent wind angle, even when equipped.
My new (used) boat has an integrated autopilot/plotter that does have the capability to hold a course based on apparent wind angle. I've used it very little with mixed results. Part of the problem is that here in the Salish Sea we rarely have stretches of consistent wind. However, the few times when we had a relatively constant reach, it has worked reasonably well. I imagine it would be nice for long passages, but in that situation I wouldn't want to drain the battery so I'm not sure how useful the feature really is.
Most of the time, I use the autopilot to hold a compass heading and trim sails as needed or use it under power.
We've found that if you tune the AP for, say, motoring in calm conditions at hull speed, she's too insensitive to handle the heading under sail in some chop or waves, esp close hauled.
For a long sail, off the wind, I might bother to retune it, but mostly we use it for setting and dousing sail, long windless days, and for short term departures from the wheel..
After all, as coastal cruisers if we're sailing, we prefer to steer anyhow.
We've found that if you tune the AP for, say, motoring in calm conditions at hull speed, she's too insensitive to handle the heading under sail in some chop or waves, esp close hauled.
For a long sail, off the wind, I might bother to retune it, but mostly we use it for setting and dousing sail, long windless days, and for short term departures from the wheel..
After all, as coastal cruisers if we're sailing, we prefer to steer anyhow.
Ditto here. I've had a lot of experience with PID controls in manufacturing processes, and the concepts are exactly identical. The "proportional" part of PID is your gain setting, the "integral" part is referred to as "AutoTrim" by Raymarine, and sums up the cumulative error in your bearing or track, gradually increasing the amount of correction to bring the boat to the setpoint. You can basically tune these parameters for motoring or for sailing, but not both. And even when tuned for sailing, it may be unreliable unless you're REALLY GOOD at balancing the sails, because conditions can push the boat off its course in ways that your own senses will detect, but the AP will not. (For instance, you will immediately notice a change in heel and subconsciously adjust - but most APs will not detect this at all.)
To summarize, most modern APs have three modes:
"Standard" bearing mode, where you press a button the AP locks onto the bearing (from its integrated compass) and keeps the boat pointing in the same direction. Actual COG can/will vary as current and/or wind push you in a different direction that you're pointing. This is the most commonly used mode, because it requires no interfacing - though to really use it you need to tune the controller parameters.
Track mode when interfaced with a chartplotter, where you set a waypoint and activate a course to the waypoint. When you press a "track" button (or similar) to activate, the AP starts out pointing your boat toward the waypoint, but as current or wind push you off course (increasing XTE - cross-track error), the AP will change your bearing to eliminate the XTE and keep you on course. IMO this is best used when motoring - under sail, this could cause you to point higher into the wind than your boat is capable of, or worse, to broach. But apparently many people do use it for long-distance cruising.
Wind Vane mode when interfaced with an electronic wind sensor. When activated the AP calculates your bearing relative to wind, and keeps you there. Supposed to work like a real wind vane.
How many of you have an actual wind vane? I have a friend who bought one a couple years ago, and has mixed results.
my AP has a "wind vane mode" that I really like. Pick an angle of apparent wind and it will steer to that angle, meaning you dont have to trim the sails again once you have them right, so long as the wind stays the same. If the wind shifts more than a few degrees it beeps and asks if you want to accept the course change. Best of all for singlehanding, is the autotack feature of the wind vane mode. It will tack the boat through a preset number of degrees (default is 100 degrees but you can change that), meaning that once you hit the button you are free to handle lines without having to worry about steering the boat until you are ready.
It has worked very well for me so far, but as SD says it is more useful the steadier the wind is.
Auto tack is a cool feature and I find it works reasonably well. I find it typically over-steers the tack to be sure to catch wind on the other side. Just be sure you are pointed about as high as possible, before you engage it.
Well the ST60 and X5 (raymarine) seem to work fairly well, it will say BEEP BEEP BEEP when the wind shifts more than 20 deg and you have to reset (press both buttons).....it is one reason I bought it.
We use ours primarily on long passages. As CD said offshore there tends to be more consistant direction so it holds a course well.
Its great for holding a course into the wind when raising the sails when you are singlehanding also. I prefer the feel of the wheel and the motion of steeering the boat most of the time however on the Bay.
If the sails are trimmed right and the boat is well balanced, it should sail to apparent wind without an auto pilot. As the boat leans it rounds up slightly and then levels off. As the wind lets up, the boat straightens up and rounds down. While I've not had the boat on a large lake, I've sailed for over a mile with the tiller cleated. The boat found its own course based on wind. I have heard of tieing off the main sheet to the tiller. using a bungee cord as a counter balance to the tiller.
I have an ST6001 and it is the best, most reliable piece of kit on my boat. It steers a course under sail, under power, to a course or to the wind. There are two things about AP's that are important to remember.
The first is that they tend, depending on the gain and sensitivity settings, to correct more than necessary when first engaged. But then they start to "learn" repetitive adjustments and begin to ignore them. The frequency of adjustment on a long voyage goes down to such an extent that on a Pacific crossing, I used to often wonder whether it was still working because the wheel wouldn't move for minutes at a time and then almost imperceptibly.
Why is this matter important? Because often people are critical of the holding capacity of the AP immediately after it has been engaged but they all do that for a while. Also the perception that they eat up power is erroneous on a longer voyage because with the adjustments becoming so small and infrequent, the AP uses very little electricity.
The second is as SD has already said, the wind vane setting needs time to settle and will not successfully adjust to the frequent wind shifts caused by buildings, hills and so on. But once at sea away from the influences of land, the boat will hold a relative course to the wind unerringly. We sailed a course to the wind on a 45nm trip across open water and the AP held the course with absolute precision. I do not believe that a skilled helmsman could have done it better.
There was one question above about how many members have actually got wind vanes on their boats. Well, the Raymarine and I suspect most other AP's will interface with the NMEA signal coming from the standard wind instrument and don't need a dedicated vane. The down side to that is that with a high degree of heel the wind vane at the mast-head provides a reading that may not be as accurate as one would wish for. However, for long distance cruising where most of the sailing is done off the wind, this is of little concern.
These are just my own observations, YMMV. One thing I will say with absolute certainty, I will not go on a long trip without my AP working. Imagine a crew member who never sleeps, never needs lunch breaks, never goes to the head, never gets tired? That's your AP.
I'd also point out that more advanced autopilots will have a yaw sensor, and can tell the rate at which the boat is turning, in addition to having a compass. This can make it far more usable.
As for having a windvane... most of the boats out there don't. Some don't due to issues with having a windvane work properly on them. This is often the case with multihulls and high-performance monohulls.
To be sure, there are many variables. I've found that looking the vane when the AP is strugling (my boat or others) will often reveal the problem; if the vane is swinging all over due to motion at the mast head, it will strugle. There is damping in the circutry, but only with limits.
How does mine perform?
* Flat water. Perfect, any point of sail, compass or wind. Sometimes I think it steers better than I can.
* Swell. Good up wind, OK off the wind but higher power consumption (hand steering is more work too). I can point better hand steering. I can fly the chute a bit better hand steering. Set sails more conservatily/over trim a bit if hard on the weather or running chute. Other courses, set normally.
It would be nice to have a simple button to increase the gain in swells, to help it anticipate the way a helmsman can.
But I have never found conditions, other than wing-and-wing in a blow, where I couldn't trust it for hours.
That said, my last boat was a performance cat (Stiletto 27). Would I trust the AP under sail? Nope. The boat was just too tender and the AP couldn't keep up unless the water was flat and the wind very steady. Of course, lashing the tiller would have been pittiful also. It was VERY dependable under power, though, in any conditions.
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