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Old 23-01-2015, 11:16   #46
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Re: Autopilot

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Originally Posted by Dockhead View Post
Don't you guys use wind following mode? I use it almost exclusively sailing hard on the wind or DDW. Used it with the old Ray pilot and just as much with the new B&G pilot. It's the t*ts for this.

I use all the pilot modes, actually, except wind-nav mode, which I haven't figured out, and I use the tacking function to tack as well.
Nope!
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Old 23-01-2015, 16:50   #47
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Re: Autopilot

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Don't you guys use wind following mode? I use it almost exclusively sailing hard on the wind or DDW. Used it with the old Ray pilot and just as much with the new B&G pilot. It's the t*ts for this.

I use all the pilot modes, actually, except wind-nav mode, which I haven't figured out, and I use the tacking function to tack as well.
I use it close hauled. On other points of sail I use compass course. Mine tries too hard to stay with wind when broad reaching as the the apparent wind moves around from accelerating off waves.
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Old 23-01-2015, 16:59   #48
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It also adjusts sailing angle to optimize VMG.

Mark
Bloody hell. What will they think of next?! Need to re-read that manual.
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Old 23-01-2015, 17:00   #49
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Nope!
Try it; you'll like it! It's the very t*ts when going upwind. Much better than any human helmsman.
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Old 23-01-2015, 17:09   #50
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Re: Autopilot

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I use it close hauled. On other points of sail I use compass course. Mine tries too hard to stay with wind when broad reaching as the the apparent wind moves around from accelerating off waves.
By default, our Simrad automatically switches to true wind when the wind goes aft of the beam, and to apparent wind when forward. It also automatically changes the rudder response level when sailing to wind instruments off-wind.

This can be setup manually to be different if wanted, but I find it to be rock-steady downwind when it is following the true wind.

Perhaps yours also has this option to go to true wind?

Unlike GBN, this is another example that I think does differentiate different AP's.

Mark
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Old 23-01-2015, 18:14   #51
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Re: Autopilot

This thread makes me all the more excited to get a new AP. I think I'm going to hook a manual rocker switch to the existing Autohelm 5000 and use it for remote steering only from companion way. I have been eyeing the b&g equipment for a while, my system is N2k so I think it would work great

- Ronnie...on the geaux
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Old 24-01-2015, 06:17   #52
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Re: Autopilot

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Originally Posted by colemj View Post
By default, our Simrad automatically switches to true wind when the wind goes aft of the beam, and to apparent wind when forward. It also automatically changes the rudder response level when sailing to wind instruments off-wind.

This can be setup manually to be different if wanted, but I find it to be rock-steady downwind when it is following the true wind.

Perhaps yours also has this option to go to true wind?

Unlike GBN, this is another example that I think does differentiate different AP's.

Mark
I can sail to the true or apparent wind with my AP. One issue with true wind is there are more errors introduced in calculating the true from the apparent wind. Since driving to the compass while broad reaching works great, I don't think I'll change.
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Old 24-01-2015, 07:07   #53
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Re: Autopilot

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I can sail to the true or apparent wind with my AP. One issue with true wind is there are more errors introduced in calculating the true from the apparent wind. Since driving to the compass while broad reaching works great, I don't think I'll change.
Ours works very well in true wind - steady as a rock. Maybe it has to do with compass, gps and calculation differences?

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Old 24-01-2015, 07:21   #54
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Re: Autopilot

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Ours works very well in true wind - steady as a rock. Maybe it has to do with compass, gps and calculation differences?

Mark
As I said calculating true wind adds more errors, as it requires more sensors to be calibrated together and accurate at the same moment. Its a non-problem for me as I'd rather sail to a compass course while broad reaching and keep a good watch. Any misstep driving can be have some bad effects when the seas are up and the sails are way out. That is one reason I dumped my Raymarine AP computers, as they would occasionally take a flier and head off at 90%. This happened on at least 2 different AP computers.
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Old 28-01-2015, 06:55   #55
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Re: Autopilot

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Ours works very well in true wind - steady as a rock. Maybe it has to do with compass, gps and calculation differences?

Mark
Mark
I was thinking about this statement while we were sailing downwind yesterday. The errors that get into the instantaneous true wind are usually pretty high. With the mast head moving through a 6 or 10 foot arch the mechanical windvanes are going to have enough momentum to induce some pretty large errors. Add in the instantaneous SOG errors and the net can have a pretty large error. Overtime it averages out pretty well, but the short term numbers are not great. Now on your boat, a cat, the mast head does not move through anywhere near the arch that my mono does, plus you are using an electronic, not mechanical, wind sensor, so I'd expect the calculation to be a lot closer to reality.
That ought to make it easy for the AP to steer to the sensor input. That said, as I understand it, most of the AP algorithms that use wind are basically using the gyro/compass for course control and slowly updating the heading to match the change in wind angle over time.
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Old 28-01-2015, 07:48   #56
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Re: Autopilot

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Mark
I was thinking about this statement while we were sailing downwind yesterday. The errors that get into the instantaneous true wind are usually pretty high. With the mast head moving through a 6 or 10 foot arch the mechanical windvanes are going to have enough momentum to induce some pretty large errors. Add in the instantaneous SOG errors and the net can have a pretty large error. Overtime it averages out pretty well, but the short term numbers are not great. Now on your boat, a cat, the mast head does not move through anywhere near the arch that my mono does, plus you are using an electronic, not mechanical, wind sensor, so I'd expect the calculation to be a lot closer to reality.
That ought to make it easy for the AP to steer to the sensor input. That said, as I understand it, most of the AP algorithms that use wind are basically using the gyro/compass for course control and slowly updating the heading to match the change in wind angle over time.
.
That makes sense. I didn't think about us being a more stable platform downwind. The ultrasonic wind is sending data at 10Hz - I don't know what its actual sampling rate is (whether it averages between PGN sending), nor how that compares to a mechanical one. Our AP definitely uses the rate compass for calculation, although I think I may have the option to use COG.

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Old 28-01-2015, 09:44   #57
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Re: Autopilot

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Originally Posted by colemj View Post
That makes sense. I didn't think about us being a more stable platform downwind. The ultrasonic wind is sending data at 10Hz - I don't know what its actual sampling rate is (whether it averages between PGN sending), nor how that compares to a mechanical one. Our AP definitely uses the rate compass for calculation, although I think I may have the option to use COG.

Mark
Your Maretron WSO dampens wind speed and direction readings over 1.5 seconds time period (default value, but configurable). The algorithm is fairly obvious, throw out the outliers and then use exponential decaying averages. Of course, each designer would develop such 'art' for the product using his choices in the algorithm.

The mechanical transducers/displays perform a like dampening process, but, in my experience, most are not configurable. Then of course the 'art' comes into play on the exact performance.
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Old 28-01-2015, 10:12   #58
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Re: Autopilot

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Ours works very well in true wind - steady as a rock. Maybe it has to do with compass, gps and calculation differences?

Mark
Just Curious, what would be the advantage of steering to True wind as opposed to Apparent ?

It seems to me that the sails only care about apparent ? What am I missing ?

Cheers,
JM.
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Old 28-01-2015, 11:09   #59
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Just Curious, what would be the advantage of steering to True wind as opposed to Apparent ?

It seems to me that the sails only care about apparent ? What am I missing ?

Cheers,
JM.
You're right, but very fast boats, especially ones which surf, can change the apparent wind so much that you steer an unnecessarily erratic course, if using apparent. Then you use true and trim for the apparent wind at the normal speed.
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Old 28-01-2015, 11:34   #60
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Re: Autopilot

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Just Curious, what would be the advantage of steering to True wind as opposed to Apparent ?

It seems to me that the sails only care about apparent ? What am I missing ?

Cheers,
JM.
Steering by apparent wind when going downwind could risk jibing if the boat is accelerating and slowing while chasing a constantly changing apparent wind angle. Even without jibing, the boat is steering around a lot if chasing the apparent wind instead of the true wind.

Mark
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