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Old 15-12-2016, 13:56   #1
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Windvane Autopilot

Hi,
I have just created a new plugin to provide a Windvane Autopilot (WVAP) for OCPN. The idea being to allow an autopilot to follow the wind rather than a route. It does this by creating new NMEA sentences, WVAPB and WVRMB. If the plugin is installed and a route is active the contents of these will be the same as ECAPB and ECRMB. If you activate the Windvane Autopilot these sentences will change to contain information needed to follow the wind, i.e. virtual waypoints, zero cross track error and a direction or location. So to use this plugin you will need to ensure that ECAPB and ECRMB are NOT transmitted to the autopilot and WCAPB and/or WCRMB are transmitted.

The WVAP adds a new icon to the main toolbar which when clicked will cause a new window to appear on top of OCPN. This looks very similar to the dashboard wind angle display (actually it is based on it). This will show the current wind angle, a smoothed wind angle, a desired angle bug and a sensitivity slider. The sensitivity slider smooths the wind angle over a given number of seconds to help stabilise the readings. The desired angle bug can be left mouse button dragged to any desired angle with the initial angle being the current smoothed wind angle.

I have created an Alpha release, 0.0.2, for initial testing and is really a proof of concept to see if it is workable. You will find installables here:
https://github.com/jongough/windvane...ses/tag/V0.0.2
It should work with OCPN 4.4 and 4.5, and it uses wxWidgets 3.0.2 so may not build/work on systems with wxWidgets 2.8.

Jon
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Old 15-12-2016, 14:17   #2
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Re: Windvane Autopilot

What is the purpose of this plugin? How can you steer to wind while also following a route?
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Old 15-12-2016, 14:36   #3
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Re: Windvane Autopilot

The idea is to either steer by following a route OR steer by following the wind. Quite often when sailing having a route is all well and good, but you cannot follow it and need to follow the wind and have the yacht keep a constant wind angle. This is what this plugin is trying to do.
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Old 16-12-2016, 02:51   #4
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Re: Windvane Autopilot

This seems like a great idea. My AP has steer to wind built in, but when using OCPN to steer it would be nice not to have to switch back to allowing the AP to take control. Not sure how I could do any testing of the Alpha while the boat is on the hard?
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Old 16-12-2016, 05:39   #5
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Re: Windvane Autopilot

Hmm, when my AP steers to wind, it just tries to keep the apparent wind angle constant at the level set. It does a good job handling shifts as well, which is really cool to watch while sitting on the front tramps and watching it do it's thing. Isnt that a simpler program than virtual waypoints. My ST60 is over 15 years old and still does a good job.
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Old 16-12-2016, 10:36   #6
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Re: Windvane Autopilot

Quote:
Originally Posted by jongough View Post
The idea is to either steer by following a route OR steer by following the wind. Quite often when sailing having a route is all well and good, but you cannot follow it and need to follow the wind and have the yacht keep a constant wind angle. This is what this plugin is trying to do.
So the plugin allows you to steer to route first, then after adjusting sails, switch to wind steering holding the current wind angle?

Of course if the wind shifts then you now are no longer following the original route.
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Old 16-12-2016, 10:58   #7
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Re: Windvane Autopilot

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So the plugin allows you to steer to route first, then after adjusting sails, switch to wind steering holding the current wind angle?

Of course if the wind shifts then you now are no longer following the original route.
I think you're missing the point or getting hung up on the route thing.

Using an AP to steer to wind is used just like using a windvane. You set up the boat how you want it, get everything nicely balanced etc.. and switch on the pilot. It keeps the sails drawing nicely etc..

I rarely use it on my own pilot in this mode (I have an Aries) but often when delivering bigger boats with plenty of power (and no windvane) it is the primary autopilot mode.
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Old 16-12-2016, 12:07   #8
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Re: Windvane Autopilot

I use the word 'virtual' because there are no waypoints created but the RMB sentence requires them. So, when building the sentences I assume a waypoint about 1nm away in the direction I want the boat to go and give the heading, distance to this point and give it a zero cross track error to avoid the autopilot trying to attain a zero cross track error.

I know that newer or more expensive autopilots offer this feature, however mine, a TMQ AP4 does not. Also, due to the boat layout, cockpit arch, davits, etc. I cannot add a windvane to it. So I thought this may be the next best thing.

The WVAP does, or tries to, do exactly what your ST60 is doing but as it is not integrated to the autopilot has to do it through available NMEA sentences. Also, as OCPN spits out autopilot sentences as EC, and this is not controllable from a plugin, I have to use these to build equivalent ones as WV so that the connections configuration does not have to change once you have installed the plugin and configured it the first time. This allows switching between route navigation and wind vane steering by clicking on the toolbar button.

Quote:
Originally Posted by sailjumanji View Post
Hmm, when my AP steers to wind, it just tries to keep the apparent wind angle constant at the level set. It does a good job handling shifts as well, which is really cool to watch while sitting on the front tramps and watching it do it's thing. Isnt that a simpler program than virtual waypoints. My ST60 is over 15 years old and still does a good job.
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Old 16-12-2016, 21:20   #9
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Re: Windvane Autopilot

Suggestion

I use an ST60 in wind mode quite often. Catamarans cannot typically use a conventional windvane.

What would be really nice is to have a feature that allowed you to follow a route unless the wind angle prevented you from doing so, whereby it switched to a predetermined close hauled wind angle. It could then allow the boat to crack off as the wind direction changed until it was able to resume the "route".

This is what a human helmsman does after all.
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Old 16-12-2016, 21:27   #10
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Re: Windvane Autopilot

If this plugin actually works (I cannot try it at the moment as I am not near the boat), which is the reason for the alpha/proof of concept, then that would be relatively easy to add. It would need to be user selectable from the preferences panel with the default settings.

But first things first we have to see if it works and if it is stable (can stabilise the wind direction without causing other issues) enough to use to control the autopilot.
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Old 16-12-2016, 21:32   #11
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Re: Windvane Autopilot

I know you have used virtual waypoints. Just for information the ST60 converts the wind angle to a compass bearing and continually adjusts this until the variation is (5 degrees?) then throws up a wind shift message.
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Old 17-12-2016, 00:12   #12
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Re: Windvane Autopilot

What is the purpose of the wind shift message? Would this not get annoying in gusty conditions where the gust is likely to change the apparent wind by more than 5deg (I see 10-15 deg when this happens)?

It would certainly be possible to add a warning message if the wind changed by more than a certain number of degrees. This would have to be user selectable both in the default setting and during use.

It looks like you can use APB and RMB messages to drive the raymarine autopilot (the old ones as the latest seem to use NMEA2000). If you can use APB it 'may' work better as it really only contains direction messages whereas the RMB has lat and lon as well.
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Old 17-12-2016, 00:35   #13
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Re: Windvane Autopilot

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What is the purpose of the wind shift message? Would this not get annoying in gusty conditions where the gust is likely to change the apparent wind by more than 5deg (I see 10-15 deg when this happens)?
It does get bloody annoying. If you add that feature please make the trigger point adjustable and provide the ability to turn off any audio alarm. A further refinement would be to filter the apparent wind by some significant value of say 5 minutes.

From memory on the newer Raymarine gear wind shift is triggered by a fixed value of 16 or 18 degrees but that is nowhere near enough when you are getting knocked about by waves or in big swell.

Beep beep bloody beep....
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Old 17-12-2016, 02:29   #14
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Re: Windvane Autopilot

5 degrees ?? was a finger in ear guess. Yes to have it user defined or to switch it off would be fantastic.
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Old 17-12-2016, 12:01   #15
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Re: Windvane Autopilot

At the moment there is no warning, the whole thing is very simple, a bit like using a real wind vane auto pilot. It will sail you around in circles if that is what the wind is doing. It does not care what angle you are sailing at as long as it the correct one to the wind.

I suppose, if this plugin works, we need some requirements for the bells and whistles. The simpler the better for the first few. But I would like some feedback as to whether it actually does what it is supposed to. I cannot test it on a boat for another month or so.
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