gps - NMEA - and tiller pilot

J

Johnboy2004

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howdy folks...

i got the following, garmin gpsmap 76S , and a raymarine st1000+ tiller pilot,

i want them to talk to each other, i know that i need to set the garmin unit to NMEA standard, and get the bare wire kit , to connect it to the tiller pilot...

is it tricky to get it working? also this is my understanding of how it should work..
on my gps i have a pre programmed route on my gps, i push the NAv button, and tell the gps to navigate this route, then using nmea protocol, the garmin gps sends signals to the tiller pilot, telling it which way to turn...

am i correct? does anyone have experience of actually , setting this up?

cheers
John.

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I have a Navico tiller pilot talking to Garmin 128 via NMEA. It works the way you suggest.

I dont find it very useful way to use the pilot and rarely use it in practice.

Ian

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I have this set up on my boat though gps is Furuno. Simple to wire up if instructions followed NMEA output to tiller pilot only 2 wires, these are led to 7 pin plug that comes with tiller pilot. The advantage of the system is that you tell the tiller you want to go to an active waypoint and it will track direct to it compensating for any drift caused by cross tide etc. This means on a ln passage across a strong tide you will track the minimum distance from A-B. Very usefull here for me on trips across the North channel. All data with regard to WPT i.e dist to go, bearing, track and cross track era is displayed on tiller pilot. I sail mainly single handed and therefore the best piece of kit on board. Can be interfaced with a wind instrument but that only of use if you want to keep sailing as close to the wind as possible, in my book not worth the effort, I still enjoy tweaking the sails.

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Using Tiller Pilot

I agree that using "goto Waypoint" isn't all that valuable on a yacht.

My preferred MO (in constant tidal stream) is to...
- Point the boat in what I think (or have calculated) is the right direction
- Compare the resultant heading with my required heading
- Tweak the autolhelm by a few degrees until they match

This has the following benefits.
- Less hassle to set up
- Closer to traditional methods
- Less scope for careless mistakes
- Appeals to the luddite in me!

If the tidal stream is variable, there's even more argument for using calculations rather than relying on goto waypoint. But that was beaten to death (hopefully) in another thread around 6 months ago.

Rich

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Re: Using Tiller Pilot

I agree that steering to waypoint isn't that much use.

The main issue is that it starts off using the course to steer from the gps, then monitors the cross track error and adjust its course. As the fluxgate compass in the pilot is rarely accurate in an absolute fashion (normally you use it in 'relative' mode), this means that the boat heads off in the wrong direction, and gradually comes round. Fun to watch the first time (there was a 30degree difference the last time), but soon gets infuriating & you end up just pointing the boat in the 'correct 'direction.

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Re: Using Tiller Pilot

Would have to disagree with you here Rich, and so would Auto helm that originally made the tiller pilot. The auto track mode to a waypoint was designed with the intention that any deviasion from cross track error would be compensated for by the tiller pilot, and indeed a very good job it does too. I would challenge you to sail friom here at Troon on a passage across the North channel with its fierce cross tide to Bangor. Firstly you could only guesstimate from the tidal atlas what tide would affect you. In practice and I have done it many times you either over or under estimate the stream and therefore end up sailing a curved track to destination. In auto track mode although in intially for a few minutes the pilot may track a wild course as it thinks about the drift it will soon become established on the direct track line to desrtination. The track may be 270 but if it detects a strong drift to the south will steer maybe 290 to keep on track. I have done it many times in auto track or manual and I think if you compare the track plotter at the end of the passage you will find auto track has saved at least 3 or 4 miles OTG. I must admit like you I tend to point the boat in the right direction and just lock on the HDg. However if a strong cross tide is to be encountered auto track will always win the day.

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Re: Using Tiller Pilot

I think that my approach could be described as doing what the autohelm does, but manually. Which means I periodically monitor my course, and update the autohelm if necessary. Which, in practice, means that my course shouldn't be too unfavourable compared to that produced by the auto helm when tracking to a waypoint.

I can't justify this approach as being in any way better than the more automated one. It just fits my current style of navigation quite well - no need to set up waypoints beforehand, less error-prone, and feeling more "in control".

When it comes down to it, I'd suggest that anyone with these facilities should give them all a try. Go for whatever you enjoy - most of us sail for fun (I hope).

Rich

PS. Not long before you're off to Sweden now, Stbd. Hope the trip goes well.

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Horses for courses ....

There are occasions that an auto track system - where GPS / Plotter dictates to autopilot can increase the work a boat has to do to get to the waypoint / destination. Countering tidal stream constantly may not always be best ....... the boat is then punching cross current ........ before such systems - it was common for example on crossing channel to allow the boat to be taken one way by tidal stream and then some hours later the stream would bring the boat back again .... sort of S track. The boat would be fighting current less and actual time taken would be literally the same as constant correction.
I am sure that many will not believe it - but there are many old hands out there that will confirm I am sure.

In general terms and simple areas such as solent etc. or where current is reasonably constant in direction, of course an electronic 'helm' is more economic than a human hand and actually more accurate - as it learns and updates its sea-state correction. Big ships actually save tons of fuel each day using auto-pilots against that of a human helm. Maybe only cc's saved on a yacht, or a decimal of a knot for the average yacht - but still fact.

There are arguments for and against - it all depends on where what and how you want to sail.


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/
 
I have this exact gps/autopilot comb on my sailboat. (actually, I have the Garmin48 and ST2000+) Suffice it to say, the system works very well.
After getting the data wiring configured correctly and steering to a waypoint (or route!) you only need to push the correct combination of buttons on the pilot to steer via gps.
I disagree that the method of steering waypoints is not useful - I find it extremely accurate when under power or sailing in light to moderate winds (if relatively steady in amplitude and direction).
This method accounts for set and drift unlike the magnetic heading.
Cheers, HM

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Re: Using Tiller Pilot

I think that as it only requires two wires to be connected to pins 5 & 6 of the Tiller pilot socket why not do it. When you press +10 and -10 at the same time with the tiller pilot on auto. It beeps and informs you that it is going to turn to port or starboard and the heading it will take, if you press -10 & +10 together again it will do it, naturally if it means you will smack into something or somebody or even head of in the wrong direction you press auto to stay on auto.
I think the function comes into its own on a hot day when you are motoring with no wind sitting on the bow soaking up the sun with a small bevy what joy.

Trevor

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