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I don't quite understand autopilots

Old 01-08-2016, 06:48 AM
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Default I don't quite understand autopilots

Even after some research, I need clarification on small boat autopilots for outboards, like the Raymarine EV-100. Do stand-alone autopilots have gps or some other means to hold a straight line course (not just a heading, but also adjust for wind and conditions)? My trolling motor can do that, allowing me to choose whether to hold a simple heading, or hold a "straight line" heading that adjusts for wind and conditions. I assume autopilots are at least as sophisticated, but I can't find any indication that autopilots employ gps.

If that's not possible with a stand-alone autopilot, is it possible when connected to a chart plotter? And what are the rules for compatibility between auto pilots and chart plotters? Thanks.
Old 01-08-2016, 07:13 AM
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Small boat autopilots don't have built-in GPS. They rely on an external GPS signal. This typically comes from a plotter, but it could also come from a standalone GPS receiver.

The GPS interface is typically NMEA 2000, but could be NMEA 0183 in older designs. For example, my Simrad AP24 gets GPS data over NMEA 2000 from a standalone GPS, so even if I shut down all my plotters, I can still do "straight line" path following (Simrad calls that mode "No-Drift").

The NMEA-0183 and -2000 standards define basic messages that can be used to command an autopilot from any plotter. However, some plotter makers also use non-standard messages to give their own APs special functionality.

In general, though, any plotter can supply basic routing commands to any AP.
Old 01-08-2016, 07:49 AM
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Raymarine's Evolution Autopilots can work without a GPS input. They can use Speed Through The water (paddle wheel speed), GPS or nothing.
Old 01-08-2016, 08:02 AM
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Originally Posted by CME View Post
Raymarine's Evolution Autopilots can work without a GPS input. They can use Speed Through The water (paddle wheel speed), GPS or nothing.
The same is true for Simrad autopilots, though I don't know why someone would bother to install an AP without a speed source.
Old 01-08-2016, 08:13 AM
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There are a couple of really cool developments with the Raymarine Evolution AP's that are worth reading abut...

http://www.raymarine.com/news/mynews.cfm?story=9524
Old 01-08-2016, 09:02 AM
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I installed an EV-200 and have not yet interfaced to my GPS. After a few trips I'm finding that may not be necessary for most offshore bottom bouncers. I wanted that "third hand" so that I could grab a Coke, rig some tackle, etc while underway. The Raymarine AP (We call it "Captain Ray") performs that task very well. Also when we troll (not often) it holds a line very well at all speeds.

I do intend to interface it when I figure out the Lowrance to Raymarine interface.

After using the AP for a few trips, I can't believe I fished without one.

BTW I did not install the included rudder feedback unit. Works fine without it.
Old 01-08-2016, 09:05 AM
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I also have the EV-200 and absolutely love it. 1st boat with Autopilot and will never own another without one.
Old 01-08-2016, 09:17 AM
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Originally Posted by hjorgan View Post
The Raymarine AP (We call it "Captain Ray") performs that task very well. Also when we troll (not often) it holds a line very well at all speeds.
That's encouraging regarding the Raymarine. But what if I'm trolling between two parallel lines of crab traps, and there's a cross wind? Is there a way to set the autopilot so the boat won't drift sideways into the traps? Can you do that with a stand-alone autopilot, or even with a networked one?
Old 01-08-2016, 09:30 AM
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Originally Posted by dove72 View Post
That's encouraging regarding the Raymarine. But what if I'm trolling between two parallel lines of crab traps, and there's a cross wind? Is there a way to set the autopilot so the boat won't drift sideways into the traps? Can you do that with a stand-alone autopilot, or even with a networked one?

you would simply point the boat until the COG on your gps shows that you are running parallel to whatever line you want, punch in "auto" and the AP will hold that course pretty accurately (unless the cross wind velocity changes dramatically or you cross a current line). for example if the course to steer was 000, and the breeze or current was from starboard to port causing a set of ten degrees, you would point the boat at 010 and engage the AP. the boat will then have a COG of 000 until something in the environment changes....
Old 01-08-2016, 09:34 AM
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The EV-200 adjusts to cross current/wind conditions pretty well. One of the reasons I want to interface to the GPS is for the trolling patterns and increased accuracy to waypoint. A following sea on a slow troll can cause some issues.
Old 01-08-2016, 10:38 AM
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Originally Posted by yabbut View Post
The same is true for Simrad autopilots, though I don't know why someone would bother to install an AP without a speed source.
MANY sailboats do not interface with Gps
Old 01-08-2016, 11:23 AM
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Originally Posted by CME View Post
MANY sailboats do not interface with Gps
Understood, but I was thinking about powerboats, like the OP's and the boats we typically discuss on THT... "small" powerboats, as opposed to very large boats and (non-sailing) ships. I could have been more specific about that, I suppose... ;?
Old 01-08-2016, 03:29 PM
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I installed an EV-100 in my boat 2 seasons ago and it's been fantastic. Don't know how I lived without it.

I use it in 3 different ways. First, if I have the chart plotter set to guide me to some point, the autopilot will keep the boat on the line generated by the plotter. The pilot automatically adjusts for currents and winds such that the boat stays right on the line.

Second, when trolling, I'll use the autopilot to maintain a heading. No GPS involved for this and, therefore, no automatic compensation for cross winds or currents. You can, however, steer the boat with the autopilot control knob. Each click of the rotary knob changes heading by 1 degree. It would be easy to manually adjust for cross winds.

Third, when trolling, I'll use the automatic patterns. Running 7 rods off a boat without outriggers always made turns a chore. With the autopilot, I just specify a direction (port or starboard) and the radius of the turn. No more tangled messes! I don't believe the pilot is using the GPS for this. I think it's internally calculated using only a speed input, time and heading.
Old 01-08-2016, 04:09 PM
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Originally Posted by hjorgan View Post
I installed an EV-200 and have not yet interfaced to my GPS. After a few trips I'm finding that may not be necessary for most offshore bottom bouncers. I wanted that "third hand" so that I could grab a Coke, rig some tackle, etc while underway. The Raymarine AP (We call it "Captain Ray") performs that task very well. Also when we troll (not often) it holds a line very well at all speeds.

I do intend to interface it when I figure out the Lowrance to Raymarine interface.
hjorgan, adding the GPS interface will be way easier than installing the whole AP, which you've already done. If anything is unclear about how to connect the plotter to the AP, just fire off a THT post, and you'll get lots of help & feedback. Go for it!
Old 01-08-2016, 04:40 PM
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Originally Posted by hjorgan View Post
We call it "Captain Ray"
The AP is usually called "Iron Mike"...
Old 01-09-2016, 01:05 AM
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APs have 3 forms of steering.
1 Windvane steering for sailboats use the masthead unit for wind speed and angle. Steering is using apparent wind angle, following a compass course. Tacking is enabled and a timed warning that a tack is about to be performed tells the crew to duck! or gives a single handed sailor, time to set sails. The use of GPS on sailboats allows for speed and off track distance between tack changes, saving battery consumption. Without it, usually 2 paddlewheels are installed in the hull with pendulum switch to select one or the other for yacht speed...VMG.

2 Auto Steering that locks onto a compass heading. No GPS required. Pushing non follow up keys or spinning rotary control on pilot controller usually enables a 1 or 10 degree course change either side of relative bearing.

3 Nav Steering... whereby the AP takes the GPS receiver from point A to point B regardless of sea state or weather conditions. Doesn't matter if its a boat or a tractor. Mechanical movement, by whatever means, just moves the GPS in a straight line to a lat long coordinate or follow a route consisting of a number of waypoints sequentially. This steering is known as XTE, for cross track error steering. You can set the amount of 'off track' deviation before a course correction is executed. The actual heading and course are considerably different depending on conditions. This method saves fuel.
GPS provides the speed info to set the 'transition speed' from low speed to high speed and vice versa. High vessel speed and large low speed rudder excursions can cause a rollover, so the pilot needs to know if the boat is a Planning, Sail boat or Displacement hull.. So this transition speed requirement is done at Dockside setup.

You do not connect a GPS directly to an AP you connect it to a chart plotter. The plotting of a waypoint outputs steering information in either NMEA0183 or NMEA2000 which is a language the autopilot understands. Hope this helps. Difficult to elaborate in a few paragraphs.
Old 01-10-2016, 07:05 AM
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I think it's internally calculated using only a speed input, time and heading.[/QUOTE]

I think this would be difficult to do using just speed, time and heading. I think the software would need to calculate a temporary waypoint, which is the center of the circle the boat is rotating around. Then the AP would calculate a series of temporary waypoints on the circumference to go to. It would be easy to tell how the AP does it. Turn off the plotter then ask the AP to run the trolling pattern.
Old 01-10-2016, 07:46 AM
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The EV-100 sounds great for anything I'd want to do, and it seems to be the least expensive and easiest to install. I just wonder how much function I'll lack if not connected to a gps. I'd like it to get gps data from my Garmin or Humminbird, but it may only understand Raymarine "SeaTalk" data. If so, buying a separate Raymarine gps is a real complication. I guess I could just try it stand-alone and hope for the best since I don't go out in big seas that would push the boat around a lot.
Old 01-10-2016, 07:51 AM
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Originally Posted by isitstuffed View Post
You do not connect a GPS directly to an AP you connect it to a chart plotter.
Most casual users of modern navigation equipment use "GPS" and "Plotter" interchangeably... Mainly because the equipment they see are GPS Plotters...

I remember seeing my first GPS over 30 years ago... It was a Magnavox GPS on Panamax Container Carrier... Big heavy box the size of a 14" TV... Green screen... Just showed numbers... You had to take the numbers to the paper chart...
Old 01-10-2016, 07:54 AM
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Originally Posted by Chessyman View Post
Turn off the plotter then ask the AP to run the trolling pattern.
That won't work on my Raymarine EV-200...

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