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Old 13-06-2014, 14:47   #376
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Re: Why Integrate the Autopilot ?

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Originally Posted by sy_gilana View Post
......
Depending if you have your plotter (laptop) configured to send APA or APB sentences can make a difference. Let us assume you are on a course of 045į between waypoint 1 and 2 in a route. Distance between assume 5 Nm. You have laid a course that clears starboard danger at 4 miles from WPT1, by 0.3 Nm.
2 miles into the leg, you see a ship approaching on reciprocal, and decide correctly to head off a few degrees to Stbd.
you pass safely, and re-engage the AP to follow the leg. Here is what happens.

Under APB, your autopilot corrects for the dodge, and attempts to get you back on to the ORIGINAL line between 1 and 2.
Under APA, your autopilot takes you directly from your new position to WPT2, reducing or removing the 0.3Nm safety clearance from the dangers ahead......
Both APA and APB contain XTE. Your conclusion makes no sense as the AP is continually monitoring XTE regardless of BTW from origin waypoint or current position. This is how the AP corrects for leeway. BTW is used for initial heading, then adjustments for XTE will dictate whether BTW and heading stay in sync. If you have leeway, the AP will crab the vessel to stay on track, hence heading does not equal BTW any longer.

In your example, the AP would have 2nm? to 'get back on track' before the 'danger'. I've witnessed APs that will turn perpendicular to the track just to get back to it.

Yes, an AP can put you in irons, it can also put you on a beach. As mentioned early, an AP doesn't navigate! An AP steers the boat as the navigator instructs it, either via magnetic heading, wind direction, or a track to a waypoint.
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Old 13-06-2014, 15:16   #377
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Re: Why Integrate the Autopilot ?

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Both APA and APB contain XTE. Your conclusion makes no sense as the AP is continually monitoring XTE regardless of BTW from origin waypoint or current position. This is how the AP corrects for leeway. BTW is used for initial heading, then adjustments for XTE will dictate whether BTW and heading stay in sync. If you have leeway, the AP will crab the vessel to stay on track, hence heading does not equal BTW any longer.
My autopilot is a Robertson AP-20 (bought it before Simrad arrived), and it operates as described above. It focuses on zeroing out the XTE. Maybe others do it differently.

We do deviate from plotted courses for traffic and other reasons. In such cases a higher level of attention is required.

We also cross check chart plotter data to other instruments and visual cues. The depth sounder matches the chart plotter, the radar shows the same buoys, boats and shoreline, and looking out the windows also matches. Never rely on a single source.

We have discovered chart errors in the process, reported them and received corrected vector charts as a result. AIS is pretty good for finding such errors. I have sent screen shots back to the chart vendor that show our boat 300 feet ashore when docked in a harbor. Going through narrow channels shows up such errors as well, but you have to guess at the magnitude.
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Old 13-06-2014, 15:36   #378
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Re: Why Integrate the Autopilot ?

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Originally Posted by Greg4cocokai View Post
Mines usually set to wind angle.
And you don't drift or have leeway when set to a wind angle?

I don't think you understand how autopilots work. Having a bazillion miles is meaningless here.

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Old 13-06-2014, 15:51   #379
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Re: Why Integrate the Autopilot ?

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Originally Posted by sy_gilana View Post
Several points have been raised about "what are the dangers"
I don't understand your first two examples. In the first one, our AP certainly doesn't act like you describe unless I go in and specifically reset the XTE.

In your second example, setting for a heading only when there is a coast or other danger nearby could put you on the rocks. In that situation, a waypoint would be a far safer choice.

But the biggest mistake people make with this is assuming that because the autopilot is in communication with other instruments, that it can only be used that way. Bringing up specific examples of ANY mode of usage where it would get one into trouble is silly.

We use ours set to heading, or set to a heading with no drift allowed, or set to a navigation waypoint, or set to a wind angle, or set to a navigation waypoint while using a wind angle (there are two very useful modes in that list that you will only have if you have the correct autopilot ).

In other words, we use the autopilot mode most appropriate for the situation.

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Old 13-06-2014, 17:22   #380
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Re: Why Integrate the Autopilot ?

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Originally Posted by sailorboy1 View Post
You don't drift if set to a waypoint, you just go to it! You can just forget about all that old fashioned chart drawing stuff.
Drift is offset caused by current. Set is "sideslip" caused by nobody has a 100% efficient keel.

If you set to a waypoint and make no adjustment the boat will sail a parabolic curve unless sailing deep dw or a broad reach and somewhere along the line luff the sails and get stuck in irons.

It is actually like a new helmsman who aims at the mark. instead of "upwind" of it. How far upwind to aim requires knowledge of one's boat, the current and the length of the leg.

Setting AP to wind angle works as long as one is actively navigating. Changes in wind could actually steer the boat right at those rocks you are trying to avoid.

My AP is in hdg mode 95% of the time. I generally only set to WPT if I am motoring or motor sailing. Wind angle has never been used.

That isn't to say the course is not plotted. Waypoints are entered, course is plotted and Otto is told which way to head the boat - just like a junior helmsman.

I don't see how you could steer to WPT upwind anyway. It's a zig-zag course.
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Old 13-06-2014, 17:57   #381
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Re: Why Integrate the Autopilot ?

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Originally Posted by Ex-Calif View Post
I don't see how you could steer to WPT upwind anyway. It's a zig-zag course.
You don't have the correct autopilot.

Ours does this very well. You set the WPT, then put the AP in WindNav function and it sails to the wind continually optimizing VMG and calculating laylines toward that waypoint. When it calculates the layline has been met, it calls for a tack and continues again.

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Old 13-06-2014, 20:03   #382
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Re: Why Integrate the Autopilot ?

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Originally Posted by Ex-Calif View Post
If you set to a waypoint and make no adjustment the boat will sail a parabolic curve unless sailing deep dw or a broad reach and somewhere along the line luff the sails and get stuck in irons.
No. If you send the AP a track there will be no curve, it'll track a straight line from origin to destination waypoint, motor or sail, regardless of current (assuming you have enough power to overcome current).
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Old 14-06-2014, 11:28   #383
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Re: Why Integrate the Autopilot ?

[QUOTE=DotDun;1563642]After listening to your 'soapbox' more than once, it brings up a question.

It's not a soapbox, as I don't give a tinker's what other people do or don't, or how they spend their kitty. I do enjoy giving a airhorn blast to boats that cross my own track under AP and decide to go below for "just a minute" to make a coffee for 20 minutes. But the question is "why integrate?", not "why AP?" I love APs. Hand-steering is for chumps and racers.


An AP simply takes care of the menial task of turning a wheel or push-pull a tiller, nothing more.

Again, I bear no malice for APs. I'm on the verge of buying a W-H for my hydraulic two-station helm. Makes a nice companion to the extant wine vane. But I think you learn more about what the sea is doing by sailing to a compass bearing via AP than by sailing to a waypoint via AP integrated with GPS. In the latter case, you can lose sail trim and miss factors like current because the AP/GPS is all about steering to a fixed co-ordinate. I suppose if you are just motoring, that's fine. My comments on situational awareness relate to direct observation of the behaviours of people in boats under AP/GPS. How can I tell they've integrated the two? The flurry of activity aboard as they narrowly avoid putting their stemhead through the buoy. I have actually seen this. I suppose it's a tribute to WAAS, but it's a deficit to seamanship when you "set and forget" and don't grasp simple concepts like "offing".
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Old 14-06-2014, 11:56   #384
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Re: Why Integrate the Autopilot ?

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Originally Posted by colemj View Post
So do you propose a test for this?

If so, what would it look like?

Would you get off your soapbox if everyone told you they have already gone through this phase?

Or would you need proof of that (see first question)?

One last question if I may - Do you know of any learned good navigators who came to grief because they got set into trouble by current or leeway?

Mark
The sea proposes the tests. It looks like a SAR exercise.


Proof is subjective in the absence of any codified training in North America. People don't need much in the way of it to sail/motor in these parts. In other countries, it is a long and involved process of learning and testing to get a licence to sail.

Navigation is a process (http://www.cpf.navy.mil/foia/reading...-grounding.pdf). If one cedes portions of that process, the very human tendency is to assume that the automation has interests in a safe arrival, as do the humans. That's not true, of course. If you have to check on what the machines are doing, you retain more executive function. You asked me " Do you know of any learned good navigators who came to grief because they got set into trouble by current or leeway?" I would say no, because if they got into trouble, they by definition weren't good navigators. I took an RYA course in Brittany last fall in a strongly tidal area...a shock to the system for a Great Lakes sailor. But it gave me plenty of insight into the problem, and how to solve for vectors that allow a boat to crab to its desired destination in safety.

But I do have a semi-recent "horrible warning". Many here have read the book "Black Wave", about a big cat the smashed into a Society Islands reef, despite having, yes, integrated AP/GPS. I think in this case a '70-era sailor was baffled and had his seamanship compromised by an over-reliance on his nav gear. I wrote about it here: Volumes of Salt: Black Wave: Leaving seamanship in the dark

Such a case is hardly unusual. Listen, if you know what you're doing, run the boat from a Garmin Quatix watch or via your iPhone. It's just another tool. But first, perhaps, evaluate "knowing what you're doing" against some sort of impartial judge. Personally, it's because I'm still learning that I can recognize those who've stopped, or those who don't get that there's more to learn than plugging in a lat/lon and hitting "auto". A key attribute of seamanship is prudence.
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Old 14-06-2014, 12:04   #385
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Re: Why Integrate the Autopilot ?

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One time, it saved our bacon. We were committed to a harbor entry where the port control had told us to enter between to huge bulkers, under engine. A squall hit, and we could not even see the mast, it was a total white-out. we were in a dredged channel, and could not "bail" either way. Laura stayed below, observing the chartplotter and the radar and soundings. She told me to correct course while I was in the cockpit. She kept us on course, turning when she saw the radar picture of harbor tugs merge with the big ship ahead, we identified the outer breakwater and the inner harbor wall, and were motoring along at 3 knots with this big black stripe down the radar, when the squall, just as suddenly lifted. We were about 10m away from the side of a sugar bulker and traveling parallel to it. If we did not trust our electronics we would have made a mistake, but in order to trust your electronics, your real situational awareness must be verified continually.
An excellent post and a great example of using the electronics actively. I've done something less dangerous but analogous motoring in a restricted channel with subsequent shallows in heavy fog by taking GPS bearings to known nav aids and by having my wife at the bow yelling back to the pilothouse "Red fairway at 2 o'clock!" I plotted them out previously and just steered those plots. Had I missed one, I would have come about on a reciprocal course and started again from the previous buoy. I can't wait for buoys to be AIS targets. That would suit me fine in busy harbours.
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Old 14-06-2014, 12:25   #386
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Re: Why Integrate the Autopilot ?

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Originally Posted by S/V Alchemy View Post
I do enjoy giving a airhorn blast to boats that cross my own track under AP and decide to go below for "just a minute" to make a coffee for 20 minutes.

[B]How can I tell they've integrated the two? The flurry of activity aboard as they narrowly avoid putting their stemhead through the buoy. I have actually seen this.
Wouldn't both of these be true for an AP just steering to a compass bearing?

In the first example, I can't see how it matters one bit. How the AP is working, or even if an AP is being used.

In the second example, couldn't an AP steering to compass also hit something if one was not paying attention. It is a rare buoy indeed that I find not only precisely in place, but also precisely charted. And even rarer the people I know who set waypoints on buoys.

I know I have seen boats hit things while hand steering, let alone under autopilot.

I think you invent demons so you can fight the battle you want.

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Old 14-06-2014, 12:29   #387
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Re: Why Integrate the Autopilot ?

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ou asked me " Do you know of any learned good navigators who came to grief because they got set into trouble by current or leeway?" I would say no, because if they got into trouble, they by definition weren't good navigators.
Good lord, I don't even know what to say to this. That response is truly a sad one.

Other than it is only a matter of time until you prove yourself to be a poor and unlearned navigator.

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Old 14-06-2014, 12:57   #388
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Re: Why Integrate the Autopilot ?

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Wouldn't both of these be true for an AP just steering to a compass bearing?

In the first example, I can't see how it matters one bit. How the AP is working, or even if an AP is being used.

In the second example, couldn't an AP steering to compass also hit something if one was not paying attention. It is a rare buoy indeed that I find not only precisely in place, but also precisely charted. And even rarer the people I know who set waypoints on buoys.

I know I have seen boats hit things while hand steering, let alone under autopilot.

I think you invent demons so you can fight the battle you want.

Mark
I think you invent conflict where none exists.

I'm presenting a viewpoint, not a casus belli. "Not paying attention" is what I'm critiquing. I think integration is a temptation for those already predisposed to not paying attention. I also think the marketing of complex MFD-based, integrated systems is appealing to people raised on Star Trek. I think there's more money than seamanship at play.

So if I have not been sufficiently clear on this point, here it is more plainly: A greater reliance on automation strikes me as an invitation to take shortcuts in the supervision of a vessel, period, whether under automated helm control/nav functions or not. This has been my experience. If you were raised with magnetized spoons and sunstones, and can navigate like a Polynesian in an outrigger, you are not the sailor that would concern me. Use what you will shall be the law of the sea. But it's best to realize what's being emulated, and that, as has been pointed out, reality agrees with the virtuality.
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Old 14-06-2014, 15:54   #389
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Re: Why Integrate the Autopilot ?

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So if I have not been sufficiently clear on this point, here it is more plainly: A greater reliance on automation strikes me as an invitation to take shortcuts in the supervision of a vessel, period, whether under automated helm control/nav functions or not. This has been my experience. If you were raised with magnetized spoons and sunstones, and can navigate like a Polynesian in an outrigger, you are not the sailor that would concern me. Use what you will shall be the law of the sea. But it's best to realize what's being emulated, and that, as has been pointed out, reality agrees with the virtuality.
And I believe every man should build his first house using a hand saw as power saws cause accidents due to inattention by the user :roll eyes:

If using track mode on your AP causes you to lose the ability to navigate your vessel, then please, don't use it.
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Old 14-06-2014, 16:21   #390
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Re: Why Integrate the Autopilot ?

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If using track mode on your AP causes you to lose the ability to navigate your vessel, then please, don't use it.
Good discussion.

Question: could you please DEFINE "track mode?"

I think we all understand steering to a waypoint, and I agree with Mark that it's rare to use nav aids for waypoints, 'cuz you can hit them (!) and only mobos do that, right?

But on my GPS, "tracK mode" means, to me and in the manual, a line of "cookie crumbs" as to where I have been, not where I am going.

My GPS (Garmin GPSMap 76Cx) does waypoints, XTE (digitally and the old highway thing) and lots of other features. But it doesn't "project" (i.e., predict) "tracks," it only saves them

Please help us understand.

Thanks.

PS --- I sail in tidal waters, so I understand current and drift, and am old enough to know and employ "traditional" navigation.

This question has nothing to do with integration, just wanting to understand by definitions which may be different between what my GPS tells me a "track" is and not understanding what you mean by that phrase.
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