How close is close

I have two Garmin hand held GPS, I have to acknowledge the proximity arrival at the waypoint or it contiues to tell me the bearing and distance to said waypoint once I have past it, once acknowledged it will jump to the next one,

<hr width=100% size=1>Julie
 
My plotter is a Furuno but I had the same thing with an old Autohelm on a previous boat

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The Garmins work as I have decribed, so to the Autohelm and I guess the Furono does as well.

If you set a route and are near enough to approaching the waypoint that you get its proxinity alarm first then you would never notice because you are on route and near enough.

However if you are a mile out, with say the waypoint to starboard, then at the point you cross the line a right angled triangle can be drawn with you, the current waypoint and the next waypoint The nearest route is to go straight to the next waypoint - the alternative is to head down the other two sides of the triangle - a longer route. Hence the GPS sets the next waypoint as you pass the right angled line.

To say this is not safe is incorrect. If as above you are a mile out to starboard then the mile trip back to the first waypoint is just as unknown as the trip along the the other side of the triangle to the next waypoint.

Nothing removes the responsibility of the skipper knowing the route and checking its safety = given that you were a mile adrfit both toutes have to be checked.

I think that all GPS units work as I have described its just that if you are always failry near to the target waypoint, you have no need to notice the right angled bit. Try setting a wapoint on a route and then passing it to port or starboard at a distance greater than the proximity alarm - the GPS will set itslef to the next waypoint when the right angled line is crossed.

This thread started off with a Garmin handheld GPS behaving exactly the way I have described. It caused confusion and the thread has exposed a misunderstanding that should be cleared up because its important that everyone understands how GPS's work.

<hr width=100% size=1>Paul
 
Sorry cant remember the exact model. Works well enough except the display isnt too good in bright sunlight
Agree with you on the safety angle. Changing to the next waypoint when you miles abeam of the present one is potentially dangerous

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Good- another point is that waypoints now have to be accepted by the user.
When the right angle or proximity trigger triggers the next waypoint, it asks if it should be accepted. - this is now the safety standard on autohelm etc althjough some units have to catch up. So if you are a mile adrift on your XTE - you have the choice head straght to the next waypoint (shortest route) or continue to head to waypoint 1.

I often will divert from my planned route to see a feature or something. I only do this when I can clearly see what is on my route - the result is that I am passing waypoints sometimes a few miles away to my port or starboard and the trigger to the next waypoint still happens. If you check you manuals on this, it should explain.

<hr width=100% size=1>Paul
 
"the nearest route is towards the next waypoint" How can this be so if the next waypoint is for example, in your scenario, more than 1 mile away? I might, by choice, miss a route waypoint by a mile and want to go to the next one which is 20 miles away.
Interesting Thread this one - shows how some of us think we know what's happening but don't necessarily. Come to think of it, that happens to me most of the time /forums/images/icons/laugh.gif

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"Changing to the next waypoint when you miles abeam of the present one is potentially dangerous "

Nope- being a mile adrift without knowing is dangerous. Having the GPS offer the next waypoint to you to refuse or accept is dangerous.

The trip back to the current waypoint is no more or less dangerous than the trip straight to waypoint 2. No matter what it is the skippers job to know what hazards are in the water ahead of them.

So its illogical to claim that the 90 degree line bit is dangerous, its just a pointer telling you that you have crossed the line and is therefore safer than having none.

Agree?

<hr width=100% size=1>Paul
 
""the nearest route is towards the next waypoint" How can this be so if the next waypoint is for example, in your scenario, more than 1 mile away? I might, by choice, miss a route waypoint by a mile and want to go to the next one which is 20 miles away. "

Its the shortest distance for the route. In other words the straight line to arrive at waypoint 2 is a shorter trip than going back a mile and then travelling 20 miles. The boat tyat goes stright to wayopint 2 from a position a mile abeam of waypoint 1 will get there faster than one that travels back the mile and does the two sides of the triangle.

I am dealing with common misperceptions here and important ones at that - things are not as they first appear :-)


<hr width=100% size=1>Paul
 
Both GPS are a year or so old, So the change of waypoint has to be accepted by me. All my waypoints are marked on my charts and the major ones have a angle and distance web around them. For high speed navigation I find this with the GPS is great,
Thanks again,

<hr width=100% size=1>Julie
 
<<<Hence the GPS sets the next waypoint as you pass the right angled line.>>>

Haven't had reason to check them in practice but the current Raymarine manuals state that this only occurs after you have acknowledged the alarm for both the case of entering the circle of arrival or crossing the line at right angles to the track which passes through the target. In their words, something like the alarm goes for both those conditions and after the acknowledgement the waypoint is swapped to be the origin and the next waypoint the target.

I would be interested if they don't behave as the manuals say.

John

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Can't altogether agree with that. Obviously the skipper should know where he is relative to the present waypoint and other hazards but having to arrive within say 1/4 mile of the waypoint before the course to the next waypoint is flashed up ensures that you will follow your pre-planned track which you know will be free of hazards because you looked at the chart beforehand. Arriving say 2 miles off a waypoint, the temptation is to simply follow the course to the next waypoint without consulting a chart which may be difficult to do anyway if you're bouncing about in a small boat.

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"Haven't had reason to check them in practice but the current Raymarine manuals state that this only occurs after you have acknowledged the alarm for both the case of entering the circle of arrival or crossing the line at right angles to the track which passes through the target. In their words, something like the alarm goes for both those conditions and after the acknowledgement the waypoint is swapped to be the origin and the next waypoint the target"

Its a case of OR not AND.

My raymarine setup is a few months old and triggers on either - it doe s not need both. In fact within the proximity zone the GPS treats you as if you were at the waypoint - more of a WayZone than a waypoint and offers you the bext one before you cross the right angle.



<hr width=100% size=1>Paul
 
"Can't altogether agree with that. Obviously the skipper should know where he is relative to the present waypoint and other hazards but having to arrive within say 1/4 mile of the waypoint before the course to the next waypoint is flashed up ensures that you will follow your pre-planned track which you know will be free of hazards because you looked at the chart beforehand. Arriving say 2 miles off a waypoint, the temptation is to simply follow the course to the next waypoint without consulting a chart which may be difficult to do anyway if you're bouncing about in a small boat. "

Sorry that does not make sense. If you arrive 2 miles off a waypoint the choice is either you head straight to the second or head at 90 degrees to the first - both routes were not planned beforehand. So the error has already been made in departing from your pre-planned route - the fact you are offered a choice means that you decide from where you are. The offering of the choice is better than offering none. Both routes are now unplanned and you are sitting in unplanned water already! You are blaming the messanger for the cock up of being two miles out in the first place!!!! :-)



<hr width=100% size=1>Paul
 
"this only occurs after you have acknowledged the alarm for both the case of entering the circle of arrival or crossing the line at right angles to the track which passes through the target"

I think that as written is correct but it means that in both cases the skipper is asked for confirmation - not that it needs both criteria to be asked!

<hr width=100% size=1>Paul
 
You misread me, and respond with the obvious - the point in the manuals is they say that the unit does not change to the next waypoint until the acknowledgement is made, regardless of whether the alarm has been set by the circle or the right angle line.

John

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After lask week's discussions on what the forum is for, Monday morning and we have a cracker! and I think many are getting a good illustration on the importance of good old chartwork, and not totally relying on electronics when it appears few have Gludys awesome comprehension-although if you ARE using the XTE, you should in fact know where you are..., So all round to Gludys house for a training course on GPS?!!

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