How Reliable is the Ferry Angle for Crossing Currents?

[leong]

Twice in the last 7 days I crossed from the south end of Plum Island to Lanes Cove (once with two paddling partners and once solo). In both cases GPS’s were used to maintain a direct beeline to Lanes Cove. These gadgets are great … you just follow the arrow and it keeps you on the straight line track between the two points (no worrying about ferry angles). Both crossings were done near maximum floodtide and the current was particularly strong where Ipswich Bay enters into Plum Island Sound, Essex Bay and the Merrimack River. There were quartering headwinds of about 10 knots with gusts of about 15 knots. Here is a track of the trip from Lisa’s GPS (I don’t think she’ll sue me for using her track, I don’t have the s/w to display my track). BTW, the return trip through Fox Creek was aborted because we ran out of water to paddle through.

I began to think about how hard it would have been to make this direct crossing with just a compass and chart. Of course, for most of the crossing I (we) could see Lanes Cove so a fairly decent beeline could have been approximated without a GPS or compass. But, suppose, we couldn’t see Lanes Cove for the entire distance, but had charts and compasses aboard. Could a direct beeline crossing be paddled without the help of a GPS? So I did some calculations to investigate this.

A reliable ferry angle estimate requires:
1. An accurate estimate of a constant paddling speed (especially as affected by wind and waves).
2. An accurate estimate of the speed of the current. As it varies the ferry angle must be recalculated.
3. Either no wind or a constant wind that is incorporated into the speed of the current.

In general, the speed of the current is not constant and neither is the paddling speed. So, as a minimum, repeated ferry angle calculations would be required. Also, because of the relatively strong and variable winds, some way to include the effects of the wind into the current speed would be needed.

The attachment considers a very simple scenario: Crossing a 7-mile wide river with a constant current and no wind. The math calculates the miss distance from a waypoint on the other side of the river as a function of under (over) estimates of paddling speeds. A graph of this miss distance is on the last page of the attachment. For example, if the estimate of the constant speed of the current is exactly right (1.5 mph) and the constant paddling speed of 2.6 mph is overestimated as 3 mph, the waypoint will be missed by approximately 0.6 miles when the other side of the river is reached. And the miss distance would probably be greater because, in the real world, the currents and winds would be varying. Not coincidentally, the straight-line distance from Plum Island to Lanes Cove is also 7 miles.

Mathcad - Ferry Angle Miss Distance.pdf

Edited August 5, 2013 by leong

[Phil Allen]

You're point is valid, particularly over long distance with no other corrections. That's why it's good to use a range that you adjust as needed (even lobster pot to lobster pot in the fog). And GPS can be wrong as well, if you've got some smart grad students wanting to give you a hard time:

http://gizmodo.com/students-take-control-of-80-000-superyacht-using-fake-951409579

best

Phil

[leong]

And GPS can be wrong as well, if you've got some smart grad students wanting to give you a hard time:

http://gizmodo.com/students-take-control-of-80-000-superyacht-using-fake-951409579

best

Phil

Hmm, good point about fake GPS signals taking control of mega-yachts. I hope it’s not too late to cancel my order for this one!

[billvoss]

These gadgets are great … you just follow the arrow and it keeps you on the straight line track between the two points (no worrying about ferry angles).

I agree that the GPS is a great gadget. In this application it is wonderful to have an arrow pointing directly towards your destination. Especially if fog or other issues prevent you from seeing your destination. However, the GPS systems I'm aware of display an arrow pointing directly towards your destination, they do not compute the correct ferry angle.

To quote your PDF attachment.

If you paddle that adjusted heading all the way across, you will track straight across to the waypoint on the other side, even though you are not pointing at the waypoint.

The GPS points to the destination, that is rarely the correct ferry angle. The higher the speed of the current relative to the speed of the paddler, the more this becomes an issue.

Attached is a rough sketch showing what can happen when the paddler simply keeps their boat pointed toward the destination shown by the GPS when the current speed is close to the paddler's speed (no GPS spoofing required).

GPS_Ferry.pdf

[leong]

I agree that the GPS is a great gadget. In this application it is wonderful to have an arrow pointing directly towards your destination. Especially if fog or other issues prevent you from seeing your destination. However, the GPS systems I'm aware of display an arrow pointing directly towards your destination, they do not compute the correct ferry angle.

To quote your PDF attachment.

The GPS points to the destination, that is rarely the correct ferry angle. The higher the speed of the current relative to the speed of the paddler, the more this becomes an issue.

Attached is a rough sketch showing what can happen when the paddler simply keeps their boat pointed toward the destination shown by the GPS when the current speed is close to the paddler's speed (no GPS spoofing required).

GPS_Ferry.pdf

No, Bill. The GPS doesn't point to the waypoint. If it did when you're drifting sideways it would cause you to follow a long curve eventually ending at the waypoint (at least after an infinite time).

Here’s how it works: The GPS knows the kayak’s location and the waypoint’s location in some fixed earth coordinate system. It doesn’t know it’s own orientation (what direction it’s facing or even if it’s pointing backwards or straight down). It also doesn’t know the heading angle of the kayak. But it does know the Course-Over-Ground (COG) that the kayak is moving along as you paddle and drift with the wind and current. If the COG coincides with the beeline from your present location to the waypoint, the GPS’s arrow (at least it’s an arrow with my GPS) points to the top of the screen. If the kayak’s COG for this latest update is to the left of the present beeline, then the GPS’s arrow points to the right (indicating that you should change your heading to the right), and vice versa. Of course, your COG is the result of the vector sum of the kayak’s forward speed and the cross-velocity vector due to current, wind and wave action. So, the GPS doesn’t really have any idea of current velocity (I mean water speed and direction) or wind or anything else that’s pushing the kayak. All it really knows is the COG and the latest beeline to the waypoint. If you try to keep the arrow always pointing to the top of the screen (via heading changes as necessary) you will be following a straight line to the waypoint.

-Leon

PS

The GPS doesn't actually compute a ferry angle. It just keeps you on the right track that is a straight line to the waypoint. Note, if the GPS has a compass, it must be disabled for this to work correctly.

PPS

You can easily show that your GPS works this way:

1. Establish a waypoint at some tree or something (maybe a hundred yards away). With my unit I would just walk over to the tree and press one button and that would enter the location as a waypoint.

2. Go back to your starting point and make sure the compass is disabled.

3. Put the unit into the pointer mode (or whatever it’s called) and then start a Goto a waypoint (or whatever it’s called).

4. Point the GPS at the tree.

5. Start walking towards the tree. The GPS pointer will swing to the top of the screen.

6. Then walk off at a 45-degree angle to the left of the beeline to the waypoint. In effect you’re simulating a kayak in a crosscurrent (n mph towards the tree and a cross-velocity drift of n mph).

7. If you notice that the GPS pointer swings around to 45 degrees to the right of the tree you’ve proved the point; i.e. GPS is not pointing to the waypoint; instead it’s pointing to the correct ferry-angle adjusted direction.

Edited August 5, 2013 by leong

[MPARSONS]

So it sounds like you use the GPS the way one might use a range or transit. I never thought of using a GPS that way. In a range, if the rear object moves to the right you have drifted off couse and need to adjust to the left. On your GPS, if the arrow starts to point right, you have drifted off couse and need to adjust to the right. That would mean your bow may not be pointing in the direction of the arrow, but you should be moving in a relatively straight line.

[billvoss]

No, Bill. The GPS doesn't point to the waypoint. If it did when you're drifting sideways it would cause you to follow a long curve eventually ending at the waypoint (at least after an infinite time).

Yes, a long curve is what I was trying to describe with my rough diagram.

The GPS doesn't actually compute a ferry angle. It just keeps you on the right track that is a straight line to the waypoint. Note, if the GPS has a compass, it must be disabled for this to work correctly.

Almost all of my GPS units have had compasses. Perhaps that is why I have never seen the behavior you describe.

What version of GPS do you use? I want to look up the user manual.

[leong]

So it sounds like you use the GPS the way one might use a range or transit. I never thought of using a GPS that way. In a range, if the rear object moves to the right you have drifted off couse and need to adjust to the left. On your GPS, if the arrow starts to point right, you have drifted off couse and need to adjust to the right. That would mean your bow may not be pointing in the direction of the arrow, but you should be moving in a relatively straight line.

If I understand what you're saying I don’t completely agree with you. A few comments follow:

The GPS doesn't need to be aligned with the boat. The GPS's display could be oriented arbitrarily (for instance, even sideways, backwards or upside down). So even when you're moving on the line from the current position to the waypoint, the arrow isn't necessarily pointing in real space towards the waypoint; however, it definitely is pointing to the top of the display.

Also note, that when you're paddling at a constant velocity as well as drifting at a constant velocity you're always moving along a straight line, but not necessarily on the straight line from your current position to the waypoint.

With respect to ranges, there are several disadvantages:

1. There may not be ranges lined up with the direction from your current position to the waypoint or the ranges may be too far away to be visible or it may be too dark or foggy to see them.

2. Also, you said, “if the rear object moves to the right you have drifted off course and need to adjust to the left”. But that’s not really a good solution if you’ve drifted very far. That’s because, for your current location (wherever it is) there is a straight beeline to the target. A GPS will try to move you to that new beeline, not the original “beeline” that you drifted away from; i.e. that old “beeline” is no longer the correct straight beeline from your current location to the target.

A GPS alleviates the problems above.

I'm more of a theoretician than a practitioner with a GPS. Other's (especially NSPN member LHuntington) have much more experience and practical knowledge using these cool gadgets.

-Leon

PS

I don't have decent map display on my low-end GPS, but other paddlers use the map page to paddle to a waypoint. Also, I think the better GPS's use a line instead of an arrow.

[leong]

Yes, a long curve is what I was trying to describe with my rough diagram.

Almost all of my GPS units have had compasses. Perhaps that is why I have never seen the behavior you describe.

What version of GPS do you use? I want to look up the user manual.

Bill,

Yes, I understood your diagram. The curve is actually called a pursuit curve in mathematics (a dog chasing rabbit follows a pursuit curve). Although I’m familiar with pursuit curves from differential equations in graduate school, it was John Huth who pointed out to me that this paddling curve was a special case of pursuit curves.

My GPS is a real low-end gadget: Garmin Etrex Venture HC. I’ve yet to find a Garmin manual that adequately discusses how the GPS takes care of sideways drift and tries to hold you to the straight beeline from your current position to the waypoint, thus avoiding the ferry angle problem. It’s kind of amazing because this avoidance of the ferry angle problem is one of the nicest things about the GPS.

I think you can disable your compass by setting some speed threshold. LHuntington might know how.

-Leon

[lhunt]

On the Garmin GPSMap GPS's under "setup" for "heading" you can tell it to use the compass only when your speed is below something for longer than something seconds. I have it set to 0 for 90 seconds when kayaking.

Note that when you disable your compass you can still use the "compass" page. But it will be showing your direction based on how you move rather than which direction you point in. That means North might not actually point North. If you have your GPS positioned normally on your deck, and are moving North, the "compass" will show North straight in front of you. But if there is a current involved, you might actually be pointing NorthEast. It's a little disorienting, though it does get you there in the end.

I like to use the map page and follow the find pointer (actually a line) there. You get the same effect - the waypoint you are moving toward might show as being right in front of you on the screen, but the actual island or whatever might be off to the left of your bow. Still, I find that to be less disorienting, somehow. Maybe I'm just used to it.

-Lisa

Edited August 6, 2013 by LHuntington

[Phil Allen]

Leon & Lisa

Sounds like the garmin GPS's are actually showing you the course over ground (COG) to the waypoint, not the heading or the bearing to the waypoint? Is that the default setting, a special setting, or what it defaults to when you turn off the magnetic compass?

best

Phil

[EEL]

Just a random thought. While the methods described for using a GPS should (actually I cannot imagine they would not be) be more accurate and efficient than calculating a ferry angles and using a compass; as a practical matter one weakness of using a GPS in the manner described is that it requires the needed waypoint to be in the GPS. This may or may not be a matter of significance to a given paddler on a given trip, but it suggests to me that knowing how to use ranges and/or estimate ferry angles on the fly remains a useful skill.

Ed Lawson

[leong]

Leon & Lisa

Sounds like the garmin GPS's are actually showing you the course over ground (COG) to the waypoint, not the heading or the bearing to the waypoint? Is that the default setting, a special setting, or what it defaults to when you turn off the magnetic compass?

best

Phil

Phil,

Perhaps what you’re saying is equivalent, but I’m not sure. I don’t think that the arrow shows you the COG to the waypoint. It shows you whether your current COG is to the right or left of the COG to the waypoint. But when the arrow points to the top of the display your current COG corresponds to the COG to the waypoint. I’m mentioning the arrow because that’s what I use with my Etrex Venture. There are other screens like a line on a map that do the equivalent.

I’m almost certain that all GPS’s must work this way because of the physics and mathematics of how a GPS system works. What I said earlier in the thread applies to any GPS system:

“Here’s how I believe it works: The GPS knows the kayak’s location and the waypoint’s location in some fixed earth coordinate system. It doesn’t know it’s own orientation (what direction it’s facing or even if it’s pointing backwards or straight down). It also doesn’t know the heading angle of the kayak. But it does know the Course-Over-Ground (COG) that the kayak is moving along as you paddle and drift with the wind and current. If the COG coincides with the beeline from your present location to the waypoint, the GPS’s arrow (at least it’s an arrow with my GPS) points to the top of the screen. If the kayak’s COG for this latest update is to the left of the present beeline, then the GPS’s arrow points to the right (indicating that you should change your heading to the right), and vice versa. Of course, your COG is the result of the vector sum of the kayak’s forward speed and the cross-velocity vector due to current, wind and wave action. So, the GPS doesn’t really have any idea of current velocity (I mean water speed and direction) or wind or anything else that’s pushing the kayak. All it really knows is the COG and the latest beeline to the waypoint. If you try to keep the arrow always pointing to the top of the screen (via heading changes as necessary) you will be following a straight line to the waypoint.”

-Leon

[leong]

Just a random thought. While the methods described for using a GPS should (actually I cannot imagine they would not be) be more accurate and efficient than calculating a ferry angles and using a compass; as a practical matter one weakness of using a GPS in the manner described is that it requires the needed waypoint to be in the GPS. This may or may not be a matter of significance to a given paddler on a given trip, but it suggests to me that knowing how to use ranges and/or estimate ferry angles on the fly remains a useful skill.

Ed Lawson

Ed,

You can enter a new waypoint by placing the pointer at the desired location on the map page, so I don’t think that that’s a problem.

-Leon

PS

My original purpose for starting this thread wasn't to belittle non-electronic methods of navigation. I consider them very important tools that everyone should learn. In fact, I rarely use my GPS. My purpose was to quantify the waypoint miss distance when estimating ferry angles based on inaccurate estimates of paddling speed or current speed, especially in the presence of strong and variable winds.

[lhunt]

Leon & Lisa

Sounds like the garmin GPS's are actually showing you the course over ground (COG) to the waypoint, not the heading or the bearing to the waypoint? Is that the default setting, a special setting, or what it defaults to when you turn off the magnetic compass?

best

Phil

Another way to think of it... A GPS with no internal magnetic compass does not know your compass heading. How could it? We are so used to a compass that you point in this direction or that to see which way we are pointing (compass heading). But you can take your compass-less GPS and spin around to your heart's content - the display will be meaningless if you are standing still.

The GPS can only figure out your "heading" by taking your location now, and again in one second, and again the next second. It compares the coordinates to get your current direction of travel, and spins the display ("compass" icon or map) accordingly, putting your direction straight up on the screen. If you are walking with the GPS pointing in front of you, it seems to work like a compass (because you are moving and pointing in the same direction). But when you are paddling, as we know, the direction you are pointing in (compass heading) is often different than the direction you are moving in. The GPS only knows the latter, so that's what it works with. Turns out that's much more useful information anyway.

So the simple answer is that's how they all work if you turn off the magnetic compass. Dumber is better.

Oh, and I'm assuming it is set to "track up", not "track north".

...one weakness of using a GPS in the manner described is that it requires the needed waypoint to be in the GPS...

Well, not really. If you are aiming at a point, a harbor, or an island, you can use the map display. Zoom it appropriately, then orient yourself so that the feature is at the top of the screen and Bob's your uncle. Depends, of course, on how good your display is, and how good your eyesight is... but it works for me more often than not. Mostly you just have to watch the display until it stabilizes, then figure out some shore feature or something to head to, then check the display periodically for updates.

-Lisa

Edited August 8, 2013 by LHuntington

[leong]

The GPS can only figure out your "heading" by taking your location now, and again in one second, and again the next second.

I think you mean COG, not heading. Or are you meaning to imply that heading in quotes might not corresponding to the kayak's heading?

[lhunt]

...Or are you meaning to imply that heading in quotes might not corresponding to the kayak's heading?

Yes. Looks like a heading on the display.

...it suggests to me that knowing how to use ranges and/or estimate ferry angles on the fly remains a useful skill.

I meant to answer this one, too... Yes, of course. It's faster and more fun, and we have lots of lobster pots around here (!)

GPS is a good backup if it's very important and there are no good ranges.

[EEL]

Lisa:

How do you attach/mount your GPS so you can check it easily while using it as you described? I ask because i assume it is necessary to have the screen facing you which suggests some type of mount as opposed to stuck under bungies.

I find it interesting how different paddlers have different preferences and wonder if they are founded on why, how and where we tend to paddle. For example, I can see how maintaining the best COG is important to a racer/fitness paddler while for a minimalist wandering tourer like me navigating with the least equipment and an emphasis on quick and easy solutions that can be done on the go appeals.

Ed Lawson

[spider]

Not sure I am following the gist of any confusion. i know I use a GPS frequently..map & compass to get to the general area and then GPs to find an exact spot (in my case usually a campsite).

( I never use an electronic compass of any kind so I disable it)

I know that you can set the GPS to actually look like a road and it will show you if you are off course, might even tell you how many degrees, can't say for sure as I never use it that way.

As soon as I use the "go to" function it works much like billvoss has in his diagram therefore I use that function sparingly as I figure the gps has no brains and is only showing where my destination is. If I drift heavily, for example, it will constantly recalculate the length of time it will take me to get to my destination..but I don't expect it to calculate in advance what my drift will be, only what is happening at that moment.

Perhaps I am under using it, but I am thinking drift and what not needs our brains...point or go to gps is a no brainer and the gadget just points the way and doesn't give a hoot how we get there..as far as it is concerned if I have to paddle across several islands and a housing development that's fine and dandy..

So it kind of leaves me wondering where the confusion is...then again I have been know to live in a confused state of mind for many a year..

Edited August 8, 2013 by spider

[leong]

Not sure I am following the gist of any confusion. i know I use a GPS frequently..map & compass to get to the general area and then GPs to find an exact spot (in my case usually a campsite).

( I never use an electronic compass of any kind so I disable it)

I know that you can set the GPS to actually look like a road and it will show you if you are off course, might even tell you how many degrees, can't say for sure as I never use it that way.

As soon as I use the "go to" function it works much like billvoss has in his diagram therefore I use that function sparingly as I figure the gps has no brains and is only showing where my destination is. If I drift heavily, for example, it will constantly recalculate the length of time it will take me to get to my destination..but I don't expect it to calculate in advance what my drift will be, only what is happening at that moment.

Perhaps I am under using it, but I am thinking drift and what not needs our brains...point or go to gps is a no brainer and the gadget just points the way and doesn't give a hoot how we get there..as far as it is concerned if I have to paddle across several islands and a housing development that's fine and dandy..

So it kind of leaves me wondering where the confusion is...then again I have been know to live in a confused state of mind for many a year..

The main confusion was that some erroneously thought that with a “gotto”, the GPS continually points to the waypoint, even when there is a cross current. I think that between what Lisa and I stated it should be clear, that, if you keep the GPS’s arrow to the top of the display (or whatever mode your using), it will keep you on a straight COG to the waypoint. That is, Bill Voss’s diagram was incorrect. Restated, here is the experiment that should convince you of this:

1. Establish a waypoint at some tree or something (maybe a hundred yards away). With my unit I would just walk over to the tree and press one button and that would enter the location as a waypoint.

2. Go back to your starting point and make sure the compass is disabled.

3. Put the unit into the pointer mode (or whatever it’s called) and then start a Goto a waypoint (or whatever it’s called).

4. Point the GPS at the tree.

5. Start walking towards the tree. The GPS pointer will swing to the top of the screen.

6. Then walk off at a 45-degree angle to the left of the beeline to the waypoint. In effect you’re simulating a kayak in a crosscurrent (n mph towards the tree and a cross-velocity drift of n mph).

7. If you notice that the GPS pointer swings around to 45 degrees to the right of the tree you’ve proved the point; i.e. GPS is not pointing to the waypoint; instead it’s pointing to the correct ferry-angle adjusted direction.

You said, “If I drift heavily, for example, it will constantly recalculate the length of time it will take me to get to my destination..but I don't expect it to calculate in advance what my drift will be, only what is happening at that moment.”

No, the GPS doesn’t calculate your drift at all (and there is no possible way that it could do it). All it knows is how the kayak is moving, the net result of all of the forces on the kayak (paddling, waves, current and wind). Between two updates, the GPS calculates the course the kayak moved along. For instance, if you keep the arrow at the top of the display, the GPS will lead you on a straight line to the waypoint. That’s one cool feature of a GPS system for a kayak that’s drifting due to current, waves or wind. Ferry angle calculations are not needed.

BTW, if your paddling speed and the net drift rate remained constant, the GPS’s estimate of ETA should be correct. As paddling speed or wind or waves or current change, the GPS will adjust the arrow to keep you on the COG to the waypoint and adjust the ETA appropriately.

Respectfully,

-Leon

Edited August 8, 2013 by leong

[spider]

Thanks... I'll put that on a "rainy day" list of things to do..hopefully that will be in a few days .

[spider]

ok couldn't resist doing the "tree test" I made a mark walked all over the place using the "go to " function and it consistently pointed to the mark no matter what I did or stated otherwise just has it has done all these years hundreds of times.

but thinking it through we have a favorite saying on paddling trips...we are most lost when we are actually at our destination. Also stated otherwise... the gps gadget lies most to us when we are already there. Then it will tell us we need to go forward backward off to the side or whatever as it fluctuates within it's area of accuracy...

Therefore in practice, which I have done in the dead of the darkest of nights, we wait until the arrow is completely at a right angle to our destination before we change course, we find the most success using that method. If we point directly at the object in near proximity the closer we get the more the arrow will lie to us...however a text will appear and say "you have arrived at your destination" and for all purposes the arrow becomes meaningless.

So perhaps that is what is happening to you with the tree experiment....then again I could be wrong... for after all it is not a rainy day and I should be tending to chores instead...

(no need to quote me in it's entirety I seldom say that much of any great importance,..)

Edited August 8, 2013 by spider

[lhunt]

How do you attach/mount your GPS so you can check it easily while using it as you described? I ask because i assume it is necessary to have the screen facing you which suggests some type of mount as opposed to stuck under bungies.

Here are my low tech Rube Goldberg solutions so far... The first one is ugly but you can mount both your GPS and a seagull at the same time (seagull permitting, of course). The second one is more minimalistic and probably only works because of the cockpit recess on my new baby. I also once made one out of a wedge of foam, with a hole drilled for a skinny piece of PVC pipe, and the bungees went through the hole. That one was good but didn't let the wind through.

In a pinch you can put a wedge of foam in the drybag with the GPS and put the whole thing under the bungees.

This is mostly just to have speed and distance, by the way, and to keep a log of where I've been. Getting a ferry angle is just a sideline.

...it consistently pointed to the mark no matter what I did or stated otherwise just has it has done all these years hundreds of times...

Ah, but were you pointing it to the tree? Or in front of you?

When walking the GPS works as you expect it to. To simulate kayaking, you have to "sidle" at a 45 deg. angle away from the tree while pointing the GPS at the tree. Because in a kayak you think you are going to the tree, but the wind is blowing you sideways.

The GPS will tell you to sidle left some more, some more, some more, there, that's it. If you turn the way it suggests (still sidling), you will eventually end up walking sideways toward the tree. When the pointer goes to the top of the screen, you are sidling toward the tree, even though you are pointing the GPS AWAY from the tree.

I know it's complicated, but just think "I'm in a boat. That tree is a lighthouse. I'm paddling straight toward the lighthouse, but the wind is blowing me sideways."

[leong]

ok couldn't resist doing the "tree test" I made a mark walked all over the place using the "go to " function and it consistently pointed to the mark no matter what I did or stated otherwise just has it has done all these years hundreds of times.

Okay, what Lisa said will work. However, if you're like me and not into sidling, then do what I said and it should work; however, in step 6, you must continue pointing the top of the GPS towards the tree even though you’re walking at a 45 degree (or whatever angle) away from it. Here’s the experiment repeated, emphasizing where to keep pointing the GPS in step 6:

1. Establish a waypoint at some tree or something (maybe a hundred yards away). With my unit I would just walk over to the tree and press one button and that would enter the location as a waypoint.

2. Go back to your starting point and make sure the compass is disabled.

3. Put the unit into the pointer mode (or whatever it’s called) and then start a Goto a waypoint (or whatever it’s called).

4. Point the GPS at the tree.

5. Start walking towards the tree. The GPS pointer will swing to the top of the screen.

6. Then walk off at a 45-degree angle to the left of the beeline to the waypoint (but keep pointing the GPS towards the tree). In effect you’re simulating a kayak in a crosscurrent (n mph towards the tree and a cross-velocity drift of n mph).

7. If you notice that the GPS pointer swings around to 45 degrees to the right of the tree you’ve proved the point; i.e. GPS is not pointing to the waypoint; instead it’s pointing to the correct ferry-angle adjusted direction.

[spider]

Problem solved...I cut down the tree ;->

not really I took out the manual and saw that the ... "Go to" is the default.... bearing to destination

or you can set the "Go to"...to a course that goes to the destination....

or

you can toggle between the two choice accidently or not depending if the" page" button gets held down for a moment or two...

amazing what is in those manuals if we read them

...........never did like that tree anyway.....