lhunt

Wow, Scott, v-e-r-y nice. Many nice ones there, but I really love #49. -Lisa (no points on my tube, though...)

Thanks for calling this great trip, Doug! -Lisa

Map to Lane's Cove -Lisa

We seem to have reached agreement on the basic core of discussion which was in contention before. That is, that a GPS is capable of directing a paddler into the correct ferry angle to make a straight line in a cross current or wind. Some reservations (about particular models of GPSs) might remain open until people get a chance to actually try it. Here is one snippet from my side of the conversation (such as it was), in case it is of general interest. Note that some GPSs have an internal magnetic compass that allows them to find magnetic North (or true North, depending on settings). This snippet has some references back to my picture from earlier, and also refers to that internal compass. "Forget the waypoint and the tree for a moment. The GPS has an internal map which it can display on its screen. It needs to know how to orient the map on its screen. If you choose "North up", no problem, it always puts North at the top of the screen. If you choose "Track up", it orients the map so that the interesting part, which shows the places you haven't been to yet, is at the top of the screen. That's how most of us use it, so I'm talking about "Track up". Scenario #1: If your GPS has a magnetic compass, and you hold it level and point it Northwest, it displays the Northwest part of the map at the top of the screen. Scenario #2: If your GPS's compass is disabled, and you move towards the North, it displays the North part of the map at the top of the screen. It figures that out by getting the point you were at a second ago and comparing it with where you are now. If you are in a kayak, pointing Northwest, but moving North because of a current, the GPS has to decide whether to use the compass and put Northwest at the top of the screen (#1), or ignore the compass and put North at the top of the screen (#2). In other words, the GPS can orient its map based on either the compass or the direction of travel, but not both. Now, having understood that, mentally put the tree back on the shore directly North of your kayak, and put a virtual tree into the GPS's map as a waypoint directly North of your little virtual kayak dot. Current is coming from the West. You have a good ferry angle - your real kayak is pointing Northwest but moving North. The pointer from your virtual kayak dot to the waypoint (virtual tree) [on the map] is definitely going North. But in Scenario #2, North is at the top of the screen, so the pointer is straight up, encouraging you to keep the ferry angle. In Scenario #1 Northwest is at the top of the screen. North, and the pointer, are to the right. If you follow the pointer, it takes you out of your ferry angle and has you point directly at the real tree, giving you a pursuit curve. ----------------- If you are standing still, obviously it's better to determine direction based on the compass than the direction of travel. My GPS (and also the eTrex Vista) allows you to tell it to use the compass below x mph. Setting it to 0 (or maybe 1) mph disables the compass under most conditions. Looks like factory default is 10 mph. This is done under settings->bearing for both types of GPSs. The compass issue is further complicated by a couple of things which are off topic here: You have to hold the GPS flat to get the compass to work, so if it is enabled it will sometimes stick or swing around unhelpfully in a kayak in rough water. Also, even GPSs with no magnetic compass have a "compass" screen where it displays a round thing that looks like a compass and gives you your heading based on direction of travel rather than the magnetic or "true" north." And another snippet, about GPS usage in general.: "I use the map page but don't pay much attention to the map. There is a pointer to the waypoint and that's all I have to see. I zoom in on the map so that the pointer will be long even when I get close, and I just keep it at the top of the screen. Of course, I seldom use the GPS to find my way or to know where I am. I'm always doing day trips in familiar places. The crossings aren't that long (Isles of Shoals being the longest), and I never go alone. If these things weren't true, I would not rely solely on the GPS. I use the GPS primarily for speed and distance. I keep a GPS log of everywhere I've been and can display all the tracks on a map. I use it for getting a straight line in a cross wind or current. Once or twice I was glad to have it in a fog, but at no time was it a matter of life or death. Once I used it to backtrack and find a lost paddle. I think absolutely the biggest reason not to use a GPS is to avoid dumbing yourself down. You can lose your sense of connection with North, South, East and West with a GPS. The "old fashioned" way of navigation increases the challenge and, for many people, the fun. It's like deliberately going out in rough weather, or surfing, or rock play - we all seek something that makes us work harder for exercise (mental and physical) and to keep ourselves young. The other reasons most people give for not using a GPS (batteries running out, it might break, etc.) are legitimate but more manageable. You wouldn't leave on a trip without your chart, and I wouldn't leave on a trip without topping off the juice in my rechargeable batteries. I keep the gadget in an electronics drybag and check the drybag every so often for leaks. If I think there is any chance of my needing the GPS for "real" navigation, I bring a spare for backup." I think on difficult expeditions or dangerous crossings even diehard chart/compass users might want a GPS for backup, and vice versa. I also agree with Jason that sometimes the shortest trip (in time) between two points isn't a straight line. In that case, the "old fashioned" way might be better. You might like having a GPS around to help you zero in on the endpoint during the last leg. Hope this summary helps. I really learned a lot from this discussion. Lisa

Yes! Got it in one. I'm sure that Ed has it right - I didn't explain it well in the beginning. I was using the terms "heading" and "course" and being too wordy. Oh, well, practice makes perfect. To answer Ed, the track I've been using to show that it does work in at least some "real world" conditions is the one from a race, here. The straight piece from Land's End to Brace Rock was done purely with the GPS. There was a stiff offshore crosswind and the rest of the racers were way out to sea. I have also used it very successfully in very rough water. There are plenty of other examples. My GPS (which is a pretty standard model) calculates the direction every second or so, and the line is easy to see. It doesn't swing around any more than a compass. I'm not sure what you mean by "outlier data"? If you mean momentary swings because of satellite errors or being sideswiped by a wave - it happens but goes away so quickly it isn't an issue. During acceleration the line swings a bit, I've noticed. -Lisa

Hi, Katherine, Yes, I see your point, but can you stand it just a little while longer? I think there is a thread within this thread which has stuck pretty well to the practical concept under discussion and I'd like to see it through if it can be done. It's an elusive concept; I've tried many ways to explain it in the past (and in this thread), and the last drawing has been the most successful summary so far. It's a little like getting a roll: It's not intuitive, but it's easy when you get it. The topic of ferry angles is pretty apropos for a kayaking club - if it turns out a relatively high percentage of people don't know that there's a gadget you can use, that might be useful information. It won't necessarily drive people to use a GPS (there are many drawbacks, as everyone knows), but it does round out one's breadth of knowledge about a common subject, I would think. Bear with us - we promise to be good :-) Lisa

Hi, Peter, yes, that is the point of the whole thing. But maybe it's hard for you to see? The example is Case #1, Using a good Ferry Angle", and it says "GPS is happy because direction of travel is towards the waypoint". It goes on to state: "GPS doesn't know that it isn't, itself, pointing at the waypoint". Wish I had something that would make a .pdf or something, that would help. I guess I could print it out then scan it in (ugh). The arrow definitely does not point at the waypoint, if by that you mean the visible tree. If the GPS is happy (as it is if your boat is moving toward the waypoint), the arrow points to the top of the screen regardless of how you hold the GPS. When moving at a good ferry angle, if you have your GPS pointing toward your bow, then the arrow points towards your bow. As long as you keep the pointer at the top of the screen, your ferry angle is good. It's a little disconcerting when you look up and the tree is to your right, but that's the way it is supposed to be. You get used to it. The simple reason it is this way is that the GPS, (when it doesn't use its internal compass (if any)), doesn't know in which direction it is pointing. It only knows in which direction it is moving. If you were in a tandem, and the stern paddler kept the ferry angle while the bow paddler held the GPS up and pointed it at the waypoint rather than at the bow, the arrow would still be at the top of the screen, and would now be pointing both in the direction of travel and at the waypoint. But it is unnecessary, obviously. The point is to keep the arrow at the top of the screen, period. When using a GPS for hiking this isn't an issue, because one normally points the thing in front of one, which is also the direction of travel. Only in a boat (or a plane) is the direction of travel (course) frequently different from the direction you are pointing in (heading). Lisa

Just to give myself a sense of finishing the practical part of this discussion, here are 2 drawings of a GPS pointer in a cross current. In the first one, the paddler is using a ferry angle to get a straight direction of travel. In the second one, the paddler has spaced out and is just using a set heading. If you find these difficult to see on your monitor, I also have them uploaded here - use full screen mode to view. Here is the case of a paddler just going stupidly straight ahead without looking down at the GPS: I'm not much of an artist, so forgive me for that :-) Hopefully this helps a little to explain how a pointer based on the direction of travel gives you a ferry angle that changes with conditions. -Lisa

Great photos, as always, Doug - thanks! -Lisa

V-e-r-y nice, Bill, I enjoyed that - thanks! -Lisa

C'mon, John, don't desert us now! At least read through this and let me know what you think and that will be the end of it. Your old GPS is not less sophisticated than mine or Leon's, it's more sophisticated. You have the compass enabled. If you disable the compass you'll be there, I promise. Do one more thought experiment with me: Take your tree and put it in a field. You are hiking and can see the tree. Here are some questions (and answers). #1: Stand completely still and point the GPS at the tree. Which way is the pointer pointing? Answer: It's a trick question, because the pointer is random. Maybe it's stuck where it was the last time you moved (that is, if it was pointing to the left of the screen it's still there), or maybe it's swinging wildly around as it gets little errors from the satellites. Point is, it doesn't know which way you are pointing because you are standing still. #2: Start walking toward the tree. The GPS pointer swings to the top of the screen. It's happy because you're moving toward the tree. You're happy because the pointer is pointing at the tree. Good. Now, while walking toward the tree, pivot the GPS 45 degrees to the left. Which way is the pointer pointing? Answer: It's pointing 45 degrees to the left. That is, it's happy, because you're walking toward the tree, so the pointer is at the top of the screen. The fact that you're pointing the top of the screen to the left is unknown to it. You can hold the device at any angle and the pointer will always be at the top of the screen as long as you walk toward the tree. #3: This is the same as #2, but is more obviously a metaphor for a drifting kayak. While pointing your face and the GPS at the tree, walk with a sidelong gait 45 degrees to the left of the tree. Which way is the pointer pointing? Answer: It is pointing to the right of the tree. Why? The GPS is unhappy because you are not moving toward the tree. It tells you to bear right by moving the pointer 45 degrees to the right of the screen. You are (seemingly arbitrarily) pointing the top of the screen towards the tree, so the pointer is pointing to the right of the tree. To your perception, the whole map is pivoted "off" the real world by 45 degrees, but that's only because you are holding the GPS 45 degrees "off" your direction of travel. Continuing with #3, now, continuing to use the same sidelong gait, turn your body and the GPS right (traveling more to the right) until the GPS pointer is straight to the top of the screen. Your face and the GPS are pointing to the right of the tree, but you are sidling to the left towards the tree. Now the GPS is happy because you are moving toward the tree. The pointer still seems to be pointing to the right of the tree, because you are holding the GPS to the right of your direction of travel. This is a metaphor for the kayaker using the correct ferry angle. David, I'll read up more on the "course" pointer. I've never used it, but I think it isn't what you want. It would, as you say, give you the whole "A" to "B" thing, but would stick you with a particular course. If you drifted off that course for any reason, it would want you to get back on the original line. I would rather have a new line which is straight to my destination. -Lisa

OK, David, you got me there. I was wrong when I said A is your current location (sorry). A is the location you were in one second ago. You don't have to set A, because the GPS continually re-computes your direction. Remember, it doesn't know which direction you are pointing in (it has no compass). It records a one-dimensional point where you are, and one second later it takes another point. The difference in location between these two establishes a direction of travel. When you are using a ferry angle, or when you are not using a ferry angle and should be, you are pointing in a direction other than your direction of travel. The GPS gives you its pointer based on the direction of travel, so the pointer is "off" by the ferry angle relative to the tree you actually look at on the shore. That is true if the GPS is using a compass. It confused the bejesus out of me when I began using it for paddling. I had the compass set to kick in below 3 mph. Imagine my confusion when, as I accelerated, the whole map swung around as soon as I reached 3 mph and seemed to be "off" by some mysterious angle. In fact, if you are using the GPS in a boat, an integral compass/GPS combination is a bad idea. If you want a compass, it should be a normal compass. The GPS knows where the tree is, and it knows where you are, but it doesn't know what direction you are pointing in. Pointing the GPS at the tree doesn't help. You have to actually move toward the tree before the GPS tells you everything is OK. So, yes, the answer is #1. Looks like I shouldn't have gone to bed last night! More after I read John's stuff more carefully.

I joined the L3 pod late, so I won't try to write up a trip report proper, but here are some pix. I can only say the weather was custom-made. Perfectly calm for the paddle, pleasant right through the PPPO, then a nice deluge on the highway for the automatic boat washer. Then (for me, at least) back out of the storm for just long enough on the drive home for a boat blow dry. Very nice. And oh, the f-o-o-d! 'Nuff said. -Lisa

I guess I mostly agree with this, except for 2 things. One is the "somehow" statement: The GPS simply responds to your current course, thereby correcting for whatever happens to be messing with your course. It's pretty simple. The other issue I have is that you never have to set "A". The only "A" is your current location. The beauty of this is that if you drift off course from inattention, doing a rescue, avoiding rocks, etc., etc., etc., the GPS will happily compute the new heading that will give you a straight line from your new "A". OK, I understood when Jason pointed out that it's OK to let a current push you to the right as long as you know another current is going to push you back again. I'm willing to believe that. I now understand (I think) that you are also saying it's OK to let a current push you to the right as long as you know there is less of a right-hand current later on when you have to paddle back to the left to get where you want to go. Hmm... maybe. But if it's wind you're talking about I'm less sure - not so predictable. And I'm sure there's some mathematical sweet spot for how much drift to allow for how much difference in currents and all that. Some skepticism here, but I won't say you're wrong. Sorry, I know I'm quoting you out of order, but this is the one I don't get. If I read it carefully, then paraphrase, it sounds like you are saying simply pick a direct compass heading and stick with it, regardless of changes in wind or current. I find that hard to believe. If the wind or current pushes you off to the right, regardless of your heading, you won't get there. Actually, last time we talked about this I think you said later that the thing was to compute a ferry angle then reduce it linearly. Which means you need to know the strength of the current or wind ahead of time, I think. But, as you say, we've seen this movie, so I won't try to play it again :-) Of course you can do a good job with a compass and a chart - people do it all the time and it's amazing. I think I'm just saying the GPS is easier and somewhat more accurate. Anyway, that's it for now, I guess. Thanks very much for the discussion! Lisa

OK, maybe we're getting somewhere now, not sure. Us diehard fans (actually, I think there are many reasons not to use a GPS, this just isn't one of them...) know the GPS isn't pointing to a waypoint on the opposite side - that is, it isn't setting a heading that points directly towards the waypoint on the opposite side. You still think the GPS works just like a person who can see the tree and is paddling pointing toward it. Yes, if it worked that way you would get a curve - apparently a "pursuit curve" as stated. Referencing your drawing, here is a thought experiment that might help: I put a GPS on my deck with a find on the tree. I start across the current, which is coming from the left. As I start to drift to the right, I look down and see my GPS pointer changing. I modify my heading so that the pointer is straight up to the top of the screen. Once I find the pointer has centered, I look up. Am I now pointing to the left of the tree,to the right of the tree, orright at the tree?If you know the answer to this question, you understand how the GPS works. Please note that the GPS does not have a compass working at the time.

OK, yes, I think I can see the problem. If the GPS's you've used had compasses, the compass was messing you up. There is no need to sit still and evaluate the speed of the current. You turn the compass off, and use the heading the GPS gives you. This will give you the correct ferry angle "as you go". You adjust your heading so that the course pointer is at the top of the screen. When you look up, the landmark you are heading for won't be at your bow, because you are already on the right ferry angle. Your GPS will show the waypoint as being straight in front of you, but on the "real earth" the waypoint will be some degrees off that. That's because the GPS doesn't know what direction you are holding it in (it doesn't have a compass). It only knows what direction you are heading in. I'll check this more tonight or tomorrow - gotta go now... Lisa

I'm enjoying it too, but the frustrating part of the conversation is simply this: I suspect the two most vehement detractors don't know how the GPS works. I think probably Jason knows how a GPS works and likes his way better, which is nobody's business but his own, so I'm setting Jason aside (no offense, Jason) :-) The previous statement by John that "This makes me think that perhaps GPS'es should have a little mini-calculation thrown in to give a ferry angle on-the-go, with some inputs from the user.", and by David that "So the upshot of your example is that a GPS will not do anything for you in the case of significantly non-uniform cross-current." make me think they don't understand how it works. I'm probably not explaining it well, and I don't know that one more time will make the difference, but here goes: The GPS gets your position. One second later, it gets your position again. It doesn't know or care which direction you are pointing in. It knows which direction you are moving in. If you are moving too far to the left, it tells you to turn right. Variations in current make it tell you to move more or less to the right. No user inputs are needed other than the location you were a second ago vs. the location you are in now. It has no sophisticated way to measure current, it measures current by knowing your direction of travel. It is a garden variety hikers' GPS (at least that's what I use - I bought it before I ever started paddling). With all respect to Leon, maybe the point would be better made by getting the protagonists together, giving each a GPS, and taking away their compasses just for fun, on a nice day where everybody knows exactly where they are and there is one good non-uniform current to cross. No danger to muss up the experiment. Within 5 minutes you will get the main point of how the thing works. After that, whether one uses a GPS or not is a completely different question. I think if I were going on a long and dangerous trip of any type, I would want a chart, compass and a GPS (or two). Getting back to Jason for a moment, yes - of course if you have two opposing currents of equal ferocity, a straight line is a bad idea, so your GPS would only be to help you if you have some unforeseen problem that messes up your trajectory significantly. Anyway, I'm off to the Solstice paddle. Hope to try the experiment someday! Lisa

Yep, a great time for all, even though I can't (yet) roll my new boat! And, oh, did that water feel nice and cool! Pix here.

As I said before, and Leon repeated, I'm not trying to say that a straight line is the best way to go, but if a straight line is what you want, the GPS gives it to you with very little extra effort. Maybe I'm not understanding the arguments about "zig zagging" or, in this case "continually telling you to alter your heading", but... The GPS tells you what heading to use and it doesn't change all that much. Here is how I use the GPS: I do a find on a waypoint, then start paddling. Once I get up to speed (in a few to several strokes), I check the GPS for a heading. I do this every couple of seconds until I get to a point where most of the time when I look down I'm on the heading - usually within 15 seconds or so. Then I establish a point on the horizon (if there is one), and use that. Every minute or so I look down to make sure the heading is still good and adjust if necessary. The adjustments tend to be, as David has pointed out, linear. That is, the ferry angle lessens as I approach the endpoint. I can also see the ferry angle go up for extended wind gusts and when I cross a current, which is what I want. I don't think the adjustments I have to make every so often, or the intermittent swinging of the pointer when a wave pushes me around, vary negatively from what a compass does during a crossing, so I'm discounting the small confusion that causes. If you take a step back, using a GPS is not terribly different from using a compass, except that the GPS corrects you based on course, not heading. That is a big difference, but the actual "in practice" way you go about following the pointer is about the same. The fact that the GPS keeps a track of where you went, and can display it on a map afterwards, gives very good feedback as to how straight the line was. If you want to see the "pursuit curve", check out the straight lines here, particularly the long one on the southeast side. Anyway, again, I'm not trying to talk people into using a GPS, but this topic might be of interest to someone thinking about it, so I want to be clear. Also, if readers have made a conscious decision not to use a GPS, it is worth at least making the decision based on real-world data. The theories I hear about how it "must" work are often wide of the mark.

It's funny you bring this topic up - it's the thing I'm currently struggling with. I set my hands wider and they start sneaking towards the center within a few strokes. So I'm no expert, but... It seems to me that when hands are far apart I get more out of the trunk muscles. Meaning I feel the stroke more in the obliques and less in the pecs. I would expect it to be the other way around - when the hands are wide you get more leverage from the top arm on the push. But that's what it feels like to me. Still working on it, though.

Oops - can't go tomorrow - I'll come Thursday if it's OK.

I would think you would adjust for upper body height by selecting the right paddle length.

I'm good for Wed 6/21...

Here's a good description for racing, or any distance/power stroke, (by Greg Barton and Oscar Chalupsky) -Lisa

Because the GPS computes its pointer based on course, not heading, it is a very efficient way to get a straight line across all these things if you have a waypoint on your destination. The GPS doesn't know it's correcting for anything other than your direction of travel - if you move too far left it will simply keep telling you to bear right. Of course, if you have a situation where a straight line is not the fastest route based on current or wind forecast or any other factors (like an island being in the way :-) ), you would have to program multiple waypoints, or follow an existing track. A GPS set to find a destination "off road" isn't smart enough to avoid obstacles or to determine the fastest route given prevailing paddling conditions. But it's definitely good at straight lines. -Lisa