djlewis

Me too. A mapping GPS is also particularly useful in a marsh or other complex place where there are lots of twisty little passages, all alike (an energy bar to the first to identify the reference, without googling, binging or the like). Also, I think there's a theorem in there somewhere that amounts to -- a GPS is useful (as outlined so nicely by Lisa) only when there is no significant reversal of current over the course. I think that's the same as saying that the GPS is useful on the last leg, that is, after paddling past all the significant changes in current direction.

Hey, Leon... I'll bet you $100 that... oh, wait... not supposed to do that... unghhh... can't resist... compulsive gambler...$100 that... nono... resist...yow...that...that...that...that............. (nice music from a compulsive gambler involving boats and divine consequences)

It's "semicolon", Herr Doktor Professor Godfrey-Christopher -- no hypen! (Mind if I use the British comma?) Who will police the punctuation police? -- Herr Doktor Professor Lewis

Whoops, forgot to answer Lisa's question: Using bearing pointer ==> #3 -- pointing straight at the treeUsing course pointer ==> #1 -- pointing left of the tree--David

Here's a page from a Garmin manual which, I think, illustrates my understanding well. If you are talking about a Bearing Pointer, then the GPS will direct you always directly toward the destination, and you'll get a pursuit curve. But if you are following a Course Pointer, then you will always be on the straight, A to B line, and will take an optimum track. --David

From what's been said so far, I would have thought that the arrow is directing you back to your original, A to B (A = where you started, B = the tree) straight line course, and that means correcting for your rightward drift, so #1 -- left of the tree. But your statement below about resetting A to your current location would lead me to say #3 -- directly at the tree. However, I am skeptical that is what happens because, if the GPS always sets a straight course from "here" to B, it is doing no more than mimic a visual "always paddle directly toward B" strategy (maybe in dark or fog when you can't see B with your eyes), and that strategy gets you a pursuit curve. So, I'm guessing that the first case holds, and #1 happens, that is, you will be directed to get back on the original straight line from A to B. And the compass can, in principal do that same thing. It doesn't give you a direction to point to do that, you just overcorrect on your own until the bearing to B is what is was to begin with, that is, you are back on the original straight line from the original A to B. BTW, your surprise (doubt?) that this compass method works is roughly equivalent to your (and Leon's) contention that the GPS is automagically correcting for drift. It is doing that, in effect, but mathematically all it's doing is keeping you on the original straight A to B line. And so is the compass method. PS -- We definitely should get together on the water and hash this out. Unfortunately, other obligations are keeping me land-bound for the time being. But I think we could meet somewhere in town with a GPS, compass and pencil and paper and do about the same thing.

Hi, John (Leon might want to ignore this post, as he has already rejected everything in it): Just for the record, here was my original bet with Leon -- it had nothing to do with any kind of contest on the water. Leon says you can use a GPS to stay on the theoretical best course from A to B, namely the straight line from A to B. The GPS somehow automatically adjusts for wind, current, sunspots, etc. You set A and B as GPS waypoints, look at the straight line on the GPS map display, and keep your GPS position on it (which modern GPSs apparently help you do). I agree and say... The bet: You can use a compass (without a GPS) to do the same thing, in principal. The method -- and mathematical proof of this statement, whose truth or falsity is the bet -- is simple. That theoretical straight line from A to B has another property, namely it is exactly the set of kayak locations on which the compass bearing from the kayak to B is the same as the compass bearing from A to B. So, just use your compass to always keep that bearing to B the same as it was when you started at A. I'm not saying that is a great method in practice -- in fact it isn't, and neither is the GPS method. Both will produce a slightly zig-zag course, as I showed Lisa, though the zigs and zags with the GPS will typically be smaller than with the compass. The good method in practice is to set a correct ferry angle to start and keep reducing it linearly as you approach B. You can use the compass or GPS to monitor how you are doing on that. And, as Jason pointed out, the best course from A to B is a straight line if and only if the current (and wind) between A and B are totally uniform. So when that's not true, the GPS waypoint/straight line method will not work, and neither will the simple compass bearing method, and even the ferry angle method will be quite a bit more complicated.

I like route #2 -- but unfortunately, I won't get a vote. Sorry, life is just a tad too complex these days. Have a great paddle and potluck! --David.

Hey, Leon -- I'm mostly staying out of this now, partly because I am confused by your responses. Seems to me that the status of the things we are discussing is pretty clear... with uniform current... the least-distance, least-energy course is a straight line from launch point to destinationas Lisa said fairly clearly, you can use either a compass or a GPS to stay on that lineyou can also compute a ferry angle and do the linear reduction trick; again as Lisa explainedwith significantly non-uniform current (thanks to Jason's wake-up call)... the optimum course is not a straight linethe correct headings depend on the current patterns and boat speedtherefore, a GPS is not much use, except perhaps to help determine those patternsthe total-ferry-angle method with reduction is required (but linear reduction would only be an approximation)that (potentially changing) angle can be monitored with a compass or a GPS being used only as a compassI think that's the basics. There are a lot of details and tricks in the total picture, but they mostly involve executing the ferry-angle strategy.Bye --David.

I see your point -- using the opposing current to allow you to paddle from A to B even with a cross-current that would ordinarily preclude that if there were not an opposing current. In fact, this applies to any situation where the current is not uniform, that is it varies during your crossing. Well, that's still a ferry angle kind of situation. You set the ferry angle by calculating the total eastward (say) drift on the destination shore during the time of a hypothetical driftless crossing. Then aim at a point on the far shore that drift distance west of your destination. In your exaggerated case with opposing currents, there is no total drift east or west, so your ferry angle is zero, which says, aim directly at your destination. So with non-uniform current, the course set by a ferry angle is not a straight line at all -- good point. And in fact, your course with a ferry angle is a straight line if and only if the current is uniform! 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. You will need to fall back on actual knowledge of currents and calculate the ferry angle based on the total drift you can expect over the crossing, taking into account the non-uniform current. You will also need to vary that ferry angle as you approach your destination, except in a case (like your) where the total drift is zero and the ferry angle is zero -- just leave it at zero. Leon, Lisa -- what say you? (Of course, this method assumes that the current varies only in one direction, the direction from the start to destination) and not at right angles to that direction, that is, it's not one speed in the middle and a different speed off to the side. If that isn't true, then things get really hairy. Also, if your crossing is long enough that current varies significantly over time, then it will also be more complex.)

Below is an explanation of zig-zagging. There is your zig-zagging! You start with a heading directly on your destination waypoint. That means you immediately drift down-current a bit -- zig #1. Then you look at the GPS and correct by turning upcurrent -- zag #1 Say you do that three times more -- zig #2, zag #2, zig #3, zag #3, zig $4, zag #4 At that point, you are presumably setting a heading and distant point upcurrent from your actual destination. You have finally set a ferry angle! You now won't zig-zag any more, until... Each adjustment will be a small zig-zag, perhaps inconsequential, especially if you use the linear reduction method, as you say. Of course, if you stubbornly insisted on using the initial method -- drift, adjust, repeat -- all the way to the destination, never setting a ferry angle, then you would zig-zag all the way. You don't do this -- great. But then why not start with a guess at the ferry angle and eliminate or reduce even the initial zig-zags. It's not that hard to make a good guess to start and then use the GPS to correct, but less correction and zig-zagging will be needed. Precisely! That's what I have been trying to say for a week. But I will grant that with a GPS the zig-zags -- initial or all the way across -- will be less than with a compass. That's because the GPS tells you quicker and more accurately than a compass when you are off the ideal straight-line course, so your zigs and zags are smaller than with a compass.

I'm here. And I'm confused by Jason's example. Assuming we are in a craft that can handle 12 kts of cross-current, I don't see why a straight line from launch to destination (at 0 degrees) is not the fastest course. Of course, 0 degrees is not the heading you would take. That's 270 + ArcTan(4/12) -- about 298 -- for the first 3 hours, then 90 - ArcTan(4/12) for the final 6 hours -- about 72. But the resultant course would still be 0 throughout, assuming your boat is not destroyed when you cross the 24 kt zipper!. Perhaps the issue is the heading you would steer vs the resultant course your boat would describe given the current. Jason apparently used the phrase "correct direction" as if it were the heading, and "GPS arrow" to mean resultant course. Of course those are not the same in the presence of any cross-current -- you don't need an exaggerated example to prove that. And the original disagreement between me and Leon was whether you could use a compass to stay on the correct course (the unique straight line from launch to destination), or is that something only a GPS can do. I still maintain you could use a compass, assuming it had adequate resolution to go up against the almost instant precision of a GPS, which it certainly wouldn't in Jason's case. But that's a practical issue, and as the great Yogi said -- in theory, practice and theory are the same. In practice they aren't!

That fits with my experience, both personal and when I give advice to others -- hands farther apart ==> more oomph from the lower back and hips. That's good, right? But there's obviously a limit.

I'm a definite maybe.

Ern: I've always assumed it was elbow/forearm, and said "elbow angle" to convey that. Leon: I assume narrow ==> more torque; wide ==> better cadence -- right? But it also seems like a torque/leverage issue. Otherwise, you'd go for max torque and put your hands very close together. But that decreases leverage, that is, the force you can apply to the shaft. That spectrum ought to be a fairly simple mechanics problem at about the freshman physics level. I have no idea how to handle cadence, however.

Good point -- that adjusts the length of the paddle outside your hand grip points. Which raises the question -- exactly what are the underlying factors that you are tuning when you change your grip width?

Thanks, Lisa. 75-90 degrees, typically 80, sounds about right to me, and that's what I use and teach. I was specifically looking for Ben Lawry's method, however, since it's entirely different but, of course, comes out about the same for most people. Sal seems to have recalled it, and here's my detailed reconstruction (a cubit is an elbow-to-tip-of-hand measurement, in ancient times using the King's specs). Put one elbow on the shaft's center seam (or more accurately, the center of the shaft)Stretch that arm out along the shaft and grip with that hand where it fallsWith your other hand, grip the shaft just outside but snug against the first hand's gripThat's where the second hand belongsNow let go with the first hand and grip symmetrically on the other end of the shaft.I just tried that with a paddle, and it came out with an angle by the other method of slightly larger (wider) than 90 degrees, that is, outside ChalupskyBarton's range. Interesting. Well, you should always probably adjust a bit as you go, though Lawry does mark your paddle with yellow tape after using his method, as if to say, stick with that. Or maybe it's just a rough guide. Lawry also has a way of having someone throw the paddle to you, you grab it in a particular way and go through some version of his sequence to get the placement. But I can't recall that at all. Anyway, I wonder what kinds of bodies lead to what differences between the two methods. Presumably Lawry has that in mind when he prefers his method. The standard method (documented by Chalupsky and Barton) seems to use shoulder width and upper arm length, while Lawry's almost exclusively forearm length, with a bit of hand size influence. Neither, however, uses upper body height, which seems like an important factor to me, if you're going to this level of nuance, as that changes a lot about how you attack the water.

Hi, Jason -- I do have Firefox, but browser spell-check is completely disabled -- not even a squiggly red line under misspelled words. I see those squiggly red lines when composing messages in facebook and other places, but not on this forum. Without that squiggly red line, I cannot even see the "Languages" option on right-click. I have verified this difficulty on two different systems, both using FF, but not other browsers. And I have never had to configure things the way you suggest. Thansk -- Davdi

Thanks always and sincerely to the folks who maintain and upgrade the message board and web site -- your extensive volunteer work is much appreciated! That said, I do have one question about the new message board -- what happened to spell-checking? It looks like my browser's built-in spell checking is disabled on message text, and there is no replacement function on the toolbar. Without that, you're going to see a lot of msispeelede words from me -- not that I can't spell, but my fingers do not always accurately express what my mind is thinking! Thnaks --Dvaid

How far apart should your hands be on the paddle? I generally use the rule that it's about the width of your elbows, or equivalently, if you hold the paddle over your head, your elbows should be at roughly 90 degree angles. But Ben Lawry has a different method -- which I have forgotten -- involving, I think, forearm length and palm width. Anybody recall what Ben's method is? Or other opinions or ideas? I understand that it's not exact, should vary a bit as you paddle, and will be determined differently with bent-shaft paddles (which I don't use) Thanks. --David

Whoops... two copies of this post somehow got posted. The replies are on the other one. Unless/until the moderators delete this one, if you find yourself here, please go to the other one.

Tide and current predictions are often innacurate. There are lots of reasons, some static, like the complexity of the local environment which defies accurate modelling (all tide predictions are based on models which are inherently inaccurate, just usually not off enough to notice) -- and some dynamic, like wind, storms, changes in topography, sunspots (just kidding) etc. I'd think Hell's Gate falls into the complexity category. Local knowledge can compensate for static errors and give you some help in dealing with dynamic variances.

Glad you enjoyed it! Yes, a GPS is great in a complex marsh -- assuming things haven't shifted since the chart was made. Down on the SE Cape, for example things are always changing. Also, just for the record -- everything you can do with a GPS can also be done with careful chart/compass work. It just takes a lot of practice and skill that way, while with a GPS you just follow the dynamic map, which anyone can do with relatively little training. Well, as we showed yesterday when we almost started up a dead end creek, you can still make mistakes in a complex place, even with a GPS. And finally, yes you are absoltuely on target -- local knowledge is really useful, sometimes essential. That goes for almost everyplace on the water.

11 interpid kayakers (yes, they're still intrepid) launched from Pavilion Beach in Ipswich just a few minutes after the scheduled time of 9:30, to ride the tide through the Great Marsh and thence on the Rowley River to Rowley for lunch. The tail current in Plum Island Sound proved no obstacle for our intrepid pod, and soon we were deep in the marsh, spotting egrets all around (but which kind?), trying to distinguish the creeks that lead to our destination from the dead ends. A bit of collaborative piloting -- in fine intrepid CAM style -- assisted by numerous charts, compasses, gps's and dim memories, got us there with no mistakes. For a return trip we decided to venture out into the Sound, where the expected E wind was more SE,. and therefore kicked up a bit of chop against the ebb. But everyone handled it intrepidly, and arrived back safely at Pavilion. A terrific day on the water! Below is the GPS track -- white outbound, yellow return -- as displayed in my ancient version of Garmin software -- sorry, it won't export to Google without a lot of trouble. Many folks were snapping pictures, which they will certainly post.