djlewis

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.

Absolutely lunch, and some energy snacks in your PFD pocket. I'm wearing a full wet suit. And don't forget that the clothes under it should be 100% syntheic -- no cotton anywhere, ideally not even in your hat (unless it's a Tilley ) Also, it would be terrific to print out the http://www.gmap-pedo....com/?r=5510333 topo map and bring it along on your foredeck in a ziplock bag. Not only is it a good habit to carry a map or chart anytime on salt water, it will increase your enjoyment of the route and get you started on some navigation skills (strictly speaking, piloting, not nav)

Assuming everybody who has signed up is coming (minus Liz, plus Al), I think we should consider this trip closed.

Weather, tides and conditions for Sunday, Plum Island Sound temp: 55F on the water, 65F on landearly fog -> clearing and 15-20% cloud cover by 10:00 AMwind: 6 -> 9 kts from the E, gusts to 11water temp: high 50's - low 60stide: PI Sound south (where we launch) low @ 5 AM, high @ 11 AM, low @ 5 PM; add 30 minutes for Rowleycurrent: about 1.0-1.4 kts in Plum Island Sound, tail current both wayswaves: 2-3 from the SE outside (not terribly relevant); little or no chop in PI Soundroute: http://www.gmap-pedometer.com/?r=5510333 So, we'll have a bit of a head and crosswind on our return trip. That plus the tail current means we should take care manuevering in Plum Island Sound around the docks and moored boats at both ends of the trip -- more at the beach briefing. Air temp on the water will be on the cool side, abetted by the E wind. Driving directions: http://goo.gl/maps/sRdK Beach briefing and launch -- 9:30 AM sharp.

Two more people -- they don't change the decision. We are getting a bit large at 9-10, but we can break into pods. Also, if anybody wants, we might have a separate group leave from Eagle Hill. I know we have a couple of expreienced/trained folks along, including one who's done the route, so that might be feasible. --David

Hi Chris -- OK, see you on some other paddle. Summary and decision... We have 8 people, including me (both OK, prefer Pavilion) and my wife Deborah (a maybe; both OK, prefers Eagle Hill). Everybody is fine with either trip. Four prefer the 10-11 mile trip, launching from Pavilion; one prefers the short one, launching from Eagle Hill. So the decision is to launch from Pavilion. Beach briefing Sunday, 9:30 AM, launch immediately thereafter. Here is a directions map from Ipswich to Pavilion -- http://goo.gl/maps/sRdK -- use your favorite route to get to Ipswich.

Axiom 1: A capsize begins in an upright position Axiom 2: A capsize ends in an upside down (non-upright) position. Axiom 3: The only way to get from an upside down (non-upright) position to an upright position is to execute a successful roll. Theorem 1: Let N be the number of consecutive capsizes you make. Then the number of successful rolls you executed is N-1. Proof: By induction. For N = 1 capsizes, you executed, vacuously, N-1 = 0 successful rolls. Assume true for N = K, that is, whenever you have K consecutive capsizes, then you have executed K-1 successful rolls. Consider N = K+1 consecutive capsizes. After the first K of them, you have, by the induction hypothesis, executed K-1 successful rolls. By Axiom 2 you are also upside down (non-upright). Consider your (K+1)th capsize. By Axiom 1, you must have begun that capsize in an upright position. By Axiom 3, the only way to have gotten upright after your Kth capsize is to execute an additional roll, giving a total of (K-1)+1 = K successful rolls. QED.

I realize I did not answer your question about distance. On the short route, the 6-7 miles will be on flat water, not the ocean, so it will be similar to your experience on lakes. Figure that will be about 3+ hours of paddling and sightseeing. So if you are OK with that amount of time paddling, you will be fine for this distance.

I know some who've done more with involuntary capsizes! ;-)))

Hi, Janice: First, CAM trips don't have "leaders", so that's not my role -- I am just the proposer and organizer. As such, I don't grant or withhold permission to come -- it is your own decision. I can offer advice, but the decision is up to you. And here's some of that advice... With your level of experience my advice would be not to paddle in Plum Island Sound when there is any current, and we will have 1.0+ kts. That sounds mild and it is, but with the boats moored in the Sound, the current makes it into a bit of an obstacle course unless you have some stroke and maneuvering practice under your belt. So, if the group decides to take the longer route and there is no split into pods, my advice to you would be to wait for another opportunity. If we take the short route, then the factors to consider are the length of the paddle -- can you go 6-7 miles in a day? -- and the coldness of the water, still in the low 50's, so how would you do if you did capsize? Not having practiced reentries puts you at a big disadvantage there, and you'd be depending on the skill of your paddling mates to help you get back in your boat without ever having practiced. Also, you should definitely practice a wet exit at least once or twice, and until you've done that with a skirt, you should not wear one. That's not a problem in the marsh or the short stretch of the Parker River we will be on (the powerboats are not allowed to create wakes on that section). Your idea to attend lake sessions is exactly right. Though I know you're disappointed that there hasn't been one yet at Walden, I do advise waiting until you attend and get a chance to practice those important skills, especially wet exit, with or without a skirt, reentry, other safety issues and basic strokes.

Just discovered topo mode for this -- nice way to see the route, with more island and river names... http://www.gmap-pedometer.com/?r=5510333 When paddling at high tide, however many of these features are not apparent -- it's a beautiful, broad expanse. --David

I just chose wet/dry because I thought that's what the Epic video was saying, in essence. If I were going to circumnavigate Australia, I'd probably pick a Royal Caribbean Cruise Ship. Hey, a false premise implies any conclusion, right?! And compared to that, we're all snobs -- and plebs too.

Oops, sorry. I meant "snob", that is, tongue-in-cheek, since I myself prefer a wet ride boat -- the 'Naut is one of the wettest -- and so that kinda makes me one of them. But I was thinking of performance in this context more as rough-water handling than raw speed. The 'Naut excels there, probably better than an Explorer. (Sorry, I'm not up on the latest generation of boats.) Yes, rocker is probably a big factor too. But for the bow, I don't think the overhang is part of wet/dry ride, but the lower part of the bow, the part that's mostly in the water -- what's the volume and shape. So I agree with you that plumb vs overhang has little or nothing to do with wet vs dry or pearling. Just imagine a very sharp, skinny plumb bow, with a convex (indented, low-volume) shape at or below the waterline, vs a fat plumb bow with a bulge. The former will be very wet and perhaps prone to pearling, the latter very dry and will rarely pearl. Well, maybe pearling is more complex, since a dry ride boat may pitch more fore and aft.

Yes -- quite a difference in the Epic video. But the narrative is disingenuous -- there is no such thing as a "conventional kayak" when it comes to riding up over or punching through waves. In fact, the narrative is really screwed up when it says the Epic is riding smoothly up and over -- it's actually slicing through the waves more than the "conventional" boat (an Explorer?) -- that's why it is relatively smoother. There's always an end to a wave so the bow has to emerge at some point even if it sliced into it to start. The correct distinction is the "wet ride vs dry ride" boat. Whether a boat has a wet ride, that is, slices through waves (like the Epic, despite the narration) rather than riding up and over them, depends on a bunch of factors, mainly the shape and volume of the lower part of the bow, but not at all on the upswept bow or lack thereof (as Epic demonstrates). For example, my Aquanaut has quite a convex shape on the lower half of its bow and a sharp front edge, and it's a wet ride. An Explorer has a bit of a bulge in the side of the bow, and it's considered a relatively dry ride. But there are waves and there are waves -- and there's always one big enough to give everyone a dry ride... and an "exciting" road-runner moment and drop on the other side (or if you are a bit late to the top, a big break in the kisser). It's also somewhat a matter of personal preference, though the performance snobs (like Epic apparently) prefer a wet ride because it's smoother, more efficient and avoids the potentially jarring rise and drop that can throw you off course, slow you down, or worse. It may also be because it's more heroic to be constantly getting a faceful of water in conditions. Kayaking is a water sport, after all.

Great Marsh -- this Sunday -- high tide, no greenheads! Perhaps last chance for that combination on a weekend until late August or September. http://www.nspn.org/...nt&event_id=814 Launch time -- 9:30 AM (to catch the tide) This will be a CAM trip, but there is a decision to be made in advance, namely between two launch points with different routes: Eagle Hill -- 6-7 mile route, easy L2, no current, limited parking (maybe 5-6 cars) and a bit of poison ivy to dodge.Pavilion Beach -- 10-11 mile route, upper L2, 1.0-1.5 kt tail current at beginning and end -- lots of parkingBoth routes are the same in the marsh, with an extra 2-mile leg each way in Plum Island Sound on the longer one. The plan: leisurely paddle through the heart of the marsh, hitting the Parker River as late as possible; lunch on the grass in Rowley (with plumbing); return by the same route or variant, with possible excursion across PI Sound. Bring bird books or cards if interested. Planned route -- http://www.gmap-pedometer.com/?r=5509465 -- Pavilion Beach is the start point; Eagle Hill Beach is at mile marker #2. If you are coming and have a preference, please express it. Right now, it does not look like there will be enough to make two pods, but that may change as the day approaches. If we do split, we might join up on the water, or not. --David

Interesting -- thanks, John. It does seem to say that a "pursuit curve" is a rather general family. I wonder if the one in question for kayakers -- with a fixed prey and moving frame of reference -- has been analyzed and published before?

Well, there is John Huth -- a top-drawer physicist and NSPN denizen. I have the desire to think about this, but not the specific math background -- never did much analysis before heading off into theoretical CS. So I'm at the mercy of you and the guys on math.stackexchange that did this work. Your plot looks reasonable. I think "pursuit curve" is being used here as a general term for a certain kind of curve defined mathematically rather than the result of a specific pursuit scenario. But still, doesn't thinking of the side current as a moving frame of reference make the fixed target waypoint into a moving one, in effect a moving prey? That's what the guys who solved it on math.stackexchgnage seem to be saying. But as I said, I have to take everyone's word for it. As for energy, the guy did point out that his model assumed constant kayak speed over water, not over ground. I do know enough to know that means a shorter path is perforce a more efficient one, energy-wise.

"Waterproof to 10 feet" is a lower standard than most decent waterproof cameras -- I forget the codes - J-something-something. Given that I'm not sure I'd trust it under water at all -- sounds more like splash-proof. But for $74 -- hey, about the round trip cost of gas to Bar Harbor.

Ok, some other time. Daughters and fathers are important!

OK, forget the bet. And definitely peace -- I apologize for my rude, snarky remark in the prior post you quoted, and will avoid that in the future. I really enjoy our conversations (and disagreements), and hope they don't get rancorous. Yeah, the two methods do sound contradictory, strictly speaking. The first one is just theoretical, to compare using a compass with the GPS. It uses the compass instead of the GPS to stay on the straight line, the track to the waypoint. In practice, I use a combination of them -- start with a ferry angle, keep reducing it, but also keep checking the compass to see how close I am to the ideal. Actually, the combination method requires a slightly different technique when using a deck-mounted compass. I know this sounds like a third method, and technically it is, but please bear with me -- it's the practical one, IMHO. Since I start out aiming upcurrent of my waypoint target, the compass reading on the deck compass will not be the ideal one, for the straight line, but say 10 degrees above it. So to keep taking exact compass readings to the target I'd have to occasionally turn the boat (10 degrees down to start) to point at the target, which is a nuisance, especially in conditions. (Of course, I could estimate the variance by eye without turning the boat.) Instead, I just keep reducing the compass reading on the deck compass linearly, from 10 above the ideal to zero in this case, to correspond to the linear reduction in ferry angle, aiming to end up with the straight-line reading. Of course, the ferry angle and linear reduction are only estimates, and so will never be as good as the GPS or even as good as the hypothetical compass method above (the first method in your order). But now that we've had this discussion, I realize that if I want higher accuracy than that estimating method will bestow, I can use a handheld compass to keep checking the angle directly to the target (or check a GPS to see how far I am from the ideal line, which is theoretically equivalent but more accurate). In practice, I find that the estimating produces a pretty good track, but not as arrow-straight as the ideal one. The next question is how much this matters. So I took out my Maptech software and set a course from Lands End to Brace Rock, with two legs. When the two legs line up in a straight line, the distance is 3.74 nm. When I put a kink in the middle with a variance of 5 degrees (moving the midpoint of the route about 0.2 nm off of ideal, the total distance increases to 3.76 nm. So for this, a 5 degree error adds 0.02 nm or 0.5% to the distance, or about 24 seconds to the total crossing time of about 45 minutes at 5 kts. (Ah, I guess I could have done that with simple trigonometry, basically the law of cosines -- ok, did it, and it comes out the same.) For recreational paddling, 24 seconds in 45-60 minutes not a big deal. But for racing, it's a very big deal on what amounts to about 20% of the Blackburn course. So yes, racers should use the GPS method for both its extreme accuracy and ease of use. So, sorry to confuse you with multiple methods -- and then to add a third. Perhaps this would be easier to discuss again on the water, where we can both demonstrate our points in a live situation. Peace. --David

Gee, Leon -- you have my proposal totally wrong. I would not start pointed at the destination and keep that -- we dispensed withthat in the first bet, that you rejected. Check my answer to Lisa to see what I would do. In any case, I am not proposing a bet on performance. I agree that a GPS would zig-zag a bit less. What I am betting is that the compass method and the GPS method would both keep us on or clsoe to the same straight line IN PRINCIPLE. But read what I sais to Lisa about resolution -- the GPS method would zig-zag less because of its higher resolution. Then there's the method whereby you set the initial ferry angle with your mind and keep it adjusted with your mind and compass as you go -- which is how the real kayak navigators do it.

I am saying start with the ferry angle estimated as I outlined and linearly reduce it as you approach your destination. On Friday, crossing from Essex mouth to Lanes, there were no objects at all that could be used for ranges, from start to finish. No buoys of any sort. No two features on the distant shore that you could see lined up. No islands. But even if there are two objects at one point, when you pass the nearest object, you have to find another one in just the right place. That's really not very common for long-ish crossings. I now get how the GPS works for this. It has very high resolution for staying on the track, so yes, very little zig-zagging. When it gives you its first correction, presumably within a minute or two of starting out with your bow pointed toward your destination, it is, in effect, giving you the initial ferry angle, and you haven't zigged much. But if you started with the correct ferry angle, you wouldn't zig at all. Now, if you didn't have a GPS but have to fall back on your ancient gadget - the compass (which having no batteries or electronics, rarely fails!) AND you started off pointed toward the destination, you wouldn't get your first "reading" about being off course until you could see that the compass reading was now off a degree or so from its initial value. IOW, you'd take a bigger zig before getting to that initial ferry angle. So when using a compass, its lower resolution makes it more important to estimate a good ferry angle to start. But in principle the GPS and the compass perform exactly the same function and keep you on exactly the same straight line to your destination waypoint. The GPS just does it with higher resolution and more accurate information about when and how to get back on track. But of course, estimating the ferry angle is a very useful skill, which you have concluded you have no need for, since you always have a working GPS on deck. Well, I hope your GPS never dies or washes off deck. ;-))) I accept that the GPS gives you the ferry angle, and I don't mind that it's in that roundabout way. But it's really not so hard to take a swag at the initial ferry angle using the original gadget -- your mind -- and start with that. One more gadget (GPS) to relieve us from using our minds, eh! (I'm not really a Luddite -- I have all the requisite gadgets in my armory, and I'd be as distressed as the next guy if my cell phone crapped out, despite having lived many decades without one.)

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I don't bet on performance (aka horses), especially my own. I bet on facts, and for $100, only facts I am 100% sure of. ;-))) Anyway, here's my fact bet. If instead of looking at a GPS, you simply look at your compass when your start the crossing and take the bearing toward your destination, then keep that bearing as the heading on your compass throughout the crossing, you will track a straight line, in fact, exactly the same straight line that the GPS shows from the starting point to the target waypoint. Bet? That was the bet I proposed as we departed, so I'm not sure why you say I failed my part -- except that I did not write it down. Moving to the next stage, the desirability of calculating and taking an initial ferry angle is as follows. If you just watch the GPS (or compass), you are in effect neglecting all knowledge of actual conditions, and letting observed drift guide you after the fact. Given the less-than-perfect visual resolution of both a tiny GPS screen (if that's what you are using) or a compass out on your foredeck, you will have to drift a bit before you see that you are off course, maybe 1 (one) degree or so. And so on throughout the crossing. That means you will actually take a slightly zig-zag course, and it won't be perfectly optimal. The practical difference may be small, of course. But is there a feature on a GPS that will you when you are off the waypoint line even a teensy bit, like 0.1 degrees? If so, then you will zig-zag less, but not zero. I don't know, because I don't use GPSs much, and not in that way at all. The way to avoid, in theory, any zig-zagging, however small, is to take account of the actual conditions and calculate the approximate ferry angle to start. That's done as follows. (a) estimate the time to cross, taking wind and current into account (that is, the fore/aft component of wind and current), say 1 hour; (b.) estimate the (average) speed of cross-drift (port/starboard) due to wind or current, say 1 kt at right angle to your course; © calculate the approximate cross-drift distance on your destination shore as (a) times (b.); 1 nm in this case; © look for a feature on the target shore that is about that far (1 nm) upcurrent/upwind from your actual target, assuming the target shore is perpendicular to your course; adjust to simulate that if not; (d) aim there to start -- that's your initial ferry angle; (e) reduce your ferry angle linearly as the crossing proceeds, down to zero as you approach the target, and/or keep an eye on your compass and/or GPS and make indicated adjustments as discussed before. Of course, none of this is exact. The cross-current is not uniform all through the crossing. The wind varies and shifts. There are some approximations built into that method, for example, your crossing time. You paddling speed varies. Target shores are rarely exactly perpendicular to your course. There's some mathematical fudging in this method. Etc. But this will be a good deal more accurate than just waiting to observe drift (by GPS or compass) and then adjusting, and especially repeating that throughout the crossing. Or, for a quick "proof" -- it just cannot be as good to ignore conditions and wait for them to manifest as drift; a GPS with a fixed waypoint cannot know those conditions. I know you doubt the latter, but you'll have to prove it. Or maybe your GPS is a lot smarter than mine, and is actually a little weather station too ;-)))