JohnHuth

I think you can use the 1:2:3:3:2:1 rule for current as well, you just have to change which hour you're talking about. Max current is just midway through the high/low cycle - they're both sinusoids and all that 1:2:3:3:2:1 does is give you an approximation of the sine (or cosine). Just offset one by three hours to get the other. But I don't want to confuse, I'm just responding to Phil's question "what do you use" - having one rule for me is easier and knowing how to apply it is what I do.

I always called it the 'rule of 12ths', but I know what you're talking about. The way I look at it, the 1:2:3:3:2:1 sequence is just describing the rough shape of the sine curve by breaking it up into hour-long pieces - so depending on where you are within an hour (beginning or end), you probably need to tweak things. For example in the 0-1 hour interval, at the start, you have zero (or close to it) current, but at the end of the hour, you would have 1/3 of the max flow. In any case, in my last post, I tried to compare the rule or 12ths for tide height and compared that to what showed up as the actual prediction and got to within about half a foot for a 12 foot tidal range for each of my predictions - it worked out reasonably well, but these were for the actual end of hours (e.g. end of hour 0-1). To get anything better than that, I'd do an eye-ball interpolation and call it good. So, I guess we're testing out the efficacy of these things. I'm having more trouble estimating max current in some random place where there's not a NOAA prediction. I tried to do this for the entrance of Machias Bay, and I *think* I did OK - but I had to play around a lot with trying to estimate how much the current picked up between, say, Casco Passage, Moosabec Reach, and then Eastport - and take an educated guess.

Here's a write-up on Figuring out Tides I *think* the postings now represent more or less a complete set of what I presented at the two REI workshops. I'm now going to make an introduction with links to each of the postings and make sure they're all cross linked. I also need to update a few based on some helpful comments I've received. If anyone has a topic that I didn't cover in the postings that were in the workshop, or they feel should be addressed, please let me know.

Anyone know how the compass works in iPhones? Magnetic field or GPS? Seems like it follows the magnetic field - but I haven't looked into it.

Origin of the tides, part 2

Hi, Leon - It turns out the motivation for the blog *was* NOAA's website. You can do the calculation in an inertial frame, as I did and the construction is to look at the diverging field lines. You can also do the calculation in an accelerating frame and invoke a 'centrifugal force'. Both will give the same results, but I find the accelerating frame calculation unnecessarily complicated. One carries along "test masses" throughout the calculation and it's not intuitive to me that you would derive an away-side bulge that is symmetric to a near side bulge. I'm in contact with the NOAA web maintainers and they say they're going to revise it this year. The reason I like this derivation is that I can also touch base with an accelerating frame in the following way: the average field in effect "goes away" because the earth's center is in free-fall about its barycenter. The remainder are parts of the earth that are not precisely following their geodesic (natural free-fall path) and hence feel a force - but that's simply the residual force given by the tidal field times the mass of the object.

Static theory of tides This one is very math-y, so stay away unless you want the gory details. I'm mainly putting this up there for anyone who has taken a course in physics and wants to see how the static theory can be derived without reference to a centrifugal force.

Tides, Part 1

Whoops! I'll look it over but I certainly could have slipped up. Thanks for pointing it out!

Great report! It had me smiling from ear to ear. So well done!

Last posting on vectors (aren't you glad?) This one shows a graphical way to figure the ferry angle.

A huge list if I were to stop and think about it, but one in particular. There are a bunch of fiords around what was called called the "Eastern Settlement" in Greenland. This is where the Norse had a large colony going from about 1000 AD until 1350, and there are a number of ruins there. My "dream" visit is to spend time paddling, camping, and exploring the ruins. It looks like the fiords are reasonably protected, but I haven't (yet) information on Greenland to assess the likely conditions. Sounds like a good winter project!

Vector subtraction using a current problem as an example I know, you probably have to be pretty hard-core to do this, but here's a quote of one of the aims of the 5* navigation syllabus: To apply the above relevant information in calculating vectors and negotiating open crossings and/or coastlines with no landing zones and/or tide races and overfalls Ah-ha….so the 5* guys are supposed to know vectors…sez here…..

For those of you who might be interested, I'm hosting a symposium on navigation on Nov. 14th (a Friday) at the Radcliffe Institute for Advanced Study (Harvard Sq.) - it's an all-day event, open to the public. Now, this probably will *not* help you with your kayak navigation skills, although who knows. We'll have talks on the neural basis for cognitive maps (Nobel prize this year in Medicine got it), the behavior of lost persons, animal navigation, culture and navigation, and the far out ideas like using pulsars as an interstellar GPS navigational system. Here's the link to the symposium

Next in series: adding vectors Again, the main point here is to give purely graphical solutions people can work with, using a backpacker's compass. To keep the clutter down in the figures, I used a protractor and ruler, but you should be able to see how to substitute a compass.

A typical way of doing this is to have two (or more) people who are the guinea pigs, and the instructor who puts them into various situations. Example: I did training with a Maine guide who took me out with another paddler. He would say …."OK, paddle into that slot-cave" when some swell was charging into it. "OK, now *you* wet exit"….."OK, now you - other guy - rescue him…." Or…"tow that guy through the eddy line." Over time, you build up enough permutations of conditions and scenarios that you begin to connect the dots. Having said that, I'm just doing a lot of paddling and camping at the moment, so I really haven't had a lot of experience rescuing people in weird conditions since I did that training. I probably should get back to it, and yeah, it's kind of fun - certainly a lot of good stories.

There's nothing like having a Maine Guide put you through your paces!

Yup, that would work, too. The main point is that I wanted to give people the idea that there is some imprecision introduced when making these graphical solutions. Thanks for reading it!

I'm testing out a purely graphical way of teaching vectors - this is first part in a series. It's not for everybody, but when we got to figuring how to find ferry angles at the REI navigation workshop, I realized that it was a bit much for some folks. Maybe some math-averse people might want to take a look and give me feedback. Link here

I had something of an epiphany - I was paddling with a 220 during a workshop. The instructor had us switch paddles with the person next to us. I swapped paddles with a woman who wasn't very tall. It was amazing. I asked her how long it was - 205. I was ready to downshift - and got a Werner Kalliste in 205. A bunch of people above have cited a lot of experts, so I won't repeat that, but only my anecdotal experience. I've coached a number of events in track (sprints, javelin, long jump) and become something of a student of biomechanics. The general rule-of-thumb is to find techniques that employ the core muscles as much as possible because they're the strongest. Without having done an exhaustive analysis of my forward stroke, I find that with a short paddle, I can get a fairly wide grip on the paddle without having wide elbow angles - this means I can get more of my shoulders rotated parallel with the blade during the strokes, which means I can get more of my core engaged. Also, as mentioned above (and tied into the stern rudder discussion) - it makes me feel like I can link strokes together. In particular, the transition from a forward stroke to a stern rudder without a lot of shoulder exposure is a big plus for me. I suppose I should be in a longer paddle given the sizing chart, but I've adapted my style to the 205 and like it a lot - I feel like I have a lot of control with it.

I've made another addition to my posts, this one is on dead reckoning. Here's the link. (suggestions always welcome)

A good stern draw is tough. I'm still trying to perfect mine. I try to keep my elbow at no greater an angle than 120 degrees and move it closer to my center of rotation. Don't over-extend the elbow as you put yourself at risk for a shoulder dislocation. Try giving that a shot. It's also the stern draw with an elbow angle of maybe 100 degrees in combination with boat lean - have you worked on that combination?

I've had this happen to me too. I think that you are just making a transition into turbulent flow so a lot of force develops even at small attack angles - intrinsically unstable. I don't have any good solution except to enjoy the ride and get ready to brace when the kayak starts to yaw to one side. I'd be interested in hearing if anyone has a solution.

Wave descriptions can get quite complicated if you get into all the details. Still, anything that provides at least a starting point, and simplifying assumptions is good. I'm in the process of doing some numerical wave simulations of waves interacting with land, and it's no walk in the park, let me tell you.

What MITA does can be quite effective and one can cover a lot of coastline with some organization. It takes 3 components - a 'mothership' that hauls trash to a primary take out place, some skiffs that can put people on a shore easily and then extract them and take garbage to the mothership, and then there are the trash-pickers. In areas like MITA this can be pretty effective. In more remote coastlines, I don't have any great suggestions, except to try to consolidate, bury, and burn what you can. (of course pack out, but this can become daunting)