JohnHuth

Simply going by the table, and my own experience - the shift in Nantucket Sound to a wetsuit is mid-May, and the Shift at Bar Harbor is mid-June. In Nantucket Sound, I'm back to a wetsuit by the end of Sept, and then into a drysuit early November.

Water temp in Nantucket Sound is 37 degrees F today, 39 up in Jonesport. 55 deg water temp is what I go by - I may shave it to 53 degrees, depending. It depends on the season. The water temps this year are colder relative to last year. I paddled March 1st last year in Nantucket Sound and the water temp was 38 degrees F. Part of what I do is continuously sample the water temps. When I burp my drysuit, it gives me a chance to get fully immersed, and get a sense of the water temp and what I have layered inside the drysuit. At a certain point, I can feel where it's time to switch over to a wetsuit. As in the previous posts you mention, the water temp is a primary consideration, but air temp is a secondary one to consider, along with wind speed. As far as going farther north into Maine, there comes a point where water temps are invariably below 55 degrees almost all year round, like downeast Maine. When the air temps get high, that's where dilemmas set in. Just going by the water temp, you'd wear a dry suit, but then you'll sweat like a pig if the air temps are high. In that case, there's some judgement call about how long you might be in for a swim, and that kind of thing. I usually wear a farmer John and a neoprene top with warm air temps in downeast Maine, but also carry a dry top in case things get hairy or I want to do something challenging where I might swim. Everyone has their own system and I definitely consult with others who I'm paddling with on their layering system before setting out.

Here's a link to the Nantucket Sound tidal current calculation. As you can see, getting the bathymetry entered is quite a project: http://fvcom.smast.umassd.edu/research_projects/Nsound/ You need to scroll down to see the actual animation and click on it to enlarge.

How do I post them, Peter?

Yup, those lines all point magnetic north. I sometimes do it with a divider. I've gotten pretty fast with it. I now have a new, cheaper of of doing it - I download the maps as PDF's and use Adobe Illustrator to put them in, and then I go to Kinkos and print them out. Costs nothing and I can get maps at any scale I want.

Thanks, Pru. Yeah, sorry for the complexities at the end, there. I think some people got the details. It gets easier with practice. I found what I think Warren was talking about - it's www.deepzoom.com - but it seems to only work in the Puget Sound area - I could get it to work off the coast of Maine. Maybe it'll gradually spread? I think it requires a fair amount of input of bathymetry data to work, and that's kind of time consuming to get for the coasts of the US.

Bring the Boston Harbor chart from last time - you probably won't need parallels or dividers, but they definitely help if you're used to them. Some extra sheets of paper to work notes on, a ruler for sure. If you know how to use a compass as a protractor, so much the better - bring that, but if not, bring a protractor. A pencil with an eraser is a good idea, as opposed to a pen.

Just to clarify - using the label of hypothermic to a person to me implies that you should try to treat it. Certainly one symptom is cold hands, but there are plenty of cases where a person has cold hands and is in no danger of hypothermia, as long as the cold hands is the result of something well established - like taking gloves off temporarily during lunch. Once you start paddling, the hands warm up again. I'd look for more symptoms. I recently had been told about the causes of paradoxical undressing - people who are in advanced stages of hypothermia discard their clothes. Evidently the act of vasoconstriction (the things that makes your hands cold) takes active burning of glucose for the blood vessels to constrict. When all the glucose runs out, the vessels can no longer constrict, and they open up - leaving blood flooding back to the limbs, which creates a sensation of sudden warmth.

I generally don't see cold hands as a symptom of hypothermia. This is a general reaction of vasoconstriction in response to cold that preserves your core temperature. It can be painful, but not necessarily hypothermia. Hypothermia is when your core temperature starts to drop - so the 'umbles' are the first sign, then shivering. Recently I found out that paradoxical undressing (end-stage hypothermic victims shed their clothes) is the result of the glucose burning that creates vasoconstriction exhausts the supply of glucose - the blood vessels relax and blood floods back into the limbs, giving a sensation of warmth. Often times, after a meal, the diverted blood flow to the gastrointestinal system can divert blood from the limbs. A bunch of friends and I had this happen while bushwhacking in New Hampshire. Just after lunch, we noticed that our hands suddenly got cold. At no point did I think we got even close to hypothermic, however.

Link to Boston Harbor Chart JPEG It's 10.6 MB, and has decent resolution - the whole chart. Link to Boston Harbor Chart with variation lines JPEG Variation lines are spaced 1 nm apart.

I pretty much do like David Lewis, and picture things in my head, but I realize that some people do better with mnemonics. So, I figured it was worth doing a survey and trying to pick out one that struck me as being the easiest. CADET seemed to be the best of the lot for me, but I can easily imagine others would work better for some. I suppose the one thing that I would reiterate from the workshop is this: try to always keep both a magnetic and true bearing/heading going in your mind when you're on the water, and in the trip planning stages.

If you click on the icon, you'll see it trying to download. Then, you'll see an arrow in the lower right hand corner - click on that. You'll then get a message saying that the file is too large for google to process, do you want to download anyway? Click to download, and you should get it. It's a large file. Yup, I noticed that typo already, but thanks. There are some others in there.

Add/subtract mnemonics I've collected: East is least, west is best (Subtract easterly, add westerly variation) Maps Tell Almost Everything (Mag To True Add East) True Virgins Make Dull Company (True heading minus Variation plus or minus Magnetic variation plus or minus Deviation equals Course) CADET - Compass Add East for True Can Dead Men Vote Twice (Same as CADET) Of these, I like CADET the best, as it's all purpose If you go left to right - you have "Compass Add East for True" - then if you substitute "West" - you know it's Compass Subtract West for True" - and then if you go the reverse direction it's True subtract East for compass, and True add west for compass. You have to keep the arrows in mind - left to right and right to left, but it's an easy way to remember addition and subtraction. The virgin one is just plain confusing to me.

Try going to the lower right hand corner and there's an arrow that will allow you to download.

I posted my slides at this URL. It should be public, but I don't know if this works. If you cannot (or can) access them, please let me know. https://drive.google.com/folderview?id=0B35Z4TtP-ZZhN2ZNY0RpUWRQOFk&usp=sharing Note that the files are kind of large, so you you'll probably have to download them from the site.

Rather than waste bandwidth with more topics, I'm attaching here a little chart of typical angles associated with hand widths. I'll give a formula for figuring range in just a bit.

Hi - This is mainly for people who took the navigation class on Sunday (thanks for your enthusiasm by the way). So, here is an illustration of how to use the compass as an angular measuring device. Recall the exercise yesterday where you saw the Boston Lighthouse with an extended finger next to it. The lighthouse was at a bearing of 30 degrees magnetic and from the finger size relative to the lighthouse, you were supposed to get a position using a line-of-position and range. This is illustrated in the two attached figures. Without anything fancy, here's how you can use the compass to solve the angle problem - note that I went around and showed people this. First, you need the chart prepared as we did with the variation lines drawn in. Disregard the compass needle, you'll only need the dial and baseplate for this. First, rotate the dial by the angle of the bearing (30 degrees in this case). Flip the compass 180 degees to get the back bearing. Align the orientation lines on the dial with the variation lines, and then move the edge of the baseplate so that it touches the object sighted - in this case the lighthouse. That line (dotted in the Step 2 illustration) - will give you your line of position. No calculations- just one rotation and alignment of the compass. Note - I had some e-mail exchange with John Carmody, and I'd like to pass along some notes. He prefers to do the addition and subtraction for variation. He's seen students who do not have the concept of variation and this is dangerous if, for example, you don't have a map with variation lines drawn in. This is one reason I'm always thinking in terms of both true and magnetic. Secondly, he fears that drawing lines on the map may cover up features like rocks. So, these caveats are good to keep in mind. I find that different people find different ways of doing things that's to their preference, so I don't know if anything is 100% foolproof - like the poor guy who got east and west declination confused and got lost in Nova Scotia!

I think of navigation as a process of successive approximation - deal with the biggest effects first and then whittle them down as you go along. In some cases, the effects of wind can outweigh a modest current. On the other hand, a strong current can overwhelm wind effects. It's a question of figuring out what the biggest issues are, addressing them and then turn attention to the lesser issues. That's both in the planning phase and also on the water.

I was only saying that the two times I've been into kinkos or staples to print out topos, they've refused. On the other hand, when I altered it, they seemed OK. I think it's more of a "cover your butt" attitude so they don't have to get into details of individual kinds of maps and such.

Attached is the graphical method. 1.) First, establish a scale - e.g. half an inch equals one knot. 2.) Draw a vector that has a length representing your paddling speed. 3.) Draw a vector with a length and heading that represents the current speed and direction 4.) Extend a line from the tail of the current vector that represents your desired heading - make it as long as possible. 5.) Take your paddling speed vector - place the tail on the tip (arrowhead) of the current vector. 6.) Rotate that paddling speed vector until it touches the line representing your desired heading. 7.) The angle of the rotated paddling speed vector (touching line) is the heading you need to make *in* the current to make the course made true with respect to land. 8.) To find the actual speed and heading you end up with - extend a vector from the tail of the current vector to the tip of your rotated heading vector. This gives you the heading with respect to land, and the length gives you the speed. Note: if the rotated paddling speed vector never touches the desired heading line, you're out of luck - there is no solution. Can all be done with a backpacker's compass and a piece of paper.

I agree with Nate that plotting them using vectors is definitely a straightforward and intuitive way to go. A backpacker's compass can be used with a pencil. Lacking that, there are some rules of thumb that can be used if you assume a 3 kt paddling speed and a current perpendicular to the crossing.

If you don't have the full kit, try to bring the two kinds of compasses - the magnetic kind and the kind that draws circles. Also a ruler. I think we'll have at least three sets of dividers and parallels coming. We can also form small teams, which is a good exercise anyway.

As long as it covers as far south as Cohasset and as far north as the Harbor, it should be OK. It should also have a legible scale of distances in nautical miles.

You can get print on demand charts from anyone of a number of suppliers - like Ocean Grafix. That chart is definitely available - I ordered a copy on Thursday.

There are two charts that typically go by the name "Boston Harbor" - one is the 1:25,000 which is the one I'm proposing to use - you can look at it here: http://www.charts.noaa.gov/OnLineViewer/13270.shtml The other is called "Boston Inner Harbor" and is 1:10,000, which I won't use. I chose the Boston Harbor one because I thought that it's more likely people would have it, and also if they didn't it might come in handy for some local paddling. Finally, I learned a bit of history about the approaches to Boston Harbor - didn't know this until I gave a talk in Hull - but the old time route before channel dredging went past Hull, which is why there was a major life saving station there. So, all these conspired to make me think this would be a good choice for a chart. I'm also going to bring some printouts of areas where there are modest currents, so we can do a bit of work on crossings (which seems to be a popular topic on this website).