Please visit our home site at www.TRILOBOATS.com.

Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Saturday, February 25, 2012

Lord of All I Survey: Notes on the Chart

Typical Chart of Tricky Bit


I hear that the ability to take in significant detail from a perusal of a chart is an acquirable skill.

Not me. Not yet, anyway. But not for want of trying!

One problem is that it's often wet, windy and wild just as we're negotiating a tricky bit of coast... entering or leaving a cove, threading a rock pile or reef, running into or out of a river.

Another is that so much of where we sail - in the shoal fringes inaccessible to deeper craft - is either not charted at all, or wildly inaccurate.

Here's a set of tricks that help with both problems...


We'd draw this after a row-by survey noting what was marked by kelp or not,
and checked on LOS ranges (can see 'boot'/creek mouth?),
current set and that all danger reefs are visible.
Note considerable simplification and detail omission.


Hand Chart

We start with a notebook of weather-proof paper - the 'write in the rain' type - and pencil. We're going to draw a 'chartlet' that we can hold in hand, on deck, in the thick of things for quick and continuous reference. It will be our guide, without having to run down to check the chart every time short term memory draws a blank (pretty often, for me... short term memory).

[Note: We like mechanical pencils with a fine, medium lead for chart annotations... write concisely with a light hand for easy erasure (corrections). Any old pencil with thicker lead works for Hand Charts... look for a heavy, dark line, visible longer in low light conditions.]

From the chart, we copy a representation of important features; coast outline, rocks, shoals, channels. This doesn't have to be too accurate or detailed; just enough to clearly identify features and a safe course. It helps to strip out information you won't need. Draw in a route whose dangers and courses are marked by identifiable features.

Identifiable features may include points, islands, exposed rocks, depth contours (need to sound for these), and ranges.

Ranges are any two things that line up to establish a line of sight (LOS), or a line of position (LOP). The difference is that the line of sight is the strait line determined by two points, while a line of position is one that you're sitting on. These can be used as danger lines (e.g., don't cross that there LOS, it's a rock pile on t'other side of it), or safe passage lines (e.g., line up that big, white boulder with the peak and stay on that LOP to the first bend... you'll be clear).

Useful line ups can be marked right onto the chart.

Compass bearings can be useful, though in our grounds, we hardly use one (lots of shoreline detail and distinctive background. For various reasons, they're seldom as spot on as an LOS.

Survey

The first time into a new area, all you've got to go on are your charts with notations of any local knowledge that might have been passed your way (note it on your charts, but treat it skeptically), and the information from your senses. If it's a complicated spot, consider a row-by to nail down details.

We make up our Hand Chart, and update it as we go. Sometimes it'll be a correction (as in, they drew the shoreline wrong), but most often, it's visual LOPs using uncharted features (e.g., trees, boulders, ravines), an addition (reef, rockpile, mudhole, etc.), description (bottom type, beach characteristics, etc.).

Hasty sketches of profile views can be drawn in. How do things look on the the approach? Where's the channel, visually speaking? When, where and what am I looking at for my ranges?

After we're settled (preferably sometime the same day) we often go for a hike or row. This is a time to take a more complete and less hurried survey. Compass bearings can be taken or checked, without boat's motion. If we're out at low tide, many hazards are visible that were not, on the way in. We can use this time to calculate heights of channels and bars, using the Rule of Tenths. All info goes onto the Hand Chart, which is by now looking a bit worse for wear.

Once back beside the fire, we tidy up the Hand Chart and redraw a fair copy in the log. We've wanted to collect these into a binder, organized in line with the Coast Pilot, but so far haven't gotten to it. If there are specialties, here, we note 'em... thimbleberry stands, orach, a freshwater stream.

One of the benefits of the process of drawing and re-drawing is that the picture you're developing gets its best shot at making the jump to long term memory.



Yes, but is it ART?
 The Mental Map


The generation before ours spent a great deal of attention on cultivating a sense of profile navigation. Ideally, one could look at a picture from anywhere within the cruising range and - from the profile of islands, mountains, sea and spits - know exactly where the picture was taken.

I'm still a novice at this - my brain doesn't work well in that way - but my powers are increasing! Especially from the decks of a slow boat, one has hours to contemplate, analyze and identify one's environs, purely in terms of profile. I play it as a sort of game, using the chart to back up my (increasingly educated) guesses.

Over time, my picture of our cruising grounds is slowly building into a mental map of the entire region. Every season fills in new gaps in the map. It's getting common to sail into some far nook we last visited a decade previous, and find it not only familiar, but fresh - the Hand Chart redundant for today.

*****
The Delorme Topographical Gazetteers (Atlases), taken together, are another resource. These are available for all 50 states. They're small scale (cover more area with less detail), but give a good sense of the lay of the land.
These help identify peaks (usually marked as points on the chart), runs of ridges, valleys and contours... all of which are very helpful for visual navigation. As a perk, they can help clue you in to how winds might flow in a given locale, helping toward the selection of an anchorage

They're not to be used as a sole reference for navigation, but then, what is?




6 comments:

  1. For me, profile sailing, watching the hills, nooks and crannies, has worked best in the big lakes I've sailed in New England.

    Along the Nature Coast of FLorida, it's not so helpful. There might be the occasional water tower, smokestack, or airport beacon that sticks out, but much of the coast is a long thin line in the far distance. Often I'm 5 - 8 miles out to get deep enough water to drop the 4'4" swing keel.

    The chart and GPS have been pretty good at nailing down my location. However, mostly I sail by compass bearing. My landmarks are channel beacons, rock and shipwreck markers.

    The ICW is well marked, and often there's not a lot of water outside the channel. We pay close attention to the chart to find water deep enough to tack against the wind. With any sort of draft, you might as well be running on rails.

    It gets interesting when I lift the keel and rudder and cut across the skinny water. Often we pull it off. Sometimes we are stopped and make chicken soup while waiting for the tide to give us a few more inches.

    It's been an interesting learning experience.

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    Replies
    1. Hi Sixbears,

      My hat's off to you lowland navigators! Pretty easy in my neck of the woods.

      Most of what I know of your area comes from THE COMMODORE'S STORY by 'Commodore' Ralph Monroe and V.Gilpin. Some great reading, that, and sets one longing for warm breezes and sandy bottoms!

      Do you ever use a pelorus, or feel like one might be helpful? Seems like they'd be a great companion for sailing by bearings.

      We've been carrying a full, mountable, swingable compass for two decades, now, still in the box. One of these days...

      Dave

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  2. The compass is perhaps my most important navigation tool while in Florida. I've a small battery powered GPS. To save battery power, I'll find a waypoint, note the compass bearing, and then turn the GPS off. Of course, I'm aware of how wind and current are behaving so that's allowed for. Once in a while I'll turn the GPS on to see how I'm doing.

    I've never even seen a pelorus and there's only so much one can mount on a 19 foot boat. Now I'll have to investigate them . . .

    Thanks for the book recommendation.

    My wife and I have only been sailing for little over a year, so we are on a crash course to learn all we can. We actually taught ourselves to sail in the Gulf of Mexico with a borrowed GPS and a donated compass. At least we have our own now.

    ReplyDelete
    Replies
    1. A pelorus is nothing more than a sighting notch along a rotating dial (like the spinning arrows of chance one flicks in a kid's game), mounted over a rose oriented to the boat's centerline (which can be painted on a hatch, say).

      It's used for taking relative bearings off the boat's heading (compass or otherwise). Simple, compact, DIY and fun, not to mention useful, and salty as heck.

      8)

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  3. The gulf of mexico is our old cruising grounds and we have fine memories of those waters. Indeed warm waters and sandy bottoms, sometimes glowing green on white limestone sand bottoms. Some days spent sheltering under a bimini with side panels then sultry nights sailing in a long sleeved t-shirt under a startlingly crisp milky way. The big bend portion is so shoal that crap trap buoys get thick miles offshore. Unfortunately we didn't have a shoal draft boat to get up some of the smaller rivers to their crystal clear springs origins. Barrier island, shoal bay sailing is a whole nother scene. Warm water..... hmmm hmmmm hmmmmmmm.

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