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On Thu, 16 Oct 2003 11:14:47 -0700, Royer, Doug wrote:

>I would like to ask the members of the list who sail or pilot power vessels
>how or what techniques they use to find their DR pos. while underway.I am
>only interested in what methods you use and don't wish to get into a
>discussion of accuracy as yet.

My most frequent forays out of sight of land (except for fog) are
annual trips to Maine. After Cape Cod, I generally take a rhumbline
course from Race Point to Frenchboro Long Island, south of Mount Desert
Island. The first time, ca 1978, was without Loran or radar. I used
textbook DR, checking with twilight shots of two planets in the
evening.

We were aware of tidal currents, but assumed they would cancel out over
the 50-hour trip in a 30-foot sailboat. They did. We came in as
expected, but could see the coastal lights at Matinicus Rack and Mount
Desert Rock far enough so it didn't matter. The Main coast is a big
target over 180 miles.

We did use a TI 59 calculator with navigation software for sight
reduction. On a later trip with friends between Nova Scotia and Maine
my wife programmed a spreadsheet for sight reduction in a 1985 DOS
laptop.


Nowadays we mark hourly gps fixes on chart 13260. If motoring, we leave
the radar running. If sailing, we leave it on standby and scan every 10
minutes. We keep a Loran running also as a check against any weirdness.

The 13260 is overdue for replacement, and many years fixes make a swath
across it.

We don't use navigation software or chartplotters.

If the Loran dies we will probably use two gps receivers. We do carry a
handheld GPS but don't run it normally.

My wife and I are both trained in formal DR plotting, and we have used
it before the electronic devices were available or affordable. We keep
two hand-bearing compasses and a compass binocular for visual piloting.
We use them most often when tacking to windward near land. We plot
danger bearings on headlands and use them to decide when to tack. For
example, coming down Penobscot Bay.

With two people on a 36-foot sailboat, we don't come close to the
procedures of a Navy bridge as described in Dutton's, but we do keep
track of where we are.


>1.Do you use paper charts,rules and dividers?
>2.Do you use mathematical methods such as the following:Lat=Lf + -
>e[S/60(cos T*)] ; Lon.=Lon.f + - e[S/60(sin T*/cos Lf)]
>3.Do you use chatplotters and gps?
>4.Do you use a computer or laptop with navigation software and gps?
>5.Do you use gps only?
>6.Any other method not listed above or a combination of the above.
>Steven,thanks for telling me your training.In future conversations I now
>have a baseline and know how to frame my questions or discussions with
>you.By the way,thanks for the work you did on the Lunar files.I hope to make
>some use of them.
>Jared and Dave,I'll get the brand name of the LED nav. lights when I get to
>the yard this week to work on the skiff and post that info.




Rodney Myrvaagnes J36   Opinionated old geezer

Eagles may soar, but weasels don't get sucked into jet engines.

   

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