One of the most interesting stories in naval history is the problem with navigation because of the difficulty with determining longitude. Whole flotillas were lost. There is a terrific book called Longitude <http://www.amazon.com/Longitude-Genius-Greatest-Scientific-Problem/dp/080271529X/ref=sr_1_1?s=books&ie=UTF8&qid=1417715483&sr=1-1&keywords=longitude> from Dava Sobel that talks about the history of working this out. A story of intrigue, science...compelling read. If you have not read it you would love it as a sailor. Daniel Rich M15 Kestrel On Thu, Dec 4, 2014 at 9:34 AM, Conbert Benneck <chbenneck@gmail.com> wrote:
On 12/4/2014 10:55 AM, Conbert Benneck wrote:
On 12/4/2014 7:09 AM, Thomas Buzzi wrote:
Addendum to my email:
If you are out of sight of land, you get a position using your sextant for a latitude, together with a time from an accurate chronometer that give you a longitude (that is why everything is based on Greenwich Mean Time).
Connie
Hi Tom,
My blue water sailing days were long before modern GPS became readily available.
You navigated on paper charts by drawing your course line from A to B; took a departure time as you left the harbor, and kept track of your boat speed. From your chart you know the distance between your departure point (A) and your destination (B) in nautical miles.
Time X boat speed =s distance traveled (roughly) - you also have to calculate tide flow; direction and velocity: with you or against you; or at some angle to your course so that you know how far the tide displaces you from your course line. Your average boat speed divided into total distance to travel gives you your ETA. (Estimated Time of Arrival) at your destination (B).
You keep track of where you are along your course line by taking compass bearings of visual objects; light house / church steeple / buoys enroute, and note your time of passing on your chart. That way, if you get into a sudden fog, you know where you were; where you are going and what to look for along that route.
Tom, remember, GPS is a wonderful tool as long as it works, but when the battery is empty, and the screen goes blank, what then....? Electronics and salt water or fresh water don't get along with each other reliably for very long
Learn dead reckoning navigation, and you will always have something to use when the electronics quit, and quit they will. MURPHY decrees that they will always fail at the worst possible moment for you.
It's much better to wear suspenders and a belt to keep you trousers up than to rely on an electronic Tinkerbell to do it for you.
A GPS is a great tool, but never rely 100% on it to take care of your navigation.
Connie Have sextant, 7 X 50 binoculars, hand bearing compass, lead line, and stop watch, and know how to use them.
Am looking for recommendations for a gps setup to use on my 17 for
coastal cruising. Will a handheld suffice? Would I need one that will download charts? How will I know where I am when I am far enough off shore such that no physical markings are visible on the gps screen? Does the gps give lat/long readings which I then need to look up on a chart? Any advice will be appreciated. Tom B, M17 #258