At 1712 your GPS indicates a position of LAT 36 54.8'N, LONG 75 39.8'W. Your are on a course of 319 per standard magnetic compass at a speed of 9.9knots. At 1800 your GPS indicates your position at LAT 37 00.0N, LONG 75 45.8'W. What were the Set(direction the current pushed the vessel off course) and Drift(overall speed of the current)? variation 15W deviation 0
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What Chart do I need?
First , current course is given as per ships compass? I arrange a TVMDC table to find the true course to steer? Then I need parallel ruler to find true course from my starting position, oh, I need a chart of where? Wait I will get back to this.
First , current course is given as per ships compass? I arrange a TVMDC table to find the true course to steer? Then I need parallel ruler to find true course from my starting position, oh, I need a chart of where? Wait I will get back to this.
im just guesstimating but it looks like you had
a half knot current going north east out of the mouth of the chesapeake.
a half knot current going north east out of the mouth of the chesapeake.
Just finished the exam for Piloting course with
the local power sqaudron. Your question sounds like it came right from the test book. Right now it's making my head hurt!
the local power sqaudron. Your question sounds like it came right from the test book. Right now it's making my head hurt!
Using my calculator
I get 5.46 kts @169 M. I must have hit the wrong buttons, my answer isn't close to the plotted answer. Fair Winds, Clyde
I get 5.46 kts @169 M. I must have hit the wrong buttons, my answer isn't close to the plotted answer. Fair Winds, Clyde
Answer
Right, sorry, 275T at 2.0 knots. I'm rechecking my math because I was off as well. This is the answer per coast guard exam. I know Ross, not much interest, but I needed some reason to pull out my charts.
Right, sorry, 275T at 2.0 knots. I'm rechecking my math because I was off as well. This is the answer per coast guard exam. I know Ross, not much interest, but I needed some reason to pull out my charts.
But you have to know this stuff
That far out from the bay there are no crab pots to check the current with.
That far out from the bay there are no crab pots to check the current with.
Either way off, or right on....
I get a set of 35degrees TRUE and Drift of 2.85 KTS working off a large area chart, it's hard to get accurate numbers Converting, that would be a Set of 50 Magnetic AND PSC Jeff
I get a set of 35degrees TRUE and Drift of 2.85 KTS working off a large area chart, it's hard to get accurate numbers Converting, that would be a Set of 50 Magnetic AND PSC Jeff
William, do us a big favor please.
Go back to the original problem and check to see if you transcribed it correctly. My plots and numbers suggest the the current would add 1.6 miles westing and about .1 mile northing to the 334 course, and 48 minutes at 9.9kts is 7.92 nm. The gps positions don't work for me as the second position doesn't seem to show the effect of the drift on distance over ground. The 7.92 without the drift on a course of 334 true is the same distance as from gps fix 1 to gps fix 2.
Go back to the original problem and check to see if you transcribed it correctly. My plots and numbers suggest the the current would add 1.6 miles westing and about .1 mile northing to the 334 course, and 48 minutes at 9.9kts is 7.92 nm. The gps positions don't work for me as the second position doesn't seem to show the effect of the drift on distance over ground. The 7.92 without the drift on a course of 334 true is the same distance as from gps fix 1 to gps fix 2.
Different Answers
It Seems like we all have different answers...so I'll Throw another into the mix I am comining up with 61 degree set and a drift of 4.13 knots.
It Seems like we all have different answers...so I'll Throw another into the mix I am comining up with 61 degree set and a drift of 4.13 knots.
How to get the answer
There are two ways mathematically and using a vector plot. The math is easy if you know trig but real hard to explain over a typewriter. The vector method is pretty easy once you have a map. First convert every direction to either true or magnetic. It does not matter as long as you don't mix them or if you are a wiz keep them straight. Plot both start and finish lat and long on the map. Connect them with a line. Starting at the start point lat and long, draw another line along the course steered for the distance traveled. The distance traveled is the Rate X time (in hours not minutes). The gap between the two end points is the vector representing the set and drift (and leeway for use sailboaters). You can read the set right off the compass rose just like any other direction. The drift takes a simple calculation. Since Distance = Rate X Time we can rewrite to get Rate =Distance/Time. Since you can measure the distance directly all you need to know is the time between start and finish and convert that to hours (minutes will give you a really odd answer).
There are two ways mathematically and using a vector plot. The math is easy if you know trig but real hard to explain over a typewriter. The vector method is pretty easy once you have a map. First convert every direction to either true or magnetic. It does not matter as long as you don't mix them or if you are a wiz keep them straight. Plot both start and finish lat and long on the map. Connect them with a line. Starting at the start point lat and long, draw another line along the course steered for the distance traveled. The distance traveled is the Rate X time (in hours not minutes). The gap between the two end points is the vector representing the set and drift (and leeway for use sailboaters). You can read the set right off the compass rose just like any other direction. The drift takes a simple calculation. Since Distance = Rate X Time we can rewrite to get Rate =Distance/Time. Since you can measure the distance directly all you need to know is the time between start and finish and convert that to hours (minutes will give you a really odd answer).
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