Set & Drift

During my schooling for the USCG Captain's License, I breezed through all the 'hard' topics that the other students were having problems with. "Rules of the Road" with subjects like the different lights a variety of ships performing their duties must show at night. The differences of the three main light colors of Red, White and Green placed in a myriad of positions depending on type of vessel or duty.

Fishing, Trawling, Pilot, NUC (Not Under Command, RAM (Restricted Ability to maneuver), CBD (Constrained by Draft) and even Mine Sweeping all have their specific color and placement of the 3 lights or by daylight shapes of cones or other hanging markers.

There are dozens of sound signals all meaning something VERY important to moving, towing or even anchored ships. I had no problems with these elements of the schooling and I maxed this part of the tests. It was all logical, simply rules you had to learn. Where I had my problems was in the paper chart calculations, especially 'Set & Drift". This was also the only part of the 5 part tests that I did NOT get all the answers right.

Set & Drift is calculating how much the current is pushing you away from your destination and by how much. The 'Set' is the direction of the current, the 'Drift' is how fast it is moving. You have to know the exact distance from your boat to the destination, the exact compass direction, computing things like magnetic variances and wether to add or subtract from the readings depending on a chart code. This all gets placed in a formula and is compounded by a special term called DR or 'Dead Reckoning".

I got the three questions wrong but you are allowed 3 incorrect answers on the whole test so I just squeaked by and got my 'Captain's License". I even went on to my "Master Mariner" with no more problems. Of course the questions that the Coast Guard is still asking is, to my logical mind, antiquated. They have a dozen questions on the LORAN positioning system but do not even mention GPS!

Now that I am on my new boat with all the latest electronic gadgets, I feel confident that these will guide me around the world. I have three complete GPS systems, One built in with the RayMarine "Mariner Package", One separate and independently powered for the laptop computer and one internally powered handheld with downloadable charts.

To these GPS systems, I also have 3 complete charting systems. The Navionics Platinum on 2 Gig memory cards go in the RayMarine slot in the plotter, one for each of the 20 areas of the world. On the Laptop, I have the complete World Charts from Nobeltec on a CD and a handheld GPS plotter able to download the Navionics charts depending on which area of the world you are in.

The best thing about the RayMarine E series chart plotting system is that it calculates SET & DRIFT FOR YOU. An example is on the following photo from this morning. This is my 'NavPod' containing the 12 inch RayMarine E-120 plotter. It is connected to all the other RayMarine instruments like wind, depth, speed, engine readouts and to the main plotter, the E-80 down in the Nav station. That is where I place the 2 gig memory chip. This genius reads all the electronic data from the other RayMarine units and computes many important things, among others, 'Set & Drift'!

On the left is Nicaragua, to the right is Columbia. The red square with the cross in the middle is my destination, Colon Panama
The boat in the middle has 5 lines emanating from it. This is my current position at 09:08:11 this morning. My current boat speed SOG is 9.6 knots, my 'Course-Over-Ground' COG is 206 degrees. This heading has calculated my 'Set & Drift' for me and actually steers the boat for me with the Auto-Pilot down the black dotted line in the middle of the 3 thin lines going South from the boat.
The 5 lines around the boat are;
1) the thin red line (left) is the course the boat is steering to keep the boat headed in the direction of #2
2) the thin black line (middle) is the direct heading to the destination without any variances, or as sailors call it 'the Rhumb Line".
3) the thin green line (right) is the actual 'Course-Over-Ground' COG
4) the thick blue line is the direction the current is pushing me off course. The thicker the line, the more power it has. The red line shows how the boat has to steer to compensate for this 'Set & Drift'. the green line is the actual course. The red and green lines are always moving around and sometimes line up with the black line. That is what the course computer is doing, trying to get to the end of the black line at the red square with the cross in it.
5) the thick yellow line is the wind, also trying to blow me off course, the thicker the line, the more power in the wind. It is coming from ESE with the arrowhead touching the middle of my boat. The wind speed and direction are on the right column. Direction of the wind, apparent, (meaning the 'true' wind plus or minus the boat movement = what the boat feels - apparent wind)) is 85 degrees, wind speed is 13 knots.

Isn't modern technology amazing? I just put the curser on my destination, hit "Go To", then tell the auto-pilot to 'track' the heading, and finally go down below and make some tea.