Drop buoy navigation the electronic way

While many mariners may not have heard of it, “drop buoy” navigation is an old piloting technique. We can employ this idea for intricate channel navigation by using the man overboard (MOB) button on a GPS as the drop buoy. In olden days, when a sailing ship was navigating an unmarked channel, the crew would often go to a known point in the channel and know that they had to go so far in a certain direction from that point. To do this they would drop a spar buoy on a weighted linewhich could be discardedand take bearings from that buoy for the next leg of the channel and continue to drop buoys as they progressed.

Our man overboard function on our GPS will do the same thing for us and save time from having to enter all the waypoints for each turn in the channel, which can lead to numerical mistakes. The nice thing is that on most GPS units the MOB function is quick to set compared to the usually intricate method of setting multiple waypoints.

So here is how it works: We get to our known point and hit the man overboard button, then take up the compass course for the heading of the next leg while watching our GPS, which will tell us the exact range and reciprocal course to that known point. It is pretty easy to jog the boat left or right the few dozen feet to keep the reciprocal course on the mark. When the GPS says we have gone the prescribed distance of that leg of our course from our man overboard position, and when that man overboard position is on the correct reciprocal course, we hit our MOB button again and steer the new compass course for the heading of the next leg on the chart, repeating the same procedure and steadying up on the reciprocal course again as soon as the GPS catches up. We can keep repeating this and be very accurate without having to load up our GPS with a bunch of waypoints.

Drop buoy navigation is simple and easy with the advent of the MOB function on our GPS. This technique is much more accurate when differential GPS is used.

John F. Bryan IV owns a 1965 Pearson Vanguard sloop that he refurbished. Bryan lives in Pascagoula, Mississippi.

By Ocean Navigator