When you start your journey into being a full-fledged yachtsman, you will be confronted with all sorts of nautical terms. Luckily, nowadays, you can get away without knowing much with an array of electronics, GPS chart plotters, and depth sounders. Just point the arrow to where you want to go, set some alarms, put an autopilot remote in your pocket, and be on your way. To get to this point, though, a moment in time where you can simply hit a couple of buttons on a touch screen and watch your destination get closer took thousands of years of sailors mapping out the ocean.
The world of nautical terms and how they came about bears no importance whatsoever when it comes to your modern-day boating. But knowing a thing or two can gain you some points at the dock with your boating neighbors and probably get you an invitation to a boat BBQ, for better or for worse.
Fathoms are a unit used to measure the depth of the sea floor. It’s a unit of around six feet or so. In modern charts, it is 6 feet exactly. This measurement is based on what was accepted as the standard approximate wingspan of a man when standing up with arms outstretched. Old-world chart-makers measured depth by taking a rope with a rock or weight tied to the end and throwing it into the ocean. Once they felt the weight touch the ground, they would bring the line up. When they did this, they would count how many wingspans of rope they were bringing up and then mark those wingspans on the chart, called fathoms. It was a quick and easy way to measure ocean depths. Five fathoms here, eight fathoms there. “Captain, only two fathoms! Cut the sail - I said cut the sail!” It was probably extremely tedious and dangerous work.
Fathoms today aren’t on many charts, but they were very popular before the 21st century and modern GPS mapping. They are still used officially by some countries or businesses. If a friend gives you some old charts, or you find some in a consignment store; chances are high that the depths are in fathoms.
Do fathoms have any modern-day use? Aside from being the standard still on some charts, measuring out and marking your anchor line in fathoms or whatever your desired scope may be can be extremely useful. If you want a 6:1 scope in anchoring, and the depth is 12 feet, then you know you need just to let out 12 fathoms of your anchor line. When you are sitting on the flybridge and your friends are at the bow asking how much anchor rode to let out, and you tell them to let down 12 fathoms, they will probably have no idea what you are talking about. They’ll ask you to explain, and you’ll know just what to say. Your long explanation of the heritage of depth charting may impress them or bore them to the point that you lose your friends, but either way, they’ll know you’re a true boater.