When two prominent features appear in a line, one behind the other as seen from your boat, it forms a line of position, or a range line. Before electronic position fixing, the use of ranges was the tried-and-true method of staying in the center of a channel and knowing when to make a course change. Even if your boat is equipped with a suite of modern electronics, a range line can come in handy. The use of ranges is especially valuable when you want to increase situational awareness without taking your eyes off the horizon. Monitoring a range line is one of the best ways to assess the set of the current or to distinguish safe from hazardous water.
Man-made range markers, lit or unlit, are built in many areas to mark centerlines of important channels. Conspicuous shore structures such as lighthouses, cell towers, water tanks, cupolas and flagpoles all lend themselves to forming ranges too. Many great ranges occur naturally, such as a small island or a pronounced outlying rock in line with a mainland element in the distance. Just be mindful about shoreline features changing with the rise and fall of the tide. I don’t recommend using buoys because they can, and do, get out of position.
Navigational beacons and daymark ranges are elegant in their simplicity. Pairs of fixed aids are provided on shore and on pilings or towers in the water, one lower and distant from the other. They are designed to be readily visible and easily identifiable for ships’ pilots inbound and outbound from sea, providing safety and efficiency without distraction. On the Intracoastal Waterway, tug and barge operators navigate shallows and bends with proficiency by using ranges. On charts, these man-made ranges are indicated by broken or solid lines. Solid lines indicate that part of the range is intended for navigation. Broken lines guide the navigator to the range structures themselves. Distinctive leading light characteristics are shown on the chart too, designed to make the range markers plainly distinguishable from other aids to navigation.
Coming in from offshore in rough weather, sometimes there’s a lot going on, particularly on a sailing vessel after a demanding sea passage. Arrival at night can be stressful in a busy channel with a lot of traffic, coupled with a dizzying array of shore background lights. I find it comforting to be guided in by a big, bold, unmistakable range. It allows the crew to devote their full attention to the seas, the rig and traffic avoidance. Following a range while also monitoring instruments helps the skipper keep priorities straight instead of focusing only on a screen.
Many of us use ranges all the time, sometimes without even realizing it. How do they work exactly? You are “on the range” when the two objects are directly in line. If you are off course and to the right of the centerline you are attempting to make good, the distant range marker will appear to the right of the one closer to you. Conversely, if you are off course to the left of the track, the far marker will appear to the left of the front one. I always imagine chasing the front marker as I steer a range. Still don’t visualize it? Set up two coffee mugs on a table in front of you and lean side-to-side to simulate going off course. Then practice it underway.
When a channel has a jog (a required course change), a good boat handler can follow one range to stay mid-channel, then pick up the second set of range markers to alter course gradually, setting up perfectly mid-channel on the next leg without over or under steering. While steering a range, set and drift are easily recognized and can be intuitively compensated for.
A range also is useful when setting up for docking. If you line up a light or flag pole, the peak of a distinctive building or any fixed object in the distance with another closer object, such as a particular piling, you’ll have a made-on-the-spot range to immediately judge which direction the wind and/or current is setting you (or not) as you plan your approach. It’s easier to check your set than it is to recover from it afterwards in tight quarters.
Two natural range features can be lined up to guide a vessel to the safest route through a hazardous area or tight spot between islands. This is common practice in remote cruising grounds with poorly charted data, where the note on the chart says, “Local knowledge required to attempt this passage.” Locals will often offer guidance such as, “Just line up the big square rock on the hill with the pipe sticking up on the cay in front. You’ll be fine coming through.” Seamen have been navigating like this for millennia.
The same goes for areas to avoid. A danger line can be established by lining up two shore features, delineating one side as deep, safe water and the other as dangerous with rocky or shoal areas. You can tell at a glance if you are on the safe or hazardous side of that range line. Fishermen often employ two range objects to create a line of position, marking known features on the bottom to fish over.
Traditionally, fixed ranges were used to “swing the compass,” to derive a compass deviation card. True direction of a range is noted from the chart and variation is applied to determine the equivalent magnetic direction. As the vessel crosses the range on various compass headings at prescribed intervals, the compass bearing of the range is observed. The difference between the magnetic bearing and the compass bearing will reveal the compass deviation at each interval. You can do a quick and dirty check of your compass in this way whenever you are steering a range. I’m always surprised when I hear someone question why they still need a magnetic compass. Yes, even though we have GPS, the magnetic compass remains a primary piece of equipment that ought to be accurate. Electronics can fail. Then what?
I love gunkholing with small, simple sailboats, often without electronics. It’s intimate and entertaining, and helps me keep my skills exercised. The truth is though, arrival time is never guaranteed with an engineless small boat, and one of my favorite secret spots is difficult to pick up in daylight, never mind after dark. But at night, if I head in on a range made with a cell tower ahead and a light house directly aft (a back range), I will reliably find the opening when the green blinker off to starboard marking another channel disappears behind a giant bold sand bluff. In this way, just like our ancestors did before electronics were around, two ranges create a fix.
Local knowledge is easy to develop when you use a comfortable range to get on a favorite fishing spot, ease into the best holding ground in an anchorage or avoid ledges without constantly monitoring electronics. Be familiar with the prominent ranges in the waters where you operate, and practice using ranges when you cruise. Ranges can heighten your situational awareness, augment and verify navigational equipment onboard, and enable you to plan for set of the current. It’s all part of the art of navigation.
This article was originally published in the December 2020 issue.
