How to Time a Light for Safer Landfall

Here’s another great cruising tip from our friend Captain John at!

Imagine that you are underway on a wet, windy night, straining your eyes with a binocular to sight the entrance buoy to the safe harbor four miles away. Four-foot beam seas cause your 32-foot sailboat to pitch and roll. You and the crew are tired and just want to get into the harbor.

Are you sure the light you see will be the right one? Triple-time any light you see. Use a stop watch, wrist-watch or the “hippo-count” technique described below.

There it is again–You sight an intermittent blip, then another a few seconds later. Well, not quite the right interval, but it seems close enough–or is it? Read on to discover a simple three-step sailing tip for sailing navigation safety…

Time a Light Before You Make a Decision

To time an aid to navigation, use a watch or stopwatch. Count from the first flash in the pattern to the first flash in the next repetition of the pattern. For instance, when sighting a buoy that flashed every 6 seconds, you would time from one flash to the next. Your watch should read 6 seconds.

To time buoys with groups of flashes, you start the watch when you see the first flash of the group and stop it when you again see the first flash of the group.

For example, if the listed pattern is Gp Fl (2) 20s, you will expect to measure an elapsed time of 20 seconds from the start of one pattern repetition to the start of the next. If the time you measure is 15 seconds, either you’ve measured wrong or this is not the light you thought it was.

But boats and buoys pitch and roll in heavy weather, making positive identification tough. Err on the side of safety. Slow down and get closer. Heave-to if necessary and wait until daylight to enter an unfamiliar harbor. Wait to proceed until you have used the triple-timing verification technique described below.

Use your nautical chart (or in US waters, the USCG Light List; in International waters, the List of Lights) to find the light characteristic of any lighted aid to navigation. Dry Tortugas Light shows a light period of flashing 20 seconds. This period includes the intervals of light (about 2/10ths of a second) and dark (the remainder of the interval). Time the light three times for sailing navigation safety.

Use Triple-Timing for Sailing Navigation

Time light periods three times in a row to verify your landfall or to transit unfamiliar waters. Follow the steps below for a safe passage in these conditions.

1. Raise your height of eye so that you can see the light more consistently and at a greater distance when a sea is running.

2. Slow your approach; get closer so that you can see the aid’s distinct light pattern.

3. Time the light period three times in a row. For example, if the light characteristic shows flashing 20 seconds (see illustration), you would time the light from the first flash until the next time you see the flash. Each flash will last about 2/10 of a second. The remainder of the light period will be darkness. The total of light and darkness should read 20 seconds on your watch (US lights are timed to an accuracy of about 1/10th of a second).

If an aid to navigation flashes every 4 seconds, verify three successive 4-second intervals. When sighting a mid-channel light with its characteristic Morse (A) pattern, verify three consecutive sets of short-long flashes

Timing by Hippopotamus? More Accurate Than You Think!

How can you count seconds in your head to time a light? If you use the common “one-thousand-and-one; one-thousand-and-two, then you might be surprise to find out that it can be less accurate than you might think.

Long ago, I read a well-known author’s recommendation to use “hippopotamus” in place of “thousand-and-one”. After thousands of tests, I too recommend you drop the old standard and go with the new.

I believe it’s easier and much more accurate. With just a bit of practice, you will find your own mental timing close to that of any stopwatch: “1-hippopotamus; 2-hippopotamus; 3-hippopotamus…” Try the “hippo-technique” with any buoy or light. You might be hooked once you give it a try!


Use this time-tested sailing tip to verify any light, lighthouse, or lighted buoy that you sight at night. Spend a few seconds of time to avoid the possibility of grounding, and to keep your sailing crew safe and sound on the waters of the world!

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