Night Traffic

For us, the start of the winter boating season also means the start of our night boating season. We got a bit of a reprieve this year with the longer Daylight Saving Time, so this weekend likely will be our first night run since the beginning of the year. We don’t boat at night necessarily by choice. In winter, daylight is long gone by the time we get to the marina on a Friday evening after work. If we didn’t run at night, we’d be stuck at the dock. We don’t venture far, but by traveling after dark we can spend Friday night on the hook, wake up Saturday morning swinging gently at anchor, and later watch the sun rise as we eat breakfast. Nothing could be finer.


Our boat Dirona is moored at Elliott Bay Marina, near the Port of Seattle, and the closest anchorages are across the Vessel Traffic Service (VTS) lanes. Although the presence of large ship traffic adds stress to nighttime navigation, having VTS lanes nearby can be helpful. All boats larger than 40 meters (131 feet) must participate and check in frequently, and the VTS channel gives information about what big ships are out there and their positions. Any sized vessel can report to the VTS center and request information about traffic in their area. We turn the VHF radio on before leaving our moorage to be aware of nearby traffic as soon as possible. Day or night, at a minimum we scan channels 16, 22A and 13, plus the appropriate VTS channel for our area. By the time we leave the marina, we often know if any ships are moving nearby.


At night, we navigate from our unenclosed upper helm. The tinted glass in our lower helms restricts night visibility; height is a real advantage when looking for hazards in limited visibility; and sound perception is better outdoors too. Our radar is on to monitor other vessels whenever we are underway, but we especially rely on it at night. Near cities, navigation lights can disappear into background light. Small boats often run fast, and without proper navigation lights. Relying on sight alone means we might not spot these vessels. And the boats we can see, particularly big ships, seem to close more quickly at night because their visible range is shorter. For example, vessels longer than 50 meters must display a masthead light that is visible for 6 miles and side and stern lights that are visible for 3 miles. In other words, if a ship is approaching at 20 knots, the time between seeing its sidelights and a collision could be as little as 9 minutes. If the boat is moving towards that ship, the time will be less. Radar gives us valuable advance warning.


We know people who will use their radar only from inside the lower helm, despite the visibility restrictions, due to cancer concerns. According to the World Health Organization, these concerns are largely unfounded. In most situations, the exposure levels are a few percent of current public safety standards. Although a marine radar’s peak power may be high—up to 30 kW for large systems—the usual power is 25Watts or less, because radar emits pulses rather than continuous waves. Even this power level is not constant, because the radar beam is narrow and changes directions as the antenna rotates. Exposure levels outside the main beam are typically far lower than within. Our boat’s radar is mounted high enough that the upper helm is outside the main beam anyway. Although this mitigates the cancer risk, the main reason is that a radar’s range increases with height.


We are familiar with common navigation light configurations, and if in doubt, we leave lots of room and look it up. (We like Davis Instruments’ hard plastic “Quick Reference Navigation Rules.” For a more detailed discussion, we use Chapman Piloting, an excellent all-around reference that all boaters should carry). Tugs are a particular hazard at night because their tows are dimly lit, can be hard to see, and might be a quarter mile behind the tug. When a tug displaying towing lights is visible, we make sure the tow is too. The tows are usually visible on radar, but seeing them by eye is safer. We became even more vigilant about matching tug and tow, particularly in heavy traffic or with background light, after learning of an accident at the annual fireworks in Vancouver’s English Bay several years ago. A departing pleasure craft, a sister vessel to Dirona that was carrying a large family group, passed between a tug and its tow. The vessel caught on the tow line, flipped, and several on board drowned.


Fishing vessels with gear in the water are another potential, although less common, hazard. We got really good at spotting fishing gear after a night run through Johnstone Strait during a gillnet opening, but it’s not an experience we can recommend.

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2 comments on “Night Traffic
  1. Robert House says:

    Hi James. I thought I would chime in regarding radiation exposure from the radar. It just so happens that I purchased a Geiger counter off Amazon last week because my cat is undergoing radioiodine therapy for hyperthyroidism. Though our exposure will be very limited, I decided this would be an educational opportunity to see exactly how much ionizing radiation he gives off and at what distances.

    I was surprised how affordable Geiger counters are. The model we purchased was a GQ GMC 300e-Plus and was less than $110.

    It would be interesting to know if there is a measurable increase in ionizing radiation on the flybridge vs the pilot house on Dirona. I was always under the impression that the emissions from the radar are too narrow to collide with anyone when properly mounted but perhaps the beam has a wider arc than I envision.

    • Our big RADAR is 25Kw which is a pretty massive transmitter. But, what I’ve read is the transmit cycle is so incredibly short that the actual emission levels are fairly small. Also the beam width is fairly narrow so the PH is well below the focused beam. I’m not particularly worried about it but, what you have in hand is much better than my guess. You can now measure it and there are health safety regulations that you can use to calibrate your thinking on what is a “lot” vs “not much” — I’m super interested in what you learn in measuring it on some boat and, if you are ever near Dirona, I would love to do the experiment with you.

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