Marine Traffic Control During Dive Operations

By Gus Marchetti, Salvage master. Reviewed by Dana Whitcombe, technical reviewer.

Commercial Diving Contractors Alabama | Commercial Diving Contractors Alaska I remember a morning off the mouth of the Columbia River, water grey and flat, and a diver was cutting a mangled propeller free from a crab boat that had gone on the rocks. A log ship that had been sitting at anchor for two days picked that exact minute to get underway without a word. Our standby boat ended up revving to intercept while the diver thumbed the abort button on his comms. You don't forget that kind of close call. I've run salvage and wreck removal for 22 years, and I still say dive operations are the most dangerous part of this job. The diver's underwater, the boat's on the surface, and every other vessel in the water column is a potential killer. Marine traffic control isn't a paperwork exercise—it's a live, hour-by-hour problem that decides whether your diver comes home. Call it a dance, call it a fight, but it's the first thing I plan before anyone suits up.

Know the water before you go in

The first thing I do is pull the vessel traffic picture. That means calling the local Vessel Traffic Service—say, the one run by the Coast Guard in Puget Sound, or the VTS centers on the Gulf—and getting the schedule for inbound and outbound ships. I also grab AIS data from receivers or a service like MarineTraffic. These give me a look at what's moving, but they don't tell you which captain might decide to leave early. So I get a written agreement from the port or harbor master about the safety zone and any times when we'll restrict traffic. I'm a big believer in having a safety zone that extends at least 500 meters around the dive site as soon as the divers are in the water. That's not always possible in a narrow channel, but you ask for it. You also need to know your own anchor pattern, currents, and tug availability. It's all connected. If you don't know the water, you're just hoping.

Put a sentry on the surface

A diver on the bottom is nothing but a voice in your headphones, and those headphones only work if you've got a tender who's watching the radar, not his phone. I always have at least one dedicated standby vessel—a rigid hull inflatable or a pickup boat that's got its own radio, radar, and an AIS transponder. On a bigger wreck removal job, we use a shallow-draft barge with a crane and a dive console, but we still keep a fast boat on the edge of the zone. That standby boat's job is simple: tell every approaching vessel to stay clear, and if one doesn't, get the diver out. The operator has a duty to monitor VHF channels 13 and 16, and I've used both. You can hail a ship by name and call him on the hailer. Sometimes you even see a fishing boat heading your way flying the dive flag, and you have to think, 'Does he not know, or doesn't he care?' It depends on the local crowd, give or take a few idiots.

Mark it like it's invisible

In U.S. Waters, you're required to use the centerline dive flag—a red flag with a white diagonal stripe—plus the International Code Alpha when you're on a vessel. During daylight, I also put the flags on a buoy and a couple of plastic cones if the water's rough. At night, we rig a series of lights: red all-around strobe on the dive boat, and for moored buoys we use small battery-powered lanterns or glow sticks. But the ocean doesn't care about your flags. A modern tool I use is an AIS synthetic Aton—a virtual buoy you can broadcast from a base station to show a symbol on every ship's electronic chart. Pair that with a guard zone on the AIS receiver that sets off an alarm on the dive boat when a target crosses a range ring, say 800 yards. It's a layer of protection, not a substitute for a lookout. I've had a container ship blow past a flag at 12 knots, and the only thing that saved the diver was a radio call and a cautious abort.

Talk to the guys who don't want to talk

Every once in a while, you run into a lazy crew that treats your dive zone like a suggestion. The Coast Guard can issue a safety marine information broadcast or a temporary vessel traffic restriction, and a port captain can hold a ship's sailing order. But when you're on scene and a tug is towing a barge straight at your stern, you don't have time for the chain of command. You get on the radio, you light a flare, or you physically put a hull between him and the diver. I've done the last one more than once. We move the largest available offshore barge or tug onto the up-current side of the dive site, pointing the bow out. It doesn't block the legal channel, but it makes the message obvious. You also need a clear abort plan. The dive supervisor calls 'diver up' on comms, the standby boat gives a quick pull on the line, and the diver surfaces on his own. Contingency is everything. And if a vessel does blunder through, you write it up. Bad reviews are useful.

The dive isn't over until the diver's boots are on deck

Once we start, I stay on the channel like a hawk. Every half-hour we take a traffic check, mark target positions on paper, and talk to VTS. If the current picks up or a squall rolls in, we call it early. That's when a lot of divers get the bends—not because of depth, but because they're rushed out of the water. I've seen guys use a hang line and a stage to decompress under an overhang while the surface crew keeps an eye on the radar. Emergency procedures are drilled before every dive. We have a diver recall dive line, a standby diver already suited, and a first-aid kit with oxygen and a hyperbaric stretcher. That's not me being paranoid. I've been on a job where a diver cut himself on a sharp piece of wreck and had to be surfaced—over a military ship channel, mind you. The standby diver went down, the traffic ended up waiting on a buoy, and the guy was fine. But everyone understood the rules of the game.

Frequently Asked Questions

Can a dive operation close a shipping lane? Not on your own, no. You need a safety zone from the Coast Guard or the port authority, and even then they may only restrict traffic, not close the channel. You work around it: schedule dives during daylight, use chase boats, and keep your work area as small as possible. What's the most important piece of equipment for traffic control? A sharp lookout on the tender is number one, but an AIS receiver with a guard alarm is a close second. Radar helps in fog, but AIS gives you names and course, so you can call a ship directly on VHF. Why do dive boats fly both a dive flag and the Alpha flag? The red-and-white dive flag is a recreational signal that means 'diver down.' The Alpha flag is the international code for 'I have a diver in the water, keep clear.' Vessel traffic operators recognize both, but Alpha is legally required on a commercial vessel. What if a vessel ignores the flags and enters the safety zone? You abort the dive. No argument. You haul the diver up, then you file a report with the Coast Guard and the port. The risk of a prop strike or a wake injury is never worth a few more minutes on the bottom.