BoatSense

Navigation Safety: Rule of Thumb, Constant Bearing

This information, in different form, was originally published on boats.com.

It's not always easy to tell someone how to spot something far away. Mariners, like carpenters and tailors, can estimate with their thumbs.

There are plenty of times on boats when a lookout has to relay a sighting on the horizon to someone else on board. This can be tricky if the second person can’t focus right where the lookout is pointing.

Going out the channel, the first green can is about a thumb to the right of the big island, and about a fist to the right of the nun. The second green can is about half a thumb to the right of the nun, a couple hundred yards farther away.

Hand-bearing compasses and open binnacle compasses are the most accurate tools for sighting angles, but for quick-and-dirty measurements the handiest thing is...your hand. A hand or fist held at arm’s length covers about 8-10 degrees of the horizon. A thumb’s width covers about 2-3 degrees. But you don't really need to think about numbers. Most people’s hands and thumbs are close enough in size and length to transfer effective ballpark estimates back and forth.

If there’s a reference point close to the object you’re sighting, you can just call back to the cockpit, “It’s two hands to the right of the light. " Or, "It’s just a thumb to the left of that anchored blue boat, maybe a mile beyond.” And the helmsman or navigator can put his or her own hand up and orient their search to the same criteria.

Two things to remember: Sight with one eye closed to avoid parallax confusion, and keep your hand at arm’s length when sighting.

How to tell if you’re on a collision course in a crossing situation.

For people new to boats, or who don't have much experience at the helm, it can be a bit alarming that boats on the open water are allowed to scamper around with no traffic lanes, no stop signs, and no traffic lights. The Rules of the Road are there for a reason, and anyone at the helm of a boat should know them. However, knowing them and knowing how to gauge situations and act on them are different things.

The bearings of these two boats aren't changing as their distance apart decreases. They're converging on a single collision point. The give-way boat should take action to avoid the stand-on boat, and make the action obvious so there's no doubt in the mind of the stand-on helmsman.

One of the most vexing problems for new boaters is the crossing situation, and knowing how to judge who's going to cross whom. If it's not obvious, then it usually comes down to the concept of "constant bearing, decreasing range," which is the perfect definition of a collision course. Here's how to tell:

1. Hold your course
2. Take a bearing on the other boat, either by sighting across an open compass or with a hand-bearing compass
3. A little while later, take the bearing again. If the second bearing is the same as the first, your courses are converging on a single point. It will be a collision or a close call.
4. If you’re the give-way vessel, start altering your course sooner than later, so the other boat knows what you’re up to. If he’s the give-way vessel, watch him like a hawk and be prepared to avoid him. A lot people on the water don’t know the right-of-way rules, or don't know how to put them into action.
5. If the bearing is changing, you won’t collide. The faster the bearing changes, the farther apart you’ll be when you cross.

But wait, there’s more. If you can see land behind the boat you’re converging with, you can gauge the danger of a collision without compass bearings. Some people call this concept "gaining land” or “making land.”

1. Again, hold your own course steady.
2. Watch a feature of the distant land near the bow of the crossing boat, and keep watching.
3. If that land feature disappears behind his bow, he’s gaining land on you, and will cross you. The faster the land disappears behind him, the more distance he’ll cross you by.
4. If the land feature draws ahead of his bow, as if he’s falling behind on the land from your perspective, then you’re gaining land on him, and will cross him.
5. If the land feature stays right where it was on his bow when you first started looking at it, then you’re on a collision course, or one that's too close for comfort.

Radar, AIS, and other electronics can help you gauge range and bearing to other vessels, but they all require you to take your eyes off the water and look at them. In normal boating situations in decent visibility, and especially if there are a lot of boats milling around, your eyes, your compass, and fixed references will serve you better.

-- DL

The Boy Who Fell to Shore: A Cautionary Tale

Thomas Tangvald was born on a boat under sail. He was a toddler when his mother was murdered by pirates in the Sulu Sea. He was not yet ten when his stepmother was struck by the boom and swept overboard in an accidental jibe far offshore, never to be found. And he was fifteen in 1991 when his father and young half-sister died, tossed up on a reef on the windward side of Bonaire, boat and people smashed in the middle of the night. Thomas at the time was being towed 300 feet astern of his father aboard his own leaky boat. Neither vessel had an engine. Neither had a VHF radio. There was nothing Thomas could do. He abandoned his own boat before it was wrecked, and survived the night on a surfboard. The next day he identified the remains of his father. His half-sister’s body was found the day after that.

In March of 2014, when he was not yet 40, Thomas Tangvald left French Guiana, bound for Brazil singlehanded aboard another decrepit sailboat, and has never been seen again. He almost certainly perished at sea, leaving behind a wife and two young children. But, bearing in mind the story of his short, intense, fascinating life, told by Charles Doane in The Boy Who Fell to Shore, it’s possible to entertain the thought that Thomas somehow survived, as he had survived so many other scrapes, and might be living somewhere removed from the tainted modern world from which he had learned to distance himself at an early age.

Toying with such notions leads to clouded thinking. So does tempting fate and getting away with it too many times. Doane is careful to separate the regrettable conclusion from the fantastic.

Thomas’s story had to be told within the context of his father’s life, his guiding principles, and his achievements. Peter Tangvald was one of a generation of shorthanded and singlehanded ocean sailors who started their adventures in the 1950s and ‘60s, and who wrote and appeared in books and magazine articles that captured the skills, derring-do, and romance of the calling, but often didn’t do a great job of revealing the downsides of the lifestyle and the character flaws of some of its pursuers. Peter was a skilled sailor and a charmer (he was married seven times)  but also dogmatic, reckless, and lucky well beyond the standard issue of the sea gods. His was a tragic act to follow but, almost inevitably, Thomas had to try.

Peter and Thomas, their many women, and most of their friends were part of the global cruising and liveaboard community, which is much larger now than it was when Tangvald the elder, along with Robin Lee Graham, Bernard Moitessier, and a handful of others became famous among sailors. Even with YouTube and TikTok and harbors stuffed to the gills with plastic boats, it’s still a small part of the sailing population and a minuscule part of the population overall.

Charlie Doane (an old colleague and friend) is no stranger to this community. If you’ve read his earlier book, The Sea is Not Full, you know how well-qualified he is to speak on the topic. He has walked the walk plenty. This is from his introduction to the new book: 

“For the fact is most people living on land don’t even know such a community exists. Just as Thomas for a time could not imagine there was a much larger society beyond the harbors and anchorages where he touched land, those on shore can’t see that those littoral refuges and the sea beyond them are home to a much smaller society…

“Once inside the bluewater cruising community, you soon realize how small and tight-knit it is, with only one or two degrees of separation between most persons within it. You realize also how spread out and dissipated it is, and how, in spite of this, people often run into each other again and again. We are, I’ve always liked to think, a small tribe spread out over a very large territory.”

Telling the story of the Tangvalds, père et fils, became a mission for Doane. He's done it expertly and compassionately, with the help of surviving family and friends who provided memories, insights, and documents. With members of the cruising tribe as a Greek chorus, he spins a fascinating, inspiring, melancholy yarn, one that will provide rich connections for anyone who has spent time in that world, as well as both inspiration and caution for those who might want to become part of it. 

- DL