Navigation Safety: Rule of Thumb, Constant Bearing

This information, in different form, was originally published on

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.

Crossing situation
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

BoatSense Included in ⁠"Best Boating Books of All Time⁠"

BoatSense is currently listed by The Book Authority in the 15 Best Boating Books of All Time . The Book Authority uses "a proprietary technology to identify and rate the best nonfiction books, using dozens of different signals, including public mentions, recommendations, ratings, sentiment, popularity and sales history." They don't do business with authors or publishers, and they don't accept requests to list a book.


BoatSense Reviews:

Soundings: Sea Stories 

Good Old Boat 

WaveTrain  and Points East 

Carol Newman Cronin - Boats Meet Books 

Sailing Scuttlebutt: Why We Are Who We Are

Professional Boatbuilder

BoatSense Talk at the Jamestown Library: Chaos and Seamanship

A cumulonimbus chaos agent near St. Thomas. Doug Logan photo.

We had a discussion about BoatSense (both the book and the idea) recently at the Jamestown Philomenian Library in Rhode Island, with a couple dozen old and new friends, among them shipmates from over the years and former colleagues from Sailing World and Cruising World. Pretty much everyone in the room was an old hand as far as boats are concerned, and there were some serious racing sailors there — one Olympian and at least two others who had won championships at the national or international level.

We focused for a while on one of the themes of the book — chaos. The world that boats operate in, at the intersection of two vast fluids, is by nature chaotic, if only because those two fluids are of very different densities. The intersection is a zone of uncertainty, and each fluid has a profound effect on the other. And they both have profound effects on boats, which then tend to exhibit chaotic tendencies themselves. So, life aboard boats is to a great extent about dealing with mayhem, both natural and man-made — anticipating it, preparing for it, averting it, mitigating it, and learning from it.

Racing sailors, in particular, challenge chaos in a conscious way, tacking and jibing in tight quarters, or keeping a spinnaker up those extra 20 seconds in order to claim room at a turning mark, knowing that the potential for chaos increases with each second of delay, and welcoming the challenge. But all sailors and powerboaters, if they stick with the game long enough, develop an appreciation of the forces that seem to conspire to make their time on the water more challenging. And their relationship to those forces, whether in preparation or response, is defined by the practice of seamanship. 

— DL

BoatSense Review by Carol Cronin

There's a welcome review of BoatSense by Carol Cronin on her blog, where she collects her thoughts on a variety of topics, mostly marine-oriented. Carol is an Olympic sailor (Athens, 2004), a meticulous editor, and novelist. She's also an old (not to say aged) friend ⁠— the kind who would actually take the time to read a book through and then offer a thoughtful response.

Carol Cronin — author, editor, Olympic sailor

First she pegs me as a curmudgeon, or maybe curmudgeon-in-waiting, and I can see where she gets that impression. A lot of what she read of my writing when we worked together came from that sort of viewpoint, which I hasten to add was encouraged and sometimes commissioned by our mutual friend and editorial director at the time, John Burnham. But then she dives into what we could call the philosophical parts of the book, most of which came from an earlier time when I was editor of Practical Sailor. In those parts I hoped to promote the idea that much of the real pleasure and fulfillment you can get out of a boat is fundamentally different from what's advertised by the people trying to sell boats (and all the gear that's supposed to make you happier and safer and more comfortable on boats), and also fundamentally better and more valuable both on and off the water. And Carol gets that, as people who have been steeped in boats for a long time all get it, even if they work in the boat-selling industry and have trouble saying it out loud. (Practical Sailor, by the way, is subscriber-driven and accepts no advertising.)

Carol points out that the collection of yarns and advice is "varied" and  "somewhat difficult to categorize," and she's right about that, too. I have a lot of yarns, but I tried to pick a few that would get across a range of pleasures and points of worth. And I have a lot of advice (some good, some suspect, some gratuitous), but there are already several excellent reference books out there full of the stuff. So I wanted to lay out maybe a dozen or so points of specific practical advice for the new or lightly experienced person who might be in the market a boat—advice that I think is not given enough, but that can make a big difference in whether that person will end up in boats for a long time or leave early in disappointment.

Then, after she hauls me under the keel for several uncaught word repetitions in the book (a form of typo to which I am prone) she says, "It might be a hard one to categorize, but this book will make an easy gift for anyone who thinks deeply about the world, especially if they like stories that center down on boats."

Can't ask for better than that. Thanks, Carol.

— DL

The Hunt for a Boat Diesel Coolant Leak

A few posts down in this feed there's one called Give Me Pressure. It had to do testing for a leak between the raw-water side and the coolant side of a heat exchanger. The leak itself was one of those creeping, intermittent, insidious little sneaks that puts white steam and the sweet smell of coolant into the exhaust with no sign of external leaks on the engine, and no bad gaskets. 

He2The new heat exchanger (left), built from plans over 20 years old, had to be pulled back off the engine when the header/expansion tank (right, marked Nor'Pro) proved to be the leaky culprit. That tank has an upper chamber that holds the coolant reservoir; its bottom chamber opens to the exhaust ports. That space is supposed to be dry. It wasn't. There was rust. And two pinhole leaks. Let's not call the new heat exchanger unnecessary. Let's call it a proactive purchase. No hard feelings. We'll keep the old one as a spare.

Ha (I laugh bitterly), if only I'd known when writing that post what I know now... that there was no breach in that heat-exchanger; that parts for old, off-brand, marinized diesels are not to be found on any old shelf; that by the end of summer I'd be as fast as a Le Mans crew chief swapping out major parts, knowing the peculiar recalcitrance of every bolt, every hose clamp... well, I guess I'm glad I didn't know.

The good folks at Sen-Dure in Fort Lauderdale made me a new heat exchanger from plans dating back to the last century that I think even they were surprised they still had. I installed it, started up the old Isuzu, and the leak continued. This was... let's say it was disappointing.

So, having eliminated as culprits...

  • The coolant-side heat exchanger end gasket (replaced)
  • The head gasket (pressure-tested)
  • The heat-exchanger itself (replaced)
  • The transmission oil-cooler (doesn't circulate coolant in this engine)

... I figured the only thing left to leak was the big header/expansion tank, which in this engine contains coolant in a chamber directly above a dry chamber that receives exhaust gases from the cylinders.

PortsideengineGood view of the port side of the engine, and a chance to bust some more rust, touch up the paint, check the water-pump impeller...

So, out came the new heat exchanger, off came the header tank, and in the lower chamber where there should have been carbon but no rust, there was rust. In the dark of night I stuck a LED gooseneck light down into the fill hole on top of the tank, peered into the exhaust-elbow opening... and lo, there was a pinhole of light. I rust-busted around it and took the tank to a talented local metal fabricator, who welded a small steel plate over the pinhole. This whole procedure happened twice, because another pinhole appeared after the second rust-busting.

Header3There was a lot of rust and a couple of small leaks from the coolant reservoir into the chamber of the header tank where the exhaust comes to mix with seawater on its way to the discharge.

And finally (never say finally) the tank, which I tested with both water and air, was leak-free. I reinstalled everything, filled up with fresh coolant, took the boat on a couple of late-season runs to double-check everything, then topped up the tanks and changed the oil. Now the boat is hauled out. The next steps are to winterize this carefully coddled cooling system, cover the boat, and call it quits for the year.

Header3Most of the surfaces cleaned up pretty well with solvents, 3M kitchen scrubbers, rags, and wire brushes. WD40 is a good, relatively cheap cleaner for jobs like this. It works especially well sprayed on the threads of studs and bolts that have a lot of grime in them.

The chances that more pinholes won't appear over the winter or next summer are slim. Maybe the tank will last one run, one week, another whole season? But there's no replacement tank out there. When it leaks again it will be time for major surgery. With luck the shell and the welded-on exhaust couplings will survive, but it will have to be cut open for new channels and chambers to be custom-made and installed. Which is why I'll be dreaming this winter of repowering, of sailing, of rowing, of swimming.

-- DL


Mayflower II in Mystic

The original Mayflower brought the Pilgrims to New England in 1620. Her replica, Mayflower II, was launched in England in 1956 and voyaged across the Atlantic under command of the great sailorman Alan Villiers, himself a human bridge between the days of square-rigged sailing ships and the modern day.

Mayflower 2Above, Mayflower II was relaunched on September 7, 2019, after a three-year refit at Mystic Seaport. (Doug Logan photo)

Since then, Mayflower II has been kept and cared for by Plimouth Plantation. When it came time for a major refit, Plimouth partnered with Mystic Seaport in Connecticut. Mystic had the facilities and skilled shipwrights to take on this massive task, and three years later, on September 7, 2019, Mayflower II was lowered slowly down the ways  into the water again.

The keynote speaker at the relaunching ceremony was Nathaniel Philbrick, bestselling maritime author, who published a lively history of the Mayflower in 2006. Here's an excerpt from Philbrick's address:

Jeremy McGeary to Fiddler's Green

This summer the world of sailing journalism lost one of its best, Jeremy McGeary, an Englishman who came to the U.S. many years ago, already steeped in so much nautical know-how that he could have rested on his laurels and just let the rest of us know what was what. But his mind and his curiosity just kept expanding, and anyone who had a chance to work with him grew richer for the experience, while having a tremendous amount of fun at the same time.

MacMcGearyWhen we were together at the Cruising World and Sailing World offices in Rhode Island, Mac and I would take a walk at most lunchtimes, discussing boat design, the latest gear, the weather, navigation, and, for lack of a better phrase, the Water Rat's Worldview. I learned from him on every single outing. We worked together on reviews, Boat of the Year projects, and Cruising World's first website. (Mac was a wary but perspicacious contributor to that brave new world.) Whenever another editor had to do a deep dive on a particular boat's design, Mac was the go-to. He was a naval architect with a gift for making difficult ratios and equations understandable; he could turn them into concepts to be understood at the seat-of-the-pants level.

For more on Mac, read Darrell Nicholson's tribute, Eight Bells for Jeremy 'Mac' McGeary in Practical Sailor.

Darrell and I barely overlapped at Cruising World before I was seconded by the company to set up a new web project in New York. After that I went to be editor of Practical Sailor while Darrell and Mac worked together in Newport. Then, eventually, Mac went to Good Old Boat, Darrell became editor of Practical Sailor, and Mac ended up doing a lot of test projects for Darrell on the side. The world of sailing journalism is pretty tiny. The loss of a man like Mac is felt right around the compass.

A Boat Reviewer's Boat: The Boréal 47

\ \Charles Doane, a colleague at Sailing World and Cruising World long ago and one of the wittiest scribes in the biz, gave BoatSense a fun review in his Wave Train blog, which is also syndicated at SAILFeed. Charlie is now the Cruising editor at SAIL, where he gets to test all sort of boats.

It's instructive to see what a professional boat reviewer chooses to own, and I've spent a chunk of the day online studying Charlie's boat, an all-aluminum offshore speedster full of chines and clever (but not over-clever) systems, the Boréal 47. Here's a SAIL review of the Boréal by Adam Cort, and one in Cruising World by Tim Murphy, another former colleague and a wonderful marine writer.

The Boréal is a centerboarder, and one of the neat things about her is that she can rest on her keel and low-aspect rudder when the tide goes out, as it apparently often does. The keel/skeg runs well forward, merging into the flattish bow section forward of the mast, which then absorbs and evens out the resting load. If the boat tips a bit, it settles at the next chine. All this is helped by the gathering of weight around the keel box/centerboard trunk. The hard ballast, the tankage, and even the chain rode are grouped in the center of the boat.


Above: a Boréal 47 doing its thing. Or one of its things. Photo courtesy of Boréal. 

There are crash bulkheads forward of the lazarette and aft of the sail locker. There's great visibility under the hard dodger and in the saloon. There are daggerboards either side of the rudder that can be lowered and raised to ease the load on the helm and keep the boat tracking in the groove. This works as well as twin high-aspect rudders, and even better when you consider that when a rudder hits a hard thing underwater, breaks off, and maybe breaches its bearing,  it can ruin your day. Losing a leeward daggerboard isn't as big a sacrifice or as much of a danger far offshore.

Very much looking forward to getting together with Charlie and catching a ride on this thing.

-- DOL



Boat Launch vs. Book Launch

Here's a clip of a friend's Young Brothers 38 descending the ways a few springs ago.

Blocks and wedged removed, crowbars to get the wheels moving, and a quick run to catch the boat at the other end. 
It's an exciting launching method. You have to keep your fingers out of the way. Do not try this at home.
Turns out that a book launch is pretty similar — a bit of crowbar work, a dash, a scramble, and then... it's afloat.

(Click on the YouTube logo, lower right, once you get going.)



Essential Knots and Hitches

There's not much marlinspike-speak in BoatSense, but there's an idea running through the book that skills are better than gizmos and labor-saving devices. Skills are completely portable. They're cheaper than gear. They tend to be valuable everywhere, not just on the water. And most importantly, they make you happier in the long run. 

These videos were made a few years ago for with marine videographer Paul Cronin. The knots and hitches shown are the ones most often used on modern boats. They'll work for 90 percent of the jobs you'll find on the water, and they're super handy on land, too, for camping, for securing loads in your pickup truck,  for tying up banners and signs, and so on. 


The bowline is beloved for its utililty, simplicity, elegance, and releasability. And it drives novice boat people crazy. If you don't know how to tie one, or you're trying to teach someone else to tie one, read this article:  How to Tie a Bowline: Remember the Two Loops.

Then come back and watch this video with the two-loop concept still in mind.

Clove Hitch and Rolling Hitch

Use a clove hitch for tying a line around a railing, stanchion, pipe, or similar object. Use a rolling hitch to make a grip on another line or object to resist a lateral pull.

Stopper Knots

Use a stopper knot to keep a line from pulling through a block (pulley) or fairlead aperture -- or your hand. 

Sheet Bend and Carrick Bend

Use a sheet bend to tie together two lines of different diameters. Use a Carrick Bend to tie together two lines of the same diameter.

Trucker's Hitch (Wagoner's Hitch)

Use a trucker's hitch for temporary tie-downs with extra purchase for holding power.