Bye, Bye, Birdie: Look Out!

Passage Maker - - Contents - Robert Reeder

Over the course of the past year or so we have seen a large num­ber of well-doc­u­mented col­li­sions be­tween ves­sels, rang­ing from kayaks to tankers to war­ships. The com­mon thread be­tween each of these seems to be a sim­ple lack of a vig­i­lant and com­pe­tent look­out, on at least one—and usu­ally all—of the ves­sels in­volved.

So let’s see what our ac­tual re­quire­ments are for keep­ing a look­out and what is con­sid­ered gen­er­ally pru­dent seamanship. In this case, the Rules of the Road are sim­ple and ex­plicit—and the in­ter­na­tional and in­land rules are iden­ti­cal.

Rule 4, in this con­text, sim­ply tells us that ev­ery­thing in Rule 5 ap­plies at all times—day or night, fog or sun­shine, no ex­cep­tions.

And Rule 5 it­self be­gins with the clar­i­fi­ca­tion, “Every ves­sel shall, at all times....” This is pretty un­am­bigu­ous. Whether we are un­der­way, at an­chor, or tied to a moor­ing buoy, and whether the weather is clear or foul, we must al­ways, al­ways main­tain a proper look­out. The only ex­cep­tion is when we are ac­tu­ally moored fast to a dock, pier, or wharf.

“Main­tain a proper look-out by sight and hear­ing.” The look­out must be able to see and hear, un­ob­structed, 360 de­grees around the ves­sel. De­pend­ing on the con­fig­u­ra­tion of the ves­sel, this may well re­quire more than one look­out on watch. In some cases, if they are not dis­tracted by the re­spon­si­bil­i­ties of driv­ing the ves­sel, the helmsper­son may serve as one of the look­outs.

“As well as by all avail­able means ap­pro­pri­ate.” This in­cludes radar, ARPA, and AIS. These sup­ple­ment but can never re­place our vis­ual

look­out. None­the­less, if we have an op­er­a­tional radar, we must be us­ing it “to ob­tain early warn­ing of risk of col­li­sion and radar plot­ting or equiv­a­lent sys­tem­atic ob­ser­va­tion of de­tected ob­jects,” per Rule 7.

“In the pre­vail­ing cir­cum­stances and con­di­tions.” Weather, visibility, and traf­fic den­sity may dic­tate that we need even more look­outs than the min­i­mum al­ready de­scribed.

“So as to make a full ap­praisal of the sit­u­a­tion and of the risk of col­li­sion.” This is cru­cial: Our look­outs must be as knowl­edge­able about the rules of the road, nav­i­ga­tion, and col­li­sion avoid­ance as the cap­tain is. Oth­er­wise they aren’t look­outs at all, just pas­sen­gers with a bet­ter view.


Even if you are a soli­tary helm/look­out watch­stander, it is some­times help­ful to think about a newly ac­quired con­tact as if you were the look­out re­port­ing it to the helm sta­tion.

A sim­ple mnemonic for the in­for­ma­tion we want for eval­u­at­ing risk of col­li­sion is “TARSEC,” which stands for type, azimuth, range, speed, es­ti­mate CPA, cor­re­late. A lit­tle about each of these mean­ings:


This is your ini­tial im­pres­sion of what type of ves­sel you are ob­serv­ing. “A ship” is less use­ful than “a con­tainer ship,” and “a con­tainer ship with a blue hull” is more use­ful still be­cause you may be deal­ing with more than one. Why does the type of ship mat­ter to a recre­ational power­boat? Be­cause dif­fer­ent types of ships be­have dif­fer­ently, travel at dif­fer­ent speeds, and will go dif­fer­ent places. For ex­am­ple, a con­tainer ship will al­most cer­tainly be trav­el­ing at about twice the speed of a bulk ore car­rier.

Do we know more from her lights or day shapes? Is the ves­sel re­stricted in her abil­ity to ma­neu­ver? Some de­tails may not be ap­par­ent ini­tially, so up­date your con­tact ap­praisal as more in­for­ma­tion emerges.


“Azimuth” just means a ves­sel’s bear­ing along the hori­zon. We could, of course, just say “bear­ing,” but that makes our mnemonic clunkier. In any event, what is the rel­a­tive bear­ing of the con­tact? We can think of this in terms of de­grees or a clock­face, or even com­pass points if we’re so in­clined, so long as ev­ery­one on the boat is speak­ing the same lan­guage (in units). Bear­ings should al­ways be given rel­a­tive to your own bow, as your look­outs might not al­ways have ac­cess to a com­pass.


Es­ti­mat­ing dis­tances on the wa­ter can be chal­leng­ing. Prac­tice, es­pe­cially while com­par­ing vis­ual and radar ranges in clear weather, def­i­nitely helps. As with azimuth, you have a choice of the units you can use to re­port dis­tances—some use nau­ti­cal miles, some use kilo­me­ters, oth­ers use thou­sands of yards or me­ters. But be­cause most modern radars are cal­i­brated in nau­ti­cal miles and we’ll be cor­re­lat­ing our vis­ual con­tacts to that, we’ll use nau­ti­cal miles for this ar­ti­cle. An im­por­tant tool for es­ti­mat­ing dis­tance on the wa­ter is know­ing the dis­tance to the hori­zon based on your height of eye.

Due to the cur­va­ture of the earth (yes, it’s curved), the greater our height of eye above the wa­ter, the greater the dis­tance to the hori­zon. If we are in a kayak, with a height of eye of 3 feet, the hori­zon would only be about 2 nau­ti­cal miles away. From the wheel­house of a trawler, with a height of eye of 12 feet, the hori­zon would be about 4 nau­ti­cal miles away. Know­ing the ac­tual height above the wa­ter­line of your wheel­house win­dows, and also any other likely look­out sta­tions, is use­ful in many other ways as well.

So, if the hori­zon is 4 nau­ti­cal miles away, a ves­sel ex­actly on the hori­zon is 4 nau­ti­cal miles away as well. If a ves­sel is sig­nif­i­cantly closer than the hori­zon, we will see all of the hull in front of

the hori­zon; we call this con­tact “hull-up.” If the con­tact is half-way to the hori­zon, its range is 2 nau­ti­cal miles. Con­versely, if a con­tact is be­yond the “hill” of the hori­zon, part or even all of the hull will be ob­scured by it. We call this con­tact “hull down,” which in this case means that it is greater than 4 nau­ti­cal miles away.

How far we can see a con­tact be­yond the hori­zon is a func­tion of its height. The masts of a ship with a mast­head height of 100 feet can be seen 12 nau­ti­cal miles be­yond the hori­zon. This fig­ure, added to your 4 nau­ti­cal miles to the hori­zon, would place the ship 16 nau­ti­cal miles away, which seems like quite a long dis­tance away and hardly a con­cern. But if that ship is ap­proach­ing us at 25 knots, and we are ap­proach­ing it at 15 knots, our rel­a­tive clos­ing speed is 40 knots. On a col­li­sion course, we would hit in 24 min­utes.


So how do we know the ship is go­ing 25 knots? Cer­tainly at that range it’s a bit of sloppy guess­work, es­pe­cially be­cause at that point we only have its masts for iden­ti­fi­ca­tion. As the ship gets closer, our speed es­ti­mate can im­prove.

This is why it’s im­por­tant to iden­tify the type of ves­sel as early and as ac­cu­rately as we can. Weather and con­di­tions be­ing op­ti­mal, we can ex­pect a con­tainer ship or a cruise ship to be run­ning about 25 knots. A car ferry might run about 20 knots. A tanker or bulker might run about 15 knots. A tug and barge might run about 8 knots.

Even a slow-churn­ing 8-knot tug, on­com­ing at 5 nau­ti­cal miles away, will have a com­bined clos­ing speed of 23 knots if you are go­ing 15. You could still col­lide in only 13 min­utes.

And here you thought those silly word prob­lems in sev­enth-grade math were point­less.


Our vis­ual look­out usu­ally doesn’t need to es­ti­mate clos­est point of ap­proach with great pre­ci­sion—that’s what radar is for. But we do need to have a sense of whether the con­tact will cross ahead or astern of us, whether it will pass down our port or star­board side, and if we need to ma­neu­ver to give them more room to do so. Gen­er­ally speak­ing, if the con­tact is well to the right of your bow and draw­ing fur­ther right along the hori­zon (not ob­jects on shore), or well to the left of your bow and draw­ing fur­ther left along the hori­zon, you are prob­a­bly not de­vel­op­ing a risk of col­li­sion.

On the other hand, if the ves­sel is on any azimuth and is not ap­pre­cia­bly chang­ing azimuth over time, this is called a “zero-bear­ing rate” con­tact and must be con­sid­ered a pos­si­ble col­li­sion threat.

With a de­cent es­ti­mate of the other ves­sel’s range and speed, we can also cal­cu­late roughly when we will reach CPA with the con­tact. This is es­pe­cially critical when we are in­ter­act­ing with mul­ti­ple con­tacts, which in a busy har­bor is nearly al­ways. And in a busy har­bor, it is easy to be­come over­whelmed with the num­ber of con­tacts. The abil­ity to quickly es­ti­mate CPAs will help us fo­cus on the con­tacts that ac­tu­ally pose a threat of col­li­sion.


Cor­re­lat­ing our vis­ual con­tacts with radar and AIS, when avail­able, is fun­da­men­tal to good seamanship and col­li­sion avoid­ance. Of­ten, even in clear weather, radar will de­tect small con­tacts ear­lier than you will be able to see them. Clear com­mu­ni­ca­tion be­tween the vis­ual look­out and the radar look­out is critical for col­li­sion avoid­ance.

Radar ob­ser­va­tion will pro­vide a much more pre­cise es­ti­mate of tar­get range, speed, and CPA. Com­mu­ni­cat­ing this more pre­cise data to your vis­ual look­outs al­lows them to bet­ter as­sess in­for­ma­tion that the radar ob­server may not have, such as light con­fig­u­ra­tions. Tar­get ma­neu­vers are al­most al­ways more read­ily ob­served vis­ually than by radar, as are re­la­tion­ships be­tween ves­sels such as a pi­lot boat in­ter­cept­ing a tanker.

No sin­gle source of con­tact in­for­ma­tion is best for all pur­poses. This is why we have mul­ti­ple sources. If our dif­fer­ent sources are not in agree­ment, slow down and fig­ure out why. In nearly every col­li­sion, the cor­rect in­for­ma­tion to avoid it was avail­able and cor­re­lated, but it was un­heeded or mis­in­ter­preted. Good watch!


Want to learn more? Take my Boaters Uni­ver­sity Nav­i­ga­tion Rules on­line course. Go to this URL for more in­for­ma­tion and to sign up:

Rule 5 re­quires that we main­tain a look­out “by all avail­able means ap­pro­pri­ate.” Rule 7 specif­i­cally calls out the use of radar if we have op­er­a­tional radar on­board.

The USS Fitzger­ald col­lided with the Philip­pine con­tainer ship, MV ACX Crys­tal, on June 17, 2017. Of the var­i­ous fail­ings that led to the col­li­sion, the US Navy noted “phys­i­cal look­out du­ties” were not per­formed on the star­board side.

Ad­vance­ments in radar tech­nol­ogy have made tar­get ac­qui­si­tion and track­ing much eas­ier with in­te­grated AIS and Doppler radar.

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