According to the this answer, in the US buoys on the right are red when returning to a harbour, with green on the left. This is in contrast to most of the rest of the world.

What caused this split in the conventions?

  • Not sure how best to fix this (or I'd just do it), but the wording is oddly stilted here, and it isn't just the US that uses the convention it uses. Arguably most of the major trading nations in east Asia use it too (China being the big exception).
    – T.E.D.
    May 18, 2022 at 15:09
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    IALA B is the Americas, Japan, Korea and the Phillipines. IALA A is the rest of the world.
    – user55099
    May 18, 2022 at 19:12
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    Yeah, it's not just the US, I can confirm that it's the same in Canada, "Red Right Return" was a catechism that you memorized when getting your boating license. This is only conjecture, but I think that this catchy phrase, which doesn't translate into European languages, is why the US didn't switch and the other places that have it are those where the US navy has a lot of clout. Otherwise it's like which side of the road you drive on, pretty irrelevant.
    – Eugene
    May 18, 2022 at 21:45
  • ?? All the ones I see in New England are black, not green. But yeah, RedRightReturning is the rule here May 19, 2022 at 12:06
  • I was thinking it might be an analog for driving on the highway at night - red taillights on the right, white headlights on the left, and it's reversed for the UK and Australia because they drive on the other side of the road - but then, so does Japan, so that theory is busted. May 19, 2022 at 18:49

2 Answers 2


There used to be very many more buoyage systems in use around the world which resulted in confusion and danger. An agreement to unify the system was agreed at Geneva in 1936 by the League of Nations, but the collapse of the League and World War II scuppered that. In 1965 IALA (the International Association of Lighthouse Authorities) created a Technical Committee to work out a solution.

In 1976 IALA region A rules were accepted which combined the lateral marks (red can to port, green cone to starboard when proceeding upriver) and the cardinal marks (N, S, E and W) and this was accepted throughout most of Africa, Australia and Eurasia except where there was a predominantly US influence (Japan, Korea etc).

The US (principally) wished to preserve its existing investment in buoyage. Changing would be expensive and a major undertaking covering all the coasts and rivers. Retraining of both commercial and amateur sailors would be required resulting in costs and uncertainties during the changeover. Therefore IALA system B rules were incorporated into the international rules in 1980. Shapes are common to both systems, as are the cardinal marks, isolated danger, safe water, special and most recently new danger. However in IALA region B the colours for the lateral marks are reversed: green can to port, red cone to starboard when proceeding upriver.

A good summary is available at: IALA: Maritime Buoyage System (Wayback machine) and also in most books on navigation published outside of the US after 1980. From my reading, some US books only concentrate on US waters and fail to mention IALA A, and also some include US internal conventions without always being completely clear about their extent.

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    Thank you for your answer. Do we know why the US had already invested in that buoyage system? I would have assumed that US nautical traditions would have ultimately descended from European systems?
    – thosphor
    May 18, 2022 at 10:09
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    It was only during the 20thC that any sort of conventions developed. Prior to that masters would be expected to know their waters or take a pilot aboard. You still find minor channels marked by withes which may mark one side, the other, both or a hazard. Lit buoys had to await electricity or else be beacons on land. Prior to 1848 ships didn't even carry navigation lights.
    – user55099
    May 18, 2022 at 10:46
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    As always, @LorenzoDonatisupportUkraine, there is an XKCD for everything!
    – FreeMan
    May 19, 2022 at 15:02
  • This answer could be improved if the one sentence that addresses the question, "the US (principally) needed to preserve its existing investment in buoyage", were extrapolated upon.
    – TylerH
    Aug 3, 2022 at 14:14
  • Done. Clearer now?
    – user55099
    Aug 5, 2022 at 9:58

@Martin's existing answer is good, but I'd like to emphasize a point behind his point: Basically, the reason that standards consolidation has not gone further is because it is more trouble to change it than to live with it.

As has been noted, the world started out with few or no standards, each harbor doing its own thing. As trade increased, there was value seen in having a standard and, sporadically, areas coalesced to a shared standard -- but not necessarily to the same standard each time! (This is a good example of a symmetry-breaking phase transition.) In particular, countries tended to settle on a single standard for all their own harbors.

As the size of a region covered by a standard increased, the cost of changing to another standard increased while the value of changing decreased. (The larger a region, the more of its trade comes from elsewhere within the region and gains nothing from adopting a different standard.)

So, in general, smaller standardized regions tended to merge to larger (or more powerful) regions, often adhering to the standards of their larger trading partners, while larger standardized regions tended to stay as they were.

The rules for air travel came to a different result because of different conditions. Why didn't this balkanization happen with air travel? Why does nearly the whole world follow one very standardized set of flying rules? Three reasons: First, air came in much later and setting an international standard had become commonplace. Second, after WWII, just as international air travel was really taking off, the US briefly dominated aviation and most countries found it easier to adopt the US system right from the start.

Third (and most important), the tempo of decision-making in the air is roughly 100 times faster than on a ship. A ship's master (i.e. the person in charge of the vessel at that time) can afford the time to look up the rules for an approaching harbor and even to double-check the rulebook when they see a buoy. A pilot approaching an airport and landing is busy and has no time at all to remember arbitrary local rules -- it's hard enough dealing with local traffic patterns which must be different in each locality. (This is why ATC uses feet for elevation -- meters might be tidier, but experience tells us that changing over would, for a time, add enough confusion and extra workload that would without a doubt result in multiple collisions and crashes.)

For ships, the cost of multiple standards is low. For planes it is not.

The bottom line is economics: The world has now reached a point at sea where the cost of retaining several standards is lower than the value gained from switching to a single standard.

  • 2
    Captain is a rank. In the Navy it is equivalent to Colonel in the Army, and would only be held by the commanding officer of the largest ships. It is applied as a courtesy in the mercantile service to the commanders of the larger ships. Master is a legal function and is the person in charge of the vessel at that time. "master" is the term used in the COLREGS and "boatmaster" in the CEVNI regs that apply to inland European waters.
    – user55099
    May 19, 2022 at 19:49
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    If you take a long enough timespan, consolidating from differing standards to a single universal standard would most certainly pay for itself, even if you begin with two equal compact regions. How long? In this case, quite long. May 20, 2022 at 0:46
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    Thanks for your answer - I like your point about there being more time at sea to double check the local custom if necessary.
    – thosphor
    May 20, 2022 at 15:51
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    @Deduplicator. On the surface the answer is simple, just repaint the buoys as they are serviced, BUT then the region that is changing would have a mixture of buoyage for several years which could easily lead to strandings and possibly deaths. The alternative is an immediate change, which would require massive numbers of service vessels, men and of course a complete set of new buoys. Given the size of the Pacific and Atlantic oceans it's easier and safer to leave things as they are.
    – user55099
    May 22, 2022 at 8:17
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    When considering cost and benefits, do remember that the cost is all incurred now, while the benefits come in gradually over time and there is a pretty significant (and increasing) discount rate for future benefits? "I will gladly pay you Tuesday for a hamburger today." may seem fair, but what about next year? Next decade? Not so fair a deal!
    – Mark Olson
    May 22, 2022 at 13:57

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