Canals limit ship sizes?

While reading this thread about the Emma Mærsk, I came across the Knock Nevis. The wikipedia article says:

“When roaming the sea, the vessel had a fully laden draft of 24.6 m (81 ft), rendering it unable to navigate the English Channel, the Suez Canal or the Panama Canal when its load was up to capacity.”

What would be the rationale of building a vessel too large to navigate the most important routes on the seas! Doesn’t that completely defeat the goal of low cost shipping?

and, Do these channel limits actually limit the design sizes of super tankers and container carriers today?

Cost reduction via economy of scale outweighs the increase in fuel usage/trip time sailing around, say, South America (or South Africa, or other long detours). Besides, plenty of shipping routes don’t involve narrow or shallow channels/canals, so the big ships can be used on those routes, and only occasionally be assigned to use the restricted routes (via those long detours I mentioned above)

Sure, for examplePanamax shipsare, as you may expect, designed to be the maximum size ship profile capable of fitting the Panama canal (which is being enlarged, but still)

and Suezmax. Thanks, wasn’t aware of these terms earlier. Very Informative.


It may be of interest that the Panama Canal is currently constructing a 3rd set of locks which will be able to accommodate the larger sea-faring vessels in production.

There was a good show about the Panama expansion a few moths ago on Discovery Channel. I think it was one of the Build It Bigger series.

Some of the ships currently using the canal have just a foot or two of side clearance.

yes, there is a very tight squeeze for the biggest ships that go through the Panama Canal.

Way back there was a plan to build a bigger canal through Nicaragua but that obviously did not happen.

My recollection from working on related issues some time ago is that Panamax and Suezmax ships are actually on the small side these days.

A big part of cargo shipping, at least with tankable liquids, is the ability to transfer cargo at sea to smaller ships (called “lightening”). Either to store some of your cargo so your draft isn’t as deep when you go in to port, or even just to take the cargo to port for you so you don’t have to go into the shallows at all. And given that these services are generally available at some reasonable cost, it may make sense, as SirRay notes, to build really big ocean-going tankers and just figure they’ll offload onto smaller ships instead of at port.

The other issue here is that different ports all over the world have different draft restrictions (and all sorts of other differences, too – ports are by no means uniform). And so if you were to build a ship that could dock at any port where you might have business, you really limit your design choices in ways that could seriously compromise the ship’s ability to transport enough cargo with enough efficiency to be profitable. (Note also that ships stay in service for a long time, and often have multiple owners.)


The truth is the Jahre Viking (Knock Nevis, Seawise Giant, or whatever the hell it’s called this month) was too big. It wasn’t a success. It’s spent a lot of its life acting as floating storage. Vessels so large they can’t transit the English Channel are very, very rare. They are used as the spine of a feeder route, carrying large shipments for distribution outwards from hubs.

“Small” is going too far. Panamax is kind of medium, and Suezmax is medium large.

I read somewhere that the main limitation on expanding the Panama canal is the volume of water that feeds into Lake Gatun. Every time the locks cycle fresh water is lost into the oceans, and too much would lower the lake level below navigability. Is this so?

This has been a considerable concern regarding expansion of the canal and increased traffic. When expansion of the canal was first proposed, one of the initial plans was to build three huge new artificial reservoirs (one of them almost the size of the present Lake Gatun) on the Caribbean slope west of the canal and feed the water into Gatun through a system of tunnels. The plan was very controversial due to the fact that it would have flooded some tropical forest and displace some of the local population. (I worked on biological surveys of the area between 2001-2003 as part of the environmental impact assessment.)

The new set of larger locks has a design that will recycle some of the water used in each lockage. (In the present locks, all the water used in a lockage is lost to the ocean. The locks work purely on gravity flow, without pumps.) Because of this, it is now considered that the present supply of water in Lakes Gatun and Alajuela (Madden) will be sufficient for operation of the expanded canal.

The big problem is storing sufficient water to get through the four-month dry season. There is normally plenty of rain during the rainy season from mid-April to to mid-December. However, the lakes have to store enough to get through the dry season when very little rain falls. This requires careful calculation towards the end of the wet season to make sure the lakes are as full as possible, without risking overflowing due to a big storm late in the season.

The problem becomes most significant during El Nino years, which cause decreased rainfall here in Panama. In the severe 1983 El Nino, draft restrictions had to be placed on ships transiting the canal in order to save water.

Incidentally, I can see the Pacific entrance to the Panama Canal from my apartment window where I’m sitting typing this. My office is right at the entrance itself near the Bridge of the Americas. Seeing a Panamax ship cruise by is pretty impressive.

Edit: too late.

There are “lakers” – ships plying the Great Lakes – which are substantially too large to negotiate the Welland Canal locks. There is also still quite a lot of Transatlantic trade, and I believe Transpacific as well. Economy of scale makes shipping on these routes sensible even with ships which cannot negotiate the canals. I believe that timing along with economy of scale also makes it sensible to build ships which must round the Cape (of Good Hope) rather than smaller ships that could pass through Suez.

After the Suez was in 1956, the canal was closed for several years. This meant that oil tankers, in particular, had to go around South Africa to take oil from the Persian, er Arabian, Gulf to Europe and North America. That being the case, they started building supertankers to at least benefit from the economies of scale. Having done that, they were committed to that route even when the canal reopened.