Draft, Air Draft and Beam: What Limits Which Ships a Port Can Take

Not every ship can call at every port. A vessel that is too deep, too wide, too long or too tall simply cannot get in safely. Four measurements do most of the work in deciding the limit — draft, beam, length and air draft — and three of them appear directly on the port pages in this directory. Here is how to read them.

Draft versus depth — the key relationship

Draft is how deep a ship sits in the water: the vertical distance from the waterline to the lowest point of the hull. The more cargo a ship carries, the deeper its draft. Depth is the property of the port — how much water there is in the channel, at the anchorage and alongside the berth. A ship can only enter if its draft, plus a safety margin called under-keel clearance, is less than the available depth.

That is why the channel depth shown on a port page is so important: it is usually the binding constraint. A port reporting a channel depth of around 11 m can physically take vessels drawing up to roughly that figure (minus clearance) — broadly Handymax/Supramax bulkers and mid-size container ships — while a 16 m channel opens the door to Capesize bulkers and large tankers. Our depth & draft guide breaks down each depth figure in detail.

Beam — width through the locks

Beam is the width of the ship. It rarely limits an open berth, but it is critical where ships must pass through locks or narrow channels. The famous “Panamax” class exists because the original Panama Canal locks were about 32 m wide; ships were built right up to that limit. When the canal’s larger locks opened in 2016, a new “Neopanamax” limit followed. A port’s recorded maximum vessel beam reflects the widest ship its approaches and berths can accommodate.

Length — berths and turning room

A ship’s length overall has to fit the berth it ties up to and the turning basin it must swing in to get there and leave. Very long vessels also need more tugs and more careful manoeuvring. The maximum vessel length on a port page is the longest ship the port reports being able to handle.

Air draft — the limit you can’t dredge away

Air draft is the height of a ship above the waterline. It matters wherever a vessel must pass under a bridge or power line to reach its berth. Unlike depth, you cannot dredge more clearance — the bridge height is fixed — so air draft can permanently cap the size of ship a port can take, no matter how deep its water. Tall container ships and car carriers are the vessels most often constrained this way.

It isn’t only about dimensions

Physical size is the headline, but other recorded factors shape access too: tidal range can mean deep-draft ships only move on a rising or high tide; shelter affects whether cargo can be worked safely; ice or heavy-swell restrictions can close a port seasonally; and compulsory pilotageand tug availability govern how a large ship is actually brought in. All of these appear in a port’s profile.

Putting it together

When you read a port page, look first at the channel depth and maximum vessel figures — they tell you the class of ship the port can serve — then at the restrictions and services that govern how. To see the contrast, compare a deep global hub with a small regional harbor by browsing ports by country.