A deep sea port is a port whose approach channel and berths are deep enough to receive fully laden ocean-going vessels alongside, without first transferring cargo to smaller ships. No single legal depth makes a port qualify. Published thresholds run from about 9 metres to more than 20 metres depending on the trade in mind, which makes the label almost useless on its own.
The number underneath it is not useless. This guide covers how port depth is measured, draft versus air draft, the draft each vessel class needs, and how depth translates into cost per tonne.
Last updated: 28 August 2026
What Is a Deep Sea Port?
A deep sea port has enough water in its approach channel and alongside its berths to take large ocean-going vessels at full load. The defining test is functional rather than numerical: a vessel arrives loaded, berths, and discharges directly to shore, with no lightering and no partial loading.
The published thresholds disagree, and it is worth seeing how widely.
| Source type | Stated threshold | What it reflects |
|---|---|---|
| General maritime reference | around 9.1 m (30 ft) and above | The older distinction between coastal and ocean trades |
| Statutory and regulatory definitions | 13.72 m (45 ft) and above | Post-Panamax capability, written into national port law in several jurisdictions |
| Container terminal industry practice | 16 m to 20 m and above | Ultra-large container vessels calling at hub ports |
None of these is wrong. They describe different trades. A 9-metre berth is genuinely deep for a regional dry bulk feeder and genuinely shallow for a 20,000 TEU container ship. So an operator evaluating a site should ignore the label and ask a narrower question: what draft can this berth accept, on what tide, on what day.
At the other end of the same spectrum sit lighterage ports, where vessels anchor offshore and cargo moves ashore by barge, adding handling, time, and damage risk to every tonne.
How Port Depth Is Measured
Port depth is quoted against a vertical reference called a chart datum, and in Indonesian and most Southeast Asian practice that datum is Lowest Water Spring (LWS), the lowest astronomical tide. A depth of -10 m LWS means ten metres of water below the lowest expected tide, so there is usually more water available than the figure suggests.
That is the good news. The bad news is that published depth is not the draft a ship can use. Three deductions sit between them:
- Underkeel clearance (UKC), the safety margin between hull and seabed. Port authorities commonly require 0.5 m to 1.0 m in a sheltered basin, and 10% to 15% of draft in an exposed channel where swell moves the vessel vertically.
- Siltation since the last hydrographic survey, which degrades depth between maintenance dredging campaigns, particularly at estuarine sites.
- Squat, the additional immersion a moving vessel takes on in shallow water.
The practical consequence is the most common misreading of a port brochure. A basin advertised at -10 m LWS will typically permit a declared draft closer to 9 m, and less if the last survey is old. What a bulk charterer plans against is the declared draft the harbour master permits on the day, not the design depth in the masterplan. Ask for the survey date alongside the depth.
Tidal windows recover part of the difference. A 2 m tidal range admits a deeper vessel on a rising tide, at the cost of scheduling flexibility and the risk of a missed window becoming a waiting day.
Evaluating a site against your own cargo profile? Sumalacca’s published port figures, approach channel data, and planned terminal configuration are available on request. Email info@siipe-port.com or message the team on WhatsApp.
Draft and Air Draft Are Two Different Limits
Draft is the distance from the waterline to the lowest point of the hull, and governs whether a vessel can enter the channel and berth at all. Air draft is the distance from the waterline to the highest fixed point, usually a mast or crane, and governs whether it can pass beneath a bridge or power line on the approach.
The two limits are independent and a site can fail on either. A deeply dredged channel is worthless if a bridge downstream caps air draft below the vessel class the terminal was built for. Air draft also moves opposite to draft: a vessel in ballast sits higher and needs more clearance than the same vessel loaded. Confirm both before committing to a berth design.
Vessel Classes and the Draft Each One Needs
Vessel classes are defined by deadweight tonnage bands, but what matters to a port is the draft that comes with the tonnage. The table below sets the working bands for the dry bulk fleet against published class draft and length ranges, with an indicative basin depth of loaded draft plus roughly 10% underkeel clearance. Treat that last column as a planning rule of thumb, not a substitute for a port authority’s declared limits.
| Class | Deadweight | Typical LOA | Loaded draft | Indicative basin depth |
|---|---|---|---|---|
| Mini bulk carrier | 3,000 to 15,000 DWT | 100 to 130 m | under 10 m | 8 to 10 m |
| Handysize | 15,000 to 40,000 DWT | 130 to 150 m | around 10 m | 11 m |
| Handymax / Supramax | 40,000 to 60,000 DWT | 150 to 199 m | 11 to 12.2 m | 12 to 13.5 m |
| Ultramax | 60,000 to 65,000 DWT | up to 200 m | up to 13.3 m | 14.5 m |
| Panamax | 65,000 to 90,000 DWT | 200 to 230 m | 12 to 14 m | 13 to 15.5 m |
| New Panamax | up to 120,000 DWT | up to 366 m | up to 15.2 m | 16.5 m |
| Capesize | 90,000 to 200,000 DWT | 230 m and above | 17 to 18 m | 19 m and above |
Two features of this ladder matter more than the numbers.
The geared classes, Handysize through Ultramax, carry their own cranes and can work a berth with no shore equipment, which is why they dominate minor bulk trades and reach small ports. Panamax and larger vessels are typically gearless and depend on the terminal’s shore gear, so depth alone does not qualify a berth to receive them.
The cost curve is also not linear. Moving from Handysize to Supramax sharply cuts freight cost per tonne on many routes, and moving to Capesize cuts it again on long-haul ore and coal trades. Each step has a depth price attached, and that is the economic argument for dredging.
Why Depth Decides Cost
Insufficient depth does not stop cargo moving. It makes cargo more expensive to move, through four mechanisms that land on different lines of a shipper’s cost sheet.
- Lightering. A laden vessel that cannot enter anchors offshore and transfers cargo to barges. Every tonne is then handled at least twice more, which adds days, cargo loss and contamination risk, and for liquid bulk such as crude palm oil a temperature-management problem on each transfer.
- Part-loading. A vessel entering at reduced draft sails with empty capacity, and the charterer still pays for the whole ship. A Supramax restricted from 12.2 m to 9 m may sail with roughly 30% of capacity unused, raising the cost per tonne shipped by a similar proportion.
- Class exclusion. The most expensive constraint never appears as a line item. A terminal that cannot receive Panamax vessels leaves its tenants permanently priced against cheaper freight elsewhere, and no efficiency at the berth recovers that gap.
- Waiting time. Tidal windows and berth queues convert into demurrage. A vessel waiting for water is a vessel on hire.
Consider an exporter moving 500,000 tonnes a year of a minor bulk commodity.
| Scenario | Vessel class | Calls per year | Relative freight cost per tonne |
|---|---|---|---|
| Berth limited to 9 m declared draft | Handysize, part-loaded | around 20 | baseline |
| Berth at 13.5 m declared draft | Supramax, fully laden | around 9 | materially lower |
The assumptions are deliberately visible so a reader can substitute their own. Parcel size, route, and commodity density all move the result, but the direction does not change: fewer, larger calls beat more, smaller ones on almost every long-haul route, and depth decides which a site can offer.
The counterweight is that depth is expensive to create and expensive to keep. Capital dredging is a one-time cost, maintenance dredging is permanent, and at high-sediment estuarine sites it can be substantial. A port advertising a design depth without a funded maintenance regime will not hold it.
Indonesia’s Deepwater Picture and the Sumatra Gap
Indonesia’s deepwater capacity is concentrated on Java, where the container hubs and largest industrial estates sit. Sumatra, despite fronting one of the world’s busiest shipping lanes, has historically been served by shallower facilities built for regional feeder trades rather than direct ocean calls.
This is a structural point, not a promotional one. Northern Sumatra generates large export volumes in crude palm oil, rubber, and other plantation and mineral commodities, and much of it reaches deepwater tonnage indirectly, through feeder legs or ports further afield. Every transfer is a cost the origin region absorbs.
The gap between traffic passing the coastline and capacity available on it is why new port capacity in northern Sumatra keeps being proposed. Whether any proposal closes it depends on the depth actually delivered.
Sumalacca Port: The Planned Figures
SIIPE (Sumalacca Integrated Industrial and Port Estate) is a planned integrated industrial estate and port development in Medan Belawan, North Sumatra, on the Strait of Malacca and about 4.7 km from Belawan Port. Its port component, the Sumalacca Dry & Liquid Bulk Port (SDLBP), is planned, not built. Nothing described here operates today.
The published figures are:
| Item | Figure |
|---|---|
| Port basin depth | -8 m to -10 m LWS |
| Approach channel | 13 nautical miles |
| Intended cargo | Dry and liquid bulk, with crude palm oil, chemicals, cement, and commodities named as target trades |
Applying the table above rather than the brochure language: a basin at -10 m LWS supports a declared draft near 9 m after underkeel clearance. That serves mini bulk carriers comfortably and Handysize vessels at or near their limit, likely part-loaded or on a tidal window. It does not serve a fully laden Supramax, and it does not serve Panamax or Capesize tonnage. Against the stricter definitions set out earlier, a basin at that depth sits below the threshold. That is a plain reading of the numbers, and a prospective tenant will reach it themselves.
For a bulk operator, four questions separate a real port project from a drawing: what is the design depth, what declared draft will the harbour master permit, what is the capital dredging programme and its funding, and what is the maintenance commitment. A developer who can answer all four has done the engineering. One who can answer only the first has not.
Frequently Asked Questions
What is a deep sea port?
A deep sea port is a port with enough water depth in its approach channel and berths to receive fully laden ocean-going vessels alongside, without lightering cargo to smaller ships. No single legal depth defines one, so published thresholds range from about 9 metres to over 20 metres.
How deep does a deep sea port need to be?
It depends on the vessel class served. Handysize bulk carriers need roughly 11 metres of basin depth, Supramax around 13 metres, Panamax 13 to 15 metres, and Capesize 19 metres or more. Container hub terminals handling the largest vessels require 16 metres and above.
What is the difference between draft and air draft?
Draft is the distance from the waterline to the lowest point of the hull, which determines whether a vessel can enter and berth. Air draft is the distance from the waterline to the highest point, which determines whether it can pass under bridges and power lines.
What does LWS mean in port depth figures?
LWS stands for Lowest Water Spring, the lowest astronomical tide level, used as the chart datum in Indonesian and most Southeast Asian ports. A depth quoted as -10 m LWS means ten metres of water below that lowest expected tide level.
Why does port depth affect shipping cost?
Shallow depth forces lightering, part-loading, or exclusion of larger vessel classes. Each adds handling, time, or unused capacity that the charterer still pays for. Larger vessels carry far more cargo for a similar voyage cost, so depth directly determines freight cost per tonne.
Request Sumalacca Port Specifications
SIIPE is developing an integrated industrial estate and bulk port on the Strait of Malacca in Medan Belawan, North Sumatra, masterplanned so that industrial plots sit within 5 km of the estate’s own planned jetty. The port is at the planning stage, and we publish the figures as they stand rather than as we would like them to read.
If you are assessing a site against a specific cargo profile, vessel class, or parcel size, our team can provide the current port specifications, approach channel data, and planned terminal configuration, with the development phase each element sits in.
Request port specifications at info@siipe-port.com or on WhatsApp at +62 811 860 980. You can also review the industrial land available at SIIPE.
