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Captain's Brief · Maritime Learning · 2 min read · Oct 24, 2026

How Many Tugs Does She Need? Bollard Pull for Berthing and Unberthing

Learning guide for officers working toward their next rank. On the day, the port's rules, the pilot and the Master decide. Every worked example below is an ILLUSTRATION, not a figure for any real ship or port.

How many tugs does a ship need to berth or unberth, and how much bollard pull? There is no fixed number. Wind on the windage area, current and under-keel clearance, displacement, the ship's own thrusters and screws, the berth and turning basin, port rules and the pilot's judgment all decide it. Double the gust and you need four times the pull. Add a safety margin, because tugs deliver less than their rated pull. Worked numbers in the video are illustrations only.

The short answer

No single table tells you how many tugs to order. The number and power come from three things working together:

  1. The port's rules. Many ports set a minimum by tonnage.
  2. The forces on the ship that day. These are wind, current, waves and the ship's own mass.
  3. The pilot and Master's judgment. That covers the ship's own aids, the berth layout and a safety margin.

The rule is to work out the total bollard pull you need first, and only then split it into tugs.

1. Wind on the windage area

Wind is usually the biggest sideways force on high-sided ships such as container ships, car carriers and gas carriers. It is treated as a steady drag force:

F = 0.5 x C x rho x V² x A

  • F = lateral wind force, in newtons
  • C = lateral wind force coefficient. For a beam wind it is about 0.8 to 1.0, mostly 0.9 to 1.0. OCIMF publishes coefficients for tankers and gas carriers.
  • rho = air density, about 1.28 kg/m³ for dry air at 0 °C
  • V = wind speed in m/s. Use the gust speed. The Beaufort average is a 10-minute mean and is too low for bollard pull work.
  • A = the longitudinal (broadside) wind area in m²

Estimating A. Take length overall x (freeboard + height of deck cargo above the main deck), then add the superstructure that stands above the cargo. A container is about 2.6 m high, so counting the tiers gives you the stack height quickly.

Hensen's quick check. Total bollard pull in kg ≈ 0.08 x A x V². This already includes a 25% safety margin.

The key fact: force grows with the square of the wind speed. Double the gust and you need four times the pull.

Worked example (ILLUSTRATION ONLY)

The numbers below are assumed, round figures chosen for teaching:

  • Broadside wind area A = 10,000 m²
  • Beam gusts V = 20 m/s
  • C = 1.0, rho = 1.28

Drag force = 0.5 x 1.0 x 1.28 x 400 x 10,000 = 2,560,000 N. That is about 261 tonnes-force (divide by 9.81 x 1,000).

Adding the 25% margin gives about 326 t of total bollard pull.

Hensen's quick check gives 0.08 x 10,000 x 400 = 320,000 kg, or about 320 t, which is close.

Now drop the gusts to 10 m/s. The requirement falls to about a quarter, roughly 80 t.

This is why a berthing that is routine in the morning can need more tugs, or a delay, once the afternoon wind picks up.

2. Current and under-keel clearance

Current is worked out the same way as wind. The area is the underwater side of the ship, LBP x draft, and you use water density instead of air density:

F = 0.5 x C x rho(water) x V² x LBP x T

Two points matter in practice:

  • It is squared again. Double the current and you get four times the force.
  • Shallow water multiplies it. As under-keel clearance shrinks, the water cannot pass under the keel, so it has to go around the ship. With a very small UKC, the current force can be about three times what it is in deep water.

A loaded ship with a small UKC on a cross-current berth is a classic case for extra tug power. Berthing at slack water is often the cheapest tug you can get.

3. Displacement: the mass you must stop

The wind decides the sideways push, but displacement decides how hard the ship is to start, stop and hold.

On a loaded tanker or bulk carrier the wind area is small, but the mass is huge. For these ships the guidance says mass, not wind, sets the tug power. An empirical rule widely quoted by pilots is:

Total bollard pull (t) ≈ (displacement in t x 60 / 100,000) + 40

This is for large-mass ships only. It does not apply below about 40 t of total pull.

Worked example (ILLUSTRATION ONLY)

For a displacement of 100,000 t: 100,000 x 60 / 100,000 + 40 = about 100 t of total bollard pull.

Mass also explains stopping distance. As first approximations, a ship needs about 3 to 5 ship lengths to stop in ballast, and 7 to 8 lengths when fully loaded. Once a loaded ship is moving sideways toward the berth, the energy that the tugs and fenders must absorb is large.

4. The ship's own aids

Bow and stern thrusters, twin screws, controllable-pitch propellers and pods all reduce what the tugs must supply.

Port rules recognise this too. At one Manila terminal, a ship with a working bow thruster needed one tug instead of two in several size bands. A ship with both bow and stern thrusters working could be exempt, although the Master could still call tugs.

Remember: thrusters lose effect as the ship gains speed. They are strongest at or near a stop. Report any thruster defect to the pilot before the berthing plan is fixed.

5. Berth layout and turning basin

The berth and the basin set how much room there is to correct a mistake:

  • Turning basin. PIANC's concept-design guide is a diameter of about 2 x LOA where tugs assist, and 3 x LOA without tugs. About 1.5 LOA can work with main engine, rudder and bow thruster, and about 1.2 LOA when warping around a dolphin in calm conditions.
  • Berth type. An open berth on piles and a solid quay wall behave differently when the ship comes in sideways.
  • Room for the tugs. Tugs need space to get into position, and the wind and current need room for drift.

6. Port rules and pilot judgment

In the Philippines, the Philippine Ports Authority sets tug rules port by port:

  • Pilotage is compulsory for all foreign ships and for domestic ships of 100 GRT and above.
  • Tug assistance is generally optional, but it is compulsory at listed ports above tonnage thresholds, for example 500 GRT at Manila South Harbor and 1,500 GRT at Cagayan de Oro.
  • Port orders. Some port orders set the number of tugs and their horsepower by tonnage band. The Manila South Harbor and MICT orders are examples.

Every one of these orders says the same thing in different words: the Master, in consultation with the harbour pilot, may require additional tugs depending on weather and port conditions.

The table is a minimum, not the answer. Always check the current local order with the port or agent. Older orders may have been amended.

7. Safety margin and reality checks

  • Add a margin. Hensen's figures include about 20 to 25%, because tugs must not only hold the ship but also stop a drift and bring her back on track. Other studies have used a factor of 1.3.
  • Tug power on paper is not tug power on the job. Bollard pull falls with age, hull growth, propeller condition, warm seawater and a shaft alternator taking load from the main engine. It also drops as the ship gathers speed.
  • Check the ship's fittings. Strong tugs need deck fittings that are strong enough. Know the safe working load of your chocks and bitts.

Officer's checklist before arrival

  • Gust forecast at berthing time, plus the windage area for this loading condition
  • Current and tide at the berth, UKC, and the slack-water window
  • Displacement and the condition of the ship's aids (thrusters, CPP, twin screws)
  • Local PPA or port tug order: minimum number and power
  • Pilot information exchange: the tug plan, where the tugs will push or pull, and the SWL of the fittings
  • A margin of about 25% over the calculated pull

For the next rank

Expect questions like these in assessments and at interview:

  • "Why do container ships need more tugs in wind than a loaded tanker of the same length?"
  • "What happens to current force as UKC shrinks?"

Practise these topics in the Promotion Reviewer: https://maritimematch.ph/seafarers/promotion

This is a learning guide, not a substitute for port regulations, the pilot's advice or the Master's judgment.

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Sources (accessed 23 Oct 2026)

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