Nayak — Marine Pilotage · Ch. 13: Manoeuvring Inside Harbour Limits

1. Overview — Manoeuvring Inside Harbour Limits

Source: NAYAK, Capt. Santosha K. Theory and Practices of Marine Pilotage. Chapter 13 — Manoeuvring Inside Harbour Limits.

Syllabus: Anexo 2-B, Área II (Arte Naval), item 8 (NAYAK), Cap. 13 — manobra dentro dos limites do porto. Cross-list Área III, item 6.

Once the vessel has successfully entered the harbour limits, her transit through the inbound channel is already complete. Tugs are made fast to provide assistance and speed is brought down to a controlled figure. From here on the ship is exposed to the highest degree of external restriction of the whole passage, and every further movement carries a much narrower margin for error than anything experienced in the open channel.

Manoeuvring inside the harbour is therefore marked by slower speed, minimum use of the engines while a reserve engine power is kept in hand, large wheel orders when the helm is used, and commands to the tugs. It may also call for the use of anchors and other emergency methods of manoeuvre. The chapter covers what is special inside harbours, the keys to handling the ship there, how to manage the sudden onset of external disturbances, how different types of craft behave, and the contingency planning that keeps a routine movement from turning into a disaster.

2. What Is Special Inside Harbours — Restrictions and Limitations

A few special characteristics of harbours must be understood before safe berthing and safe manoeuvres can be carried out inside them.

2.1 Highest degree of restriction

From the ship-manoeuvring point of view the inside of a harbour poses the highest degree of restriction to a vessel working within its limits. Every restricted condition is present at its most severe: sea-room is very restricted in all four dimensions at once — longitudinally, transversely, in the under keel clearance and in the headroom.

2.2 Depth, air draft and length limits

Ports are normally dredged only up to the maximum size of vessel they are expected to handle, leaving a UKC of just 1–2 m. The UKC-to-draft ratio is therefore very low — even 5–10% — so the flow of water below the keel is highly restricted and the smooth movement of laden vessels suffers.

Some ports add their own peculiar infrastructure. Air draft limitation is one: a vessel may have to pass under a bridge in a river port and adjust her air draft for a safe passing, and at the berth the cargo gantries impose a further restriction on the headroom. Where a gantry outreach fouls the vessel's movement it must be lifted or moved before she passes nearby. Length limits arise from the length of the available berths and from the diameter of the turning basin.

2.3 Maximum acceptable vessel at a pier

The maximum size of vessel a pier can take follows from the pier length, the vessel's breadth and the angle the mooring lines make with the pier.

Here $k$ runs from 1.0 to 1.7 depending on the angle between the mooring lines and the pier: at a mooring angle of 45° $k = 1.0$, and at 30° $k = 1.7$.

2.4 Turning basins

The turning basin is an important and critical feature of any harbour: it lets vessels turn on the inbound or outbound passage. Its diameter is usually a little more than the largest vessel handled in the port, and it is the diameter that limits the length of vessel the port can accept. Almost every vessel is turned 180° at some point during her port stay. That large turn is made near the berth if space allows; otherwise the vessel is worked to the turning basin on her ahead or astern movement and finally allowed to turn.

3. The Harbour Risks — Collision, Grounding and Passing at Close Range

3.1 Risk of collision

Because the vessel works at very close range with the port and jetty infrastructure, with vessels berthed nearby, small craft and dredgers all in a small congested area, the traffic density always carries a risk of collision. That risk has to be completely removed by putting the appropriate control measures in place.

3.2 Risk of grounding

Grounding is also prevalent within the harbour limits, though it is a slightly more tolerable emergency than a collision with a nearby vessel. Retrieval depends on the nature of the seabed and the location of the grounding: a soft mud or sand bottom is likely to let the vessel re-float on the next high tide with the help of tugs, but a rocky bottom that ruptures the hull and starts bilging can turn her into a wreck that threatens other movements and the survival of the port itself. Pilots must be expert in re-floating a vessel grounded on a soft bottom; otherwise salvage becomes necessary.

3.3 Passing at very close range

In many developing ports the sea-room is very tight, and to maximise operations the authorities push vessels through highly restricted areas — the passing distance can be as little as 5–10 m. Holding the vessel in safe water at such range is a challenge with literally no margin of error. As she passes close to shallow patches the bank effects complicate the process, and when she passes an already-berthed vessel the interaction between the two hulls makes the berthed vessel suffer excessive surging motion and its cascading effects.

After-effects on the berthed vessel

As a vessel passes close to a berthed vessel, the shallow-water effects and interaction cause the berthed vessel to suffer excessive surging and ranging, breaking her mooring lines and gangways. The graph plots time in seconds on the X-axis against the surging force in kN felt by the berthed vessel as the other vessel passes.

3.4 Difference between channel and harbour

What would count as a close near-miss in the open sea is a day-to-day operation within harbour limits, so the pilot must identify and appreciate the additional developments the port demands.

4. Keys to Handling the Ship in Harbour

Positioning a large vessel at a safe berth, with all the limitations on headroom, stern room, side room, UKC and air draft, is a highly specialised task. It rests on the following key points.

4.1 Safe (slow) speed and reserve engine power

Inside harbour limits safe speed means a slow speed of less than 5 kts, at which both ahead and astern engine powers remain available for use. A minimum RPM is kept when needed to hold steerage, and the vessel often proceeds with engines stopped, taking whatever steerage she can. Even at 1–2 kts she gets some steerage with the wheel hard over, though it is very sluggish; in calm weather she keeps her directional ability, but in unfavourable weather tug assistance is necessary.

It is always good to run slower while keeping a reserve engine power in hand for an urgency. Consider a vessel 500 m from her berth: at 2 kts, if she loses steerage a burst of dead slow / slow / half ahead with the wheel hard over restores control quickly, adding perhaps 0.5 kt so she reaches 2.5 kt, then falls back once engines are stopped. Had she been running at 3 kts, the same burst would take her to 3.5 kt, and to shed that she must run the astern engine at higher RPM for longer — more engine stress, more unwanted transverse thrust near the berth and more tug power to manage it. The whole exercise saves perhaps 2 minutes, so the key is to proceed slower with reserve power.

4.2 References, cross-checks and visual aids

Within harbour limits there are numerous fixed land objects to give the pilot an immediate sense of every dimension of the vessel's movement. Electronic information systems carry a critical time delay, so the pilot develops the habit of observing references continuously, saving critical time for action. It is always prudent to place cross-check mechanisms in the information inputs so that an error in one source is caught by another before any decision is taken. Visual sources are the best aids; at best the electronic information is used only to compare against the visual picture and gauge its error.

4.3 Control on swing

When the vessel alters course inside the harbour, sea-room and time for the alteration are both restricted, so the course must be altered timely. A laden vessel constrained by her draft and low UKC is hard to turn; once she is swinging at a given rate of turn, inertia keeps her turning that way, and her swing must be reduced slowly and settled onto the final course before she reaches it. With the pilot's hands tied on long engine use, controlling the swing timely and within safe depths is critical and specialised.

4.4 Optimal use of tugs

For a satisfactory manoeuvre the tugs must be used optimally. When a tug pushes or pulls it should create just the sufficient effect — neither excessive nor too little — so that no further command is needed to correct the previous one. Correcting an over- or under-command is bad for the tug and bad for the movement.

A good movement is the one where there is a minimum number of commands given to the vessel. This can happen only with optimal use of tugs.

4.5 Anticipation and timely action

Manoeuvring is a continuous cycle: the pilot processes information, decides on an action, observes its effect, takes in that observation and processes again. In each cycle he must anticipate the next action; the deficit between his anticipation and the actual effect shapes his further action and forms the feedback mechanism of the sequence. Tugs are put on standby — ready to push or pull — when the vessel passes critical areas, which requires her to be below 4–5 kts; at critical points the tugs are warned and briefed of any anticipated situation.

Timely action is critical: any critical delay adds a whole set of work. The two diagrams show the effect of a delay in alteration. In the first the vessel alters to starboard smoothly at point A and back to port at point C; in the second she delays and only alters at point B.

4.6 Lateral drift, communications and berth clearances

While holding a course in the harbour the pilot must keep cross-checking her position and watch her lateral drift; once she lands appreciably away from her desired position the tugs must work hard to push her back. He also keeps a good communication schedule with port control, jetty officers, tugs and nearby ships, while keeping unnecessary traffic to a minimum so his concentration is not diverted — the jetty officer must keep things ready to avoid undue queries.

Before reaching the berth the pilot confirms that the clearances from the vessels forward and aft are sufficient. Where gantries are present on the berth they must be positioned near the mid-ship section of the vessel and kept away from where the bow or stern is planned to lie.

5. Managing the Sudden Onset of External Disturbances

Some external disturbances set in immediately, with very short notice or none at all. These pose extremely difficult conditions and call for swift decisions and actions from the ship handler.

6. Handling Different Types of Craft

Many types of vessel and craft enter the port for different purposes, each with quite distinct manoeuvring characteristics — with or without propulsion, with unusual sizes, extreme drafts, extreme lengths or excessive engine speeds.

Lighter (smaller) vessels are easier and quicker to manoeuvre in a port built for large ships, since sea-room is ample; though engine power is low, higher RPM gives better engine and helm effect, and standby tugs make control easy.

Un-propelled objects — barges, floating cranes, dead ships, vessels under repair — are irregular in most ports, so the resources are not optimised for their dimensions and the handlers have less experience. Such a movement must be assessed, with a meeting of everyone involved and a risk assessment of the dimensions and their effect. Un-propelled barges are handled by tugs, preferably three to control lateral and longitudinal speed, and handling depends largely on the barge's displacement.

Vessels with extreme drafts — with almost no UKC — have highly restricted water movement below and beside the keel and behave differently in many places; alteration of course is very difficult, inertia is very high, and even tugs at maximum power may not hold the vessel in extreme conditions. Vessels with extreme lengths usually keep engine and helm at the pilot's disposal, but turning them in restricted space is specialised, monitoring the forward and aft distances from the shallow patches.

7. Contingency Plans — Planning for the Unexpected

As long as all goes well a sense of satisfaction settles in the pilot's mind, but clear-cut, well-trained action plans must be ready for the moment something serious threatens. We plan well for the situations we know will cause problems; the situations we do not plan for catch us by surprise, because their potential for harm was not foreseen or was thought too remote. Potential emergencies may develop from engine failure, tug failure, lack of alertness, a sudden onset of weather or poor visibility, or a sudden increase in wind or current.

7.1 From the pilot's point of view — the danger of complacency

A pilot doing similar movements every day gains quickness, boldness and perfection with experience — but the same repetition breeds complacency. The feeling that everything will be all right is the killer attitude: accidents happen only once, not every day, when one or several factors go against the pilot's intentions on a fine day when least expected.

A recent five-year study of claims in excess of USD 100,000 recorded by each of the Clubs in the International Group of P&I Clubs revealed that some 262 claims were caused by pilot error, with an average cost per incident of USD 850,000.

Errors are broadly of three kinds: from the pilot's wrong actions, from wrong actions by the master or bridge team, or from misreading due to external causes. The pilot, as leader of the manoeuvring team, must think out of the box and expect the unexpected, asking at each critical point what may go wrong and what the action plan is when it does. Regular risk assessments and brainstorming sessions prepare the mind to face real emergencies with ready action, preventing critical delays. A useful session asks: the main dangers to crew and vessel; the worst-case scenarios; the plan to avoid them; and the back-up plan if the first fails.

7.2 Barriers and solutions

7.3 From the ship master's point of view

On board there is little time to stop and think; response plans and checklists exist for clear-cut emergencies, and bridge resource management has improved situational awareness through a team approach — yet a team too preoccupied with the task in hand may not consider a developing emergency at all. It is impractical to produce a checklist for every eventuality, and time is often short, which is especially relevant to pilot error. Before embarking, though, the plan can simply identify the critical aspects of the pilotage where the team must be particularly alert, and remind the whole team that pilots can make mistakes — so everyone must be ready to speak up over any concern with the pilot's orders. A final consideration of the pre-pilotage plan is whether or not to proceed with the pilotage at all.

Barriers here include language and cultural differences that discourage speaking up, a perceived lack of shore-staff support for a decision taken on board, an industry focus on speed and quick turnarounds at the expense of safe operation, and cost-saving that tempts a crew to attempt repairs before calling expensive external assistance. The most important solution remains mental preparation, supported by training, exercises and drills.