1. Overview — Entering Pilotage Waters
Source: NAYAK, Capt. Santosha K. Theory and Practices of Marine Pilotage (2nd Edition). Chapter 5 — Entering Pilotage Waters.
Syllabus: Anexo 2-B, Área II (Arte Naval), item 8 (NAYAK), Cap. 5 — entrada em águas de praticagem; efeito de vento/resistência; entrada de canal; CEMA. Cross-list Área III, item 6.
By the time the ship reaches the pilot boarding point, every relevant internal particular and external factor has already been traded between master and pilot in the MPiX, and a consolidated plan with its sub-plans has been drawn up. That exchange sets the stage for the run from the boarding point to a safe berth. While the vessel is still at the boarding point and has not yet entered the narrow channels and waterways, she remains in safe water and under the full control of the master.
Beyond that point the safety of the vessel passes largely into the pilot's hands and intentions, which makes it a critical juncture: the master can still reject the pilot and keep the ship safe. He proceeds only when fully satisfied with the plan and with the resources available to manoeuvre safely into confined waters. Once both agree to go on, they stand on the same platform — one in command, the other advising; one navigating, the other cross-checking — supported by the rest of the bridge team, and the agreement is recorded by signing the checklists and company forms.
1.1 What are confined waters?
Confined waters means an area where manoeuvring is highly restricted by the nature of the sea-room and the proximity of hazards. In approach channels most dimensions of sea-room are limited at once — depth, and the room on the athwartship and longitudinal directions of the vessel — so courses are hard to keep and to change, with tight margins on either side. The difficulty is compounded by unusual shallow water effects and by relatively unpredictable external forces, and by the need for timely speed reduction that cannot be deferred even by a few minutes.
When speed control does not go to plan, the handler must resort to emergency means, pushing engine and helm to their limits. Any wrong use of engine or helm can bring disaster to the ship and to harbour infrastructure. The distinction is stark: before the ship enters the channel, the vessel and the port are in a safe and secure condition; once she enters, the harbour is exposed to huge risk.
| Confined waters include |
|---|
| Approach channels |
| Congested anchorages |
| Straits and canals |
2. The Four Dimensions of Movement in Confined Waters
From a manoeuvring point of view every vessel needs clearances, each with a margin of safety, on four dimensions of its expected movement. Three of them are dimensions of sea-room — Longitudinal, Athwartship and Under Keel — and the fourth is Headroom.
| Dimension | What it covers | How it is measured |
|---|---|---|
| Longitudinal (L) | The largest component; covered by the fore-and-aft speed of the vessel. | Fore-and-aft speed V, read from the bottom-tracking GPS speed. |
| Athwartship (A) | The most restrictive element inside port limits; covered by the lateral drift of the vessel. | The set (in degrees) and the drift. |
| Under Keel (U) | The vertical movement of the hull below the surface caused by squat and other channel-dynamics effects. | UKC, in metres. |
| Headroom (H) | The vertical clearance from bridges, overhead cranes and similar structures. | Clearance relative to the vessel's air draft. |
Confined water is normally restriction of the 2nd or 3rd degree, meaning that at least two or three dimensions of movement are limited by some obstruction. In practice the components A and U are usually restricted, while L most of the time stays relatively open; Headroom (H) is restricted mainly when passing under bridges or when approaching the berth. Harbours pose the highest degree of restriction, often affecting all four dimensions at once.
3. Dangers Associated with Confined Waters
The character of confined waters differs from place to place, and the degree of confinement varies with the location. Beyond the increased degree of restriction on the four dimensions just described, each area is jumbled up with all or some of the following dangers that make free navigation difficult.
| Danger | Why it matters |
|---|---|
| Shallow water effects | Reduced water flow below the keel cuts manoeuvrability — poorer turning and stopping. Effects include smelling ground, bank effects (bow cushion and bank suction), unexpected swing and speed reduction, squat, canal effect, vibration, difficult steering and sluggishness (detailed in the shallow-water chapter). |
| Squat and reduced depths | Available depth over the draft is low, with a UKC margin of only a few metres. As speed rises in shallow water, squat grows and the effective UKC shrinks further, raising the grounding risk — so speed must be adjusted to reduce squat. |
| Increased traffic density | Topographic restrictions combine with heavy traffic — inbound and outbound ships, local fishing and coastal craft, and anchored vessels with cables to the seabed — raising ambiguity in positioning and collision-avoidance action. |
| Peculiar local weather and wind | Wind strength and direction vary with local topography and structures; authorities and pilots should study and record the harbour's wind patterns as a ready reference for safe manoeuvring. |
| Uncertainty of currents | Currents matter far more in confined waters than in the open sea, yet their speed and direction are less predictable than wind — driven by bottom topography, islands, narrows and reefs, tidal changes, river-mouth flows after rain, bends and man-made piers and breakwaters. |
| Sudden restricted visibility | Fog, rain, sand or hail storms can set in without notice, especially convection fog near land early morning or late night; pollution and suspended particles now make morning fog, haze and smog common near port cities. |
| Draft, air-draft, width and length limits | Ports are dredged to a maximum vessel size with a UKC of only 1–2 m, so the UKC-to-draft ratio is very low (even 5–10%). Length is limited by berths and turning basins (most ships turn 180°); air draft is limited under bridges and gantry booms. |
| Passing dangers at close range | Isolated rocks, sand bars, turbulence and sharp turns must often be passed very close, with no margin for error. |
| Failure of controls | Engine and steering are stressed by frequent orders. Steering has 100% redundancy and there is immediate takeover to emergency power, but an engine failure also loses steering; excessive use during extreme manoeuvres can make mechanical systems fail. |
| Risk of collision | High density and close-range operation raise the risk of collision with other ships, fishing craft and fixed structures, because of the reduced safe margins. |
| Risk of grounding | If a vessel is not properly controlled she may ground; a soft mud or sand bottom may allow re-floating on the next high tide with tugs, but a rocky bottom that ruptures the hull can turn the ship into a wreck that threatens the port itself. |
| Confined waters vs harbours | In confined waters the vessel keeps directional ability along the charted course at sufficient speed with close margins; in harbours she makes two-dimensional motions at very slow speed and the pilot adds external communications with port control, jetty officers and tugs. |
4. Key Factors in Handling Vessels in Confined Waters
Navigating confined waters demands extra care and alertness from the pilot and the bridge team. The task rests on the following key points.
| Key factor | Practice |
|---|---|
| Safe or slower speed | Maintain the safe speed marked for each critical point and leg; reduce further as the berth nears. Even at 1–2 kts a ship gets some steerage with the wheel hard over, though sluggish; if weather is unfavourable a tug is needed. |
| Well-marked abort points | Beyond the abort point the vessel cannot turn back to open water without external help; if uncomfortable, master or pilot must decide to abort before that point, otherwise they continue and manage the new risks. |
| Reserve engine power | Run slower while keeping reserve power in hand. From 2 kts a burst of ahead with hard-over wheel restores control quickly, then RPM comes back down; from 3–4 kts a large engine order cannot be given as freely and the extra speed must later be shed with less time in hand. |
| Visual cross-checks | Fixed land objects let the pilot sense every dimension of movement almost immediately, whereas electronic systems carry a critical time delay; continuous observation saves reaction time. |
| Visual and electronic aids | Visual sources are the best information; electronic data is used mainly to compare against the visual picture and gauge its error. |
| Timely action | Delay multiplies work — it must be nullified later, wasting time, tug hours and fuel, and cascading onto later movements in the harbour. |
| Clear communications | Keep an orderly schedule with port control, jetty officers and tugs; keep non-essential traffic to a minimum so the pilot's concentration is not diverted. |
| Best use of current and tide | A good handler exploits the existing current, adjusting speed and course to the local strength and direction to achieve the desired result. |
| Mark contingency anchorages | Not every point suits dropping anchor; the points where the vessel may anchor for safety or to buy time are marked on the route. |
| Best use of nav aids | Fixed structures, offshore installations and buoys confirm the vessel's position; small position errors in narrow channels can have serious consequences. |
| Control tests before arrival | Test all bridge, engine and steering controls well in advance so they are in good order at the timely disposal of the team. |
| Monitor other movements | Watch nearby traffic, identifying small and unlit craft; post additional lookouts where a risk assessment calls for them. |
| Emergency contacts and reporting | Keep coastal-state emergency numbers ready and follow the reporting points and procedures for the area. |
5. Checks Prior to Entry into the Approach Channel
Before entering the approach channel it is good practice to confirm a set of conditions so the risks of the passage are managed deliberately.
5.1 Berth, tugs, current and tide
- Berth clear and spacious — check with port control that the berth is clear of obstructions, with sufficient safety-margin clearances from the vessels berthed forward and aft.
- Enough tugs of adequate power — verify number and power against the movement; the count depends on port regulations, the vessel's type/size/loading, its manoeuvring characteristics and limitations, engine capability, rudder/propeller/anchor condition, turning-basin restrictions, external forces and windage area, depth/UKC/squat, clearances from hazards, the berthing plan and the manoeuvring pattern.
- Current and tidal streams — find the correct strength and direction at the critical points; tidal streams on the charts are almost correct, and a tidal atlas or port tidal chart helps.
When local regulations set no guidance, the required tug power may be estimated from the vessel's deadweight for a wind speed of 10 m/s, taking 100 HP as equivalent to 1 tonne (it varies with the propulsion method).
Even so, the pilot decides on the spot how many tugs and where to place them, after a critical analysis of the berthing plan, the vessel's type and limitations, and the external forces.
6. Effect of Wind and Water Resistance on the Ship's Head
When navigating a channel without tug assistance under wind, the pilot must know whether he can hold a course with a maximum rudder angle of 30°. Considering the vessel's speed and the wind's direction and speed, he investigates whether manoeuvring is possible in the region where the course can be maintained.
With the relative wind on the starboard side, the vessel gets a leeway and drifts to port. The wind acts at a point $W$ ahead of the centre of gravity $G$, so a turning moment $M_w$ tends to turn the vessel to leeward. As she drifts, water resistance builds on the lee bow at a point $R$ that lies ahead of $W$, and its moment $M_r$ tends to turn her to windward. The vessel turns under whichever of the two moments is greater.
To check the resultant of $M_w$ and $M_r$, rudder is applied at an angle, and its counter-moment $M_v$ controls the vessel. Wind moment, water-resistance moment and rudder moment finally reach equilibrium: she stops turning while still drifting to leeward, holding a course at the leeway angle to the right ahead.
The position of $W$ shifts with the relative wind. As the wind draws from the bow towards the beam, $W$ moves closer to $G$; when the wind is abeam, $W$ is almost at $G$; and as the wind draws further aft, $W$ moves away from $G$ towards the stern, so that $M_w$ now acts in the same direction as $M_r$.
| Relative wind | Position of W | Effect of the wind moment Mw |
|---|---|---|
| Forward of the beam | Ahead of G | Turns the vessel to leeward, opposing Mr (resistance turns to windward). |
| Abeam | Almost at G | Wind moment minimised; drift dominates. |
| Abaft the beam | Aft of G, towards the stern | Acts in the same direction as Mr. |
While all three moments stay in equilibrium the vessel keeps her course. If equilibrium cannot be reached — because the water-resistance moment grows too large — the course can no longer be held.
7. Maintaining Course — the Velocity Ratio (VR) Limit
The governing quantity is the velocity ratio (VR) — the ratio of wind speed $V_w$ to vessel speed $V_v$ — plotted against the relative wind angle.
On the graph, VR is on the vertical axis and the relative wind angle on the horizontal. In the area below the curve the course can be held with a rudder angle of 30° or less; in the area above the curve it cannot. The critical value is 3.7: if the ratio of wind speed to vessel speed exceeds 3.7, a region appears in which the course cannot be maintained for certain relative wind angles.
At a vessel speed of 4 knots inside the harbour, a wind of 16 kts from a relative angle of 45° to 135° cannot be held even with 30° of rudder. In such a case the use of a tug is inevitable. The hull shape should also be considered together with the criteria established for the harbour in question.
8. Tolerable Set, Planned UKC and the Entry Calculation
8.1 Tolerable set in the channel
The tolerable set is the maximum effective set a vessel can carry and still transit the channel with bow and stern inside the white margin, the vessel positioned on the centre line and the bridge kept central for ease of observation while the bow sits off-centre within the margin.
8.2 Planned UKC (ICORELS)
The International Commission on the Reception of Large Ships (ICORELS) offers rule-of-thumb UKC values as a fraction of draft (UKC/d) for different areas.
| Area | Condition | UKC / d |
|---|---|---|
| Open sea | Strong, long stern or quarter swell, possibly high speed | ≈ 0.20 |
| Waiting areas | Exposed to strong, long swell | ≈ 0.15 |
| Channel | Exposed to strong, long swell | ≈ 0.15 |
| Channel | Less exposed to swell | ≈ 0.10 |
| Manoeuvring / berthing | Exposed to swell | ≈ 0.10–0.15 |
| Manoeuvring / berthing | Protected | ≈ 0.07 |
8.3 Calculation to decide whether to enter
A rough calculation of available channel depth against the vessel's draft at the planned speed tells the team whether sufficient UKC exists for a safe passage. It must account for the sinkage while underway (about 0.1–0.2% of the LOA), chart depth-datum errors (up to 0.3 m for depths to 20 m, and up to 1.0 m for depths of 20–100 m), the squat in shallow water (estimated as $2\,C_b V^2$), and the acceptable UKC to be maintained.
| Worked example — LOA 300 m, draft 17 m, Cb 0.7, max 10 kts | Value |
|---|---|
| Maximum draft = arrival draft + sinkage (0.2% LOA = 0.6 m) + squat (0.35 m) | 17.95 m |
| Chart safety factor (international chart datum) | 0.30 m |
| UKC at 15% of maximum draft (17.95 × 15%) | 2.69 m |
| Minimum required water depth = 17.95 + 0.30 + 2.69 | 20.94 m |
Alongside these figures the team also confirms that visibility is acceptable, that any other planned harbour movements are cleared with port control, that the marked physical reference points are clearly visible (finding an alternative set if not), and that all emergency handling resources are in good order and ready for immediate use.
9. Entering the Approach Channel — Planned vs Executed Alteration
Entering the channel is the very first leg of the pilotage passage, and making a safe entry is a critical step. Before the vessel actually enters, and if her position allows, it is strongly advised that she be aligned along the centre line a distance of 4L–5L ahead; once satisfactorily aligned, speed can be raised to the optimum for the channel.
If she is not properly aligned and must make sharp alterations with very limited sea-room (sea room less than 1L), there is a fair chance that, after completing the alteration, she will not reach the planned position. This comes from errors in estimating the dynamics of the external forces — current, wind and tide — and from the vessel's own behaviour: displacement, height of eye, location of accommodation, manoeuvrability and engine power.
10. Channel Entry Management Area (CEMA) and Alignment Margin
To avoid missed alterations and the resulting wrong positioning, the pilot uses the CEMA — an area near the channel entrance, at the planned entry point, where the error due to external force or the vessel's limitations can be determined and then corrected to make good the desired course.
At point C, when the vessel alters for the next planned course CB, an external force — current or leeway from the starboard side — pushes her course over ground more to port. She then makes good a track of CB' or CB'' according to the direction of the force, and as she reaches a point near B (B' or B'') she adjusts her further course towards point A. Thus, just before the entrance, the CEMA is where the pilot estimates the existing external force from current and wind, reads the weather, and plans a safe further course with sufficient margins.
If the existing set is higher than the maximum tolerable set for that channel and vessel, the pilot may abort the passage. The preferred way of entering the channel is therefore staged.
- Approach at a steep angle while still far from the channel.
- Reduce the steep angle to an acute one just 1–2 cables before the buoyed line.
- Enter the channel at an acute angle of 5–15° maximum.
- Once inside the channel limits, adjust course further to bring the vessel onto the centre line.
11. Reading the Buoys — Opening of Buoys and Skewed View
11.1 Opening of buoys
Executing the alterations depends on visual observation of reference points — land objects, transit lights, buoys, shore structures, natural features, breakwaters and lit masts. A common reference is the channel buoys, whose aspect changes every second as the vessel approaches. Watching that change closely lets her land at the exact location with minimum error. The gradual unfolding of the channel as the aspect of the red buoys changes is what is called the opening of buoys.
| Scenario | Distance from channel | Approach angle | Aspect of the buoy lines |
|---|---|---|---|
| 1 | Far away, d > 5 cables | Almost right angle (~90°) | Red & green lines ~ 90° |
| 2 | Closer, 2 < d < 5 cables | 30–40° | Red & green lines ~ 30° |
| 3 | Near, d < 2 cables | Acute angle | Red & green lines ~ 10–15° |
| 4 | Bow inside channel, bridge on the edge | 5–10° | Red line 0°, green line ~ 5° |
| 5 | On the centre line | — | Equal on both sides; looks like a highway, red buoys to port, green to starboard |
11.2 Skewed view of the buoys in strong winds
It is preferable to use fixed land objects for reference, to leave no room for error; only where no conspicuous land object exists are the floating buoys used. When buoys are the reference, the navigator must keep in mind the state of wind and surface current.
Floating buoys shift their position by a few metres — 20–30 m sideways — with the strength of the wind or surface current, because the mooring chains stretch over time and let the buoys free-flow to either side. As the weather displaces both hand-marks the same way, it virtually looks as if the channel has shifted 20–30 m to one side, and the aspects are no longer equal on both sides when the vessel is on the centre line.
A navigator who positions the vessel by the buoys alone may not land on the centre line: she comes closer to the channel edge and can meet bank cushion and a sudden change of heading — which becomes an extreme situation in very narrow channels. The aim of understanding this skewed view is to enter safely without being pushed to the extremities.