1. Overview — Berthing and Moorings
Source: NAYAK, Capt. Santosha K. Theory and Practices of Marine Pilotage. Chapter 16 — Berthing & Moorings.
Syllabus: Anexo 2-B, Área II (Arte Naval), item 8 (NAYAK), Cap. 16 — atracação e amarração. Cross-list Área III, item 6.
Berthing the ship is a very precise exercise. Tugs are used judiciously so as not to deviate from the required position, pushing the vessel laterally onto the fenders parallel yet smoothly, so that the full load of the vessel is spread equally on all fenders. A good berthing needs team work between ship staff, tug staff, pilot and jetty staff — a coordinated exercise led by the pilot.
1.1 Safe berth
Safe berth is a broad term that includes the jetty, wharf, SBM, cargo-handling anchorage etc., where a vessel is positioned to carry out a specific purpose — cargo handling, repairs, bunkering and the like. Its objective is to give the vessel good shelter while facilitating the specific cargo, bunker or transhipment operation.
For making the vessel fast when alongside, mooring bitts of sufficient strength are provided on the jetty at certain intervals. Their spacing has no standard criteria; it depends on the type and size of vessel, the type of mooring followed and the strength of the bitts. The spacing may be 20–30 m when vessels berth on their sides. For a Mediterranean or Baltic moor it may be less — down to 7–10 m. The strength required depends on the size of vessel handled and on the type of bitt, which may be curved or straight.
1.2 Strength of mooring bitts
It is also necessary to verify that the bitts on the pier can withstand the mooring of the vessel. The strengths in accordance with the technical criteria for harbour-facility design standards are as follows.
| Vessel's GT | Curved bitt (tons) | Straight bitt (tons) |
|---|---|---|
| 500–1000 | 15 | 25 |
| 1000–2000 | 25 | 35 |
| 2000–3000 | 25 | 50 |
| 5000–10000 | 35 | 70 |
| 10000–15000 | 50 | 100 |
| 15000–20000 | 50 | 100 |
| 20000–50000 | 70 | 150 |
| 50000–100000 | 100 | 200 |
2. Mooring Lines and Ropes Used
Mooring lines are the ropes used to make the ship fast alongside the berth safely, so as to facilitate her cargo or other operations. When the vessel is at the berth, these lines prevent the ship's three-dimensional motions — lateral, longitudinal and transverse. Each line at a particular position has a specific job to do.
2.1 Head and stern lines
Head lines are made fast from the focs'le, mainly to prevent the bow from swinging away from the berth. They are passed at an angle of 45–60 degrees from the focs'le to the bollards on the jetty. Their tension has two components — one longitudinal and one transverse. The transverse component prevents the bow swinging out of the jetty; the longitudinal component prevents the vessel falling astern. The stern lines do the same job at the stern that the head lines do at the bow.
2.2 Spring lines
Spring lines are passed along the ship's side in a reverse direction — forward springs run aft and aft springs run forward — and are kept relatively longer. They act as a spring and pull the vessel back to her original position when she moves longitudinally. The forward spring prevents the aft motion of the vessel and the aft spring prevents her forward motion.
2.3 Breast lines
Breast lines have the sole intention of preventing the vessel coming off the berth laterally. Normally the transverse component of the head and stern lines does this job for smaller vessels; but for large vessels, or where an offshore wind blows continuously, the head and stern lines are supplemented with breast lines to prevent lateral motion at the berth.
| Line | Runs / led | Motion it restrains |
|---|---|---|
| Head / stern line | From focs'le / poop at 45–60° to the jetty bollards | Bow (or stern) swinging away from the berth; longitudinal component also checks fore-and-aft movement |
| Forward spring | Along the ship's side, running aft (relatively long) | Aft motion of the vessel |
| Aft spring | Along the ship's side, running forward (relatively long) | Forward motion of the vessel |
| Breast line | Roughly perpendicular from ship to berth | Lateral motion — vessel coming off the berth sideways |
2.4 Types of ropes used
The size and type of rope depend on the size and type of vessel, and also on the type of harbour. If the harbour is well guarded by breakwaters and the water is relatively calm and free from predominant currents and bad weather, normal ship's ropes suffice. But where the vessel is open to sea with a prevalent swell and unfavourable weather, the ropes are doubled up, or some ports provide their own additional ropes for safety. The port authorities' decision here is well defined and well researched, and many ports issue mooring guidelines to vessels.
| Rope | Where used / how handled |
|---|---|
| Wire ropes | Provided by some ports for berthing; normally handled by the shore mooring crew, using chain stoppers. The ship's crew only assist. |
| Synthetic (fibre) ropes | Largely provided and used in most ports — polypropylene ropes with an eye splice on both ends; of sufficient SWL and with good safety characteristics. |
| Natural fibre ropes | Least used for mooring, except in small ports handling small vessels. |
3. Mooring Procedure at the Berth
A good mooring operation is carried out with good coordination between the ship's crew and the jetty staff, led by the pilot. The mooring plan is discussed during the master–pilot information exchange and passed by the master to the officers and crew well before the vessel approaches the berth; the crew then make the ropes ready and stand by.
The sequence in which the ropes are passed depends largely on the weather, prevailing current and wind at the berth, and on the type of berthing plan devised by the pilot given the available resources. The first line is usually the one that prevents the unwanted movement the pilot wants to control. Making fast the first line is critical: once it is passed, the vessel comes largely under control, aided by the engine if required.
Once the first line is ashore (FLA), the vessel is brought alongside by lateral motion using the engines or the tugs. When she is completely alongside, the other lines are passed and made fast; during the process, if tugs are available, they keep pushing the vessel alongside to remove any unwanted motion and facilitate a safe berthing.
4. Special Situations Affecting Moorings
Moorings must be rearranged and managed differently when the situation is not normal. In inclement weather at the berth the mooring lines come under severe stress while holding the vessel, and the normal arrangement may not hold her safely. The ship's officers must arrange reinforcements to prevent the lines parting under severe stress.
4.1 Doubling up of lines
When the vessel comes under excessive stress from wind, rain, river currents or a passing cyclone while at the berth, the master decides to double up the lines. Depending on the direction of the disturbance, the affected lines are given priority and reinforced by passing additional lines in the same locations.
4.2 Moorings while surging in heavy weather
While the vessel surges continuously at the berth there is a risk of the lines parting. The vessel resorts to doubling up; but sometimes the forces are so tremendous that even doubled lines do not help and part. The vessel may then be set free to move arbitrarily and run the risk of grounding. In such an emergency she reports to port control and asks for tugs. Many ports keep duty pilots on emergency duty for exactly this scene, coming to the rescue with tugs and bringing the vessel to safety.
4.3 Strong current across the berth
Sometimes the current alongside the berth is very high and it is difficult to hold position. The current may rise momentarily — for a few minutes or hours — from heavy rain upriver or high tidal ranges, or it may stay steadily for a long time. If a rise is expected for a short while, the crew stand by, additional lines are kept ready to double or triple up where the lines are most affected, and the mooring winches are kept running to tighten lines as they slacken.
4.4 Ships passing close by
When loaded, heavy ships of large displacement pass near the berthed vessel they create interaction between the vessels, causing the berthed vessel to surge on her position. This surging brings the lines under severe stress and often breaks them.
As a passing vessel approaches, the lines that come across her moving bow slacken; as she passes on, they tighten when her stern passes. This sequential slackening and tightening sets the berthed vessel surging, and the resulting motion creates further stress until the lines finally break. If this happens during cargo operations it affects them badly, and a gangway resting on the jetty may deform or break when the vessel surges. The berthed vessel usually has no prior information of a passing ship, so it is the duty of the port to inform her, so the crew are ready.
4.5 Use of anchors off the berth
When the vessel faces excessive and continuous surging and no external assistance is available, the master may decide to let go an anchor while still at the berth, to prevent unwanted movement and keep the vessel safe.
4.6 Moorings on double-banked vessels
Double banking is a special operation discussed in the chapter "Approaches to Berth". Its moorings are in principle the same as others, but the head and stern lines may be passed to the jetty while the spring lines are passed to the mother vessel. If the mother vessel is not at a berth but at anchor, then all the lines are passed to the mother vessel only.
5. Mooring to Buoys and Single Point Mooring (SPM/SBM)
Many ports have no well-developed jetties, and some busy, well-developed ports have all their jetties occupied. In such cases ships are berthed by mooring to buoys: the vessel is manoeuvred and brought near the buoys to be made fast to them.
Mooring boats take the lines onto the buoys and make them fast. The lines used are usually very long, of the order of 100 metres, so the vessel must be equipped with sufficiently long lines for a successful buoy mooring.
5.1 Single Point Mooring / Single Buoy Mooring
Single Point Mooring (SBM) is an arrangement whereby VLCC tankers moor to a single buoy for loading or discharging to or from storage where no dedicated facility exists; the cargo is transferred through subsea manifold structures. The buoy is anchored to the seabed with multiple anchors spread evenly so as to keep it stable in all sea and swell conditions. The buoy is held in position in two ways — CALM (Catenary Anchor Leg Mooring) and SALM (Single Anchor Leg Mooring).
An SBM has five main parts: the buoy body; the anchors and cables running down to the seabed; the fittings for mooring; the product-transfer system that carries the product from the buoy to the subsea manifold; and the fenders that prevent damage should the vessel hit the buoy. The mooring fittings are arranged so that the buoy moves freely within defined limits.
After mooring, the hose-connection procedure follows: the hose-connection gear and crew board while approaching the SPM, and the vessel's crane lifts the hose and gear for connection. The pilot boards from a tug at the pilot station, usually a few miles from the SBM, and two tugs guide the vessel in. After mooring is complete one tug is released while the other remains standby near the vessel for pull-back when required, the pilot staying on board to help maintain position with the one tug.
6. Mooring with Anchors — Open, Running and Standing Moor
6.1 Open moor
In the open moor the vessel is anchored with both anchors leading ahead at one point on the bow. She approaches the anchor position with the wind or current on the bow. The upstream anchor is let go and slowly paid out; once one-third of the final cable length is paid out, the other anchor is let go. Both anchors are then slowly paid out to a final equal length of cable.
6.2 Running moor and standing moor
In the running moor and standing moor, two anchors are used so that one runs ahead of the vessel and the other astern. This is used where the vessel must hold a particular position and is expected to move longitudinally from time to time, with very little sea-room on either side — as in a canal, or a river with tidal streams, or a channel. One anchor is let go with 5 cables and the other with 4 cables. The method may be carried out as a standing moor or a running moor — the two names only signify how the moor is executed.
7. Special Moorings — Mediterranean and Baltic Moor
7.1 Mediterranean moor
The Mediterranean moor is adopted in ports where there is not sufficient space to berth alongside. The stern or bow of the vessel is made fast perpendicularly to the jetty or land using two sets of mooring lines, while the other end is held in position by two anchors in the open-moor position. It may be carried out in two ways — "Bow to" or "Stern to": if the bow is made fast to the jetty it is "Bow to", and vice versa.
7.2 Baltic moor
When berthing alongside, a strong onshore weather may drive the ship towards the jetty so fast that the impact would be intolerable for the ship, the fenders or the port infrastructure. If no tugs are available to assist, the Baltic moor is used to control the lateral speed of approach.
A stern rope is shackled to the weather (windward) anchor at a place called the ganger length, while the anchor is kept in the a'cockbill position. The anchor is let go at a sufficient distance from the berth; the anchor is then paid out slowly and the stern rope slacked so as to adjust the two lengths proportionately. This lets both the bow and the stern approach the berth laterally at a slower speed.
