1. Planning the Undocking
Chapter 6 covers the undocking — taking the ship off the berth and turning her to sea. The maneuver deserves the same care as the docking, yet the less experienced shiphandler too often treats it as simple and fails to plan the evolution properly. Brief the undocking pilot exactly as the docking pilot was briefed: exchange the same information and the same data card, and be sure to report the status of the anchor — especially if one is backed out of the hawsepipe or was left on the bottom after docking. It is surprising how often the docking pilot discovers, only after the last line is gone, that there are two shots of chain in the water.
As before docking, go out on the wing and use your own senses: feel the wind, read its direction from the stack gases, and look over the side to check the current. No array of instruments replaces getting a feel for the existing conditions before planning this or any maneuver.
1.1 Why Undocking Is Harder Than It Looks
Undocking is frequently done stern first, so the ship steers poorly, if at all. Starting from alongside, the shiphandler has fewer options for using wind and current than during a docking — where the stern reaches clear water and the angle of approach can be adjusted to exploit those forces. Even careful plans may have to change once the lines are gone, because it is hard to predict which of several conflicting forces will dominate. Often the ship is let go expecting wind to set her off, only to stay hard alongside due to a subsurface current.
2. Draft and Trim in Ballast
The ship is now assumed to be in ballast and light. Ideally she is ballasted to at least a moderate draft to submerge the propeller, rudder, and bow thruster and to reduce windage. Give her a few feet of drag — trim by the stern. The exact amount depends on the ship, but it is better to have a bit too much drag than too little; if stress or loading limits ballasting, at least get the stern well down. Three reasons favor good drag.
| # | Why trim the ship by the stern (good drag) |
|---|---|
| 1 | The ship has excellent directional stability with good drag. |
| 2 | Propeller and rudder are most effective: a deeper draft aft means she steers better, stops in less distance, twists less when the engine goes astern, and needs less rudder to counter the propeller torque going astern. |
| 3 | The bow should also be at a moderate draft to reduce windage and submerge the bow thruster so it is effective. |
If forced to choose between getting the bow down and a proper draft aft, choose the draft aft. Holding a light bow into the wind until headway develops is a challenge, but it can be managed with a tug or the anchor — and in most situations the advantages of having the stern down outweigh that disadvantage.
3. Singling Up
After years of undocking, pilots and seafarers grow complacent about singling up. It becomes a habit — "two and one forward and a stern line aft, Mate" — and the docking master heads for the coffee maker. Yet singling up is only usually routine: on the quiet night when the wind or current is underestimated, the ship that took several lines to hold is left hanging on a few parts stretched fiddlestring tight. Walk out on the wing, feel and see the conditions, and really think about how many and which lines to take in.
Take the lines in systematically, holding the ship in position without overloading the parts that remain. Which to leave until last depends on the conditions, so no rule of thumb suffices — but it is generally best to leave short lines until last: a short headline and spring forward, a short stern line and breast line aft. Short lines hold the ship alongside more effectively, still keep her from moving fore-and-aft, and come aboard quickly — especially important aft, since the propeller must be cleared as soon as possible so the engine can be used.
As ships grow larger, winches are geared down for higher loads and run slower, so the crew must be told if the last lines must come aboard particularly fast. The mate can leave the shortest line until last and lead it to the winch before letting go, clearing the propeller quickly. Tug assistance also holds the ship alongside and reduces the strain on the remaining lines while singling up.
4. Using Quickwater When Undocking
The ship's quickwater is an effective tool when undocking, since the ship moves astern through it as she backs from a wharf or pier. Leaving a starboard side berth, the quickwater forces the stern away from the dock, then moves the ship laterally, and — when a good flow strikes the hull forward of the pivot point — checks up the swing of the bow toward the pier. The more restricted the flow along the inboard side (by shoaling under the berth or a solid pier face), the greater its effect.
Quickwater has less effect leaving a port side berth: it is inherently weaker on the port side and acts in more open water because of the ship's angle to the pier as she starts to back. There it has minimal effect, though it does reduce that angle to the berth as it strikes the forepart of the hull.
With planning, quickwater moves a ship neatly with the minimum of bells and rudder. For example: back until the stern lifts off the pier, stop the engine, and let the ship drift astern while the quickwater moves forward to strike the hull ahead of the pivot point. The swing of the bow toward the pier is checked, and the ship backs straight out, clearing the berth in a seamanlike manner.
5. Undocking from a Wharf
Take advantage of any current from ahead when undocking from a wharf. Deliberately get the current inside the ship — the very situation you avoided while berthed: the current moves the bow off the wharf as you use engine and rudder to lift the stern, without developing any head or sternway over the ground. The ship moves laterally off the berth.
A certain feel is needed to set engine revolutions so the ship makes no headway but sets away from the berth in the current. Use enough revolutions to keep her abeam a selected point on the wharf while walking her laterally off. Where wind and space demand a tug, the tug is backed as required to maintain the ship's angle to the wharf while the current takes her off the berth.
5.1 When the Current Is Overcome by Wind or Tight Berths
More lateral force and control are needed when ships lie close ahead and astern, or a wind on the wharf overcomes the current. Either use a second tug, or back the bow tug while the ship's engine turns ahead with more power and hard-over rudder. Here tug and engine work against each other to prevent headreaching while moving the ship off laterally; the ship keeps an angle to the wharf so the current can assist tug and engine.
5.2 Current from Astern, and Matching the Current
With the current from astern, undock much as the ship was docked in that condition: work the bow toward the wharf with tug, engine, and mooring lines, then back into the stream. The key in all these cases is to hold a speed through the water that matches the drift of the current, so the ship moves laterally over the ground without ranging fore-and-aft.
| Plant | Matching the current's drift |
|---|---|
| Steam turbine | Easily holds the required speed; communicate by telephone for specific revolutions rather than standard maneuvering bells. |
| Motor ship (fixed pitch) | Harder — a high-speed diesel's dead slow often exceeds the speed needed, so the engine is stopped intermittently to make good the speed. |
| Variable-pitch motor ship | Has the advantage: pitch is reduced to exactly match the drift of the current. |
To take a ship off a clear wharf at slack water, put her bow at a small angle to the berth and steam ahead, using the rudder with care to lift the stern while maintaining that angle. If the wharf is not clear ahead, work her off using the engine in opposition to a tug, or push the bow in toward the pier and back off as for a port-side undocking from a pier.
6. Backing from a Slip
This common situation has as many variations as there are piers, but all share basic similarities, and the shiphandler adjusts methods to the local conditions. Note that these maneuvers assume a conventional right-hand turning propeller.
6.1 Berthed Starboard Side To
A ship berthed starboard side to needs no angle when backing, since the propeller torque and the quickwater move her stern to port, clear of the dock. The bow thruster or a tug may be needed to check the resulting starboard swing of the bow so it clears the stringpiece, or the engine is brought ahead intermittently with hard-over rudder to steady her. To back to starboard after clearing the slip, go astern until the pivot point is well clear of the pier, then come ahead with hard-port rudder to walk the stern to starboard as the bow swings clear.
6.2 Berthed Port Side To
Before backing from a port side docking, work the bow in and get the ship at a good angle, stern well off the pier. The propeller torque going astern walks the stern to port, so the ship comes back parallel to the berth as sternway develops, then comes easily out and is turned once the pivot point clears the pier. Four methods set up that angle.
| # | Getting the ship at a good angle before backing (port side to) |
|---|---|
| 1 | Pushing with the bow tug. |
| 2 | Heaving on the headline while holding the forward spring. |
| 3 | Backing a stern tug, if used. |
| 4 | Coming ahead dead slow against the spring line with rudder hard over toward the dock. |
Working against mooring lines is becoming less practical as ships grow in size and power: diesel ships with a dead slow of 6 to 8 knots are especially hard to undock by working against their own lines. Whether backing from a port or starboard berth, the bow tug either backs along on a stern line or falls around and follows on a single line; with room between hull and berth, a tug line led stem to stem can work either side to lift the bow and steer the ship as she backs.
6.3 Wind Off and Wind On the Pier
A wind off the pier is not as simple as it seems. Dead in the water, the wind moves the ship bodily off the pier, but a large stack or end house makes the bow or stern come away faster. As sternway develops she often backs into the wind, so the stern usually moves toward the berth — overcoming the torque in a starboard-side undocking, or accentuating the twist in a port-side one. With a wind on the pier holding her alongside, three common options exist.
| # | Undocking with a wind blowing on the pier |
|---|---|
| 1 | Slide along the stringpiece until the stern clears the outboard corner, then turn fair in the channel — the safest tugless maneuver, since the ship stays alongside and cannot be blown against the pier. She may lose paint, but "paint comes in buckets while steel comes in shipyards." |
| 2 | Put the ship at a good angle by working against the spring line, then back clear — though the bow may be blown back down onto the pier and damaged. |
| 3 | Breasting the ship off with one or two tugs. |
Once sternway develops, the ship's behavior depends mainly on her superstructure and freeboard: she may set back on the pier bodily, or only the bow may set down as she backs into the wind. Be prepared for either, unless she is being slid along the stringpiece. When the shed doors are closed, an eddy often forms as the wind reflects off the doors and sets the ship off the dock rather than on it — which simplifies the undocking, since she lies off the stringpiece. In every case the mariner uses the wind rather than reacting to it; one who waits for the effects and then responds soon feels like a cat chasing its tail.
7. Coming Ahead from a Slip
This straightforward maneuver can usually be done with minimum assistance. In a clear slip a ship can often depart without a tug unless a strong wind or current holds her on the berth — and even then she can sail tugless if there is good room off the end of the pier.
With the wind off the dock, she simply steams clear until the stern has room to swing and turns fair in the channel; a tug may be needed only if the channel is too narrow to turn unassisted. The anchor or a spring line can also work her around the end of the pier.
A wind on the berth troubles a ship docked stern in. Usually a tug lifts the bow while rudder and engine move the stern off the stringpiece, but she may depart tugless even in a moderate wind if planned well: let go all lines and steam slowly up the stringpiece, rudder about 10 degrees toward the pier to hold her lightly alongside. As the pivot point clears the end of the pier, increase revolutions and rudder angle, turning across the end and lifting the stern clear. She must have enough speed to overcome leeway when she clears the stringpiece — 2 to 3 knots usually suffices.
8. Coming Off Parallel to a Berth
Often a ship must leave a berth while staying parallel to the stringpiece — in a narrow slip, docked starboard side to with a ship astern, or at a wharf with ships close ahead and astern. Three methods accomplish this.
| # | Coming off parallel to the berth |
|---|---|
| 1 | Use a second tug made fast aft to lift and control the stern during the undocking. |
| 2 | Lash up the bow tug facing aft and use it against the ship's engines. |
| 3 | Make the bow tug fast normally and back it to lift the bow while the engine comes ahead with rudder hard over toward the dock to lift the stern. Enough revolutions must counter the tug's power, so the ship holds her position over the bottom but moves laterally off the stringpiece. |
These techniques can be used alone or combined with other methods to turn a ship in a limited space, or to do with one tug work that would normally need two — augmenting the more common backing and pushing work with tugs.
9. Backing a Ship Toward a Hazard
Given a choice, a shiphandler never presents the stern to danger — never backs toward a shoal or another ship if there is any option, preferring to back into clear water even if that means turning the long way around to go to sea. A ship can go bow first into a bank or shallows without damage, but put her rudder into the bank and she will probably spend time in a shipyard.
10. Left-Hand and Variable-Pitch Propellers
All the maneuvers herein assume a ship with a right-hand (clockwise) turning propeller. The rare ship with a left-hand turning fixed propeller is handled in the opposite manner — a starboard-side undocking (or docking) is done as described for a port-side undocking (or docking).
Variable-pitch ships often have right-hand turning propellers, but these turn the same direction going ahead or astern — only the pitch reverses to back down. So the propeller turns clockwise when going astern, just like a conventional left-hand fixed propeller, and such ships are handled like left-hand-propeller vessels when docking and undocking.
11. Turning to Sea
Turning in relatively open water is straightforward as long as the shiphandler minimizes the ship's speed. It is possible to turn a ship and control her position in a channel or turning basin while she still has sternway, steering with the engine ahead and shifting the rudder to direct the propeller's flow like a thruster. The flow acting on the stern is the result of its astern and athwartship vectors.
| Goal while moving astern | Rudder and engine |
|---|---|
| Reduce or kill sternway | Rudder amidships, engine ahead — direct the flow straight aft. |
| Keep moving astern while turning | Rudder to the side opposite the way you want the stern to move (to move the stern to starboard, rudder to port, engine ahead). |
| Change the turning/stopping force | Increase or decrease the engine revolutions. |
Treat these changes as one maneuver, like adjusting a bow thruster, not several separate ones. A shiphandler who carries sternway too long often adds revolutions but leaves the rudder hard over; instead the rudder should go amidships to direct the increased flow straight astern, and only after the speed drops is it shifted to renew the swing. And face the direction of movement — going astern, face aft, where the action is; mariners habituated to looking ahead at sea tend to handle ships in confined water while watching only the bow.
11.1 Turning in a Basin
If the ship is to be turned in a basin, seven points apply.
| # | Turning the ship in a basin |
|---|---|
| 1 | Turn in the direction that keeps the stern in the best water. |
| 2 | Take nearly all sternway off before starting to swing. |
| 3 | All else equal, turn to the right for the ship's better backing-and-filling characteristics. |
| 4 | Position the pivot point so the stern swings clear. |
| 5 | Fix the basin's diameter in your mind before starting. |
| 6 | When possible, put the end to be swung in the area of maximum favorable current. |
| 7 | Start with the ship at the end of the basin from which the current is flowing. |
11.2 Estimating the Deep Water
Discuss the basin's depth and profile with the pilot. Lacking better information, estimate shoaling from the basin's proximity to turns in the channel. At a basin in the bend (location "A"), the deepest water is usually in the bend away from the point, so swing the stern that way. Above or below the turn (location "B"), the deepest water lies on the side nearest the path of the ebb tide as it flows from one bend to the next. Midway between turns the deepest water is generally midchannel, so the ship can turn in the most convenient direction. In all cases, do not present the stern to potential dangers.
11.3 Banks, Anchors, and Visual Ranges
The stem can be put in the mud and the ship pivoted on the bow if the current strikes the quarter favorably; the anchor can be used the same way, alone or with the bank, to swing the ship.
Watch natural ranges ashore, ahead and astern, to tell whether the ship is being set along the channel axis, and abeam to check she develops no unwanted headway or sternway over the bottom. Do not hurry to come ahead after the midpoint of the turn — wait until the turn is nearly complete. While swinging, the banks appear closer than they are, so fix the basin's dimensions in your mind beforehand and remind yourself of the clearance you know is available, avoiding the apprehension that causes unnecessary maneuvering. It may impress onlookers to watch a ship stopped and swung at once, but unless she is nearly stopped before turning, there is little margin for error: reduce sternway, then turn her.
12. Dismissing the Tugs
Dismiss the stern tug as soon as her work is done — do not carry her along after clearing the slip, since she is only a hindrance. Keep the forward tug as long as it might possibly help: even with a bow thruster, a tug used coming in should be held until the ship is headed fair and clear of all obstructions and traffic. You have paid for her services, so make her earn her money — the bow thruster may quit or refuse to stop when used, or a problem may need more power than it can develop as the ship's speed rises.
Listen for the tug's signal — often a long blast followed by two short blasts — so she can be let go promptly as the ship comes ahead. Keep at least two crew members and a mate standing by a tug at all times, even if she is held for some period after clearing the berth.