Thursday, May 15, 2008

Shipboard - Making your Approach to the Pier

A good docking begins long before the ship comes alongside the pier. The approach is at least one third of the docking. If the speed is reduced, the ship properly lined up with the pier or wharf, and then steadied up so that all lateral motion is eliminated, she practically docks herself.
When berthing starboard side to the pier, assuming that the ship has a right hand turning propeller, the ship approaches at only a small angle to the dock. When the engine is put astern to take the last headway off the ship the stern moves to port, so if the ship is already at a significant angle to the berth it will be that much more difficult to get the ship flat alongside. It is natural for a ship to behave in this manner at any time when backed, and this behavior is amplified by the quickwater trapped between the hull and berth moving up the ship's side. For this reason a deeply loaded ship will normally require a tug aft to hold the stern up to the pier when docking starboard side to.

The same ship approaching to dock port side to must maintain a greater angle to the berth, approximately 10 to 15 degrees to the dock in most cases, with the bow heading for the area of the pier that will be amidships when the ship is finally in position alongside. After the engine is put astern to stop the ship, the stern will move to port and reduce the angle of approach so that the ship comes flat alongside. By using left rudder and a kick ahead with the engine to check that swing to port as the ship comes alongside, the ship can be stopped in position without needing a tug aft.
There will be some modifications to the basic angle of approach for a starboard or port side to docking, depending on:

1. Wind strength and relative direction.
2. Set and drift of the current.
3. Ship's draft and freeboard.
4. Ship's power and steering characteristics.
5. Whether the pier has an open or solid face.
6. Physical configuration of the berth.
7. Availability of adequate tug assistance.
8. Presence of other vessels in the berth or slip.

These factors all affect the docking of ship, keep in mind that it is impractical to cover each step of a particular docking. By understanding the basics of shiphandling and approaching the pier in a proper manner, the mariner can use good seamanship to adjust to a given situation.
Ships generally approach either a pier constructed at an angle to the channel or a wharf that parallels the channel. The ship may dock either bow or stern in at the pier or heading upstream or downstream at the wharf.

Berthing starboard or port side to a wharf while stemming the current is a straight forward job which should be approached as mentioned above, with some adjustment for the prevailing wind and current. There is usually some set off the pier as the ship comes alongside, in a direction contrary to the current in the stream which is running nearly parallel to the ship's heading. This set off the pier is caused by a com­bination of the eddy current that forms along the shore or shoal area, which exists in almost all cases under the wharf, and the hydraulic cushion that is created between the hull and the shallow area under the wharf. This cushion is quite significant when the face of the wharf is solid, or nearly so, as is often the case when a wharf is constructed using a bulkhead to contain the bank behind the stringpiece. This set off the wharf should be planned for so the ship can be brought alongside and held there until made fast. Tools available to the shiphandler to accomplish this include tugs, steaming against an anchor, or good breast lines. Do not expect to simply bring the ship alongside and have her lie there without some assistance until the lines are run ashore.

Docking at a wharf with the current running from astern requires greater planning and skill. The ship comes up to the berth with the intent of backing into position since she will be making sternway through the water when stopped in position relative to the pier. If the shiphandler thinks of the job in this way, that the ship is coming stern first into the current to the berth, the maneuver becomes much more straight forward.
Come abeam of the assigned berth with two tugs made fast and take all headway off the ship. Continue backing the engine while keeping the stern angled slightly toward the wharf and, as the ship gains stern­way through the water (while stopped or nearly stopped relative to the bottom), the current on the ship's offshore side moves her laterally toward the wharf. Use only enough speed to hold the ship in position and use the tugs as required to control the ship as she is set alongside by the current.

Once alongside, the tugs hold the ship against the eddy current that exists at the wharf. The mate on the stern must keep the propeller clear while running stern lines since the engine is used continuously to hold the ship in position against the current. The tugs can also help to hold the ship in position by keeping an angle into the current rather than being at right angles to the ship's hull. Their thrust holds the ship alongside and up to the current.

Berthing with the current from astern is not a problem so long as it is kept in mind that the ship is effectively backing stern first into posi­tion. By adjusting the angle that the ship makes to the current-stern toward the dock to move in that direction, stern parallel to the dock to check the lateral motion toward the pier or move away from it the ship can be efficiently and safely berthed. Any problems when docking with the current from astern usually result from trying to push the ship alongside with the tugs, rather than letting the current set the ship onto the berth. The vessel gets away from the shiphandler because the current takes charge. Use the tugs only to assist to keep the needed angle as the ship is set alongside.