Dry Docking Procedure 2c513k

FYP - Introduction

http://www.angelfire.com/rnb/drydocking/intro.htm

undefined

Introduction to Dry Docks

In this section we will touch on briefly what we will be covering in our project: Introduction to Dry Docking Aim Scope Background Knowledge Types of Dry Docks Dry Dock Operations in Short Underwater work Owners Requirements and Docks Requirements

Introduction Dry docking is a process whereby a ship is brought into a dock which is then emptied of sea water so that work can be performed on the exterior part of the ship below the waterline. Ships are also constructed on dry docks. To launch the new or repaired ship from the dry dock, the ship is either floated in place or slid from its berth. To prepare the dry dock, keel blocks are set into position at the bottom of the dock. Dock-based winches positioned at the forward end of the dock are usually used to pull and position the ship in the dock. It is important to finish the work to the submerged part of the ship when it is in the dry dock as soon as possible, to make way for other ships that need to be dry docked. Ships are usually sent for dry docking once in 3 years.

Aim Our aim is to understand and implement the knowledge of dry-docking by explaining some of the various tasks in the operation itself. A website will be launched to provide information for DMR and COC students as a form of reference. We hope that in the future our project will be continued by other students.

Scope As Dry Docking is a huge topic to cover, we will only be going into a few topics of it. These are: Procedures, Propeller work, Rudder work, Hull work and Safety measures. For procedures, we will discuss the docking and undocking sequence as well as then preparation for the dock. For the propeller work we will go into how the propeller is removed and how it is seated back. For the rudder work we will talk about how the rudder is removed. In the hull part we will talk about corrosion and how it can affect a ship. Then we will talk about ways how the ship is sand blasted and painted again in order to reduce resistance. Finally in the safety portion we will talk about general safety practices in a shipyard.

Background

1 of 3

1/7/14 5:45 PM

FYP - Introduction

http://www.angelfire.com/rnb/drydocking/intro.htm

The dry dock is the repair or service yard for the ship. The whole ship is brought to dry land so that the submerged portions of the hull can be cleaned or inspected. This dry docking is done every 12 months to 24 months. There are some machinery and systems that cannot stop while the ship is in use, these are also serviced, repaired or replaced at the same time. Large ships are brought into a dock that consists of a large basin with a gate that can be closed watertight. After the ship is positioned over carefully arranged resting blocks (called keel-blocks), the water from the basin is pumped out. As the water level drops, the ship gradually rests on the blocks. Wooden wedges are then knocked in to take up any clearances between the hull of the ship and the resting blocks. For a routine dry-docking, the usual work to be done are: Hull cleaned of marine growth. Painting with anti-corrosive and anti-fouling paints. Sacrificial anodes renewed. Hull inspection and repairs. Shipside gratings cleaned and repaired. All overboard and sea suction valves overhauled. Cleaning and surveying of tanks. Rudder, locking devices clearances examined. Propeller damage, nut looseness, blade polishing done. Tail shaft bearing wear down checked. Tail shaft removed and inspected. Coupling bolts and holes deformation. Anchor chain examined, cleaned and re-marked. All underwater stuffing boxes repacked. For the ship's personnel, this is a busy time. Although shipyard workers will do most of the work, many of the repair and servicing work will be assigned to them. As with everybody working on the ship, this is a time to be extra careful on safety. Many people are working in the same place at the same time. In the engine room, rigging workers lift heavy materials using chain blocks, while other machinery workers dismantle foundation bolts for the engine below. Welders cut pipes while others removed floor plates so that they can crawl down to inspect the cofferdams. Cleaning is carried out on the boiler especially to the boiler tubes, and soot is removed. The engine room at this point is likely to be in a mess! For safety purposes, fire hoses connected to shore hydrants are laid on deck and pressurized. Precautions are taken to avoid tools or other materials from falling from the sides of the ship. Safety helmets must be worn by all personal at all times in all parts of the ship during dry docking. Cables or hoses are positioned such that they do not obstruct excess to ageways. Fire extinguishers are made available near welding sites and are usually color coded for easy identification. In the case of cold climates, water in engines or pipes has to be drained away to prevent freezing. Some of the normal utilities may not be functional at the time of dry docking. Often, the seamen will have to use the shore shower and toilet facilities. If for any reason cooling seawater is not supplied to the air-conditioning system on board by hoses, then there will not be air-conditioning. But this rarely occurs. Sometimes repair work has to be done on the seawater piping. The boilers have to be dismantled, so there is no heating in the living quarters. Sometimes shipping companies arrange special accommodation for their crew on shore during dry-docking. But again, this is very rare. Dry-docking is not the normal routine work for the seafarer. In fact, this is the only time when the generators are not running.

Underwater Work Underwater work is the most important work that is carried out when a ship is in a dry dock. It refers to the work that must be carried out on the ships hull which is normally submerged, or underwater. It is crucial that underwater work is carried out within the timeframe that the ship is in the dry dock for. Normal underwater works include: Sandblasting to remove all paint and rust. Inspection of the hull for repair requirements. There are a large number of through-the-hull openings to bring water into the ship and to remove liquids. All of these are covered with welded steel plates. These plates must be replaced. Most of the hull plating is riveted, not welded. After all these years, the rivets are susceptible to leaking. The

2 of 3

1/7/14 5:45 PM

FYP - Introduction

http://www.angelfire.com/rnb/drydocking/intro.htm

areas containing the riveted seams must be coated with a special compound which covers the rivets. Since the hull at the waterline (where the air and water interact) receives the most corrosion, it must have a half inch thick steel plate welded to the hull from four feet above to four feet below the waterline. Once all the repair and maintenance work has been accomplished, the hull will be coated with a multiple-part epoxy coating to minimize corrosion. This also reduces friction between the ship and the seawater.

Owner's requirements Basic requirements 1) Dock's plannings 2) Water supply 3) Air supply 4) Electric Power supply Other requirements depend on owner.

Dock's requirements 1) All engines must be stopped totally. 2) Electric Power must be switch off totally. 3) All valves must be closed totally. 4) Dry docking mark is needed if ship needs dry docking. 5) All machines' codes. 6) Clear job is needed if owner want to repair some machines himself.

Back to top All Rights Reserved ® Copyright © 2004 www.angelfire.com/rnb/drydocking/ E-mail

3 of 3

1/7/14 5:45 PM