Integral Tanks

Those tanks which form a structural part of the ships hull and are influenced in the same manner and by the same loads which stress the adjacent hull structure. These are used for the carriage of LPG at or near atmospheric conditions, butane for example, where no provision for thermal expansion and contraction of the tank is necessary.

Liquefied Natural Gas (LNG)

LNG is natural gas from which most of the impurities such as sulphur and carbon dioxide have been removed. It is cooled to or near its boiling point of –165°C at or near atmospheric pressure and is transported in this form as predominantly liquid methane. Methane has a critical temperature of –82.5°C, i.e. the pressure and temperature above which liquification cannot occur, so that methane can only be liquefied by pressure at very low temperatures.

Liquefied Gas Carriers

A large number of ships are in service which are designed to carry gasses in liquid form in bulk. Most of these ships are designed to carry liquefied petroleum gas (LPG), whilst a much smaller number of ships are designed to carry liquefied natural gas (LNG).

Fuel dribble (dripping) after injection

This occurs when the fuel supply is not precisely cutoff at the end of fuel injection and fuel particles are accumulated on the tip of the nozzle. If fuel dribble occurs after fuel injection, the fuel in the cylinder will not burn completely. This will result in the emission of black or white smoke being exhausted. To prevent fuel dribble, the relief valve of the delivery valve is designed to draw back any fuel that may drip out of the nozzle after injection. Fuel dribble occurs if there is any failure in the delivery valve or injection nozzle, as the residual pressure remains in the injection pipe after fuel injection.

Chemical Tankers

The structural configuration and arrangements of chemical tankers often are basically similar to those described for oil tankers. For some chemical tankers, however, arrangements may also include a double bottom in way of cargo tanks, a double skin construction or deck cofferdams or any combination of these. Certain more hazardous cargoes may also require tanks which are separate from the hull structure or are to be so installed that the tank structure is not subject to major hull stresses. In the latter cases the scantlings and arrangements may be similar to ships carrying liquefied gases.

Dry-Docking

    Dry Dock Periods

A docking survey should be carried out twice within a 5 year period. The intermediate survey must be completed within 3 years. One of the two docking surveys within the 5 year period should coincide with a special survey. A Docking Survey is considered to coincide with the Special Survey when held within the 15 months prior to the due date of the Special Survey

An in water survey may be accepted in lieu of the intermediate survey

For vessels operating in fresh water special consideration may be given.

In-water Surveys

An In-water Survey may be accepted in lieu of the intermediate docking between Special Surveys, an *IWS notation is assigned. This requires suitable underwater protection for the hull in part taking the form of high resistance paint. This survey is to provide information normally obtained from a docking survey.
The In-water Survey is to be carried out at agreed geographical locations under the surveillance of a Surveyor to LR, with the ship at a suitable draught in sheltered waters; the in-water visibility is to be good and the hull below the waterline is to be clean. The Surveyor is to be satisfied that the method of pictorial presentation is satisfactory. There is to be good two-way communication between the Surveyor and the appropriately qualified diver.

Should damage be found a dry dock may be required for better inspection

Dry Dock file

Preparation for dry dock begins after the ship sails from its previous one. A dry-dock list of new items is created with specification sheets describing individual jobs. These sheets are compiled into a dry dock file which some time before the due date of the docking is submitted to several dry docks for pricing.
The jobs are priced individually and as a whole. This allows the ship managers to streamline the jobs to provide maximum value for money.

Preparation

The vessel must be prepared before entering the dry dock. Structural loading must be taken into account as the vessel is to be point supported on blocks. A docking plan of the ships which shows such things as drain plugs, sea boxes, underwater attachments etc is sent to the dry dock. Added to this are indications where hull repairs are required. This allows the drydock ship managers to place the blocks on which the vessel will sit.
The vessel must be trimmed so as to be equal draught with zero list. Special attention should be made when planning this for any tanks whose contents may be varied due to repair or housekeeping requirements.

In dock

The safety and fire fighting responsibilities of the vessel are handed over to the dry dock safety department for the duration of the dry and wet dock period. All hot work, tank entry or jobs requiring special safety measures carried out by ships crew must be first agreed with the dry dock safety department. A daily meeting is held to discuss forth coming jobs and any special requirements. This also allows the vessels staff and company representatives to monitor the progress of the dock.

Inspections & Measurements

·         Where a ship is in dry-dock or on a slipway it is to be placed on blocks of sufficient height, and proper staging is to be erected as may be necessary, for the examination of the shell including bottom and bow plating, keel, stern, sternframe and rudder. The rudder is to be lifted for examination of the pintles if considered necessary by the Surveyor.

·         Attention is to be given to parts of the structure particularly liable to excessive corrosion or to deterioration from causes, such as chafing and lying on the ground, and to any undue unfairness of the plating of the bottom.

·         The clearances in the rudder bearings are to be measured.

·         The sea connections and overboard discharge valves and their attachments to the hull are to be examined.

·         The propeller, sternbush and sea connection fastenings and the gratings at the sea inlets are to be examined.

·         The clearance in the sternbush or the efficiency of the oil glands is to be ascertained.

·         When chain cables are ranged, the anchors and cables are to be examined by the Surveyor