Dry Docking and Shipboard Maintenance

A Guide for Industry

David House

• Publisher: Routledge
• Year: 2015
• ISBN:
  9781317438427
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Marine Transportation
• Index: Technology & Engineering

This book covers every aspect of the dry docking of sea going vessels. It provides a guide to industry for the different dock types and docking procedures inclusive of material management, steelwork operations and dry dock legislation. Many thousands of people worldwide are engaged within the perimeter of the docking and shipboard maintenance industries to ensure that our ships remain in Class and are kept seaworthy.

Docking a vessel successfully involves many skills and trades, requiring a teamwork operation between ships crews and the shoreside docking personnel. This book describes dock types alongside the various methods of docking, stability concerns, repair activities, steelwork management, legislation and survey detail, as well as shipyard safety requirements.

• Includes a new chapter on steelwork and material management of the shipyard complex.

• Contains over a hundred photographs and illustrations, including a full colour plate section.

• Full coverage of dry dock operations, handling facilities, main ship building slips and shipyard repair activities.

1

Dry Dock Types

Introduction

During a ship’s life there will be times when essential maintenance is required which cannot be handled by employment of the crew during its normal trading pattern. These areas are often concerned with the submerged volume area of the vessel and must, as a matter of safety and routine, be addressed at some stage inside the perimeter of a dry dock.

The very size of the ship, as say with a ULCC, will restrict the availability of many docks around the world and their capability to accept the ship, while at the same time large docks present economic waste in docking a small-capacity vessel. It is therefore essential that docks of various sizes and capacities are readily available to accommodate a variety of shipping tonnage worldwide.

The ‘Graving Docks’ have long been the backbone of the docking of ships, but they are purpose-built and permanent structures and ships have to go to them. The development of ‘Floating Docks’ gave flexibility to the industry, whereby docks could be towed to the ship – a particular advantage when a ship is damaged.

The number of docking facilities have continued to grow to cater for both the large and small vessel, but at the same time innovation has advanced docking methods, with the ‘Synchro-Lift’ providing the ability of one dock to engage several ships at any one time. This development no longer keeps the dock occupied with one vessel, as with a graving dock, but employs a ship docking/park serviced by a single lifting operation.

Many smaller vessels can achieve full dry dock services by use of ‘slips’, although by sheer size these are limited to the lower tonnage market, like the smaller ferries and the leisure market yachts. From a commercial vessel point of view, dry docking is an acceptable way of ensuring that the condition of ships is retained to a high standard. It also provides an ideal opportunity to complete survey work reasonably quickly with the associated equipment and overall facilities that are all part of an operational dry dock.

The Graving Dock

A permanent dock built in stone or concrete.* It is accessible at one end from the sea by which vessels can enter inward for the purpose of repair, inspection or cleaning.

The seaward end is closed off by a dock gate called a ‘caisson’. Once the vessel has entered the dock area the water in the dock is subsequently pumped out, lowering the vessel onto pre-arranged blocks.

The term ‘graving’ originates from the practice of ‘graving a ship’s bottom’ – namely, the burning away of weed and sea water growth. The practice became dated with the advance in steel hull ships and development of anti-fouling protective paints. However, ships still need to routinely go into dry dock to complete survey work and carry out essential maintenance which cannot be carried out while the vessel is in a seagoing condition.

The advantage of the graving dock is that it has permanency and with that goes all the facilities of dock administration, workshops, local labour source, and regular supplies by shoreside services. The disadvantage of this type of dock is that it cannot be trimmed, as say with a floating dock. As such it may not be capable of accepting every type of damaged vessel, which may not be on an even keel, onto horizontally laid blocks. Most graving docks generally are limited to accommodating only one vessel at a time, because of length and being serviced by a single caisson.

The side walls of the dock are usually stepped and where distortion stresses may be encountered, or where the vessel being docked is narrow beamed, side shores can be deployed from the ‘side steps’ (known as ‘alters’) into the ship’s sides. The side shores (wale shores), made of timber baulks, are designed to prevent hull movement and the possibility of toppling from the keel blocks occurring. If used, these shores are tightened at the dock sides by wedges preventing any movement. The shipboard ends of shores are secured by gantlines passing over the ship’s gunwales and being secured on deck.

The floor of the dock is flat, but is constructed on a slight incline. The flat surface is suitable for the use of vehicles such as forklift trucks or mobile platforms. The incline, known as the ‘Declivity of the Dock’, tends to assist drainage of the flood water when the dock is being pumped dry as well as reducing the critical period when a vessel is being docked.

The use of graving docks in today’s shipping industry, where ships are being constructed much larger, has limiting market availability because of size restriction. Only the extremely large docks in both length and beam width can accommodate the large VLCC/ULCC vessels. Having said this, most docks seemingly find adequate work between routine, scheduled docking and accident repair work. A single working dock could expect to average around 200 ships per year.

Aspect of the ‘Graving Dock’

Figure 1.1 The Sea Fishery Protection vessel Sulisker lies in the William Wright graving dock in Hull, UK. The vessel is on keel blocks and supported by ‘wale shores’ either side, set between the hull and the stepped ‘alters’ of the dock sides. The ship is viewed after refitting and hull painting has been completed, with the gangway access sited to a landing on the after deck, port side.

Operational Graving Docks

The majority of major ports around the world have the capability of providing repairs to both ‘Merchant/Commercial’ and ‘Man of War’ vessels. Graving docks are prolific and major shipyards within these ports usually have two or three different sized docks, with or without floating dock facilities, to accommodate all sizes of vessel.

Many graving docks, depending on size, will be able to dock two, three or even four ships at once, again depending on physical size of craft. Such docking arrangements would necessitate prudent planning to ensure that all units can dock together and can also complete relevant work on schedule, in order to re-float together. Where a dock is subdivided by an intermediate caisson, this arrangement would lend flexibility to the docking of multiple units. A dividing caisson allows partial flooding of the seaward half-end of a full dry dock.

The operational graving dock is generally equipped with typical facilities and services of the modern shipyard, inclusive of a variety of crane capacities, repair workshops, steel stockyards, engineering and administration divisions. The permanency of the graving dock would also generally dictate the need either for a surveyor to be based on site, or to have at least regular contact with the dry dock authorities.

Graving docks have continued to flourish worldwide, probably because of the confidence of ship owners that they possess the facilities and capabilities to complete whatever requirement their ships need. The shipyard labour forces have grown with experience while free trade and competition has kept dock managements aware of the need to deliver quality service. Expansion of their equipment base and advancing technology has helped the graving dock modernise to keep abreast of the latest ship designs and increasing special needs of all aspects of the shipping industry – e.g. the docking of rigs and installations.

Graving Dock

Figure 1.2 The Clipper Point RoPax vessel seen in an example graving dock on keel and bottom blocks (no wale shores). A raised gangway arrangement on the ship’s port side is employed to provide safe access to the higher deck levels of the vessel.

Synchro-Lift Docking Operations

The ‘synchro-lift’ method of docking must be considered as probably one of the most modern styles of docking a ship within the marine industry today. It is certainly one of the most flexible, in that it does not occupy the dock space and subsequently does not deny the use of the facilities to other vessels wishing to dock. These up-to-date facilities can subsequently dock and handle a greater number of vessels at any single time without having the operation compromised with a single ship occupation of the dock.

They do have their limitations, however, in that they tend to have a maximum lifting capacity, as compared with the larger graving docks which can accommodate ships in excess of 500,000 d.w.t. Another concern would also be for loaded vessels which would be affected by a lack of ab...