Non-Self Propelled Vessels
By Mike Vaughn
When we think of non-self propelled vessels we usually think of barges. However, there are a variety of other crafts that, for one reason or another, do not contain or use propulsion units that are self contained.
A cruise ship or liner is merely a hotel with the ability to change locations, the Caribbean in the winter and Alaska in the summer. When a cruise ship nears the end of its useful life, it has the opportunity to become more or less permanently fixed in one position as a hotel ship.
There are a number of reasons that this will occur. The international convention providing for safety aboard cruise ships (SOLAS) is a changing set of rules. Many older ships are not economically feasible to bring up to the newer fire and safety standards. Consequently, they have little or no value as a cruise ship.
In many cases these ships are still very elegant craft with a history of international cruising behind them. Such ships, like the Queen Mary, now serving as a hotel and tourist attraction in Long Beach, California, go on to long and worthwhile careers. Others, without the history of the Queen Mary, find other occupations as restaurants and attractions, accommodation platforms and temporary quarters.
Very often when special events require an active cruise ship will be temporarily docked as several ships were so used in Barcelona during the Olympics.
In the United States, where the Jones Act requires that all passenger carrying vessels be U.S. built and flagged, a hotel ship can avoid this requirement by removing its propellers and propulsion equipment and become affixed to the shore.
It is important to realize that when this happens, the ships must then meet local and state building codes, as well as requirements for handicap access and use. Even with these requirements, a hotel ship can be on site and in service in a fraction of the time it takes to construct a major hotel.
FLOATING DRY DOCKS
A floating dry dock is an essential tool in the maintenance of commercial and private ships. All ships and boats must be periodically removed from the water and the hull must be inspected, repaired and painted.
For small pleasure craft and small working craft, a travel lift or marine railway may be sufficient to lift them out of the water.
However, large commercial ships which may weigh hundreds of thousands of tons can only be lifted by a floating dry dock.
A floating dry dock, is merely a large tank with walls on each side, massive pumps and compartmentalized floating chambers that can be filled and evacuated on demand. The floating dry dock will have a lifting capacity based upon the amount of displacement of water designed in the dry dock.
The lifting capacity need only be greater than the weight of the ship being lifted.
A 10,000 ton dry dock should be able to lift a 10,000 ton ship. Of course a margin of safety is always employed.
A “blocking plan” is devised for each ship when it is constructed. This plan shows the shipyard the stress points in the hull so that massive wooden or steel blocks can be strategically placed so as to support the weight of the ship without damaging it.
The dry dock is then submerged deeper than the draft of the ship by pumping ballast water into the chambers in the dry dock. The ship is then positioned very carefully into the dry dock by tugs to make certain that the ship will rest upon the blocks that are pre-positioned in the floor of the dry dock. The pumps in the dry dock pump out the ballast water and as the dry dock starts to rise it lifts the ship completely out of the water.
A dredge is one of those work-horses of the industry that no one talks about until you really need it. The dredge is a giant vacuum cleaner that is used to deepen and clear waterways.
Dredges come in all sizes, but all have the same basic characteristics. These include a cutter head that cuts or disturbs the ocean bottom and a ladder device that brings the mud or dredge spoil up to the surface for deposit in a barge or other vessel.
Dredges vary in size from 25 or 30 feet up to several hundred feet in size. The distinguishing factor is the depth of water in which it can work and the size of the dredge pipe that it uses to extract the dredge spoil.
The barge is probably the oldest form of water transportation. Today they are used in every waterway of the world, every port and for every conceivable purpose.
They will range in size from small floats to giant ocean-going platforms that will rival some of the largest ships.
The common characteristics are the lack of self-propelling equipment and a generally rectangular shape.
There are a variety of barges. The following are some of the more common uses:
- Deck barges are used for transporting cargo stored on deck.
- Tank barges are used for transporting cargo, generally liquid stored below deck.
- Bin barges have high perimeter walls that allow bulk cargo to be carried on deck.
- Accommodation barges have housing built on deck to provide living quarters for work.
- Crane barges have large mechanical cranes on deck and are used in a variety of marine construction situations.
- Notch barges are barges that, instead of a flat or square sterns, have a notch designed in the middle so that a tug boat can position the bow of the tug in to the center of the barge and more effectively control the movement of the barge. You will see both tank and deck barges built this way.
- A Spud Barge is built so that it can be positioned in one place in relatively shallow water and not move. This is accomplished by the placement of two or more long metal pipes or tubes called spuds, vertically on the side of the barge, that can be raised or lowered at will. When the barge is correctly in position, the captain sinks the spuds into the bottom and the piling then holds the barge in position. This is very common for construction projects and is routinely found on carne barges.
- Jack Up Barge is the next step up from the spud barge. It is very similarly constructed, except the spuds are more substantial and the mechanical equipment more complex. When the barge is correctly positioned, the legs are positioned on the bottom and the barge is elevated out of the water using the legs as vertical support.
Working on the water requires innovation, good design and courage. Every type of waterborne device may fail with disastrous results so it is important to choose good equipment that is designed and suitable for the project intended.