I. Field of the Present Invention
The present invention relates generally to cleaning devices which hydraulically or mechanically abrade the surface of a ship's hull to remove any accumulated deposits therefrom and, more particularly, to a carriage for controlling the movement of such cleaning devices across the hull surface of a ship.
II. Description of the Prior Art
A well-known problem encountered by seagoing vessels is that foulant such as barnacles, marine plant growth and the like accumulate upon the ship's hull. Such foulant increases the drag as the ship moves through water and therefore increases fuel comsumption and reduces the top speed of the ship. Consequently, the hulls must be cleaned periodically to remove the foulant and thus avoid the high cost of inefficient operation of the vessel. In addition to the energy savings, hull cleaning maintains the productivity of each vessel, and as a result, initial fleet investment can be minimized.
A known means for removing the foulant comprises scrapping or chiseling the foulant from the hull surface. However, manual scraping of the hull surface is extremely tedious and time comsuming. Moreover, manual scraping is best accomplished in dry dock and, therefore, prolongs the time during which the ship is not available for service.
An improved means for scraping the hull comprises the use of powered rotating brushes which are mounted on a manually guided, wheeled platform. Although such scrubbing devices have been adapted for use below the waterline while the ship is achored, they are difficult to control. Consequently, they are typically transported and controlled by a vessel separate from the vessel to be cleaned.
Another previously known manner for removing foulant comprises the use of a highly pressurized flow of fluid through a hose and against the foulant on the hull surface. The fluid can be water, or a combination of particulate matter and water, although it is typically highly pressurized air containing particulate matter which is discharged with great force against the foulant. The use of particulate matter as an abrasive medium is disadvantageous in that the particles can pit the surface of the hull and remove the paint from the surface. In addition, as the particles are deflected from the surface, they are released into the atmosphere and present undesirable safety and environmental consequences.
Thus, another previously known means for removing foulant comprises the use of only pressurized water. The pressurized water is delivered through a hose having a nozzle at the end which increases the force of the fluid stream discharge.
Moreover, due to the fact that foulant tightly adheres to the surface of the ship's hull, extremely high pressures must be generated in order to blast the foulant from the hull. Thus, although a single hose can be manipulated rather easily, and is typically held by a worker who directs the flow against the hull of the ship, it is only practical for each worker to control a single nozzle.
Although the use of high pressure water is highly effective in removing barnacles from the hull of a ship, the flow from the single nozzle contacts only a very limited area of the hull's surface. Thus, the cleaning of large vessels remains extremely time-consuming. Although this downtime is extremely costing in terms of the service lost as well as storage costs, the necessity for removing the foulant dictates that the delay be tolerated.
Of course, it would be advantageous to increase the area contacted by the pressurized fluid stream. However, the pressure required to remove the foulant causes a large force to be exerted against the hull of the ship which pushes the nozzle away from the hull. Resistance to this pushing force is provided by the worker who handles the nozzle. Because of the magnitude of the force which must be resisted by the worker, it has not been practical or possible for the worker to operate more than one nozzle in order to increase the cleaning swath and thereby decrease cleaning time. Moreover, the large forces created by nozzles presents a serious risk that two or more workers working together, each operating a single nozzle, can cause serious injury to co-workers. Consequently, it has not been practical to utilize more than a single nozzle at one location during the hull cleaning operation.