Keeping a vessel's hull clean and free of debris has concerned owners and suppliers since the earliest days of the maritime industry. Today, increasing demands on speed and propulsive efficiency require owners to keep their hulls clean.
Meanwhile, ever-restrictive legislation continues to limit the means by which this is accomplished. A New Zealand
-based company had developed a solution to this timeless problem - a quasi "carwash" for ships, which according to its creators at Orca Marine Co., Ltd., will provide a faster, safer and more economical means of cleaning ship hulls.
Hull surface roughness, particularly in connection with marine fouling, is a major contributor to ship powering requirements and fuel costs.
Excessive hull surface roughness affects not only frictional resistance, but also viscous wake, resulting in additional adverse change in propeller loading and efficiency.
Recent developments in the hull cleaning industry indicate an emerging need for a more efficient way to deploy hull cleaning devices
The movement toward reduced toxicity coatings, as a result of environmental concerns, will require more frequent cleanings for a given level of surface fouling control. For this reason, Orca has developed a Floating Dock Type of Cleaning Ship (FDTOCS), a self-propelled service vessel incorporating a system for rapidly cleaning ship hull surfaces.
The principal objectives of the FDTOC design study were to develop the initial concept in the following areas:
· To develop feasible alternatives for deploying multiple hull cleaning appliances onto a ship's hull, quickly and in considerable concentration, without the need for divers and with the required level of safety and reliability;
· To develop systems that offer potentially lower unit cleaning costs;
· To demonstrate the feasibility and desired mechanical and hydrodynamic characteristics of a brush appliance to be deployed without a diver in direct control of the appliance;
· To demonstrate naval architectural feasibility in terms of safety requirements, powering, maneuvering and station keeping, and especially stability (both intact and damaged); and
· To develop initial major machinery requirements and identify some over-all marine engineering and cleaning system requirements, intended to provide a basis for estimating capital costs.
A specific size range (Panamax beam and maximum draft corresponding to a typical scantling draft for ships of Panama Canal size) was considered for development.
Additional system elements required to deploy and retract the cleaning appliances will be developed with an emphasis minimizing development risks; and using commercially available components wherever possible.
The FDTOCS is a self-propelled, semi-submersible vessel consisting of a 217 x 98 x 14 ft. raked-end barge hull, featuring a watertight superstructure near each end. For cleaning operations, the FDTOCS is oriented under the vessel being serviced (customer ship) in the same way as a sectional floating drydock. But unlike a drydock, the FDTOCS does not deballast to support any part of the customer ship, and only the brush appliances come into contact with the ship's hull. The barge hull, between the two superstructures, incorporates a large hopper for the collection of cleaning debris brushed from the hull, including fragments of marine growth and removed surface coating material. This material is therefore prevented from falling to the seabed, and can be periodically removed from the bottom of the hopper as mud or seawater slurry, then transferred for settling, disposal or reclamation ashore.
The cleaning control station of the FDTOCS is located at the aft end of the forward superstructure. Each brush assembly installed on the FDTOCS, whether bottom or side, incorporates five hydraulically powered brushes, wheels for contact with the customer ship's hull, and an articulated subframe.
The system's control console incorporates all controls for brush arms, brushes and systems line-up of hydraulic power units. Monitoring, control and re-programming of manual and automated function for the cleaning system takes place here. In addition, displays of the position and heading of the customer ship with respect to the FDTOCS - such as distance sensor readings and Doppler velocities - are presented at the cleaning control console. A five-person manning team is planned, made up of Master, Chief Engineer, Engineer/Cleaning System Technician and two AB/Cleaning System Technicians.
The hull and superstructures of the FDTOCS are constructed of conventional mild steel. Hull sides and superstructures are transversely framed, and longitudinal bulkheads, 16.4 ft. from centerline form the inboard members of the box girders for longitudinal strength and torsional rigidity. These transverse bulkheads also support the hopper slopes, and divide the ship into eight subdivisions: four of the bulkheads directly support the forward and aft boundaries of each superstructure; three are located in way of the hopper; and one is located amidships.
The FDTOCS' propulsion system provides all mobility, maneuvering and dynamic positioning forces. It is expected a speed of eight knots will be obtained during transit and about two knots when ballasted down for cleaning operations. Four AC motors of approximately 850 hp each are incorporated, driving vectorable thrusters which will be installed as either Z- or L-drive units with motors located at the hull, or as podded propulsors. Diesel generator sizing of the FDTOCS is based on four sets, carrying the largest normal operational demand on three, with one on standby. Four Caterpillar 3512 engines have been selected, each rated at 910 kW at 1,200 rpm. Navigation systems include integrated bridge control, X and S band radars, depth sounders at each end of the FDTOCS, GPS, gyrocompass and dual Doppler logs to provide input to the DPS. During cleaning operations, the DPS will also receive input from sensors measuring the relative position and motions of the customer ship.
The objective of the FDTOCS is to deploy massed cleaning units quickly, reliably and economically by replacing massed divers with a relatively straightforward control system. In order to complete the development of the project, a more detailed system of requirements, sensor tradeoffs and block diagrams for the cleaning control systems, as well as its relationships with other systems, are planned as the immediate next steps.