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Equipment
All Underwater Services International, Inc. equipment are diver-operated, hydraulic-driven, rotary brush cleaning units. Numerous brushes and abrasive discs are available to handle almost any type of marine fouling on any underwater surface. The speed of brush rotation is adjustable by the diver to produce exactly the type of cleaning action required-to go gently and rapidly over surface with light slime or more slowly to tackle heavy shellfish. The scrubber bristles lay flat against the hull, cleaning it with a sweeping motion instead of gouging it. The diver simply guides the unit over the hull in lateral passes from bow to stern and completes the job by polishing the propeller, running gear, etc.
USI's equipment is larger, faster, and more controllable than other hull cleaning units. The scrubber moves across the hull at a variable speed of 18.3 to 36.6 meters per minute and at successive depths. The scrubber adheres to the underwater surfaces of the hull with a force exceeding 1000 pounds. The traction of the wheels is 700 pounds, which enables the scrubber to travel at variable speeds against most tidal forces. The cleaning brushes on the scrubber are made of either stainless steel wire bristles which are specially designed to ensure that their tips do not point directly into the hull, or polypropylene bristles for anti-fouling reactivation and removal of soft
algae. This scrubber allows the USI teams to provide quicker turnaround, less downtime, and more consistent cleaning with minimal paint deterioration.
Hull Performance
A vessel's fuel performance usually begins decreasing after six months from
dry-dock and continues to decrease rapidly. Underwater marine growth, barnacles, and/or
sea grass can cost a ship owner millions of extra dollars in time and fuel costs each year. To prevent spending additional dollars for fuel, a ship should be cleaned twice a year. The following table shows the projected net fuel savings, with hull cleaning, for tankers maintaining speeds of 13 knots over a 24-month
dry-docking cycle.
A new VLCC tanker uses approximately 96 tons of bunker fuel per day and 610 barrels of fuel per 24-hour period. The cost per day for fuel alone would be approximately $30,000 with an additional $20,000 for operating expenses per day. On an average 15,000-mile cruise, the VLCC tanker would make the cruise in about 25 days with a clean hull. If the ship's hull is fouled with marine growth not exceeding 0.5 inch, the same trip would take 28 days. The difference is the loss in speed of over 2 knots, which equates to 3 days. Those additional three days cost $90,000 in fuel consumption alone.
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