The increased coast for fuel for vessels operating at normal cruising speeds with a fouled hull can be averaged at 10-15%. These figures seem to be true for all types of vessels and were derived from consensus, opinions, and documentation. In most cases an underwater hull-cleaning job of even a slightly fouled vessel will pay for itself in fuel savings alone.
In the case of sailboats, even a light film of slime can have a serious effect on performance. The hull of a sailboat is designed to be slippery to create as little drag as possible. Where a powerboat can compensate for marine growth by advancing throttles, a true sailor does not want to fire up the engine to compensate for loss of speed!
The first stage of fouling is slime. Slime formation begins by bacteria attaching themselves to your hull. This process usually begins within a half hour of being in water.
Slime alone can increase fuel consumption by as much as 15%. Anti-fouling paints are designed to repel these microscopic intruders by releasing toxins into the layer of water next to your hull. Your anti-fouling paints’ leaching of toxins, initially, works well. As time goes by, the dead bacteria build up as slime and begin blocking the leaching toxins.
The dead bacteria forms a foundation upon which more advanced forms of marine growth will develop.
Stage two fouling is multi-cellular grasses. These green grasses depend on light for photosynthesis and, therefore, tend to concentrate at the waterline and sunny side of your vessel. At depth, the color of grass accumulation changes from green to brown. Any grasses growing on the side of your boat should be removed on a monthly basis before their roots take foothold. If not, the grasses will leave permanent stains and may cause paint to lift away from the hull. Topside enamels and boot stripes are not as tough or thick as hull coatings. If grasses are left to accumulate, a more aggressive abrasive action will need to be used to remove them possibly resulting in bare spots in the paint. Clean Hull Diving Services always uses the least abrasive, but effective, brushes to prevent paint wear as much as possible!
Stage three fouling is calcareous organisms. These begin as free-swimming, microscopic organisms, and attach themselves to your hull. These calcareous organisms develop into creatures that can inflict severe and permanent damage to your vessels hull.
Barnacles are the main organisms found in stage three fouling. These are usually acorn and/or goose barnacles and tubeworms. They are found from waterline to keel and will constitute the dominant type of fouling on propellers and running gear.
Stage four fouling is the composite of the first three stages, but includes soft sedentary animal growth. Together with the other types of fouling, stage four fouling becomes a dense growth covering a greater portion of the hull. The sheer weight of this growth can be tremendous. One square foot of marine growth, one inch thick, can weigh as much as 3 pounds!