"Visscher stated that over $100,000,000 was spent annually by United States shipping interests alone, because of fouling."
The tendency of ships to foul is related to the type of service in which they are employed, and, particularly, to the resulting time spent in port. This follows from the fact discussed in Chapter 13 that the larvae of many fouling organisms have
diffculty in attaching to submerged surfaces when the velocity of the water across the surface excceeds about one knot. At greater speeds than this, the growth of some organisms previously attached is also supressed, particularly if they have not been long established, and at high speeds the attached organisms may be washed away bodily."
Fouling occurs only when ships are in port due to high level of bacteria, algae and weeds in the port water. This is linked to the high nutrient / pollutant level of water in the port. If water in ports were to be treated to keep the nutrient level low then perhaps fouling can be minimised.
It has been observed the roots of Water Hyacinth have a white gel like substance and this becomes loose over time in water in which Nualgi is used regularly. A similar effect would probably be felt on ship bottoms.