Even a small amount of dirt on the hull affects the boat's performance. This particular boat was launched in April and the first inspection measurement was already done in mid-June.
Voyager 700 cabin, Mercury 225hp. The boat was launched in Helsinki on 11.4., cleaning was done on 11.6. in Herttoniemi. The boat has been in the water for 8.5 weeks.
Observations: slime and preliminary algae on the hull. The boat feels some resistance. The last weeks have been sunny.
Before cleaning: 3720rpm, 24.4knts, 33.2l/h
After cleaning: 3749rpm, 26.2knts, 30.1l/h
Result: cruising speed +7.4%, consumption -9.34%
Summary: even a small amount of dirt on the hull creates resistance, which is reflected in fuel consumption. The hull collects growth throughout the entire season starting from the moment the boat is launched. Growth accelerates as the water warms and the amount of sunlight increases.