Our Benchmark testing grounds were taking the same wellprotected "vik" or bay at full speed in pretty simular conditions before and after the boatwash to get a feel of how bad a dirty hull influences fuel and speed just before and after our boatwash.
Same crew, same weather, no real opposing winds or high waves.
The results are as expected, but it really proves it is worth to wash your hull at least twice a season (or if you are a heavy boater) three times a season as it will increase speed, and drastically reduce fuel consumption.
Measurements done against GPS Speed and engine fuel consumption.
Before:
Max speed: 22.6 knots with a steady fuel consumption of 56 liter / hour.
After:
Max speed: 33 knots with a steady fuel consumption of 56 liter / hour or 10 knots faster as before the wash.
"Mummy, I want to dress like a girl for Johannas Halloween Be Scared Party, as girls are the most scary things on earth I know ... "
— Kalle Vanrillaer