My Bavaria boat is 14 years old and the exhaust elbow has never been removed or cleaned so thought it was time, and also due to many is clocked up with carbon buildup and water deposits.
If you don't get enough water flow the engine will get to hot and cause the seawater to evaporate at the exhaust elbow.
Carbon buildup will also prohibit the engine from taking maximum rpm. and you will also get an increased consumption.

To clean the exhaust elbow from carbon buildup and water deposits the best stuff to use is
hydrochloric acid over night