Boat running slower and need to recalibrate PP

[Kozmo]

My boat has been in the water since the last week of April. I meticulously calibrated PerfectPass using a GPS in early May. Last weekend I noticed that the boat was running about 2 MPH slower at 32 and 34 MPH. (32 MPH requires about 3700 RPM and 34 requires about 3900 RPM). I needed to increase the RPM setting on the PP by about 400 RPM's at both of those speed settings to correct it. I also noticed that the top end of my boat is now about 36 MPH at 4500 RPM vs 43 in the early spring Can this be because the hull is absorbing water or grimy? The engine sounds great and vitals (temp, oil pressure, etc are fine). Thoughts?

[DanielC]

RE: Boat running slower and need to recalibrate PP

Has the bottom of the boat been cleaned? If not, get that done first.
A good bottom cleaning solution is a half and half mix of Hydrogen peroxide, and Lysol toilet bowl cleaner. get the toilet bowl cleaner that has hydrocloric acid listed and one of the ingredients. Use gloves and eye protection when cleaning the boat bottom.
Make sure your PP paddle wheel is clean.

[jasper]

RE: Boat running slower and need to recalibrate PP

Any kind of aquatic growth on the hull will have a dramatic (detrimental) effect on speed. To a much, much lesser degree, warmer water will cause a decrease in speed at the same rpm. Focus first on cleaning your hull.