Fouling and loss of speed

[Pedro]

Ive been monitoring my cruising speeds very closely this season due to changing the pitch in my prop to get the rpm up to factory spec 3,600. For 6.5 peninsular,
Rpm cam up with the expectated loss of top end speed,
However speeds really seemed slow, 14 knots at 3,100.
1.Turns out tach is off by at least 150 (according to photo tach)
2.Turns out the hull bottom and prop were spotless ,,except for the trim tabs and rudder, rudder strut..
Any idea how much speed loss is attributed to the trim tab fouling?
1-2knts? More?
I'll plan on scrubbing in the water in late August as a preventative,

[hetek]

I had an 18' Baja ski boat with a Johnson 175 hp outboard that I trailered. It was a 55 mph boat. I left it in the water at a friend's dock, without bottom paint, for a couple weeks. My friend assured me he would take the boat out regularly to "keep the bottom clean". He didn't.

I took the boat for a ride to the ramp to haul it out and it wouldn't even plane! I could have probably outrun it. When I hauled it out the fouling wasn't even as bad as I had expected.

A clean bottom is a happy bottom.