After switching from a 1,50 :1 bravo 1 ,to a 1,65 :1 bravo 3 ,I still have 20% slip.
The boat is a 28 Sonic with a single 370 hp Yanmar turbodiesel.

I had a 26 pitch stock maximus and 44-45 mph max on gps at 3500 rpm ,now I have 3500 rpm and 44-45 mph max gps too and likely the same slip....
cruise is a little better ,slightly less rpm,s ,but still I,m confused .
The B3 props are stock too,it seems this hull is not coming flat on the water ,the stern sits deep,and the bow is up on max speed ,its just like the speed is too slow to lift the stern ???

If I lower the 380 s tabs a bit ,the boat flattens a little more ,and has almost no effect on top speed .

Could the slip be so high because of that ?

Thanks stirling

Dragging tabs will increase slip.

I believe your speed is too low to help the efficiancy of the hull.