Bavaria 28 sport propeller size for a single 5.7 gxi petrol engine

[fr.surucu]

Hi everyone,
I have a 2010 bavaria 28 sport boat. My engine is a single Volvo penta 5.7 gxi (320 hp) petrol (1:95 ratio). I can only see 4300 max rev and max speed of 26 knots. After all my inspections, I suppose I have a propeller size issue. and I suspect that the previous owner might have changed it.
This is a 4 ton vessel. Anyone having the same or a similar boat, can please advise me the right prop size ? The RPM and top speed and sometimes heavy white petrol smoke should indicate a problem right ? Currently I have f3 size duoprops.

 

[fr.surucu]

I will go ahead and change the prop to one smaller size. Hope it goes as I anticipated. Update here with the results.

 

[[2068]]

I think you have an engine problem ...
From another review, 4300 and 26kts isn't far out for a fast cruise, except that max throttle should produce a top speed of 35kts or so.

I'd start by checking manifolds / risers for leaks.

'ON THE WATER
The 28 Sport was responsive with just a single 320hp V8 in the tail. At 2750rpm the boat planes at 12kts, at 3000rpm you can hold a heavy-weather cruise of 14kts, and you will clock a comfortable family clip of 21kts at 3500rpm for 51lt/h fuel burn. The sweet spot was 3750rpm for 25.2kts and 54lt/h up to 4000rpm for 27.6kts and 62lt/h.'
'Top speed was 36.4kts and it was then that the boy racer was fully unleashed within...'

 

[fr.surucu]

Changed to f2 today. With 2 people on board, max rpm reached 4800, max speed of 29 knots in a windy weather(20 knots wind), thus not a flat sea. The boat plains more easily. I think I gained some miles and saved some gas. I will test it with 4 people on the weekend, I hope it behaves the same.