Declining Speed a Turbo filter Issue?

[Nigel A Veater 6BT-5.9M 210hp]

I have a 6BT-5.9m 210 hp engine (Serial # 45795214) driving a 1999 Mainship Pilot. I have noticed over the season that the SOG has been declining – at the beginning of the season I was doing 12.7 knots easily at 2400 rpm and 15.6 @ WOT  which was just a tad south of 2600 as indicated on the tach- now the average speed has fallen to about 10.2 at 2400 and 12,5 at WOT. This is kind of a rough average taking into account currents and tides in my area (northern Chesapeake). I realize that there could be some mild growth on the bottom although in my 30+ years in this area its never that bad. The engine runs well, sounds fine and I wondered whether it could be the turbo air filter. I have had the boat going on 3 years and haven’t changed or done anything to the air filter on the turbo (it does have the envirovent system) . Is there a servicing procedure or schedule for changing this filter- or should I be looking elsewhere for my speed mystery ? Thanks in advance for any help.

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[JimmyK]

Pay for a short haul & get the bottom cleaned, perform a visual inspection of the prop(s) and the bottom.

1 user thanked author for this post.

Tony Athens

[Nigel A Veater 6BT-5.9M 210hp]

I guess that does make sense since no other other parameters are changing

[Nigel A Veater 6BT-5.9M 210hp]

The boat runs about 75-100 hours per year and has regular maintenance with annual oil and filter changes, periodic changing of trans oil- there is a robust multi stage fuel filtration system as sold on this website (those haven’t been changed in about 2 years). There has been no fluctuation in oil pressure, operating temperature etc – fuel consumption has been running about 5.77 gallons per hour- that has remained fairly constant (5.7-6.5)- I’m not sure how on this engine to measure rpm other than the tach.

[JimmyK]

absolutely nothing to do with your engine.  your engine plays no part in the relationship between RPM & boat speed.  all your motor does is turn the shaft through the gear–it’s the propeller that actually pushes it through the water.  if your speed at a given RPM is dropping, it is something external to the engine.

growth on bottom/prop

props themselves

extra weight

etc.

[pwrobert]

Not enough data.

Need more info about engine maintenance schedule. Also hard to diagnose when tachometers are not accurate. They need calibration to get real numbers. <br />also what about fuel Consumption and engine temps then and now. A lot to know. 

[Author]

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