Fuel Burn and Speed Concerns

[William McDevitt]

Just recently took delivery of a 2017 400 fly and looking for feedback on performance:
Twin Cummins 6.7 QSBs
@2700 RPM
80% load
38 GPH
Speed 18.2 knots
Props just refinished. Seems slow and fuel burn seems high.
Specs from boat test of same boat have her at least 23 knots and lower GPH.
Where do I start?

 

[nealtrombley]

Wow
I looked at newer 420 with same power and was surprised at fuel and slower speeds

my 410 with cats
23 mph 2300 rpm 18 gallons an hour


Clean bottom of course
Propped correctly

 

[EKM]

Wow
I looked at newer 420 with same power and was surprised at fuel and slower speeds

my 410 with cats
23 mph 2300 rpm 18 gallons an hour


Clean bottom of course
Propped correctly

1.27 mpg....pretty good numbers. Did your prop repitch change the fuel burn much?

 

[EKM]

Just recently took delivery of a 2017 400 fly and looking for feedback on performance:
Twin Cummins 6.7 QSBs
@2700 RPM
80% load
38 GPH
Speed 18.2 knots
Props just refinished. Seems slow and fuel burn seems high.
Specs from boat test of same boat have her at least 23 knots and lower GPH.
Where do I start?

I would post this on the yacht

Just recently took delivery of a 2017 400 fly and looking for feedback on performance:
Twin Cummins 6.7 QSBs
@2700 RPM
80% load
38 GPH
Speed 18.2 knots
Props just refinished. Seems slow and fuel burn seems high.
Specs from boat test of same boat have her at least 23 knots and lower GPH.
Where do I start?

I would post this under the sport yacht and will get a better response. How long was it sitting after sea trial...do you know the bottom is clean? How did it perform on your sea trial? Seems way off....my 420AC has much better numbers. Typically run my cummins at 2200 rpm, 22mph, 1mpg

 

[alnav]

Just recently took delivery of a 2017 400 fly and looking for feedback on performance:
Twin Cummins 6.7 QSBs
@2700 RPM
80% load
38 GPH
Speed 18.2 knots
Props just refinished. Seems slow and fuel burn seems high.
Specs from boat test of same boat have her at least 23 knots and lower GPH.
Where do I start?

First thing I would do is to test at wide-open-throttle (WOT). I think that engine is rated for 3300 rpms at WOT. If you can't get to that RPM, it usually indicates a dirty hull.

 

[mquiet]

Just recently took delivery of a 2017 400 fly and looking for feedback on performance:
Twin Cummins 6.7 QSBs
@2700 RPM
80% load
38 GPH
Speed 18.2 knots
Props just refinished. Seems slow and fuel burn seems high.
Specs from boat test of same boat have her at least 23 knots and lower GPH.
Where do I start?

Is that the load readout or is that the % you figure from WOT? During survey did it get WOT and rated speed? You did not mention how it performed during Sea trial.