Prop Choice for 233 Interseptor with twin 260 Mec


Assuming the boat as twin 260's (350 V8) then spec is 4200-4600

If your tach is "accurate" and Verify drive ratio is 1.5

Need to know what pitch prop is on it and what is the speed using a GPS (not the boat speed-o)?
 
Rebuilt Roller Cam Darts Heads, solid lifters, SEC 1.50 Drives 15.3x19 P Engine builder said motors should turn 5500 320 HP.. GPS 57 mph 4200 rpms
 
jbarrows said:
Rebuilt Roller Cam Darts Heads, solid lifters, SEC 1.50 Drives 15.3x19 P Engine builder said motors should turn 5500 320 HP.. GPS 57 mph 4200 rpms
Click to expand...

Something isn't right, plug those into a prop slip calculator and the boat is moving faster the the distance the props are. Its showing (negative) -13+ % slip

Now if your turning actually 5200 rpm then your doing great with a 8.6 % slip.

Suggest getting a hand held tach to check

http://bblades.com/propeller-slip-calculator/
 
I hope you will still weigh in. 233 Formula Interceptor, Just finished new gauges, Garmin GPS. I checked Drive Ratio 1.47 SEI Replacement. Lastest run on 10-9-20 WOT 3650 RPM 55 MPH weight 5100 est ran 42 MPH at 2800 RPM. Trimmed out Tabs and Drives. Props are 15.3 x 19P Don't understand why I am not turning higher RPMs, Speed Max is prop low 62/65. What next?
 
With those numbers your at 6% slip which is great
A GPS either works or it doesn't, so do believe your speed. If your tach is accurate then your motor would not sound like its wound out, but only about half throttle.

Are you sure the drives are 1.47 ?
 
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