Optimal prop slip?

[Sappersmurf]

I have a 1991(gutted and rebuilt in 2014) bayliner Capri BR2000. It is powered by a 2006 optimax 150. I have a turning point 14 x19p stainless steel four blade prop on it currently. The motor has a 1.87 gear ratio. WOT 4900 RPM(might be able to get another 100 with more trim but the chine walk gets pretty bad.) speed 47mph but gps and speedometer. No wake(barely in gear) to WOT has it on plane in 3.5 seconds. According to online prop slip calculators this puts me at 0% slip. Does there have to be a certain amount of slip? Should I reprop?

 

[QBhoy]

Hi

One of your input data will be wrong. I'd be pretty sure of this.
At a guess. Probably the prop pitch. Are you defo on this ?
Allan

 

[Texasmark]

Per the prop slip calculator that has proven it's worth to me: http://www.go-fast.com/Prop_Slip_Calculator.htm, your 1.87, 4900, 19P shows a max possible (screw turning in wood) speed of 47. Toss in a reasonable 10% slip (and unless turning a screw in wood there always will be slip with a prop) for an I/O and you are at 42. You have an instrument feeding you false information!

 

[Sappersmurf]

The current prop was purchased new and Has the correct numbers on it. Speed was with GPS and speedometer. Assuming the supplied prop is true in dimensions that would suggest a incorrect reading from the tachometer.

 

[Texasmark]

The current prop was purchased new and Has the correct numbers on it. Speed was with GPS and speedometer. Assuming the supplied prop is true in dimensions that would suggest a incorrect reading from the tachometer.

Well sir something is telling you a lie. The tach could be in need of internal oiling and may be sticking giving you a low rpm reading which would cause the problem.

 

[fhhuber]

Tach error or the prop is the next higher pitch. 0% slip isn't going to happen.

You can get under 10% slip though.

 

[ttankmoran]

Aren't the turning point props notoriously aggressive? Every rule of thump I have ever seen says you should probably treat this prop as a 21 pitch.

Turning Point, Stainless, 4 Blade.... It is probably operating closer to a 21 pitch.

putting the numbers in as a 21 puts you at about 9-10% slip which is plenty believable.

 

[ajgraz]

If what ttankmoran says about Turning Point props is true, then I agree the slip number is right on.

I'd be a bit concerned about 4900 rpm being WOT. You ought to be turning higher rpm at WOT, on your Opti probably about 5750 rpm ideally. Which could suggest that you need to go down in pitch...or that maybe your motor is mounted too low. Or both.

 

[muskyfins]

^^^^this. 4900 WOT? Too low.