prop question For bayliner trophy

[JJB]

I have a 1991 20' 8" bayliner trophy walk around with a 2000 175 hp johnson ob . It weights about 2750 lb and I wanted to know what would be the best all around prop for this boat . I am looking to but a aluminum prop on it . I have just put this rebuilt engine on the boat and in the process of breaking it in so I don't have a starting point as far as rpm at wot with this engine . Thanks for the input !

 

[Bondo]

Re: prop question For bayliner trophy

I am looking to but a aluminum prop on it . I have just put this rebuilt engine on the boat and in the process of breaking it in so I don't have a starting point as far as rpm at wot with this engine .

Ayuh,.......

Just like Everybodyelse,......
Without the Known pitch of the present prop,+ the Baseline of what the RPMs at WOT is,.......

Nobody can give you Any Educated Ideas of where you should be headed.........

 

[JJB]

Re: prop question For bayliner trophy

the manual said wot rps are between 4500 and 5500 rps for that engine Thanks for the input !

 

[Silvertip]

Re: prop question For bayliner trophy

We know what the manufacturer "recommends" -- what's important in this discussion is what you actually "observe" at wide open throttle with your current prop. With "observed" rpm and the type of prop you have now (aluminum or stainless, diameter and pitch, three blade or four) we can offer some suggestions. Without that data we can only guess what you need.

 

[JJB]

Re: prop question For bayliner trophy

ok just check out the size and It now has a ss 4 3/8 x 18 that came with the motor . I don't know if its the right prop to be using for break in period with this boat . I won't be able to get it out in the ocean with all this wind and winter here . I"ll be in a lot of no wake areas and keeping the rpm low with 1 -5 mins burst of higher rpms for 10 hrs . will the 4 blade prop keep the rpm to low as apposed to the 3 blade aluminum prop . The first trip out I notice I was only at 800 rpms and I was moving along at a good clip with this prop . I dont want to keep the rpm to low when in those no wake areas during break in since there are a lot of them in my area . Thanks for any input !

 

[Silvertip]

Re: prop question For bayliner trophy

You are getting closer with the information but you are still missing the two most important bits of data. The prop "pitch" determines what rpm the engine will rev to at wide open throttle with an average load. Too little pitch and the engine over revs. Too much pitch and the engine lugs. The correct pitch puts the engine rpm within the manufacturers rpm band at wide open throttle. Hub diameter means nothing. It's rpm and pitch numbers we need. Until you can run the boat wide open for a good stretch, everything you told us is of little help. I know you are probably thinking "but I don't run wide open so why is pitch that important?" Fact is, if the boat is propped incorrectly at wide open throttle it is also propped wrong at any RPM less than that except idle in neutral. There are plenty of discussions about 3- vs 4-blade props -- just Google search "Marine Propeller Theory".

 

[JJB]

Re: prop question For bayliner trophy

sorry about that silvertip it was a little dark when I getting the # last night . guess my eyes getting a little old .The prop is 14 3/8 X 18 hope that helps !

 

[Bondo]

Re: prop question For bayliner trophy

Ayuh,........

You're still lacking the Known rpms at WOT.........

 

[Silvertip]

Re: prop question For bayliner trophy

I ran the numbers through a prop calculator and using a slip figure of 12%, the boat should run about 46 MPH at 5500 rpm but that does not take into account the weight of the boat or load. That's a theoretical situation at best but may at least be in the ball park. You won't know until you run it.