prop help bayliner with force 150hp

[trailwart]

1989 bayliner cobra (center console fish/ski) 19ft few inches with 150hp force. been in family since new and still in great condition. problem is it has always over revs, and is propped wrong i believe. at some point the original prop was damaged and replaced, can not remember back story on that situation. it currently has a 12 5/8 x 21p aluminum 3 blade. this boat used to run mid 50mph with old prop(specs unknown) and this current prop is lucky to hit 40mph while reving to the moon . there is tons of clearance room for larger diameter prop. i need to bring max rpm down, would love better holeshot and can care less if it ever hits 50mph. these are some of the sizes listed on a site, all are 3 blade.
14 X 13 Cup
13 1/2 X 15Cup
13 3/4 X 15 Cup
13 1/2 X 17Cup
13 1/4 X 17 Cup
13 X 19 Cup
12 3/4 X 21 Cup

phiranna has 4 blade props, but am unsure what size direction i would need to go to get desired results.

 

[Maclin]

Welcome Aboard!

Need to know what RPM's you can hit at WOT. Right now have to assume some things like a 1.9 gear ratio, and top speed of 40mph. When specifying 10% slip in a basic prop calculator the RPM comes out to 4250, so something is not quite right with your numbers if you are going past 4250 rpm's now.

Your engine RPM band is 5000-5300 I think. If you are revving past that, or can, and are only going a true 40mph then your prop slip is really real bad at 30%. Is your speed by GPS or boat speedo?

Some basic calculations show a 21 pitch prop is close to ideal for your setup. 1.9 ratio, 5300rpm, 21 pitch with 5% slip would get you close to 50mph, close to the perfect pitch for your setup. More exact, 5% slip is 52.7mph. 10% slip is 49.9 mph.

 

[Maclin]

Sorry, left out this part, I think you need a new prop, that one is not working very well for you at all.

 

[89retta]

The props you're thinking of would be all wrong. Diameter is way to small. Perhaps try a 14.5x21. Also you don't want to go lower in pitch as this would raise your rpm's even higher

 

[trailwart]

Speed was not verified with GPS and rpm was dash tack. Boat is in barn at lake house, will try to verify this weekend actual numbers. I need to pull part number off prop to try to cross reference the brand

 

[trailwart]

Any thoughts on hustler 13.25 x 21p. Look like it is 1 of 2 options for this engine on this site for sale in 21p. I'm leaning on giving it a try. I do believe my prop is old and probably whomped out. Any downfall on going bigger diameter