prop help

[trainwrecker22]

I hit something with my prop (14.5x19p) I tried a buddies 14x23P and it cavatated. I got myself a 14.25x21p prob and now she will only wind out to 3700 rps's and top end is 37mph I am green to boating and honestly have no clue what i am doing any help would be appreciated. should I try a 18p? go back to the 19? also how can I find out then ratio its a '95 21' sea pro engine is\was a 305 alpha 1 gen 2 serial OF358602 trans:OF515872 drive: OF497376

 

[Bondo]

I hit something with my prop (14.5x19p) I tried a buddies 14x23P and it cavatated. I got myself a 14.25x21p prob and now she will only wind out to 3700 rps's and top end is 37mph I am green to boating and honestly have no clue what i am doing any help would be appreciated. should I try a 18p? go back to the 19? also how can I find out then ratio its a '95 21' sea pro engine is\was a 305 alpha 1 gen 2 serial OF358602 trans:OF515872 drive: OF497376

Ayuh,.... Bigger pitch equals a taller gear ratio,.....

If it worked fine with a 19" pitch prop, then buy a 19" pitch prop,.....

V8 motors usually run the 1.5:1 ratio, unless is a Huge hull, then the 1.65:1 is sometimes used,....

 

[steelespike]

What was the wot rpm and gps speed with the old prop?
Selecting a prop is like trying to pick a single gear in your car to do everything.
When you went to a 23 it was like selecting overdrive.
Was the performance strong with the 19?

 

[trainwrecker22]

it was good, I could hit about 40mph 4300R's she would jump on plane. I am looking to get a bit more top end. The 23p cavatated real bad. I was wondering if I maybe went to a 18p if that would increase my R's and big end mph? and whats the difference between a 3 and 4 blade prop

 

[Stingray185GXi]

If your WOT RPM with the 19 pitch prop was only 4300 then I would go down to a 17 or 18 pitch prop as this will bring your RPMs up higher and closer to your engines recommend WOT RPM. This would allow you to get up on plane faster and will cause less strain on your engine. I would expect top speed to stay about the same with one of these compared to your old 19 pitch, but that top speed would be achieved at a higher RPM.
Generally 3 blade props are better for top speed while 4 blade props are better for acceleration, grip better in turns, are slightly more efficient due to less slip, and are better for heavy loads.

 

[steelespike]

Is your speed by gps?Your numbers don't quite add up. A strong hole shot would usually have more wot rpm and your slip is kind of high at 22%.
The slightly high slip may be an indication that the speed isn't accurate.Actually may be faster.

 

[trainwrecker22]

no gps yet. installing a lowrance 4 chirp tom. I am gonna try a 18px 14.5 or 15 prob to get the r's up.