21pitch vs. 23 pitch

[spiphen]

I have a 1999 Glastron sx175 w/ volvo 4.3GL 190hp V6 w/ volvo sx stern drive. I came with a 14.25 x 21 pitch prop. My question is:

What would I gain/lose by puting a 14.25 x 23 pitch prop on my boat?

Thanks in advance,
Scott

 

[Tail_Gunner]

Re: 21pitch vs. 23 pitch

There is no way to tell you what the result's would be, without your current speed at wide open throttle and rpm's that it's running when there.

 

[spiphen]

Re: 21pitch vs. 23 pitch

It runs around 57 mph, 4600 rpm's at WOT.

 

[Silvertip]

Re: 21pitch vs. 23 pitch

It appears you currently have the proper prop. Increasing pitch theoretically increases speed but only if you have the extra power available to turn the increased pitch. Therefore, installing a 23P prop may actually slow you down. It could also result in the same speed but lower engine rpm which one would think is better for economy but because the engine is actually lugging, economy may be worse. The best prop is one that allows the engine to rev at the manufacturers recommended wide open throttle rpm with whatever the average load is. Too little pitch and the engine over revs. Too much pitch and it lugs. You can certainly fine tune prop selection by comparing props of various types form various manufactures, but you won't experience magical speed or economy changes.

 

[zeezer]

Re: 21pitch vs. 23 pitch

I had to play with a few props until I found the right one. The previous owner had a 21 pitch aluminum prop on it. I eventually put a larger diameter, smaller pitch ballistic stainless prop on the boat for its best performance. Went from 38 mph with a 13 3/4 x 21P to 47 mph with a 14 1/2 x 19P prop. So for me it was a combination of a more blade surface area, more efficient, less flex prop. This combo kept me in my recomended rpm range & got me the additional performance I was looking for.
I agree with Silvertip, I also think that you have probably maxed out your combination. 57 mph out of 190 hp is pretty darn good in my book. You could always put a big block with a bravo 3 drive & get about 75-80 mph out of it. It would only cost about 20K d

 

[Paul Carlson]

Re: 21pitch vs. 23 pitch

It runs around 57 mph, 4600 rpm's at WOT.

I believe your tach. or spedo. may be off. For your 4.3L GL 190 HP your gear ratio for SX is 1.66 to 1. Per your info 57 mph at 4600 rpm. I used 22 pitch to allow for cup
and your prop slip works out to 1.3%. It should be around 8% to 10%. At 10% slip your speed would be 51.96 MPH at 4600 RPM. I hope this info will help.
P.C.