help with prop pitch


New Member
I am not new to boating but new to boat ownership. I have 93 four winns 17ft 6 cylinder volvo penta engine. the stock prop needs to be replaced it is 14 1/4 x 21 can someone explain or tell me where to find out exactlly what these numbers mean. If I want more power than what can I go to. If I want more top speed what dementions do I need.
Also are plastic props any good?


Staff member
Welcome to the forums fourwinns - nice to have you with us.

There a couple of basic factors with props....

-Material - Composite, Aluminum or Stainless Steel
-Number of Blades - 2,3,4 or 5

Most would agree (I think) that right now, Stainless Steel is the best all around material.

The number of blades you choose will depend on your specific setup along with your specific priorities.

The pitch is largely determined by the max rpm's of your engine and how each prop responds on your boat. Meaning, you basically want to prop your boat so that at wide open throttle (WOT) your motor is running in it's maximum RPM range.

The diameter size is somewhat determined by your specific motor or drive.

I would guess based on what you posted, that you have a 14 1/2" diameter prop that has a 21" pitch.



Active Member
the 14 1/4 is the prop diameter and the 21 means that for each revolution of the prop the boat will move 21" forward. the higher this number the faster you will go, the lower the faster , but make sure you don't over rev


Staff member
thanks or your quick response. So what i gathered I need to find rpms of engine go from there?
Well propping a boat is a bit of an experiment of sorts. Every boat is a little different and responds a little different, so the best case scenario is that you find a local dealer that can loan you some props to test out. Then when you find the one that works best, you purchase that particular one.

Essentially what you'll want to look at is trying different types of props. As a general rule of thumb, usually three blade props provide the best top end and five blade props provide the best hole shot. So if skiing and tubing is your thing, then you might find that a prop like a "high five" five blader would suit you best. On the other hand, if you like top end over having a great "hole shot", then you might find you like a three blade prop best. And then there are four blades which quite often can be a compromise between a three and a five. But those are just some basic rules of thumb. The reality is that every boat is a little different so sometimes they don't necessarily all respond the same.

As far as the pitch goes, yes, you'll want to find a prop with a pitch that when you're at wide open throttle, puts you somewhere close to the maximum rpm range for your motor. Moving up in pitch will drop your RPM's down, meaning, moving from say a 21' pitch to a 23' pitch prop will reduce your RPM's. And moving down, will increase them. Additionally, adding blades will reduce your RPM's and decreasing the number of blades will increase your RPM's.

Given that, you can probably use your current props performance as a starting point and then work from there. :)