Questions about props

[LegacyT]

Here's what I have:

89 baretta phaser 230
volvo penta aq231a, 275 drive
michigan wheel 14x19 alum prop

The engine is able to overrev by 400 rpm at wot

I'm considering a stainless prop but can only find a 15x21. Just lookin for input. The extra 2" of pitch should bring the rpms down but what about the increased diameter? What performance should I expect with this prop before I buy one? There is also a 15 5/8x23 but I think thats too much prop. Also is standard rotation the same as right handed?

Thanks

 

[craze1cars]

Re: Questions about props

Depends entirely on design of the prop you're starting with, and the prop you are considering.

Diameter has far less impact than pitch. Yes RH is known as standard.

Don't be surprised if switching from your aluminum 19 to a stainless 21 reduces your rpm as much as 700 or 800 rpms. Or maybe only the 400 you are seeking. Very difficult to predict.

Changing materials can be tricky. Most stainless props bite the water much better than most Aluminum props. There are exceptions. With more bite comes lower RPMS.

I suggest test-drive if at all possible, or some type of exchange policy (you will find this is extremely rare in props). You my very well get by with a 19 pitch in an aggressive stainless design, and acheive nearly a 400 rpm reduction in the same pitch as you have right now.

And you also may not. This is why test-driving is extremely valuable and highly suggested.

 

[LegacyT]

Re: Questions about props

The prop I'm considering is a solas new saturn and they do offer them in 15x19 if that helps... dont know if they are considered aggresive pitch or not

 

[craze1cars]

Re: Questions about props

The New Saturn does not appear to be a particularly aggressive prop. So reduction in RPMS may not be as great as it would normally be with a stainless change. That said, I have no experience with that particular prop to know for sure.

I'm still wondering if maybe that particular prop in a 19 might bring your RPMS down a couple hundred from where you are now, and that prop in a 21 might bring your RPMS down farther than you'd want it to...

Sorry but I don't feel comfortable trying to predict which is a better choice...you'll just have to try one and see how it performs. Maybe someone else here can help predict better than I can.

It would probably help to know what your performance objective is? To you value holeshot over top speed? Vice-versa? Any watersports? Just cruising?

 

[LegacyT]

Re: Questions about props

I would like a happy medium I do mostly watersports with some cruising.

 

[craze1cars]

Re: Questions about props

With watersports in your regular usage, a slight over-rev is a good thing....helps substantially with holeshot. So simply switching to a stainless of the same pitch will probably drop your rpms by maybe 200 to 300? Pretty darn close to your objective.

I guess I'd recommend buying the 19 in a stainless before you bought a 21. I fear 21 will drag your RPMS down too far and hurt your holeshot more than you'd like.

And as always....I might be wrong...

 

[rwxyz]

Re: Questions about props

I guess I'd recommend buying the 19 in a stainless before you bought a 21. I fear 21 will drag your RPMS down too far and hurt your holeshot more than you'd like.

And as always....I might be wrong...

Is it bad on the I/O drive or engine to drag your RPMS down too far with a high pitch prop, I understand the bad holeshot. I just like to cruse at 3/4 throttle.