Same pitch, smaller diameter.

[Sea lyin’]

Have an opportunity to buy a stainless prop pretty affordable. It’s same pitch but an inch smaller in diameter than the aluminum one I run now. Should I snap it up or is going from 14.5”x19 to 13.5”x19 a bad idea?

 

[Squire]

If you are near the max rpms with your current prop I wouldn’t do it. If you have a bit of room it might be a good option. In my experience when everything else is the same the reduced flex of a stainless prop compared to aluminum is diminished as diameter is reduced. There are other factors such as rake, cup etc. that may make the ss prop a better option but I don’t see you gaining much more than shine In this case.
Now if was a four blade ss replacing a three blade aluminum it might be a different story.

 

[Sharphooks]

You should consider adding some background info with that question: what length boat and what outboard are you running now with the aluminum prop; what is the WOT of your current outboard and what RPM are you getting with the aluminum prop? Stainless has less flex then aluminum as you’re probably aware....dropping an inch in diameter certainly will bump up your RPM’s...thus the need for more info on what you have now and what the performance is

 

[Corey_lax]

You need to try it out before you make your decision. Just do a quick trial run and see how it goes

 

[brutus]

If your running a heavy boat it’s not a good idea, smaller prop = less trust

 

[lemmy]

Make sure the gear case is the same size as yours . Ive found a lot of 13.5 's are 4.25 " . Where as 14.5 are more often 4.75. What brand and hp motor you running?

 

[ericl]

In general when switch from AL to SS you increase pitch/diameter to maintain the RPM you reach with the AL prop. You are doing the opposite. If your current max RPM with AL is too low, then the switch might work.

 

[Sea lyin’]

Haha i guess I asked for that. Should’ve just posted the info from the start. Boat is 21’ long and has a mercruiser 165 inboard. Recommended rpm is 3900-4300. Current prop my WOT RPM is right at the 4000-4100 mark. Too speed is 23 mph at WOT. Headed to the lake right now and will switch out props to see what happens if the ramp isn’t too busy.

 

[Sea lyin’]

lost 5 mph off top speed but part of that could’ve been slight chop on the water. Smaller prop revs higher. I stopped giving it throttle at 4300 RPM but with throttle left over I think I could’ve taken it to 4500 or higher. Takes longer to get on plane and overall performance was better with aluminum larger diameter prop.

 

[brutus]

lost 5 mph off top speed but part of that could’ve been slight chop on the water. Smaller prop revs higher. I stopped giving it throttle at 4300 RPM but with throttle left over I think I could’ve taken it to 4500 or higher. Takes longer to get on plane and overall performance was better with aluminum larger diameter prop.

I told you so

 

[Squire]

lost 5 mph off top speed but part of that could’ve been slight chop on the water. Smaller prop revs higher. I stopped giving it throttle at 4300 RPM but with throttle left over I think I could’ve taken it to 4500 or higher. Takes longer to get on plane and overall performance was better with aluminum larger diameter prop.

Don’t fret about it. You‘ll never know without trying. I’ve had several disappointing results with different props even after narrowing down likely options. You may benefit from a four blade of the same diameter with an inch less pitch If you can find one. Craigslist and Kijiji were great resources that kept my experiments affordable as I generally got my money back when they didn’t work out.