Prop Question

[Ferdi]

I have a 20' pontoon with a 70HP 3cylinder Evinrude 1994 that came with a 14x13 prop made of aluminum. What would happen if I went to a Stainless Steel 13 3/4 x 13 prop?
I had trouble on the prop sites and couldn't find out anything. HELP if you can. Thanks, Ferdi aka Fred

[PawPaw Gene]

Ferdi, sounds like an even swap to me. But after saying that there are a few other factors involved. Some say the SS prop being heavier will slow the engine RPM a bit. I don't know if that's fact thou. Other than diameter and pitch there is another important feature of a prop, and that is its shape. Props run from the somewhat standard shape of your aluminum prop all the way up to big chopper props made to run at high speed and half out of the water. Some props are design for heavy loads and some for speed. It's somewhat difficult to predict exactly what the end result will be, sometimes you can get it close but most times it's a trail and error affair. That's why most dealers have try props, because even they can't be sure of the end result. I've seen the same prop on identical motors and boats perform very different. One example right here, look up "canepoles" plight with his boat and motor which is identical to "Paw Paw Perch's".

Just sharing some thoughts.

"gene"

[skintback]

you may lose some rpms because the stainless is probably going to be cupped and heavier. in general when switching from a standard aluminum prop to a "cupped" stainless steel you drop 2 inches of pitch. performance wise i don't think you would notice much of a differance unless the prop on it now is in really bad shape. you could see a 1-2 mph increase and slightly better handling. but it's like paw paw said, there's some trial and error.

[sticko]

I would call a prop repair place.

tell them what rpm the prop you are running now puts out.

then they can tell you what size stainless prop you need to get that boat out of the hole. Perform the best at top speed.

[woody123]

13 3/4 x 13 prop would work, since you really dropping in diameter alittle, The big difference with Aluminum and SS isn't really the weight, its that with an aluminum prop it flexes when put under load lossing alot of pitch making it easly to spin.

[Ferdi]

With my aluminum prop I was going around 24MPH at 3750 RPM's so I put the Stainless steel prop on and went to 29MPH at 3000 RPM's . I'm not to sure the Tach is correct because the speedometer and other gauges are a little off. I got the MPH off the GPS/SONAR unit. I won't be running WOT all the time but I figure this may help me on fuel consumption, this Evinrude likes the gas. It gets up fast and goes really good with less RPM so I'm thinking I should be okay??? What do you all think?? Ferdi aka Fred

[Barnacle Bill]

I have a 20' pontoon with a 70HP 3cylinder Evinrude 1994 that came with a 14x13 prop made of aluminum. What would happen if I went to a Stainless Steel 13 3/4 x 13 prop?
I had trouble on the prop sites and couldn't find out anything. HELP if you can. Thanks, Ferdi aka Fred

About Boat and Marine Propellers (props)

[Ferdi]

About Boat and Marine Propellers (props)

That's a good article you posted. I can only hope my tach is off and I'm operating in the safe zone. I better take it to the guy I bought the prop from and see if he has a tach I can try it with. Don't want to burn that engine up. Ferdi aka Fred

[sticko]

if your tac is right then i would say the prop is to big. you should be more in the 5,000 to 5,500 range but check owners manual for the engine.

It wont hurt your motor to run at 3,700 but you are loosing a lot of speed

travel is in inches per each rpm.