what will prop diameter change do?

[awritedin]

I have a '94 200 Johnson and it currently has a stainless steel 14.5 x 19 on now. It may be the original for all I know. I have had the boat for 5 years and it was a low hrs. boat when I got it, so I suspect it may not have been changed. The motor runs at about 5,000-5,200 WOT. The prop seems to be a little rounded (worn)at the blade edges but, overall is in pretty decent shape.
I have seen a 14.25 dia. x 19 stelleto(sp) stainless prop and wondered what the 1/4" less diameter could affect?
I have read that pitch seems to be the factor in RPM...what about dia.?
Thanks.

 

[Silvertip]

Re: what will prop diameter change do?

Diameter of propeller is a combination of two factors. 1) It must fit the engine without banging into anything. Hence, propellers are designed for a specific series of engines. 2) It is function of propeller design. That merely means as prop pitch increases, prop diameter decreases slightly and conversely, as prop pitch decreases, prop diameter increases slightly. It is a function of the design and 1/4 inch will have net zero (or very close to it) affect on performance.

 

[Dhadley]

Re: what will prop diameter change do?

Without knowing what your prop is exactly it'll be hard to compare. If it's a 14 1/2" diameter it should be a Raker but they come in even numbered pitches. It could be a 14 1/4" diameter by 19 pitch and be an SST. Or a 14 3/4 x 19 Viper. Or it could be another brand.

Generally speaking a Stiletto will act a lot like a Raker. If the prop you have now only turns 5200 at best with an average load the Stiletto would probably be a decent choice but you'll need to raise the motor to take advantage of the prop technology. I'd bet the motor is all the way down now and needs to come up anyway. Once it does you'll gain efficiency.

 

[steelespike]

Re: what will prop diameter change do?

What Dhadley said.If you have no venting problems your motor is probably too low.The antivent plate(just above the prop) even with the bottom of the boat is considered a starting point.Most motors can be raised from there.Don't change prop and height at the same time.Do the height then select the prop based on your results.It may be possible to get even more height with the new prop.

 

[mthieme]

Re: what will prop diameter change do?

There are other factors involved.
e.g. the smaller one could have more cup.
The important part is - was it made for your motor?
With the exception of a Michigan prop a friend gave me, all mine are OEM.
In general, I opt for OEM parts when possible.
All things being equal, noone can predict how it will make a difference if any on your boat. Personally, I think the difference would not be that noticeable.

 

[Dhadley]

Re: what will prop diameter change do?

The difference between a BRP SST II and a Stiletto is fairly dramatic. But we don't know what prop he really has. If he has an SST II it's one thing. If he has a Raker it'll be different. If he has something else it may be diffrerent again. We'll have to wait for his response on what he actually has.

 

[awritedin]

Re: what will prop diameter change do?

We'll have to wait for his response on what he actually has.

It is most likely the OEM 14.5 x 19, stainless steel, put on by the OMC dealer. It is on a 1994 200 Ocean Runner.
No name or special markings on the prop.
Thanks for the replys.

 

[awritedin]

Re: what will prop diameter change do?

"We'll have to wait for his response on what he actually has".

It is most likely the OEM 14.5 x 19, stainless steel, put on by the OMC dealer. It is on a 1994 200 Ocean Runner.
No name or special markings on the prop.
Thanks for the replys.