Mirage 19p vs Mirage 17p?

[boykster]

I just found out today that I don't have the 'correct' prop on my boat. The manual recommends a Mirage 19p (15.25" 3 blade w 19" pitch), but I have a Mirage 17p (17" pitch). I will admit I'm a prop noob (and haven't done my research yet - I will), but overall what difference in boat responsiveness would I notice if I switched to the 19p prop? I've never driven the boat with any other prop, and when it's running properly, I can't say I've noticed any 'issues', but the boat is an '89 SeaRay 250DA with a 7.4L/BravoI and she's not the most agile of boats, nor the fastest.

I'm not quick to just buy a new prop because the book says I'm running the 'wrong' one, more just curious how much of a factor 2" different pitch has on the performance of a boat....

 

[steelespike]

Re: Mirage 19p vs Mirage 17p?

I think you need to reread your post looks to me like your running a 19pitch like the book suggests.
Also its not unusual to select a different pitch to help improve performance for your particular
needs.

 

[boykster]

Re: Mirage 19p vs Mirage 17p?

sorry - re-read post and I meant to say I'm running a Mirage 17p...I blame the fumes from replacing my carb ;-)

I guess I'm just curious what difference moving 2" of pitch makes...I'll read some threads here and see

 

[craze1cars]

Re: Mirage 19p vs Mirage 17p?

2" of pitch probably will change your rpms at full speed by about 300 to 400 rpms. A 19 will spin your motor that much slower than a 17. Increasing pitch will generally make a boat "less responsive"....slower to plane out. Maybe bump your top speed a hair...but that all depends on how you are currently propped.

How did you "find out" you have the incorrect prop? That is based entirely on your RPMS, and you haven't shared any RPM info with us.

At full speed, wide open throttle, trimmed out, light load: How fast is the boat (mph), and exactly what RPMS is the engine turning? Based on that, we can tell you whether your prop is correct or not.

 

[boykster]

Re: Mirage 19p vs Mirage 17p?

Thanks craze1cars - by 'find out' all I mean is that 'the manual' says the boat came from the factory with a Mirage 19p, but the boat currently has a 17p on it. I know the previous owner changed the prop at least once, and I'm guess he did it to increase responsiveness. I'm aware that the 'correct' prop for a boat has nothing to do with what's written in the manual and has everything to do with rpm's, responsiveness, etc.

Thanks for the info - if I get serious about changing props, I'll make sure to come loaded with WOT rpm, boat load, etc and more specific information.

 

[ufm82]

Re: Mirage 19p vs Mirage 17p?

you are correct in the statement "there is not 'correct' prop" for the boat as listed in the manual. The correct prop is the prop that does what you want it to do while running within the recommended RPM range. I have a 19 pitch prop for my boat for fishing by myself and running at high speeds and a 13 pitch prop for pulling tubes and hauling family. Both are the "correct" prop for the application. As craze said and you agreed with, details are needed. I will say that for a large boat like that the Mirage is a great choice but it's not a speed prop in that pitch range. Mirage props have big blades, low rake and not much cupping. They are great load props for cruisers and heavy boats like a 25 footer. Many offshore boats run Mirages and do well with them. My 19 is a Tempest but my 13 is a Mirage.

UFM82