I wanna prop

Jim Grogan · 05-31-2014, 12:43 AM

I need a new prop for my 18ft 1999 Mariah Shabah 190 hp merc cruiser where can I get the best deal ? and what is the best diameter and pitch for just pleasure boating and a little skiing and tubing ?

Thanks,
Jim

***mikeyt*** · 05-31-2014, 01:31 AM

Probably a 19" 3 blade or a 20" 4 blade. Search for a Mercury Spitfire aluminum unless you really want to spend the $$$ on a SS prop.

Jim Grogan · 05-31-2014, 05:06 AM

Thanks for the information, I appreciate it.

Jim

Dredd · 06-04-2014, 02:20 PM

I've got a good 19" 3 blade with a bad diffuser ring and a messed up one with a good diffuser ring.
I'd sell em cheap but I don't know if it'd be worth the savings after shipping. PM me if you're interested.

Smokymance · 07-15-2014, 01:29 PM

Quote:

Originally Posted by mikeyt

Probably a 19" 3 blade or a 20" 4 blade. Search for a Mercury Spitfire aluminum unless you really want to spend the $$$ on a SS prop.

How much more aggressive would the 20" 4 blade be compared to a 21* 3 blade at take off?

Im in the same scenario as the Jim Grogan with the same boat basically which came with 21* 3 blade.

***mikeyt*** · 07-15-2014, 01:34 PM

Quote:

Originally Posted by Smokymance

How much more aggressive would the 20" 4 blade be compared to a 21* 3 blade at take off?

Im in the same scenario as the Jim Grogan with the same boat basically which came with 21* 3 blade.

As noted in the educational STICKYS at the top of the Prop Talk forum, there is a considerable difference between the two.

Smokymance · 07-15-2014, 01:55 PM

Quote:

Originally Posted by mikeyt

As noted in the educational STICKYS at the top of the Prop Talk forum, there is a considerable difference between the two.

Oh i read them trust me.. thanks for the great info. I just didn't know how many pitch * drops is usually a good rule of thumb...i was thinking for our 18ft boats a 19* 4 blade was a very good choise.

***ColoradoDiablo*** · 07-15-2014, 02:47 PM

The 19P - 20P 4 blade is a good choice , as mikeyt has stated in other threads with like boat / power packages.
But remember , no 2 boats will react the same. It doesn't matter if they are exactly the same in every detail.
Just a fact of nature.

None of the 18' 4.3L Mariahs' "came with" a 21P prop(that I have heard of). Someone has changed it in the past

A 19P three blade was usually the std , with 17P 3 blades on some of the other "higher elevation" boats.
Throw a set of Smart Tabs on her , and she'll come out of the hole like a rocket!

As usual just my opinion

Smokymance · 07-15-2014, 02:58 PM

Of course! Previous owner did tell me he did swap to an SS 21p...not sure why but id like to gain that lower end back up...right now deciding between an 18P or 19P 4 blade. Keeping in mind that a stock came with a 19P makes me think i should go lower as well!

Sorry for stealing thread, hope all this information helps!

***mikeyt*** · 07-15-2014, 03:03 PM

The most important thing is to get your engine running in its recommended rpm range at WOT. Once you accomplish that, the engine runs at its peak proficiency throughout the rpm range. Choosing a correct prop allows you to get things working within that range. Note though that it is not cast in stone that you have to limit at 4800. Mine will run at 4950 if it let and it wont hurt unless i'm running there for extended periods of time. Generally for our 18-20' boats at lower elevations 3 props work best; a 19" 3 blade, a 19" 4 blade or a 20" 4 blade. There are exceptions though. Higher elevations usually require a lower pitch blade to make up for the lower power level produced by the engine at those elevations. And... we do have some members who run 21" props and even a couple who ran 23" props and other run 17" and 18"said they worked just fine for what they want their boat to do. Note that these are just general rules of thumb.

Edit: couple the right prop with a pair of Smart Tabs and your boat will literally jump out of the hole!