[Lex81]

Dear All,

Last year I bought a Mariah SX22 (20 with the extended swim plateau). It is a 2009 model.

It has a Mercruiser 5.0 MPI Bravo setup (model number 4-M42027U s and serial number 1A045913) I am not sure on the gear ratio but it think 1.5/1. It still runs the original aluminium prop.

I experience the following.

At WOT with a full tank of gas and 3 avarag epeople it runs at about 5100-5200 rpm's and reaches about 85KMH on the speedometer. Isn't this a litle too high in RPM's at WOT? While turning/cornering the boat it easily overrevs. Actually really easy. A friend sayd I should look for a bigger prop.... And there it all starts!

Now I have checked several sites and I kind a like the mercury props but really don't know the size or pitch I should select. I think a 3 or 4 blad in SS should do the job but i really have no clue on the pitch and diameter.


Tried to find the markings on my current prop but can't...

Maybe someone has the same boatsetup and can tell me their experience?

Thanks!

[mikeyt]

Lex, there are 3 'stickys' at the top of the Prop Forum that will help you understand prop selection. Spending 20 mins to read thru the information will guide you in figuring out how to choose a prop for your boat. A little education goes a long ways when it comes to props.

As for your existing prop there are always markings on it. Remove the prop and check around the hub on the front inside. You will either see markings like "14.5 x 19" or a model#. That info will give you a base position to start from. And note that two similar boats running the same power/outdrive may not necessarily run the same prop.

As your outdrive is a Bravo 1, your recommended WOT range is 4400 - 4800 rpms which means you are a fair bit over at 5200. Assuming the tach is accurate it also means you are using a more fuel than you need to throughout the rpm range.
This will likely mean that you need to go up in pitch by approx 2" to get your max rpms down to 4800 and get the motor running in its most efficient range. You can also check the settings on your tach by accessing the back side of it. There is a small wheel on the back marked 2-4-6-8. Just give it a spin a few times and then re-set it to 8 (8 cylinder) to see if it makes a difference.

85 km/hr is very good for that particular boat, possibly even a little more than i would expect. Your comments about the prop over-revving during turns is typical of a prop that has lost its bite with the water. Going to a 4 blade prop will help in this regard as will trimming your outdrive in during turning. You could also consider adding a pair of Smart Tabs which will help your boat get onto plane faster, keep it there longer and flatten out your boats attitude during turns.

[Lex81]

Thanks Mikeyt,

Already glanced over them. (Stickys). Quite helpfull!
I was actually also wondering if there are people with the same setup (SX20/22 with the 5.0mpi and bravo stern) and learning what kind of prop they were running.

In anyway i will need to take a dive and figger ut the prop's numbers as taking it out is a real hassle. Need to bring those RPM's back around 4.600-4.800


Friend of mine has a 2006 SX24 with a 6.2mpi. The holeshot on that boat is bizar and it runs exactly 2km's faster than mine.

[Lex81]

Small update.

At the end of the season (Now over in the Netherlands...) it was running at 5000 WOT at 83KMH. (Hull was very dirty..)

Mercruise 50 mpi with a bravo 1 on a mariah sx22 (2010)

Drive ration 1.65
current prop Aluminium 14.25 x 21 P 3 blade

Anyone experience with this setup and a Mercury Revolution 4 prop? I'm looking for some overall performance increase.


Revolution 4 | Propellers | Mercury Marine

What would be recomandable for my setup? 3 or 4 blade? Is there a big different in holeshot from for example the revolution 4 in the comparison to the Enertia or Vengeance?

regards,

Lex

[Lex81]

Back again with this topic!

So, at the beginning of the season I checked everything again:
Boat is still the SX20/22 from 2009/2010.
Engine mercruiser 5.0mpi with the 260bhp on a 1.65 bravo stern drive. It had the original black alu 3 blade prop. 14.25x21P.
At WOT it was doing 5100RPM's and reached 81KMH on the GPS.

Putting this in mercury prop selector It turned out that a 4 blade Revolution 4 in P21 should be a good prop. Somehow I want a 4 blade but do not even know why. I want some good overall performance increase over the alu standard prop.

So yesterday I tried a Revolution4 14.625 P21 on my boat and was not amused at all.
The holeshot was even less as the engine did not rev up well. Ok, this can be adjusted by exchanging the plugs in the PVS as I was running on completely closed ones.
But the topspeed at WOT was exactly the same as with the 3 blade alu prop but now not at 5100RPM's but at "only" 4500RPM's,... My ideal engine WOT range is 4600-5000 RPM's so i think I should be at around 4900-5000RPSm's to profit the most from my engine?
Going down to a P19 ... will this, in theory, only increase the RPM's about 200 and not change in topspeed??

As the 4 blade as best for holeshot but less for the top speed,... what about a nice 3 blade in a "big" size or higher pitch and compensate the loss in RPM at the holeshot by the PVS system? Taking out all the vents should let the prop turn much easyer and revving op the engine faster?

Anyways, would appriciate some comments from people who actually know or run a similar setup on their Mariah sx20/22.

regards,

[Lex81]

ok guys, I found my prop!

Michigan Wheel Apollo 4 blade 14x22.
tried it yesterday and works fine for my set-up.
With 2 people in the boat and half a gass tank and no extra weight of tons of gear we reached 5100RPM's and 87KM's on a good GPS.
I'm happy!! It has a lot of grip in corners and the acceleration from cruise speed to top speed is super!!! Loads of torque in the middle sigment!!
Holeshot could be better.. Might look in to the venting again. When I give full throtle from stil stand the RPM's go to 3000, not more... they start running up as soon as i'm planing.