Propeller choise
 

Anyone who can tell me what`s the best propeller for my boat?

SX19
4,3l 190hp
Alpha one
max 4800rpm
current max speed 54mph (at the original speedometer)


BR
Roger

What do you have on it now? If i remember correctly the max RPM range is 4800-5000 for the 4.3L so you're pretty close. A 14.25 x 21p - 3 blade is likely correct but you could drop 2p or go up 2p depending on what you're using the boat for (ie skiing/wakeboarding vs simple cruising). Using a SS prop changes things slightly because it doesnt flex as much as a standard aluminum prop. Also, dont necessarily trust your speedo. They can (& usually are) notoriously wrong. A GPS does a far better job of providing accurate speed readings.
Here's a link to Mercury's own prop selector tool:
http://sites.mercurymarine.com/porta..._schema=PORTAL

Now I have the original aluminium propeller, but i do not know the size or pitch at this

The size/pitch should be stamped on the propellor hub somewhere.

I have a 4 blade Stainless Steel "Vensura" on my SX18 - 4.3ltr 190hp.
I get about 50mph top speed (depending on weight in boat).
We use our boat at lot for tubing and skiing. Some cruising (but then we dont go fast anyway).
The 4 blades dont give as higher top end speed as the 3 blade props. But they do have a better pulling power (and not just with the girls either).
Go to the site MikeyT supplied, it is the perfect choice to understand props better.
Onya MikeyT.

What`s stamped at the propeller is 832834A45P23

I get 4800 rpm and 43.6 knots (gps speed)

okay...that model corresponds with a Mercury Black Max 14.00 x 23" aluminum 3 blade prop. As a brief explanation of pitch..... a 23" pitch propellor theoretically moves your boat 23" with one revolution of the prop. Given your rpm max at 4800 and Mercury's recommended range of 4400-4800 (corrected from my earlier post) for the 4.3, you probably have the correct prop for your boat. If you're happy with your boats acceleration, you want the extra speed and you dont often pull skiers or wakeboarders then you should be okay with the prop you have. You could also go to a 4 blade 23" prop which will give you a little better holeshot & acceleration, a little more bite, will likely cost you 1-2 mph and wont affect the rpm and it should help with skiiers/boarders. If you want more top end then increase the pitch to 24" or 25" which will gain 2 mph and drop your rpms by 2-300. A same size SS prop would likely give you a slight speed increase w/out any change in rpm but....they cost $$$. Again, make use of the Mercury prop selector tool!

If you want a better hole shot, want to be able to plane at lower speeds, want to reduce or eliminate low speed wandering and gain a little more control at higher speeds then consider installing a pair of Smart Tabs. I've installed them on my boat and they're a good investment. They also claim that they will give you a 1-3mph increase in speed but i never saw that with mine although it could be the settings i'm using. Here's the link to the Smart Tabs mfr... he's happy to discuss your boat & what benefits the tabs will provide if you email him.

http://www.nauticusinc.com/smart_tabsSX.htm