[steve]

I Have A 1996 Mariah Shabah 18' Open Bow With A 4.3lx Mercruise Alpha One I/o.
Current Prop Is A 14.5 X 17 Pitch. Which Yields 56-58 Hundred Rpm At Top End.
Any Suggestions On Proper Pitch Prop For The Above.
Ty All Vm
Steve

[mikeyt]

5800 rpm for the 4.3V6 is way too high. It should run between 4400 - 4800 rpm. I'd almost suspect the cylinder setting on the back of your tach is wrong though so you might want to check that first. I use a 14.25 x 21 - 3 blade aluminum on mine but am thinking of dropping to a 19 pitch prop or a 20 pitch - 4 blade for a little more bite. I think 180diablo (Ryan) uses a 19 pitch prop on his 18'.

[180diablo]

its in my sig
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However I dont have a 4.3L in my boat. I think my 3.0 runs around where MikeyT mentioned, 4400-4800rpm range approx. I Agree with what MikeyT said. Check the gauge, or have someone inspect it for proper operation and then I would probably change out the prop.

There might even be a proper size selector chart on Mercruisers webpage??

[jmills224]

I have a '97 Talari 179se with the same engine and outdrive. I'm running a 17 pitch(14 3/4" I believe) ss Ballistic prop. I can reach a max RPM of 4900 by myself and half a tank of fuel with a top speed of 49mph.

When I'm loaded with fuel, cooler, wife, myself, and all other gear I usually max out at around 46mph@4700RPM.

I agree with all the others that you have a problem with your tachometer. Also, please post your top speed with your current propeller.

~J

[97 Z222]

I think that merc optimum rpm is 4600-4800 rpm at any size motor. I asked my mechanic about my prop and he gave me the 4600-4800 rpm info. I'm running a 21p on my 7.4L. seems to be the merc sweet spot.

[180diablo]

I know i have seen a few posts in my travels saying, never use the gauge on the dash as a 100% figure in your speed. Verify it with a GPS unit for more precise units.

As for me, from what I remember back in September I was running around 4000-4200rpm range. That seemed to be the noise / rpm / plane sweet spot. I have had it run around 35-36mph (dash) at 4800rpm range, but the engine noise is loud. I dont want to see a piston rocket to the moon ... heh.

After all, I purely have the boat for cruising and anchoring.

[mikeyt]

That 4800 rpm figure is the maximum rpm figure. Running at anything more than that causes premature & excessive wear on the engine so if you are propped correctly that shouldn't be an issue. The engine rpm 'sweet spot' is a completely different animal. That point is where the engine is running comfortably with a reasonable noise level & fuel consumption. If i remember correctly (it's been 3 mos now..) mine was around 32-35mph & about 3700rpm.

All that said....yep, never completely trust your speedo or your tach until you check them out against calibrated measuring devices.

[93mariah]

Our '93 18'10" Barchetta Z has the same Mercruiser 4.3LX Alpha One. Our prop is 17 x 21 pitch, with top rpm being 4800.

[93mariah]

Sorry. Ours is a 14.5 x 21, not a 17x21. My husband says you would have better performance with a 21 pitch. We've used this size prop since the boat was new.

[180diablo]

Originally Posted by mikeyt

That 4800 rpm figure is the maximum rpm figure. Running at anything more than that causes premature & excessive wear on the engine so if you are propped correctly that shouldn't be an issue. The engine rpm 'sweet spot' is a completely different animal. That point is where the engine is running comfortably with a reasonable noise level & fuel consumption. If i remember correctly (it's been 3 mos now..) mine was around 32-35mph & about 3700rpm.

All that said....yep, never completely trust your speedo or your tach until you check them out against calibrated measuring devices.

So even with your boat being a 4.3L and mine being a 3.0L, the 4000rpm range still stands out being the average.

I should have added in my previous post, that when I push it to 4800rpm, I only leave it there for about 5-10 seconds max and then drop it down again. Mostly I was doing it to just see what happens. Once I know, I dont need to use it there again.

I would love to get mine calibrated / checked out for accuracy