[gahooligan]

don't know my top speed, always have the family in the boat and haven't had it out with smooth water either. I'm on lanier in GA. BUT... I have a 20" 3 blade aluminum on my 99 Shabah 202 5.7 and it feels a little sluggish on holeshot especially when yanking a tube up to speed. Pulling or not it probably takes 4.5-5 sec to get on plane. It has good response once on plane. I figured it should jump a little better than it does but I could be wrong. I'd just describe it as slightly sluggish. No idea what rpms I'm turning as I'm waiting till winter to pull the gauge out and send it in for repairs. From what I'm reading I should probably have a 19 pitch on there for better holeshots, yes?

[rainman55343]

I would go with a 19 ss 4 blade. Will have a really good hole shot.

[EricG]

97 Z255 Shabah, 7.4L, bravo III outdrive, 26 pitch props running around 5000RPM and it doesn't matter the load or water conditions, she always does 49/50 on GPS. 3/4 throttle at 4800 is the same speed as WOT. So I very rarely open it up past 3/4, b/c it is only wasting fuel. I will say that she will go from 0-plane in about 1.5 seconds. I've never seen a 25ft boat plane out so fast. I'm attributing that to the Bravo 3 outdrive. I checked the mercruiser sight and used their prop selector and they said for performance to use 4 blade 28 pitch props and top speed should be 60mph. I'm not sure if their calculator is very accurate, I've never gained 10 mph by changing up 2p on props. I am thinking of dropping the grand to give it a try. It's always good to have a spare set of props I guess.

[ColoradoDiablo]

You'll never see 10 mph from a 2 deg pitch increase. Not to mention , the 4 blades are not made for topend. They are for torque.
But it would be interesting to see the diff.
There are quite of few members that can give you a lot of info on the B3 prop results.
I'm sure they will be chiming in soon Eric.

[EricG]

Rule of thumb for me when putting new props on outboards was for every inch of pitch up was 200-300 RPM down. For example, I had a 13 pitch prop on my fishing boat and it was running 6000 RPM, redline was 5500. I went to a 14 pitch and it dropped to 5800, gained 2 mph top end. I then changed to a 15 pitch, dropped another 200 rpm and gained 2 more mph. My outboard at WOT runs at about 5600 rpm. Then a gear chipped in the lower unit and destroyed the rest of the gears so i replaced the lower and the mechanic ordered a different gear ratio. Not really sure why. But now my outboard runs 5000 rpm wot and is sluggish out of the hole. Time to drop back on the pitch.

[rodneytx]

I have a 1996 18' Shabah with a 4.3 and a 13.75/21 Alu. prop and with full fuel and my wife and I it will go 53 GPS but very slow to plane, I have a new 13.75 / 19 I will install Friday plus a Hydrofoil, hope to be able to plane at 20.

[mikeyt]

Originally Posted by rodneytx

I have a 1996 18' Shabah with a 4.3 and a 13.75/21 Alu. prop and with full fuel and my wife and I it will go 53 GPS but very slow to plane, I have a new 13.75 / 19 I will install Friday plus a Hydrofoil, hope to be able to plane at 20.

If you install a damm hydrofoil on a Mariah you will be disowned here! You might as well wear a pair of Mickey Mouse ears while you are driving the boat around too.

Install a pair of Smart Tabs with 60lb actuators at a cost of $125 or less and do the job right!

[mikeyt]

Originally Posted by EricG

Rule of thumb for me when putting new props on outboards was for every inch of pitch up was 200-300 RPM down. For example, I had a 13 pitch prop on my fishing boat and it was running 6000 RPM, redline was 5500. I went to a 14 pitch and it dropped to 5800, gained 2 mph top end. I then changed to a 15 pitch, dropped another 200 rpm and gained 2 more mph. My outboard at WOT runs at about 5600 rpm. Then a gear chipped in the lower unit and destroyed the rest of the gears so i replaced the lower and the mechanic ordered a different gear ratio. Not really sure why. But now my outboard runs 5000 rpm wot and is sluggish out of the hole. Time to drop back on the pitch.

Eric, why would you run at 6000 when the engine is redlined (for a reason) at 5500? Not only are you using extra fuel you are over-stressing your engine & drive line. At 6k you were way out of your efficient operating range and it wasn't surprising that your performance improved when you changed your props and got your rpms down. Just note that "rule of thumb' is standard practice. Same prop, same number of blades, increase or decrease pitch by 1" will result in a 2-300 rpm change.

As for your outboard gear change, possibly it was the only gearset available to your mechanic at the time and you are right, its time to change props again...

[EricG]

Originally Posted by mikeyt

Eric, why would you run at 6000 when the engine is redlined (for a reason) at 5500? Not only are you using extra fuel you are over-stressing your engine & drive line. At 6k you were way out of your efficient operating range and it wasn't surprising that your performance improved when you changed your props and got your rpms down. Just note that "rule of thumb' is standard practice. Same prop, same number of blades, increase or decrease pitch by 1" will result in a 2-300 rpm change.

As for your outboard gear change, possibly it was the only gearset available to your mechanic at the time and you are right, its time to change props again...

I never ran it at 6000 rpm. It would hit 6000. BTW, it was another outboard mechanic who told me to run the original prop that would turn 6000. Needless to say I don't use him anymore. I always ran it just below the max recommended redline of 5500. That is why I changed the props. I wasn't faulting the mechanic. He actually saved me quite a bit of money and got me a 3 year warranty. I just have to re-prop again. Which is fine since i now have about 5 props for the boat.
I was just poking around the prop section of the forum which also has some great information. Man, I love this site!!!

[EricG]

After checking Mercruisers prop calculator I decided to bite the bullet and try some 28p props. I'm not expecting the 10mph gain that the calculator said they would give. But we will see. I found a good deal on the props on ebay. I went with the 3 blades. I will post again and let you know how they work out. I also re-read my old post and it seems like 5000 Rpm's that I said before was high, I don't think it actually was 5000. I think redline is like 4500-4600, please correct me if I am wrong. I will recheck that also before I change the props. I will also check the time it takes to plane off now and let you know the difference with the 28p props.
Does anyone know how to check for the gear ratio on the lower unit? I know there is like 3 different gear ratios that mercruiser is showing for the BravoIII outdrive.