speed and rpm
 

Im a new Mariah owner and im having a few issues. Let me start by saying I own a 96 210 shabah with 5.7 liter 1.62 alpha one drive, 21 pitch 4 blade prop. My problem is At wot im getting about 47 mph at 4100 rpms. I think the specs call for a 21 pitch, which should give me 4500 to 4800. any suggestions? Thanks

First thing you want to do is to check the setting on the back of the tachometer & ensure it is set for '8 cyl'. Sometimes vibration or some backyard mechanic (like everyone here ;)) causes the set screw to move. Get in there & move the screw around the different settings then put it on '8 cyl'. Also, check your prop & skeg for damage as that will affect performance. Lastly, make sure you aren't trailing a sea anchor behind you..... :rolleyes:

Let us know how you make out??

If it turns out to be a prop issue you could punch the info you have into Merc's prop selector tool at: https://appcenter.mercurymarine.com/...lector/home.do

I had a quick look and it shows a 3 blade, 13.75" x 23 pitch or a 4 blade, 14" x 23pitch ss prop as ideal for overall performance. Increasing the pitch to 23 should lower your rpm by 200 or so but make sure the tach's working properly first.

I am a new owner and am working with the shop were I bought the boat.

Similar issue as above.
I am running a 454 in a 1994 Mariah Talari z220 with a Bravo I.
The prop and pitch get me to 57 mph but the rpm's go to 5400 and the rpm regulator will shut the engine down to stop any potential damage... any suggestions or does anyone know what the proper pitch and number of blades is recommended? I believe the boat should do around 63 to 65 mph.

It ran with the above numbers on a five blade with a pitch of 25 I believe??? - but I could be mixing that up with the three blade prop we tried which did nothing but spin out.

The other thing I heard was I may not get the maximum speed but my hole shot is greater with the five blade as opposed to a three blade.

Any suggestions, specifications or comments on the above situation would be a great help.
Thanks.

Hi jktbea,

Go ahead and give Mikey's suggestion a go, if it fixes your problem great, if not, could you provide us with some more info?

1) What is the diameter of your current prop?

2) Carbed or fuel injected motor and it's HP rating?

3) How many people are on board and can you give us a guesstimate on their combined weight

4) How much gas was in the boat

5) Did you have any extra ear? If yes, weight?

6) Are you trimming the hull correctly?

From what your saying, I suspect your motor is over propped.

Let us know,
WetWilly

Thanks for all the help guys, I really appreciate it. First prop I tried was a three blade ss mirage 21p not sure of the diameter. Boat struggled to pull a 200 lb skier up. Moved to 4 blade ss 21p revolution 4 with 14 and 5/8 diameter. Gave me a little better bite but boat still struggled to pull a skier up and bow was straight up in air with back of boat washing from side to side. My boat is carbed with a 250 hp rating. I always carry at leased 6 people in boat with a combined weight of 900 to 1000 lbs.Boat had approx half a tank.I had boat trimmed all the way down on take off and trimmed boat out at wot just under bow bounce .I looked at my specs on my motor and says wot should be 4200 to 4600 rpm. I probably pushed it a little in my original post, Im really getting closer to 3900 to 4000 rpm wot. Top speed should be faster i would think. All the boats I had in the past would hit 50 to 55 with a 20 ft 305. Im going to try a 19p prop in a 4 blade to see if that works. Anyone willing to trade a new 21p revolution 4 ss prop for a 19p revolution 4 in new condition would be welcome.Thanks again guys.

I'm not sure i would spend the money on another prop just yet. Make sure the tach is accurate first. 47mph at 4000rpm with a 4 blade 21p prop at WOT is a little off if Merc's prop selector website is accurate since that prop should have you in the high end of your recommended rpm range. Dropping the pitch to 19 will increase your rpm by 2-300 and give you a better start out of the hole but will also drop your top speed. I would have the prop checked for hub slippage. I would also consider installing a set of Smart tabs to help get the boat on plane faster.

The prop was actually a five blade with a 21 pitch and that got me to 57 mph in a hurry. Not so much worried about reaching the top end as I am about the rpm's getting to high and doing some damage.

They are picking up the boat and going to try some different props including plugging the exhaust ports on the three blade (not sure what pitch that one is).

That is all I've got right now.