2300sc Stock Prop pitch?

[rock doc]

We just bough a used 2000 maxum 2300sc with a 7.4 mpi and bravo III. Can anyone tell me what the stock pitch is for this boat?

It currently sounds like it is hitting the rev limiter at 48mph. I tried trimming down and it is not due to prop ventalation. The props are almost perfect and I dont trust the tach.

[shrew]

MPH is irrelevant. What is the max rpm @ Wide Open Throttle (WOT)? Either you're under-pitched (max rpm exceeds recommended range), or you're overpitched (max rpm is under the recommended range).

Max RPM range is 4400 - 4800.

[rock doc]

I dont trust my rpm guage. Cleaned up the contact and it reads ok but the guage is 18 years old. Would like to know the gear ratio (the serial number is painted over) and stock prop pitch so I can d uble check based on speed. It is a light boat with a BIII. Prop slip should not be a sig issue.

I am assuming maxum would not under prop a boat to the point it would bounce the rev limiter so would really like to know the stock setup.

[mmwjr]

Originally Posted by rock doc

I dont trust my rpm guage. Cleaned up the contact and it reads ok but the guage is 18 years old. Would like to know the gear ratio (the serial number is painted over) and stock prop pitch so I can d uble check based on speed. It is a light boat with a BIII. Prop slip should not be a sig issue.

I am assuming maxum would not under prop a boat to the point it would bounce the rev limiter so would really like to know the stock setup.

How much throttle are you at when the rev limiter is hit? You should not run a boat at 4400 or high rpm for more than a few minutes.

[rock doc]

I am just running WOT just long enough to try and test the top end. The tach is suspect so I would have to go buy a ditigal tach to even bother giving you any rpm numbers. At one point it had floated up to 6000 rpm before I cleaned the contacts. I really dont think the boat is under propped to the point it should be hitting the rev limiter at 48mph with a set of 26P bravo III props. I am more worried about the potential for fuel starvation or an electical problem. Perhaps the issue is the tach is failing or a bad ground? I am going to unplug the tach the next time I go out.

[mmwjr]

The tach just gets pulses from the ignition system, the engine ecm determines rev limit so I don't think the tach is the issue.

[rock doc]

Took the boat out again today. It is showing 4900 on the tach at 48mph on GPS when it starts to cut out. Assuming a 2.2 gear ratio that would mean 12% slip. Did they really gear these boats that low? I would think it would be 1.81 or 2 for such a light boat.

[mmwjr]

Originally Posted by rock doc

Took the boat out again today. It is showing 4900 on the tach at 48mph on GPS when it starts to cut out. Assuming a 2.2 gear ratio that would mean 12% slip. Did they really gear these boats that low? I would think it would be 1.81 or 2 for such a light boat.

Get the serial number of the drive and call mercruiser, they can tell you the gear ratio. Can you tell if the drive has been replaced? Someone may have installed a different ratio drive.

Frankly I would not be worried about the engine protecting itself at 4900 rpm.

[rock doc]

That is what I was thinking...the drive maye not be original. I need to pull the drive to get the ratio. Sounds like I will have to wait until the end of the season. I did call the former owner this am and he confirmed it is underpropped. He did not know the gear ratio though.

[shrew]

4900 would be barely underpropped. dropping 1" of pitch would put you at 4700, which would be fine.

On the other hand, under what conditions would be trying to run at WOT?

[rock doc]

We had 6 adults on board and 3/4 tank of fuel and a full water tank. I just checked the manual and the the rev limiter for a 7.4 mpi is 4680 rpm. If I assume my tach is wrong and plug 4680rpm 2.2 gear ratio and 48 mph into the slip calculator I get 8% slip. This seems to be in the ballpark. I think 28p is safe and perhaps even a 30p may work. 28p takes me to 52 mph and 30p yeilds 55mph at the 4680 rpm assuming the slip does not change from 8%.

[mmwjr]

If it's the original drive the serial number should be on the engine cowl.

[rock doc]

It is not on the engine. Check already. That is where our old carbed boat had all the motor and drive info.