prop selection help needed

[1216bandit]

The boat is a 1991 19' starcraft islander. The boat struggles to get on plane with just 2 on board.

Guessing the weight to be 3000lbs with fuel 2 people, kicker motor etc.
Max speed now is 29 mph at 4200 rpm
Enginge is 3.0 mercruiser
Alph 1 gen2 1.98 drive
Prop numbers are 48 78118 A40 17P

This is a friends boat and any suggestions would be appreciated!
Thanx....Dan

 

[MikDee]

Re: prop selection help needed

It sounds like an engine problem? That 17" pitch prop should be able to pull 4600rpm, & close to 40mph.

 

[steelespike]

Re: prop selection help needed

I think the typical 3.0 on that size boat would run a 19 to 21" pitch.
The 21 would probably struggle a little with hole shot but run about 40 mph. at 4600-4800
If we assume a 19" lightly loaded should have good hole shot and make 38 or 39 mph. at 4800.
I suspect a motor issue Hopefully something simple.
Is there a hydrofoil in the outdrive
Does the throttle open all the way? Is the timing set right and advancing as it should?
Is it running on all 4 cylinders.
Do a compression check
By the way a 17" prop usually would be used for skiing with a boat load of people and may over rev with a light load.