Help, boat is not going very fast

[tkgawley]

Hey guys Im new to this site but I have a few questions, just bought a boat
2003 Bluewater Mirage 20'
5.0GL 220HP 19 pitch aluminum prop

I took the boat out and I could only get about 40-41 MPH on the crappy speedo, I have boated for many years and i definately was not faster than 40MPH the tac was about 5200RPM but i didnt have the throttle right down but I didnt want to over rev it.

My question is, the gimble bearing went on the boat that test drive. (the dealer is getting it fixed at his cost) would that be slowing the boat down? Do i need a new prop possibly 21, it had crazy power out of the hole with 2 of us in it 20 gallons of fuel.

 

[Bondo]

Re: Help, boat is not going very fast

Do i need a new prop possibly 21,

Ayuh,... That would be My guess,... The gimbel bearing is irrevelant...

 

[tschmidty]

Re: Help, boat is not going very fast

Yes, you need a new prop if you want more speed. Your rpms are fine and a 19p is small for that size motor in my opinion. You can poke through the forums and find some recommendations on what people with similar boats and motors are running.

 

[Yellow Yota]

Re: Help, boat is not going very fast

Yes, you need a new prop if you want more speed. Your rpms are fine and a 19p is small for that size motor in my opinion. You can poke through the forums and find some recommendations on what people with similar boats and motors are running.

See, I thought that too. But, I have a 21' Rinker bowrider with a 300 HP 5.7 and a 17" pitch prop. At 4700 RPM, I get about 47-48 MPH. I thought that a 17 HAD to be too conservative for my boat and motor.

So, what gear ratio is the outdrive in that Mirage? Mine is a 1.47:1, so a 17 is OK. It is spinning real fast! I just did a prop slip calculator, and came up with 6.7%. I assume I won't be able to improve on that, so apparently I have the correct prop!

I assume that the Mirage has a lower ratio (numerically higher) outdrive, so yes. I would think that a more aggressive prop is in order if you want more speed.

 

[tschmidty]

Re: Help, boat is not going very fast

Yeah, good point on the gear ratio. Would be make a big difference. But still based on the RPM and speed I would think a bigger prop pitch would be in order.

 

[thompy]

Re: Help, boat is not going very fast

yes a shot gimbal bearing can cause drag and load the engine.