need prop advice

[cometkrazy]

Hello: I'm new here and need help selecting a different prop for my 2008 1800 Crestliner Superhawk IO. It has a 3.0 Mercruiser alpha 1 running a 14.5 X 19P prop. The thing is that it will rev beyond 4800 rpm at WOT. My speed is only about 38mph at 1000ft above sea level. The boat weighs about 2500lbs loaded. I'd like more speed and to keep the WOT at 4800rpm. I was hoping for better than 40, Am I asking too much? Any help is appreciated. Thanks:

 

[steelespike]

Re: need prop advice

Not a pro but I'll try to get you started.
A speedo can be off + or- 10% A gps is the best judge of speed.
It would help to know more details on your boat,,metal or fiberglass,deep V?
Do you know your gear ratio? You might want to varify the tachs accuracy.
Aluminum or stainless prop?Prop in excellent condition?Is 4,800 the rated max rpm?
An increase in pitch could net more speed and get you closer to 4,800.
It seems to me that a 19" prop should be in the 40 mph range at 4,800 +.
Increasing pitch will generally slow hole shot.

 

[cometkrazy]

Re: need prop advice

The boat is a deep V welded aluminum using a stock aluminum prop. 2.0 gear ratio. I haven't changed anything and I'm the original owner. The factory redline is 4400-4800 rpm. I am getting my speed from the spedometer. It is 18ft long. Thanks for the reply. My tach reaches 4800 way before WOT. I would say I have about 1/4 more left.

 

[steelespike]

Re: need prop advice

Your the original owner and it came with a 19" prop?Has it allways run at
4,800? Your manual or your dealer should be able to tell you what props yield what results.21" prop from the same type should lower rpm 300 to 400.
If you boat with a full load or ski a lot the dealer may have selected a 19 to give you a little more push.You might want to verify the tach before making a prop change.

 

[df909]

Re: need prop advice

I'd make sure your tach is correct. I have a 4.3L with an Alpha 1 with a 19p 4-blade aluminum. With two kids & two adults I can just reach 4700 at WOT and maybe 45 MPH. If you went to a 21p you would gain top end and it would reduce the RPM's. I would look at getting a 4-blade prop as you'll still have your hole shot and you'd probably increase top end a bit. Aluminum is fine for a 4-blade since it's about $130 vs. $450-$500 for a SS and you will only get a few % better performance.

There are some boat shops that will let you borrow a prop to test it out before you buy, so hit them up so you can test the performance. But, I'd really make sure the tach is accurate. Good luck.

 

[cometkrazy]

Re: need prop advice

Thanks for the replies. Is it common for a tach to be off on a new boat? Mine has about 20 hours on it. From the other posts I've read it sounds like you need to try a few props to zero in on the right combination. I'm going to try a 21P prop and hopefully drop the rpm at WOT