150 hp Johnson and crestliner sportfish 1850

[T Smack]

It's a 1996 V6 150 pushing a 00 crestliner sportfish 1850 with an OEM 15.5 x 14 SST Prop. Max RPM is currently at 5800 pushing the boat closed to 40MPH. I'm looking to get more speed, what do you guy recommend? No problem with hole shot right now and cavi plate is showing at cruising and full throtle.

 

[steelespike]

Re: 150 hp Johnson and crestliner sportfish 1850

To my experience your speed is slow it seems to me you should be closer to 50 mph.
Motor is rated for 5,500 rpm by my info.If you go to same brand and style 16" prop
you'll be closer to 5,500 and get a slight speed increase.
Is the bottom clean and smooth?Prop in excellent condition?Carbs opening all the way?Does the bow come up when you trim up?Is the speed by gps?

 

[T Smack]

Re: 150 hp Johnson and crestliner sportfish 1850

The bottom is not perfect, some scratches and dent cuz it ran over something from the previous owner. The motor was not the original, I just bought it and rebuild it to put it on this boat. It was previously an inboard converted to an outboard.

Bow does go up when I trim and the trim is right at cruising and wot. 40 mph is gps. Carb is fully open and prop is in good condition still.

I was thinking about a 14 1/2 x 19?

 

[steelespike]

Re: 150 hp Johnson and crestliner sportfish 1850

Rule of thumb each inch pitch change results in "about" 200 rpm change.
If you go to a 19 you will lose 800 to 1,000 rpm.
I think your normal setup would be with a 17" pitch around 48 mph. at about 5,500
If your still breaking it in after a rebuild it may improve.You wouldn't be out of line with a 17"

 

[T Smack]

Re: 150 hp Johnson and crestliner sportfish 1850

With a smaller diameter on the prop to 14 1/2 wouldnt that offset some lost on the rpm with the bigger pitch?

 

[Haffiman]

Re: 150 hp Johnson and crestliner sportfish 1850

Your propeller is an 'obsolete' pontoon propeller not for your kind of use.
Try a 17".

 

[steelespike]

Re: 150 hp Johnson and crestliner sportfish 1850

With a smaller diameter on the prop to 14 1/2 wouldnt that offset some lost on the rpm with the bigger pitch?

Generally as pitch goes up diameter goes down.Diameter is not usually considered in direct relation to rpm. Two props of the same pitch with vastly different diameters(not likely)
The larger diameter prop may show a reduced rpm in relation to the other.The larger diameter prop might be for a specific application.

 

[T Smack]

Re: 150 hp Johnson and crestliner sportfish 1850

Thanks everyone, I'm going start shopping around now.

 

[T Smack]

Re: 150 hp Johnson and crestliner sportfish 1850

Just a lil update, I was able to borrow a 14 1/2 x 19 alum prop to try it. Motor was pushing around 5400-5500 rpm and speed was roughly around 3-5mph more.

Does that mean I can get away with a 21" and pushing around 52-5300 rpm and hopefully gain a few more mph? Is it good for this motor the be running around that range or better at 5400-5500?