Need help with prop for 3.0L Mercruiser

[penny lane]

Hello all...

I have a 1986 Starcraft with a 3.0L Mercruiser with a 1.98:1 ratio Alpha one outdrive. My problem is this: I currently have a 14.5x19p prop on it and cannot achieve WOT of 43-4600 RPM... I only get to 38-4000 with this prop, and a GPS speed of 32 mph. I have ruled out all the low WOT items in the sitcky, so my question is this...will a 17p prop get me to where I need to be or do I need to go lower pitch than that?

Thanks in advance!

 

[Bondo]

Re: Need help with prop for 3.0L Mercruiser

Ayuh,... That otta work...

 

[steelespike]

Re: Need help with prop for 3.0L Mercruiser

Typically a 3.0 alpha 1 w a 19" would run about 40 and in the 43 to 4600 range.
Unless that boat is a real bruiser something is up.A 17 is usually suggested for sking
with a caution about over reving.

 

[penny lane]

Re: Need help with prop for 3.0L Mercruiser

I checked everything else Steelespike...the boat weighs about 2500#...fiberglass deep-v hull, 3/4 plywood deck, new stringers, all new ply transom with everything covered with 1.5 oz CSM then covered with finishing cloth and resined in quite well. So aside from finding a 4.3L and matching drive I figured all that was left was change the prop out.

 

[elkhunter338]

Re: Need help with prop for 3.0L Mercruiser

You are about right, I run a 3.0 i/o in a starcraft 21 foot cheiftain and get about 26mph @ 3800 rpms wot. I am running a 4 blade adjustable prop set at 16p. I had a 19p 3blade prop with only let the rpm get up to around 3400 rpms but still 26-27mph. I run engine around 2800-3 @ 20-21 mph for cruising and find this get me better fuel economy than a lower pitch prop, but yet it still gets on plan ok.
The engine at 3800 rpms sound like it is reving plenting for a in-line 4 cylinder and I have dropped my pitch to get rpms up around 4 and didnot like it. I burn't more fuel at a 20 mph cruise speed and plain just don't like the sound of the engine up above 3200 rpms for long periods of time. (30-45 min runs).

 

[gixxerjim]

Re: Need help with prop for 3.0L Mercruiser

FWIW on my '88 Sea Ray 18ft bowrider with 3.0L I could get 36mph from a 19P Mercruiser prop at the high end of the rev range (4500 or so) and 40 with a 21P mercruiser prop a the low end of the range (4200rpm). These speeds GPS with full fuel and 400lbs of people on board.

I beleve the prop expert on here hwsiii (?) recomended a Solas Amita 4blade 19P for my setup...