New Prop Selection

[dcarver]

I'm needing a new prop and I want to get the best all around performance out of my boat.
The boat is a 1994 manta ray 189 sport with a mercruiser 4.3LX/alpha one.
It currently has a 3 blade aluminum 19 pitch.
I'm new to this size boat and new to the importance of prop selection so I want to get it right the first time.
I'm not looking to spend more than $200 if at all possible, but I do understand if I must, I will.
Thanks for the help

DC

 

[jestor68]

Re: New Prop Selection

You prop your boat so that the motor operates within it's recommended full throttle rpm range; which in this case is 4400-4800 rpm.

You base your selection upon what rpm it does with the current 19 pitch prop, and adjust up or down based on the tried and true estimate of 150-200 rpm per inch of pitch change.

 

[michaelh22]

Re: New Prop Selection

I went with a 14 1/4 by 21 pitch on my 4.3 and it does much better over with getting on plane and top end speed then the 15 by 19 pitch that was on it when I bought it hope this helps p.s. got the prop and hub kit at west marine for $160

 

[dcarver]

Re: New Prop Selection

Well with the 19 pitch I'm running 4500 RPM at 35 MPH. I don't know if that sounds right but I did have 6 people in the boat.
So the 21 gave you no problems with pulling skiers?
I found a 21 on craigslist but it went to a volvo penta sx. Guy says it has the interchangeable hub so it can fit boats with a 19 tooth spline. I haven't looked at how many teeth mine has but would it work if it does?

 

[jestor68]

Re: New Prop Selection

You want to prop the boat for whatever your "normal" load is. I believe the 19 to be about right if it can pull 4500 with that many people in there. Take some weight out, and it'll jump up to 4800 rpm.

With that load, a 21 will drop you out of your recommended rpm range. So the 19 pitch appears to be the best prop for good over all performance unless you intend to run around with a light load all the time.

Your Mercruiser prop shaft has 15 splines; not 19. A Volvo SX prop would use 19 splines. Be careful of Craigslist BS.

 

[jestor68]

Re: New Prop Selection

I went with a 14 1/4 by 21 pitch on my 4.3 and it does much better over with getting on plane and top end speed then the 15 by 19 pitch that was on it when I bought it hope this helps p.s. got the prop and hub kit at west marine for $160

All 4.3L are not created equal. His is a pre-Vortec motor. What year is your 4.3L?

 

[dcarver]

Re: New Prop Selection

It's a 1994

 

[not enuf toys]

Re: New Prop Selection

best info I can give (which may not be much) is save the headache of guessing and calculating what is out there.

find a local marina that will work with you and allow you to test / try out props. I tried out 6 one year and landed on one that I would have never even though of as my skiing prop, and maintained my original for my speed prop (even though I rarely use it - gave up approx. 5 mph on the top end but this new whole shot is impressive!)

 

[dcarver]

Re: New Prop Selection

Ya I bet that would be the best idea. I'll see if
I can find that. I just don't want to feel obligated to buy a $400 prop lol

 

[steelespike]

Re: New Prop Selection

It's only fair to patronize the dealer lending you the props to test.
after all your not the only one he's helping out.

 

[callen369]

Re: New Prop Selection

Hi , I'm running a 96 19' searay bowrider with a 4.3LX/alpha. Mine had a 14.5x21 3 blade, and I switched to a 14x21 4 blade turning point Hustler Aluminum prop. Turning Points' site says "When switching from a 3 Blade propeller to this newly designed Hustler 4 Blade, use the same pitch as your 3 Blade, unless your current Wide-Open-Throttle RPM is running in the lower third or below the recommended WOT RPM range for your engine." I agree with jestor69, with a lighter load, you would probably be running low mid 40's. And you probably have great hole shot. So stick with the 19 in a 3 blade or the Turning Point 4 blade, same diameter or close to. Turning Point will run you about $150 total for prop and hub.

You didn't mention diameter....guessing around a 14?

 

[dcarver]

Re: New Prop Selection

diameter is 13.75

 

[dcarver]

Re: New Prop Selection

Ok so I've been researching and I've got it narrowed down to 2 props. 14 1/2 19pitch 3 blade or a 14 1/4 19pitch 4 blade. I've found that the 4 blade will most likely decrease top speed by 1-3mph which isn't that big of a deal. The 4 blade does claim to have better control around the docks which would be great. So basically what I'd like to know is which would y'all recommend? The 3 or 4 blade?

 

[callen369]

Re: New Prop Selection

I like my 4 blade. Idle speed control was a big difference right away, so that helps around the dock and trailering. Plus it was a much smoother prop. I had a good amount of vibration from my 3 blade, even though it was only sratched on the edges a bit. Could have been some hidden/un-noticeable damage, but the switch made a big difference on both.
When I switched to the Hustler prop in same pitch/diameter, I actually gained 1 MPH, and kept/maybe improved my hole shot.
If you go with a different brand of 4 blade, you may consider dropping a pitch to keep your RPM's the same.

 

[dcarver]

Re: New Prop Selection

Well I ended up buying a 4 blade 18 pitch turbo brand new for $60. The guy purchased the wrong one for his boat and could not return it because it was on clearance so lucky me. I can't wait to try it out now! Really want to take it out this weekend but don't want to deal with the idiots on such a small lake. Thanks for all the help!

 

[callen369]

Re: New Prop Selection

Well I ended up buying a 4 blade 18 pitch turbo brand new for $60. The guy purchased the wrong one for his boat and could not return it because it was on clearance so lucky me. I can't wait to try it out now! Really want to take it out this weekend but don't want to deal with the idiots on such a small lake. Thanks for all the help!

Be watchful of your WOT RPM's if you speed test it. Max should be around 4800. Other than that, GOOD LUCK! Hope it works out for you.