Prop size suggestions?

[jbalsly]

Hey everyone. First time boat owner. 20ft Stingray deckboat (2017 201dc) 2700lb dry wt, with Suzuki 150 4stroke on it. Stainless Suzuki 3 blade prop, 15.5" diam x 17" pitch. Rec RPM range is 5-6k. We use it as all around boat, pulling tubes, wakeboarding, cruising.
I am hitting max RPM to point the gas cut off is letting me know to back off (around 6300). Even at that point the throttle isn't even fully forward "wide open"...My speed is maxing out at 40mph. Clearly the prop is underpitched.
My question is how much pitch increase should I go for? I'm thinking go up to 21" however I really don't want to spend close to 600 and be disappointed with over or under adjusting it. I believe top speed for that boat should be 45-50mph and each 1" in pitch equates to 1-2 MPH? so 4" increase would get me to where I need to be? Any chance I should go even higher than 21?
Thanks for the input!

 

[Sea Rider]

In a light application with a light load don't expect the +,- 200 rpm reduction per +,- per pitch, it's way over say 350 and above per pitch. How loaded , number of souls were on board when backed down the throttle ?

Happy Boating

 

[jbalsly]

Have to back down on the throttle every time thus far. Even with 8 on board and full tank of gas...

 

[Starcraft5834]

assuming your tac is accurate.. which it probably is.... you need more pitch... i'd go with 19 and back off throttle a speck

 

[jbalsly]

I'm worried 19" won't be enough to allow WOT without the rev limiter yelling at me. Maybe I will just divide the two and go 20" lol.

 

[jbalsly]

Put it this way, ideally I want WOT to be around 5500-5700 RPM's under a good sized load. As it stands right now, if it wasn't for the rev limited I'd prob be pushing 6500 rpm which makes me again think 21in is the sweet spot.

 

[WesNewell]

Get a cheap aluminum 21P and go from there.

 

[Faztbullet]

We use it as all around boat, pulling tubes, wakeboarding, cruising.

Going up in pitch is going to kill all the above..that the reason it is under pitched to have power to pull

 

[Sea Rider]

It's very difficult to dial the correct pitch you're going after with so many variable loads scenarios along different applications, that's 8 up, pulling toys, cruising with a single non existing multipurpose prop for such. Much easier is to dial a best prop in less tries with a fixed or near fixed load. How many adult souls on board would you consider the ninimum you would like to go boating with ?

Happy Boating

 

[jbalsly]

Going up in pitch is going to kill all the above..that the reason it is under pitched to have power to pull

I believe it is so under pitched that I would still have plenty of power to pull going up in pitch. Either way, I still have my 17" as a backup. I went ahead and ordered the 21" pitch. Ironically the boat next to me at storage is identical, and I checked their prop yesterday and it is identical to what I ordered so that makes me feel better. I will install Friday and take out Saturday, will update how it goes.

 

[jbalsly]

It's very difficult to dial the correct pitch you're going after with so many variable loads scenarios along different applications, that's 8 up, pulling toys, cruising with a single non existing multipurpose prop for such. Much easier is to dial a best prop in less tries with a fixed or near fixed load. How many adult souls on board would you consider the ninimum you would like to go boating with ?

Happy Boating

It's at least me, wife and two kids. If we bring anyone it is typically another family of 4-5. So it really just depends. I'll let you all know how the 21" pitch handles.

 

[Sea Rider]

It's at least me, wife and two kids. If we bring anyone it is typically another family of 4-5. So it really just depends. I'll let you all know how the 21" pitch handles.

Will be good to know the wot rpm achieved with 4 and with 8 souls on board and the rpm difference between both loads.

Happy Boating

 

[jbalsly]

Will be good to know the wot rpm achieved with 4 and with 8 souls on board and the rpm difference between both loads.

Happy Boating

Right, that's the hard part lol. My pitch is so friggin low right now I am unable to get anywhere near WOT even with fully loaded boat. Would be a much easier problem to solve if my proplem was overpitched and I was trying to dial it back. Hopefully I hear from my "storage neighbor".

 

[jbalsly]

Also, the prop is 1/2 in less diameter. So that should give me about 250RPM added back. My "hope" is right now WOT would be around 6500 if limiter didn't kick in. So 4in more pitch equals roughly 800 less RPM meaning I am down to around 5700 WOT "but" the 1/2 in lower diameter will up that to 5900 RPM WOT which would be perfect. Fingers crossed.

 

[jbalsly]

Thanks again to all the feedaback. Put on the new SS prop I ordered and it was money! W my family WOT got to close to 6k rpm. Trimmed up we were at 49 on the speedometer (I know gps is more accurate but I also know my previous speedo was 38-39 mph so in genera that’s 10mph diff). Also had more than enough pick up for wake boarding and tubing. So happy w the 15in diam 21in pitch prop!!