Prop help

[TylerT]

Hopping to get some help here, I just finished my 78 22-2 build. I powered it with a new DF200AP Suzuki out board. The prop I have on it is a 3 blade stainless 15x21r. Seams to be very under pitched at 3300rpm the boat will struggle to plain out and run at 15mph. As soon as I was able to reach 4000rpms during the break in, I can plain out quickly but only cruise at 27mph. Is there anyone out there running the same motor? What props do you run or suggest? Thanks.

[mshugg]

What is your max RPM and speed. That’s where the answers lay.  Sounds like you may be over propped - not under.

[TylerT]

That’s what I assumed as well but my local dealer is telling me this motor has a gear reduction lower unit and will need a larger pitch. I’m not positive on my max rpm/mph yet. I’ll know in the morning. Only have 3.5 hours on the motor so I’m at the point where I can open it up for small periods of time. I’ll post that info by tomorrow afternoon.

[Capt.Joe]

I’m definitely not a pro but my understanding is that every inch of pitch lower should give you about 150-200 extra rpms. You definitely don’t want to give your engine a disservice by not running it correctly. For most engines 5500-6000 rpms wide open throttle (wot) is what you want to hit.

You also don’t want to go too low in the pitch either. Running a SS prop vs an aluminum prop will make a difference. 3 blade vs 4 blade will make a difference. Also, the rake in your prop plays a major role in acceleration and top end speed. I hope this helps.

[boatnamesue]

DF200AP Suz rpm range @ WOT 5500-6100 rpms.  If you're topping out at 3300 then this isnt JUST an overprop issue.  200hp isnt gonna have a prop smaller than 17", which means theoretically, if you dropped to a 17" you'd increase rpms by 800 max.  And even then, you'd top out at only 4100....2000 less than where it shud be!!

Check engine height.  AV plate shud be no greater than 1.5" below or above bottom of transom.  Check AV height when on trailer then bring a friend on the boat and run at WOT while you or your buddy look at the AV plate...if you can't see AV plate because it's submerged then the engine is mounted too low.  Engine would need to move up a bracket notch.

If this engine weren't brand new I'd also suggest lack of rpms could be engine related.  But the engine being brand new I'm assuming it's performance is tip-top.  I know guides w/same rig as yours w/same hp engine.  200hp will jump that hull right up on plane, no problem.  Fine tuning the rpms (AL v. SS, rake, pitch, etc) is a moot exercise at this point.  Focus on the issue causing the engine to turn nearly have the rpms it should be turning at WOT.  Once you've got it turning within spec range or just under, then address the fine tuning.

[TylerT]

My motor isn’t topping out at 3300rpm. That’s just as high as I can go for the first two hours and 4000rpm is the max for the next hour for the break in. When I did push the throttle to jump up, it felt like I could red line the motor no problem. Also have a Porta bracket. I have a couple props my friends have loaned me to try tomorrow. I just did a few prop calculators online and they all are close with one another with their suggestions, 3 blade stainless 15.6x23. I’m looking for one now.

[boatnamesue]

Ooookay, so I'd of mentioned ^^^ in your 1st post.  So if im reading between the lines correctly, you have yet to open up WOT.  And if so.....????  Think im still not grasping what your question is.  Sounds like you're putting the horse before the carriage, so to speak.  You wouldn't prop test a boat/motor until the motor is permitted to run at WOT....right?  How could you know prop performance in relation to its effect when you haven't experienced its performance at WOT.  Or maybe I'm just missing your aim, apologies.   

[TylerT]

Yeah I got ya, this is my second 222 build with the same horse power just different brands. My first had zero issues as for performance. Went from a Yamaha 200 to this Suzuki 200 for this boat. It’s extremely obvious that the prop I have is very wrong for the boat compared to my last one. I was hoping to find someone on here with a similar set up as mine to see what prop size they are running, give me a good starting point. I do appreciate all the intel tho. I’m no Aquasport or boat guru by any means.

[mshugg]

Try the Mercury prop calculator:  https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one

I plugged in estimates for your setup and got a reccomendTion of 15.5 x 17 or for a 3 blade stainless.   15 x 21 would be overproped, and that would explain your poor acceleration.

[GoneFission]

The Zuki does have a 2.5:1 gear ratio - different than Merc at about 1.75 or 1.85.  That impacts the prop size and pitch.  The Zuki is a big-bore 4 cylinder that makes good torque, but is not a top-end screamer.  Although Suzuki says 5500-6100, 5500 would probably result in better reliability than 6100.  For starters, I would try a 19 pitch 4-blade prop before jumping down to a 17 pitch.  17 seems low for a 2.5 gear ratio IMHO. 

The comments above regarding transom height also are good.  You want the ventilation plate about even with the bottom of the hull - further down is just a drag, man. 

Where are you located?  Is there a prop shop nearby?  A good prop shop will often let you try out and test different props (as long as you don't damage them!) to get the best setup. 

[mshugg]

The Zuki does have a 2.5:1 gear ratio - different than Merc at about 1.75 or 1.85.  That impacts the prop size and pitch.  The Zuki is a big-bore 4 cylinder that makes good torque, but is not a top-end screamer.  Although Suzuki says 5500-6100, 5500 would probably result in better reliability than 6100.  For starters, I would try a 19 pitch 4-blade prop before jumping down to a 17 pitch.  17 seems low for a 2.5 gear ratio IMHO. 

The comments above regarding transom height also are good.  You want the ventilation plate about even with the bottom of the hull - further down is just a drag, man. 

Where are you located?  Is there a prop shop nearby?  A good prop shop will often let you try out and test different props (as long as you don't damage them!) to get the best setup.

I punched in the Zuke 200 AP into the Merc prop calculator, so recommendation was based on Zuke, not Merc.  No question, though, a 19” pitch is a better starting point than a 23.  Even more important, shouldnt make too many changes before  getting RPM at WOT.

[TylerT]

I was able to take the boat out today and ran it WOT witch reached my rev limiter of 6100. My smart gauge alarmed me at this point. At WOT 6100rmp it ran 41.5mph. I’m in southwest Florida. I did find a company in my area call propgods.com. Bold name for a company I thought. Propgods came highly recommended from numerous people I’ve talked to. He hooked me up with a 4 blade mercury marine revolution 857030A46 23P. I’m going to give it a shot in the morning.

[mshugg]

Ken at Propgods is highly recommended over on THT.  The Rev 4 is a good prop.  That’s what I’m going with on my Mercury 150.  I’m looking forward to a complete report once you get everything tweaked.

[TylerT]

I ran the Rev 4 today. Gave me great whole shot, but still was able to hit the rev limiter. At 6100rpm it would top out at 42mph. Ken with propgods feels I’m still slipping at WOT and should hit 50mph no problem so he just gave me two more to try ECO 23 and a LFS4 23 admiral propeller. Looks like I’ll be on the water again in the morning.

[mshugg]

I ran the Rev 4 today. Gave me great whole shot, but still was able to hit the rev limiter. At 6100rpm it would top out at 42mph. Ken with propgods feels I’m still slipping at WOT and should hit 50mph no problem so he just gave me two more to try ECO 23 and a LFS4 23 admiral propeller. Looks like I’ll be on the water again in the morning.

On the water in the morning - not a bad thing.