Aquasport Mechanicals - things that need a wrench, screwdriver or multimeter > Props

Prop help

(1/4) > >>

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.

Navigation

[0] Message Index

[#] Next page