Prop question from a newbie
 

Folks,

I have a 09' RX 181 with a 3.0L, my prop is a 3 bladed 14.25X 21 and I can only get up to 35mph at WOT and my plane time ois around 8 to 10 seconds. I know what all this means from the threads I have been reading, what I would to know is if I went to a 4 bladed 14.50X 18, would this help on both ends.

I feel the need for speed,
Sam

P.S. I will get some pics soon. I am having to much fun on the water to remember the camera. :D

Gee, i dunno. Anything over 30mph with that 3.0L is pretty good. Just ask 180diablo! :rolling_laugh:

Seriously though, that 21" pitch is likely too much for your boat but we need to know what your WOT rpm's are to figure out just how much of a change you can make. I'd have to look up what the recommended rpm range is for your 3.0L but i suspect it is 4400 - 4800 at WOT. Perhaps one of the other 3 litre owners can correct me here. Normally, for every 2" drop in pitch you will increase your rpms by approx 400 so your thoughts about an 18" 4 blade will likely increase your rpms by 5-600. Whether that translates into increased top end is questionable but you will definitely get out of the hole & onto plane much faster and have a little more mid range punch. You could also consider installing a set of Smart Tabs. The composite units with the 60# actuators should be just about right for your boat. They would allow you to consider a 19" pitch 3 blade prop and eliminate your planing issues as well as any low speed wander that is inherent in an I/O drive.

I knew I had left some info out, we run at around 4500 r's at WOT.
Not to worry I ordered my smart tabs sx thru west marine today.

So let me get this straight, you are saying that 35 mph is good for a 3.0 and the only thing I could increase is my hole shot with a 19 ptich prop. and add smart tabs at the same time.

Please let me know if I am correct.

Thanks,
Sam

Not quite. You may get a few more mph with the changes but its not guaranteed as prop change isn't an exact science. You could take 3 different (yet similar) 19" props with the same specs and get 3 different results so sometimes starting with some educated guesses and then trial & error is the only way to go. I think 180diablo mentioned he now gets into the high 30's with his 3 litre. Your suggestion of the 18" - 4 blade would work also and i would recommend a SS prop if you dont mind paying the extra $$ as they perform slightly better than an aluminum prop. This change should take you to the upper limit or just slightly over the recommended rpm maximum but as long as you dont run at full throttle for extended lengths of time you should be fine. The Smart Tabs will work with any prop. The prop change will provide the extra grunt as well as get you on plane faster while the Smart Tabs will also get you on plane quicker as well as keep you on plane longer at lower speeds. The only downside i've heard about the Smart tabs is that they tend to flatten out the wake somewhat which kind of defeats the purpose for wakeboarders.

Hi,

I have a 2008 SX18 and this one was delivered with a 23p 3 blade Alu prop. As MikeyT mentionned this seriously impacted my WOT, which is only 4200 rpm. This is below the range Mercruiser posts. So I am too considering changing to decrease with 2" to a 21P 4-blade SST prop. I am a bit afraid going directly to a 19P.

Cheers,

Johan

Hi Johan

I would even consider a 20" pitch - 4 blade SS prop. That 'should' raise your rpms by 600 or so as well as give you considerably more punch in low - mid range. I'm not sure how much effect it will have on your top end though....

Thanks MikeyT,
I was not even aware a 20p 4 blade SST existed, I assumed it only came in increments of 2P ( 23P-21P-19P ) :shakehead:
That would indeed be interesting.

Regarding top end, I am not that interested as driving at full speed takes a lot of concentration (if you don't want to hit branches floating in the water, etc) :)

Kindest regards,

Johan

Pity the site doesn't take video ( or does it? )as I can show you that my smart tabs have not dampened out the wake from my SX18....

Hmmm...... compression doesn't do much for the product :shakehead:

Dave

I haven't really noticed much of a reduced wake with mine but a couple of the others here said there was a noticable reduction with their boats. Again, slightly different designs in the stern (amongst other things) can produce significantly different results....

WOT Time
 

Hi MikeyT (to be formal),
I have noticed in several threads guys mentioning not to go at WOT for long periods.
Now, what would you in your infinate wisdom, consider a long period?
Not a Canadian winter I hope! Or an Australian Summer (pretty much equates to the same).
I sometimes hit it at WOT for say 5 - 10 minutes, I keep a good eye on the RPM's and temp when I do it though. Its just so damn hard to keep this boat going slow :wink_thumbup: