[Smokymance]

Originally Posted by mikeyt

The most important thing is to get your engine running in its recommended rpm range at WOT. Once you accomplish that, the engine runs at its peak proficiency throughout the rpm range. Choosing a correct prop allows you to get things working within that range. Note though that it is not cast in stone that you have to limit at 4800. Mine will run at 4950 if it let and it wont hurt unless i'm running there for extended periods of time. Generally for our 18-20' boats at lower elevations 3 props work best; a 19" 3 blade, a 19" 4 blade or a 20" 4 blade. There are exceptions though. Higher elevations usually require a lower pitch blade to make up for the lower power level produced by the engine at those elevations. And... we do have some members who run 21" props and even a couple who ran 23" props and said they worked just fine. Note that these are just general rules of thumb.

Very valuable information and all makes sense! Michigan elevation isnt high so i was thinking of looking at the 19* 4blader...that is after i check some RPM runs...

i think right now she did about 52mph (on the dreamometer on the dash) w 4 people in it...not sure of the RPMs tho...

[husker_fan]

I run a 17" 4 blade stainless, but all I do is cruise and pull tubes and wake boards. I could care less about top speed. I never use it. I bought the prop to get me and people I'm pulling out of the hole without effort.

[Smokymance]

Originally Posted by husker_fan

I run a 17" 4 blade stainless, but all I do is cruise and pull tubes and wake boards. I could care less about top speed. I never use it. I bought the prop to get me and people I'm pulling out of the hole without effort.

where do you usually leave your trim as you are taking off and towing people

[husker_fan]

All the way down to start, and just a couple clicks up when towing. I have smart tabs too, which almost makes it jump up on plane too. I usually tow the wakeboarders 15-18 and tubers a little faster depending on the ride they want.

[nosbonsing]

I went through much the same thing in the last month. I had a 19p 3 bladed prop that was putting me way over my RPMs and so I switched to a 4 bladed hustler prop at 21p. Turns out that I could only get to 4200RPM with that prop, but my speed went from 41MPH to 45 MPH. This made me think that the original prop and hub were wonky, so I went back to a 19p 4 bladed Hustler and now the RPM runs at the top of the range.

My boat is an older Mariah 1850 XL with a 4.3L and I use it mainly for watersports. The biggest difference I noticed was that the boat could hold its plane much better at lower speeds and far less RPM. On take off, it reduced the time it took to plane by about 2 seconds, but it felt far more responsive at the same time. I should also mention that, while I know they are frowned upon here, I did install a hydrofoil as well (SE Sport as it was no drill install and I had a small credit at BP so though why not) and that combined with the 4 blade prop have brought my plane speed down from 25MPH to below 20 even when pulling a wakeboarder and my time to plane has gone from 7 seconds with empty tank to 3.5 with full tank.

Those things worked for me and I am happy with it. I know its not what everyone would like, but hey, thats why there are options.

[nosbonsing]

Sorry, meant to add that my top speed now is about 42MPH. I think that a 4 bladed 20p would probably be suited more for top speed, but your not buying a 4 bladed prop for speed in most cases anyhow.

[Smokymance]

So its been about a year and iv added trim tabs to the 18ft boat and have gotten the RPM gauge to read correctly by moving the selector switch in the back a bunch of times...

Top speed went down bit w the 60# smart tabs, but she does take off way better and nose stays way down....my RPMs at WOT are about almost hitting the 5k mark with the SS 21 pitch prop...

My take off feels like it could use a bit more bite...feels like there is a dead spot in the mid throttle and she needs a little love to get up and going...she sits there for a bit and i have to floor it go get her going up on plane faster...(maybe its just the V6 LOL)

This is the prop she has in there right now

http://i22.photobucket.com/albums/b3...psmbqszcbz.jpg

http://i22.photobucket.com/albums/b3...psbf2rlb4s.jpg


With these RPMs at WOT, what you guys think i should consider for a prop situated for a better take off without danger'ing WOT RPMs?

Thanks again

[mikeyt]

Its unusual that a 21" pitch 3 blade will get your 4.3 up to 5000 rpms but i guess its not unheard of. If you want a little more mid-range without sacrificing too much off the top go to a 4 blade. If you are actually at 5000 rpms at WOT then i wouldn't go any lower in pitch than a 21"

Personally I like the 4 blade Apollo prop i have on my 180. It gives plenty of low and mid-range punch and i think i lost all of about 2 mph off my top end....but then who drives around at full speed all the time anyway?

[Smokymance]

Mikey i agree with you too on my RPMs at WOT w the 21p...ill try it again (as you mentioned how often do you go wot and stay there) to confirm...then take it from there...i always thought my max rpm should be around 4600 so i always back off when im up there, i just pushed it a few times to get a reading...i been looking at the 4 blades, just not sure what pitch to get...the merc site prop guide even mentioned a 5 blade...thats a little too much and too pricey...

[mikeyt]

I think that, as you suggested, when the prop was redone they likely altered the pitch slightly and lost some of the cupping on the blades. You have the same motor/outdrive (4.3 - 4bbl, Alpha One) that i have in my Shabah 180 and i use a 20" - 4 blade SS Apollo prop which gets my WOT rpms to 4900. As i mentioned, i really like that prop because of the extra mid-range punch it gives and i could care less if my top speed is 50 mph or 48 mph. That prop combined with the Smart Tabs make the boat literally jump when i hit it above 2000 rpms.