[blockp]

I've been reading until my eyes are ready to fall out. I've come to the conclusion that most people think prop tuning it either black magic, or a lot of trial and error until you get one/some that you like.

I have two aluminum props that came with my boat. A 14 inch 23 pitch that tops out at 4400 rpm and about 47 mph (speedo, not gps). My other is a 14 inch 21 pitch and tops out at 4800 rpm and gives about the exact same speed.

I'd like to come up with something that gives me a higher top speed and subsequently a higher cruise speed for when we're just out tooling around.

So post them up. What prop size (diameter and pitch) do you run and what are your rpm & mph coming out at? Stainless or aluminum?

[Z 202]

I run a 13.75x19p stainless. Tops out around 4700rpm and 52mph (gps)

[mikeyt]

Selecting a prop isnt quite 'black magic' but it sometimes seems that way for sure.

Part of the problem is that you can have 2 very similar boats (such as yours and Z202's) with both running the same prop and yet get slightly different results. Different outdrive ratios, difference in weight (even weight 'distribution') of the boats, differences in trimming, slightly better tuning / engine in one boat etc all contribute to the end results.
SS props 'generally' perform better than aluminum props, 3 blade props (vs 4 or 5 blade) 'generally' result in higher top speeds due to less drag, props with more pronounced 'cupping' generally provide slightly better performance, higher pitch numbers 'generally' result in highers speeds (up to a point, then the trend reverses) etc etc etc. "Propnut' says he can hit 53mph in his 180 Talari (similar to my Shabah) with a 19" pitch prop and 4 people on board. I cant come close to that number with mine and running that prop. So that's where the differences can come from (& i've probably overlooked a few) and why it seems like a lot of trial & error / magic is required to get the best prop for your particular boat.

[blockp]

Thanks Mikey. I _think_ I understand the dynamics when comparing 3 blade aluminum to another 3 blade aluminum of different pitch and/or diameter. Where I start to get confused is when talking about high rake stainless or adding cupping. I've read in quite a few places where people are saying they can run a higher pitch or larger prop because of their higher rake or they run a lower pitch with cupping and get a higher top speed. But I haven't found a comparison or anything that really makes it clear that by adding "X" cupping (is it measurable?) or going from "X" rake to "Y" rake changes your rpm or mph by "Z".

With what I've read, I'm thinking that I need to get a 3 blade 14x21p stainless with some degree of cupping to get any more speed out of my setup.

OR... here's the one I'm not too sure what the end result will be, but:
Do I go with a high rake 14x23p stainless? Not sure if I'll have the same problem I do now (max WOT rpm at 4400, giving me a top speed of 48ish mph).

I'm certainly open to suggestions and opinions at this point as this is all just in the thinking stage right now.

[indykoch]

I doubt you'd want to go up to a 23 pitch with SS. The aluminum props will slightly "bend" making it closer to a 22 pitch. The SS version wouldn't have that flex, and would likely just drop your RPM's keeping the same speed. I think you should try a 21 pitch SS.

Mine is 14.5 (I think) X 21 SS and I top out at 4800 RPM and 58 MPH for reference. I wonder if dropping to 14" would get me 100 or 200 additional RPM and help tickle that 60 MPH mark.

[mikeyt]

I agree with Indy. A 21" pitch 3 blade SS prop is likely the best way to go and if you can find one with a slightly agressive rake/cupping then that may be the optimum prop for your boat. I think a 23" pitch "might" give you another 1-3mph's but at the considerable loss of low/mid range acceleration. I would only suggest a 4 blade or a lower pitch if you were doing a lot of tubing / wakeboarding / skiing etc...and then it would be best to have 2 separate props.

[blockp]

Thanks guys. That makes sense to me and I follow the reasoning for a 21p.

Now the million dollar question... What model/type of prop?

Just looking at mercury 3 blade props, there are 6 different ones recommended for a runabout that come in 21p. Reading on Propgods.com, they seem to lean toward the Enertia for applications like mine. What are you guys using and are you happy with them?

Local craigslist ads have a mercury Tempest Plus and a Michigan Wheel, both in my size. The tempest looks like it's made for bass type boats, but I haven't found much on the MI Wheel prop.

[mikeyt]

The Enertia is a good prop from what i've heard/read. Here's a link to what I-Boats has available in a 21" for your engine/outdrive.

http://boatpropellers.iboats.com/Mer...t_id=556543438

The Stiletto "Advantage" and the Turning Point "Express" both look like good choices for your boat.

[indykoch]

I've heard the Enertia is quite good also. But that's a pricey one!!

I have the Turning Point Express. It's actually 14-1/4" X 21, not 14-1/2" like I thought. It's a decent prop, but I don't have much else to compare it to. With your engine/boat combo, I think you could benefit from a 14" X 21 SS.

[pimpadelic]

im runnjing a 14 x 19 ss made by solas. the previous owner put it on but i dont know if i should change it or keep it. looking at what other poeple say i think the 14 is about what i want but i think a 14 x 21ss would work better. and i only have the 3.0l so i dont know if that is going to make a difference.