Stainless Steel Props

[Glipat]

Question guys, I have the luxury of having a friend that owns many props so I can try. I have a question pertaining to some of the props that I am gonna try:
Vengence 21 Pitch:13 3/4 diameter
Mirage 21 Pitch: 14 3/4 diameter
Laser II 23 Pitch: 13 3/4 diameter

I have a 1990 rinker captiva 186 with a 4.3L mercruiser on it. Currently running a 21P SOLAS splined aluminium prop, WOT can achieve 4900-5000RPM recommended running at WOT is 4400-4800 on the sticker. My guess is that I can prop up a little. Currently with the 21 Solas, I achieve 44.1MPH GPS.

Does the diameter of the prop affect it that much? I think the diameter of the prop I am currently running is 14 1/4

Out of those stainless steel props, is there one that is lighter. Would I still need to prop up going from stainless? Or is this a case of just try them and see what works?

 

[Chris1956]

Since your current Max RPM is a bit high, see if you can swing that 23P prop, in max RPM range, with usual load. If so, I would stick with a 23P prop. A 23P prop is on the high end of standard props that are used on most MerCruisers.

Usually the owner (you) will choose the prop pitch. The OEM then chooses the diameter. i would expect all the SS props to be better than your Solas.


Best is to run them off against each other. Note max RPM and Speed, plus minimum planing speed, quality of hole shot and any bow rise during hole shot.

 

[Glipat]

So diameter of the prop doesn't affect the results as much. I was trying to find the largest diameter prop that I could fit with a 21P.
I will try the props out and report back

 

[alldodge]

Your tach may or may not be off a tad
Aluminum will flex and can have thicker blades, I would start/expect with the Mirage 21

 

[Texasmark]

So diameter of the prop doesn't affect the results as much. I was trying to find the largest diameter prop that I could fit with a 21P.
I will try the props out and report back

My 2c: The prop is setup for a particular gearbox diameter (the thru-hub prop barrel diameter) with a max outer diameter to fit comfortably in the lower units of OEM engines using that diameter barrel. In the case of the 13" props, staying below 14" in diameter. As the blades are designed, you start off with a zero pitch, zero rake (blades extend straight out from the barrel), blade geometry that is supportive of the thrust desired.....Mickey mouse ear if you will!

As the design progresses, the blades are twisted on a bias to the barrel to achieve the pitch requirement. Then for higher performance props (SS for a type) the blades are folded back from the tip to form a tunnel (rake) which does a better job of grabbing and holding water for higher performance. Finally for better grip at near surface operation the tips of the blades are bent back slightly (cupping).

As a result the diameter of the prop will vary. Once I get in a size range, I pay no attention to diameter.

In answering the list of props question, I ran a Laser (the first laser design before the improvements of the Laser II) on a Ranger bass boat type pad hull and just loved it. No experience with the rest of them.

 

[porscheguy]

you can change a prop in under 5 minutes. Try all and see which one works best for you.

 

[QBhoy]

Vengeance is a waste of time completely. Rule that out straight away. It’s just a heavier and shinier version of an ally prop.
The mirage and its lighter diameter might see a few rpms drop and almost certainly more top end than your current.
For me...it would be the 23” laser all the way. You’ll likely see 50mph running light and bravely trimmed out.