4 Blade Spitfire propeller with different shaped blades

[malibu3105]

I just got my new Mercury Spitfire 4 blade prop, it's a 14 x 21p. It has two blades that are rounder than the other two. I know this is by design, but just wondering what the effect of this is.... I'm assuming one shape is for better hold shot, and the other for top speed. But figure someone here may know exactly.
Sorry no picture, but maybe I can get a pic tonight.
-Frank

 

[alldodge]

Don't know for sure but if you went from a 3 blade 21 to this one, my guess is more a bit more lift. Normally going from a 3 blade to a 4 blade the pitch would be reduced by 2 degrees. Keeping the same pitch but having 2 shorter blades would help.

The question which makes me scratch my head is why would you buy a prop and not know what the manufacture was claiming, or did I miss something?

 

[steelespike]

The spitfire is supposed to not require a reduction in pitch.
It exchanges pitch for pitch with no loss of speed.

 

[malibu3105]

Hmmmm. Ok. Well looking forward to my test run this Saturday

 

[malibu3105]

No Title

Here is a picture. You will notice the blades on the top and bottom are more pointed, and the left and right more rounded. I have not measured the diameter, but it is supposed to be 14". Anyway, an interesting propeller. I'll be out Saturday giving it a run.

 

[SkiDad]

Are you sure that is not a turning point prop ?

 

[malibu3105]

Ok, I stand corrected then. After looking at the Turning Point / Hustler prop, this looks just like it. And it does have the exhaust vent holes in it as well, even though not in the picture. The website has a full description of the propeller as well as the two types of blades.
http://turningpointpropellers.com/
Thanks for that suggestion. Not sure why I was convinced it was a Spitfire....

 

[David Young]

Well, how did it do?

 

[malibu3105]

How did it do.... Awesome. I went up a pitch, 20 to 21.
My WOT was 5,000 which is too high, so that came down to 4,600 which is dead center. My top speed went from 41mph to about 46, so I gained speed.
Almost jumps out of the whole. Once I'm planing I'm just skimming on the water. Love it. Turns are much better, back end was slipping out befor, now it's like I'm on rails.

Tomorrow I'm going out with my son and three friends to ski.
My only worry is now the boat wants to jump past 20x and get into 30's or so. I was practicing yesterday, as soon as the boat starts to plane I have to back off a lot to keep it around 25. Practice should make perfect right...

 

[Chris1956]

What boat and what power?

 

[malibu3105]

My boat is a 1991 Bayliner Capri 2050. 20 foot. Has a 4.3L V6. Forget HP but I think 180 or 191, something like that.
It's an old boat, but just had engine work done so running really good.

 

[Chris1956]

That is pretty good performance for that boat/power combo. My 18' SeaRay with the 4.3LX wasn't quite that fast, with a 21P Rapture. Sounds like it is dialed in pretty well. Enjoy...

 

[malibu3105]

Thank you Chris. We were out all day yesterday, 4 of us on the boat water skiing. Performance was great. She cruises just perfect just below 30 which was about how we all skied. No problems getting anyone out of the water .
Best part is with that prop, it turns so fast and tight, at one point the port side was almost touching water. Maybe a little too much bank!! lol. Gave my passengers a thrill though . Now with the engine work done, starting is easy, and idles perfect in or out of gear. Going to be a good summer!!