Another 2 vs 3 blade post...

[JerrfyLube]

But its not a what prop should i buy post...

I have a 65 Mercury 650 that has a 2 blade 15P prop...not sure of the diameter, but thats irrelevant right now and ill research it more when the time comes to actually buy a new prop...

My question was this...given the pitch of say 15 and a diameter of 13", would a 3 blade prop push it faster than a 2 blade of the exact same pitch and diameter or is top speed relative to the pitch\diameter and not how many blades? Would one be more efficient than the other?

Im asking because i can find 3 blade props easier and a good bit cheaper than 2 blade ones...especially as you get into higher pitches.

 

[Bondo]

Re: Another 2 vs 3 blade post...

or is top speed relative to the pitch\diameter and not how many blades?

Ayuh,... It's relative to Pitch 1st,... Blade design 2nd...

 

[Frank Acampora]

Re: Another 2 vs 3 blade post...

Generally speaking, the less blades, the more efficient each blade is. This is because theoretically, fewer blades are spinning in less disturbed water.

Indeed, a good number of years back this thoery was put to use in rubber powered model airplanes where a counterbalanced single blade propellor was used for thrust.

Back to the real world, two blade props tend to vibrate a little more than three blade, and although each blade is more efficient, the overall efficiency of a three blade prop is greater than a two blade --In a non racing application--maybe! In the old days, ALL racing props were two blade. New design and technology have changed that.

However, if you are looking for maximum thrust, the three blade does have a bit more area than an equivalent diameter two blade and in high thrust applications will slip less.

HOWEVER-----Your 65 Merc just looks cool on the ramp with the two blade and that counts for a lot. Especially if it is an old school bronze prop polished to a mirror finish.

 

[JerrfyLube]

Re: Another 2 vs 3 blade post...

HOWEVER-----Your 65 Merc just looks cool on the ramp with the two blade and that counts for a lot. Especially if it is an old school bronze prop polished to a mirror finish.

True...but because the motor is on such a small boat(a 1960 Glasspar G3), its going to need a higher pitch prop than the 15. Probably at least a 17 due to how small and light the boat is. Most of the guys i know with this motor on that boat run a 17P 2 blade setup and it seems to give the best overall performance. Problem, is trying to find one without spending a fortune...where as i can get a propco 3 blade, 17P one for about 100 bucks.

 

[Frank Acampora]

Re: Another 2 vs 3 blade post...

OMG! A G3! I had one when I was 16. You do know that refurbished ones that are done well command a premium price.

My advice is to hit the old outboard site and look for props. Go to the Glasspar site and do the same. Maybe even ask where to find vintage props on the Merc forum. You just gotta have a bronze on that. Hmmmm! I have a Merc 3 blade bronze with more than 15 pitch. I THINK it was for bigger engines but depending upon your gearcase, it might fit. Send me your email in a private message and I will send a couple of photos. Also, if you are not in a hurry, keep an eye out on ebay.

 

[JerrfyLube]

Re: Another 2 vs 3 blade post...

OMG! A G3! I had one when I was 16. You do know that refurbished ones that are done well command a premium price.

Yep...and mines completely original...except for the motor. Its got a 35HP Johnson Seahorse on it right now but im getting ready to put the 1965 Merc 650 on it in the next week or so...

Including the price of the boat and registration costs, carpet, seats, and a few odds and ends, ive got a total of $500 into in...but i wouldnt sell it for 4-5 times that!