Going from 3 blade to 4 blade

[gapple12]

Im currently running a Vovlo Penta 2002 5.0L with a 3 blade 14.75x21 and getting around 50mph and about 4200 RPM. I'm sure I can push it faster with less people but its plenty fast. Now, my hole shot is very slow and weak. I'm curious if I went from my current prop to a 14x21 4 blade, will I keep the speed but gain better hole shot ?

 

[Starcraft5834]

no matter what 4 blade you go with, you will lose top end speed, about 1-3 mph and gain hole shot, maintain plane at slower speed, better handling around the dock.....overall, IMHO a 4 blade is the better choice

 

[gapple12]

So do you typically stay in the same diameter when switching to 4 blade or drop pitch a little ? Im thinking of trying a 14x19 4 blade.

 

[gapple12]

I guess im trying to figure out if i should get 3 blade lower pitch or 4 blade and stay the same pitch. I dont mind dropping a little speed at all, I just dont want to over rev my motor. My manual says 4400-4800 max rpm

 

[Starcraft5834]

4blade at same pitch should keep your rpms in range...likely drop down 100... you will be impressed with it

 

[KYsean]

no matter what 4 blade you go with, you will lose top end speed, about 1-3 mph and gain hole shot, maintain plane at slower speed, better handling around the dock.....overall, IMHO a 4 blade is the better choice

Not true at all. A Merc Spitfire of the same pitch will only get you better hole shot. You won't lose any top end. This from experience.

 

[floater212]

rule of thumb from prop sites: from a 3 blade to a 4 blade requires 1" less pitch, going the other way a 4 blade to a 3 blade increase 1" pitch to stay the same. BUT the more blades the more drag... aka.. top end will be a little slower but the grip will be greater. my 2 cents = I do a lot of towing, skiers, tubes and kneeboards so the more grip ( holeshot ) the better.

 

[KYsean]

http://www.mercurymarine.com/propellers/aluminum/spitfire/ No top end loss. Some have even gained 1mph. I lost no top end speed but sure gained hole shot.

 

[gapple12]

Thanks for the reply's everyone. I was out this weekend and with 5 adults in my 19' Monterey, I was at about 4200 RPM and 45mph top speed. I'm sure if i trimmed up the motor I could gain more. Running the 14.25x21 3 blade now, I'm thinking of going to the 14x20 4 blade.

 

[gapple12]

http://www.mercurymarine.com/propellers/aluminum/spitfire/ No top end loss. Some have even gained 1mph. I lost no top end speed but sure gained hole shot.

I take it they dont have a Volvo 19 spline Spitfire ?

 

[jestor68]

I take it they dont have a Volvo 19 spline Spitfire ?


The Merc hub kit is # 835270Q1 if you want to use the Spitfire.

Get a nice Solas 4 blade (if you want a 4 blade ) and have no problems with fitment. It will perform as well(or out perform) a Spitefire prop. VP makes 4 blade props too.

Frankly, I think that you'd be just as well off putting a nice 19 pitch 3 blade on there to gain your rpm back with a boat load of people and gain as much "hole shot" as you would using a 4 blade, without losing top speed(with the heavy load).

Right now you're propped for a light load, and you have to keep in mind that one prop can"t do it all. You prop for a specific situation, and when you change the situation(load), it always requires a change in prop pitch.

That's why most of us end up with two props; one for light load running around, and the other for heavy load duty.

Your 21 pitch does fine for light duty, and a 19 pitch is needed for those days when you've got the gang along and/or need pulling power for water sports.

 

[gapple12]

The Mercury web site does not list a hub kit for VP for the Spitfire prop. The only stern drive they list is Merc. The rest are for outboards.

Get a nice Solas 4 blade (if you want a 4 blade ) and have no problems with fitment. It will perform as well(or out perform) a Spitefire prop. VP makes 4 blade props too.

Frankly, I think that you'd be just as well off putting a nice 19 pitch 3 blade on there to gain your rpm back with a boat load of people and gain as much "hole shot" as you would using a 4 blade, without losing top speed(with the heavy load).

Right now you're propped for a light load, and you have to keep in mind that one prop can"t do it all. You prop for a specific situation, and when you change the situation(load), it always requires a change in prop pitch.

That's why most of us end up with two props; one for light load running around, and the other for heavy load duty.

Your 21 pitch does fine for light duty, and a 19 pitch is needed for those days when you've got the gang along and/or need pulling power for water sports.

So you think going to the 14x19 3 blade will still give me the top speed as well as a better hole shot then a 4 blade ? From what Im reading on other forums, going to the 4 blade with same or 1" lower pitch will keep me about the same but gain better hole shot. I love having the speed of the 21 pitch but I need the hole shot for a slalom skier.

 

[Starcraft5834]

Not true at all. A Merc Spitfire of the same pitch will only get you better hole shot. You won't lose any top end. This from experience.

good for you... most lose top end a little. if you want better hole shot for pulling skiers and tubes, 4 blade is the best answer for that

 

[jestor68]

I corrected the Merc hub number for use of the Spitefire prop. It's the same hub # for any other Merc prop.

 

[jestor68]

http://www.mercurymarine.com/propellers/aluminum/spitfire/ No top end loss. Some have even gained 1mph. I lost no top end speed but sure gained hole shot.

Your reference states that " it helps to maintain top speed". Nowhere in the video do they state that it did the same top speed as the Black Max 3 blade. It just talked about better acceleration and holding in turns.

If you are propped so bad to begin with, it's possible for it to to better. But it's not the usual out come.

 

[gapple12]

Now im thinking I should run a 14x19P 4 blade to bring the RPMS up a little.

 

[gapple12]

Anyone know anything about Michigan Props(link below) ? They have the only 4 blade i can find in the 14x20P, just not sure about the changeable hub. Are these better then the props with built in hub Assembly ?

http://boatpropellers.iboats.com/Vo..._992204_Propeller/541/1683/?cart_id=766148693

 

[Tail_Gunner]

Is this a mpi engine or carbed

 

[gapple12]

Is this a mpi engine or carbed

Carbed 5.0GL

 

[Tail_Gunner]

Carbed 5.0GL

.........2 or 4 barrell

Alum or SS for prop material...cost is alway's a key...The gearing on your leg is it 1.66????...Do you run on a small lake or large body of water, high speed burst's just for a thrill....Reading your post it seem's your looking for a prop that will enhance the boat with a full passenger load