3 blade to 4 blade

[Froeman]

Hi folks.

2008 Larson 180, Volvo 3.0L with stock 14.3 x 21 prop (3 blade). Want better hole shot for skiing, and would like to plane at lower speeds. My top end is perfect for what I need (about 42MPH on GPS, at just over 5000 RPM).

I understand that moving to a 4 blade will provide better hole shot, better planing, less cavitation in turns, etc. Given that I just need a little bit more hole shot, would the same 14.3 x 21 prop in 4 blade be appropriate? I understand I might give up 1 or 2 MPH at the top end but that doesn't bother me a bit.

Others have said moving to 4 blade requires a pitch adjustment??? Please advise.

Staying Alum. Is Solas a good brand?

Thanks!

 

[batman99]

Re: 3 blade to 4 blade

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I remember reading in the Prop Tips - 3-blade vs 4-blade section that if one goes from 3-blade to 4-blade, they need to reduce pitch by 1 as well. For example, if going 3-blade in 21P, then replace with 4-balde 20P (in same metal). Since getting 20P is sometimes difficult, one may need to go with more common 4-blade - 19P instead. Especially if looking for even more hole-shot power. Not too sure about quality of Solars / Aluminum model props...

Prop tips at: http://boatpropellers.iboats.com/propeller-tutorials/blades/?*******=985695589

Hope this helps...

 

[Brewman61]

Re: 3 blade to 4 blade

That's what I did. Went from an AL 3 blade 21P, to a SS 4 Blade 19P. Better performance, lower speed to plane, all the expected benefits. I changed 2 variables, went from AL to SS (more mass to spin) and 3 blades to 4. Dropped in pitch due to recommendation from my prop rebuild guy. He was right.
2003 Crownline 220HP 4.3L Mercruiser.

 

[HopinImFloatin]

Re: 3 blade to 4 blade

if your setup is working for you (speed and rpm), dont change anything...add smart tabs. They will do exactly what are looking for. Its amazing how well they work and are super simple to install. After i installed mine, my bow rise is near completely gone and planes almost immediately, also reduced my minimum planing speed by nearly 5mph-awesome for tubing.

 

[jestor68]

Re: 3 blade to 4 blade

Yes, it is usually recommended to drop to the next lower pitch when going to a 4 blade, due to the increased blade area.

But in your case, a 21 might be appropriate because you're running outside of your rpm range (4200-4600). The 4 blade will pull the rpm down a couple hundred due to the increased blade area. Note;this assumes that your tach is accurate, and you're actually turning 5000 rpm at WOT.

Solas is my favorite brand of aluminum prop. In actual tests, they performed side by side with competitors SS props.

 

[86 century]

Re: 3 blade to 4 blade

I made the change from 3 blade 19p un known make and model to the cheepest 4 blade 17p solas makes on a 19' bow rider with the 3.0.

Was like a totally different boat much better hole shot,lower planning speed, much better dock maneuvering with the loss of 2mph on the top end.

 

[Froeman]

Re: 3 blade to 4 blade

Thanks everyone. Re: smart tabs, good idea, but I'm also looking for better hole shot for pulling waterskiers. My boat will pull me up on one ski, deep water start, however I'd like it to take less time Agreed, I don't necessarily believe my tach is accurate, I'll verify it some day. My current prop is the one that shipped with the boat, so I can only assume it is properly "matched" with a balance between hole shot and WOT speed/RPM (i.e. they wouldn't ship a boat that would over-rev too much and blow the motor).

 

[jestor68]

Re: 3 blade to 4 blade

Running it 400 rpm over it's recommended limit won't "blow it up"; at least not right away. It'll just wear it out sooner.