4 blades ?

[Maps]

I just ordered a spare prop for my engine. To my surprise they orded a 4 blades prop (4x14x23).

My original prop has 3 blades so my question is what will be the use of this 4 blades prop ?

I have a volvo 5.0 Gxi SX engine. I mainly will be cruising and sometimes tubing.

 

[Silvertip]

Re: 4 blades ?

There is a fair chance that if the three blade prop you already have is also a 23 pitch, they did not do you a favor as you will likely lose some engine RPM. Without any wide open throttle RPM and maximum speed information we can't be of much help. Generally a four blade will help hole shot, be smoother running, but may (and I repeat may) cost you some top end and result in lugging the engine (that's not a good thing).

 

[Maps]

Re: 4 blades ?

There is a fair chance that if the three blade prop you already have is also a 23 pitch, they did not do you a favor as you will likely lose some engine RPM. Without any wide open throttle RPM and maximum speed information we can't be of much help. Generally a four blade will help hole shot, be smoother running, but may (and I repeat may) cost you some top end and result in lugging the engine (that's not a good thing).

So 4 blades will reduce top end speed compared to 3 blades.
I will have more info after futher testing

thx

 

[Maps]

Re: 4 blades ?

update :

My original Prop is 14x1/2x19 (3 blades)
My Spare Prop is 4x14x23 (4 blades)

 

[Dhadley]

Re: 4 blades ?

There are 4 blade props made specifically for I/Os that are different than OB 4 blade props. A 4 blade prop is not always slower than a 3 blade. Sometimes it's faster.

However going from a 19 to a 23 is a big jump unless the 19 was too small and your top rpms were too high. Before you even install it I'd ask why they ordered that one. I'd bet they'll tell you they ordered it from a chart, not experience of any kind. If you install it you may own it regardless.

 

[Tail_Gunner]

Re: 4 blades ?

I went from a 19 p 3 blade al. which would do 50 mph @5000 ticking the rev limiter every so often, to a 20 p 4 blade ss which would do 54 mph @ 4900 rpm, There was a difference in how the boat ran on plane that is it ran noticeably higher out of the water at all speed's. At wot and fully trimmed out there is no wake out of the side of boat, goes directly out the back or comes from underneath the stern, in a rough chop i actully have to trim her back in to get the bow to cut the chop or i go airborne skipping over the wave top's

I tried a 22 p 4 blade ss and could only get 4400 rpm but 53.4 mph (To much prop)

The boat is 19' weigh's in @ 3000lbs 4.3 efi 215hp I/O 20 degree v open bow. Prop's Stilletto Bay pro 11's, I believe lift was responsbile for the speed gain (less drag) but another member in this forum tried that prop type on a 4400lb boat with a 5.0 260 hp @47 mph and 4825 rpm not the same success indicating those prop's might not be able to lift 4400lb's, which is a pretty heavy runabout

Doing some simple math drag (wetted surface) has a lot to do with speed

1. 3000lb div 215 = 13.95 hp per lb------ 18.6' @54mph@4900prm
2.4400 lb div 260 = 16.95 per lb------22'@ 47mph@4825 rpm

Really dont know how to factor length in, just to many variable's

 

[Maps]

Re: 4 blades ?

My 14x1/2x19 (3 blades) does 28mph at 3000rpm and takes no time to plane since I have a 5.0 V8 but I have not gone WOT yet

is this efficient ?

 

[Maps]

Re: 4 blades ?

At WOT my 3blade 19'prop gives me 49mph at 4800rpm
2 adults with 1/4 tank no winds.

So what will result from my 4blade 23' ?

Im looking for better handling at low speeds and more fuel efficiency.

 

[studlymandingo]

Re: 4 blades ?

I don't think you will have the results you are seeking.

The 19 sounds like you are in the right range with your WOT, the 23 will drop that significantly and you will likely lose a good bit of low-end performance.

My guess is a 4 blade in the same pitch as your existing prop would be a better candidate for what you are looking for.​

 

[Maps]

Re: 4 blades ?

I don't think you will have the results you are seeking.

The 19 sounds like you are in the right range with your WOT, the 23 will drop that significantly and you will likely lose a good bit of low-end performance.

My guess is a 4 blade in the same pitch as your existing prop would be a better candidate for what you are looking for.​

Your exactly right. I will obtain better results with a 4 blade 18' or 19' prop than a 23'. My 19' seems ok but a 4 blade will be far better.

Therefore I ordered an 18' 4 blade prop. I'll keep an update of my results.
thx