3 blade stainless to 4 blade stainless...

[jkimball]

'99 FW Horizon 170, 115 Johnson with 13 3/8 x 17" Stainless. (recenly put on)
Originally had 14 x 19" Aluminum.

When I changed from the 19" aluminum to the 17" Stainless, I gained around 500 RPMs, now at ~5,500 at WOT
I ALSO picked up about 4 MPH WOT.

Currently under normal load, with full tank I am getting 42 MPH @ 5,500 RPMs with hole shot much improved.

The OEM Spec book called for a 19" aluminum and 41-46 MPH. So, with the 17" I think I'm doing alright.

However, this prop vents pretty bad in tight turns, and I would like to eliminate that, and I've always loved the idea of a 4 blade prop.

But, I don't want to lose anymore top end if I can help it. So, if I went with a 13 x 19" Solas 4 blade, what could I expect?

The diameter is smaller, so would that account for the increase in pitch for RPMs?

And by increasing pitch, would my top end stay about the same/ increase?

The 4 blade 19" holeshot would be better than my old 19" aluminum's, but how would it compare to the 17" stainless 3 blade?

To sum it up
1) adding a blade
2) increasing pitch
3) decreasing diameter

 

[jestor68]

Re: 3 blade stainless to 4 blade stainless...

What kind of SS prop are you running?

If you have the motor trimmed out for straight line speed, you usually have to trim in a little when turning to avoid excessive ventilation.

 

[jkimball]

Re: 3 blade stainless to 4 blade stainless...

It is an OMC SST.
When I'm cruising and trimmed out I do trim in when going around a bend in the river. My main ventilation I have complaints of is when I'm up on plane, towing a tube and come into a sharp turn.

 

[jestor68]

Re: 3 blade stainless to 4 blade stainless...

Bearing in mind that the Solas HR Titan 4 (SS) has a more aggressive blade design than your standard SST prop; I 'd recommend staying with a 17 pitch( 13 X 17 in this case).

Generally, a 4 blade of the same pitch and similar design will run about 100 rpm slower than the 3 blade.

One of the best attributes of the 4/5 blade prop is it's holding power( resistance to ventilation).

 

[steelespike]

Re: 3 blade stainless to 4 blade stainless...

your slip is about 5% a very good number.

 

[dazk14]

Re: 3 blade stainless to 4 blade stainless...

I like the HR4 Titan (not that anyone asked). Great value and performance.

The SST prop is somewhat plain Jane when it come to modern blade geometry and you are seeing some of it's limitations.

What is the age of your SST. They run back to the early 70's?

Are your speeds via GPS?

There are a myriad of higher performance 3 blade stainless props that would give MUCH better holding in turns and run a little faster on the top end. What is your budget?

On the low price scale, you could add a little more cupping to the existing blades and improve its holding power in turns.

 

[jkimball]

Re: 3 blade stainless to 4 blade stainless...

I like the HR4 Titan (not that anyone asked). Great value and performance.

The SST prop is somewhat plain Jane when it come to modern blade geometry and you are seeing some of it's limitations.

What is the age of your SST. They run back to the early 70's?

Are your speeds via GPS?

There are a myriad of higher performance 3 blade stainless props that would give MUCH better holding in turns and run a little faster on the top end. What is your budget?

On the low price scale, you could add a little more cupping to the existing blades and improve its holding power in turns.

I'm not sure of the age of the SST. I bought it used (ebay $50) and when I got it, I had to have it rehubbed. The boat seems to be much more responsive with it over the 19" aluminum. This one was originally painted, and has the brass exhaust collector... if that helps to determine age? It has a little cupping, but not overly aggressive.

My speeds are via GPS.

The Solas HR4 Titan is the prop I was looking into. They seem reasonably priced for a nice stainless prop. Like I said, I've always loved the thought of a 4 blade. Better holding, better holeshot, less vibration and a little more stern lift. I've also heard that they are much better in choppy water too, one poster I read a while back said "It's like having 4wd on his boat"

I just don't want to sacrifice too much more top end, or lose much WOT RPM... I'm not in it solely for WOT high speed, but I'm comfortable where I am, and I don't want to lug the motor by draggin RPMs down.

That being said, what 3 blades do you suggest. I'm not opposed to sticking with a 3 blade, but prefer 4 if I could get away with the above.