3 or 4 Blade Prop?

I got a 1548 SS with a 1985 25hp Evinrude on it. I need a new prop. I found both 3 and 4 blade props. My current prop is a 13 pitch 3 blade. I was going to go to a 12 for a little more bottom end versus top speed. I have been told the 4 blade will do this by itself. So what better? 3 or 4 and if a 4 should I stay at 13 or drop to 12 with it as well? I do not know alot about this so I need help. Mostly run rivers and some lakes but I would not mind losing a little top end. My boat is supposed to run 28mph right now per the previous owner using GPS to track it. I would still like atleast 24-25mph. Also would the MPG's change dramatically running a different prop? Lets hear it from those that know a little more.

Most of us can only tell you what we have experienced. My suggestion would be to find a prop doctor. They more than anyone else understand what a prop is and does. He will also have had a lot of experience with all the questions you have asked and will probably be your best source of information. Just my suggestion. Good luck, and by the way, thanks for serving. A salute to you.


"gene"


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One of the most important things to know is what your RPMs are at WOT (wide open throttle). Anything above or below the recommended the RPMs at WOT causes you to loose power. If you went to a 4 bladed prop with the same pitch you now have you will have a better hole shot but loose a little on the top end. Here is a good article on props. http://www.boatfix.com/how/props.html

I learned a lot about this prop stuff lately. Still don't know squat. It is black magic, possibly voodoo.

PawPaw, IBN and Cane are all right.

One thing I'd ad is that a 4 blade will hold it's bite better than a 3 blade and will be more stable and easier to control.

Without a tach, it's just a guess as to how to prop a boat. Having said that, propping a boat is black majic and Prop Doctors have the voodoo and the experience to get it right without a tach if you can find a good one in your area. In addition, a decent sized shop will have some that they will usually let you try before you buy.

Wannabe...

Yeah I need to just call them I guess. Anybody have any problems running SS props in rivers and such where trees and sandbars are common? I heard they hold up but could damage the engine vs the prop. Also heard my prop has a rubber hub that will break before the engine is damaged. Just hate to tear up props so fast.

you would see very little differance between a 3 and 4 blade. a 4 blade is better suited for larger boats such as a runabout. it would kill your topend and lower rpms. just stick with the 3 blade and drop pitch to 12. i ran a ss for 8 years in the oconee river and hit everything but rocks and i never had any problems.

SS is more durable. Also more easily repaired. Most modern outboards come with a rubber hub as oposed to the old pins. The theory is that they will slip or give if you hit something solid allowing the gears to continue turning, but stopping the prop. Almost like a clutch. A prop can be re-hubbed by pressing a new hub into the barrel by a prop shop, or some like Mercury Tempests and Trophies have a drop in hub system that can be replaced by yourself. Generally speaking, you can hit wood and not damage a SS prop where an alumininum would bend or break. Sand will scour a SS prop, but generally will not damage it, although you might lose some efficiency if it gets scoured too much.

Having said that, you can not predict what kind of damage might get done to a prop for hitting something. Sometimes you can't tell it's touched anything, sometimes it'll dent, sometimes it'll fold an ear. Just too many variables such as speed, angle, denstity of what you hit etc. But, generally speaking, SS will hold up much better than AL. Except for rocks. Hit rocks, you're hosed with either, except you'll be out more $ with SS.

In a rocky river system where you're prone to hit rocks frequently, you're probably better off with AL and just replacing it frequently if you don't have the option of running a jet lower.

Wannabe...

One other thing...skintback said a 4 blade would kill your top end. I don't agree. As an example, I had a Stratos 295 with a 200 Merc and 2 props, a Tempest 3 blade 25P and a Trophy 4 blade 25P. The Tempest was 1.4 mph faster, but the Trophy would snap your neck coming out of the hole where the tempest labored. Mid range was about the same, but the Trophy would hold a turn better and was easier to drive at WOT. In addition, it kept more of it's top end with a load - as in full livewells, full fuel and a partner.

Now to some, losing 1.4mph would be classified as "killing your top end" and would not be acceptable, but to me, the Trophy was overall better for my boat and the way I fished most of the time. Normally, the Trophy stayed on the boat.

Here's where the voodoo comes in - Same boat, 2 years newer with a Johnson on it and a buddy of mine prefered a 3 blade. The difference may have been prop brands, the fact that his 4 blade was not tuned to his boat, the Johnson being stronger or weaker than my Merc or some slight differnence in the hull characteristics of his year model over mine. Or it could be the amount of tackle or the weight distribution of it.

Now, that's on the high end of performance. I gather that yours is a small outboard since we're talking 12 and 13 pitch. I'd guess the speed difference would be less dramatic, but the handling characteristics would be just as noticeable.

Truth is, sitting here, we're all guessing. Find you a prop shop and get after it. Only other option you might have is to buy and try. Which is not as bad as it sounds. Usually, you can recoup most of your $ on a SS prop that has little or no hours that just doesn't work out.

Wannabe...

Yeah after I get payed I am just going to go to a shop and talk to them about it.

Like Bill said, 4 blade will pull a good hole shot, and thats all it's good for. 3 blade props are the optimized selection from the designer. I stick with my 3 blade.

All my duck hunting buddies and I all use SS props, and we hit lots of things really hard, really often and no one has had a lower unit or gears or even props broken yet. On the other hand I hate to think how many aluminum props I would have had to buy or rebuild over the last 25 years if I had been using them.

the 4 blade is like power steering and great in the turns.

also depends how deep your motor is sitting in the water .

do you have a jack plate so you can raise it up.

check the cavitation plate may have it burried to deep

if no jack plate i have cut strips of wood and put on top of
transom under the motor before they started making jack
plates so much.