Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

TheChad

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Hey All,<br /><br /><br />I Just bought A 2006 Lowe FS175 w/2006 Mercury 115HP EFI 4-Stroke..<br /><br />It came with a 13x19 Aluminum Prop. I am looking at possibly purchasing a Stainless Steel Prop in the near future.<br /><br />I understand the pitch of the prop, and will probably keep that at 19" Pitch... <br /><br />What I don't understand is the Diameter of the prop? When looking for props, i see many different size diameters available.<br /><br />What difference will the diameter make? For example, If I were to go to a 12-1/4" diameter, or a 14" diameter, and stay at the 19" pitch, what difference would either of those diameters make?<br /><br />Thanks,<br /><br />-TheChad
 

WillyBWright

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

The larger sounds like it's a larger class prop used on MerCruisers and V-6 outboards. In a given class, you'll see the diameter decrease as the pitch increase. That's to keep about the same surface area accross the range for that class. Diameter within an inch or so doesn't make nearly as much difference as the pitch.
 

Silvertip

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

Going from a 12-1/4 to a 14 inch diameter prop means you've stepped out of the range of engines that prop was intended for. Chances are the two props are for two different prop shaft sizes. Generally there will be less than an inch difference in diamter in the entire range of props for a given engine. A 12-1/4 x 15P is one popular size for a 50 HP Evinrude. The next higher pitch is 11-3/4 x 17P. Even if you did find a much larger diameter prop that physically fit the engine, chances are it would hit the torque tab or the AV plate. Also, unless you make some WOT runs to check RPM and speed with the current prop, you don't know what you need.
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

The prop that came on the engine is a 13x19... <br /><br />My question was what different would it make if it went from the 13x19 to a 12-1/2x19, or from the 13x19 to a 14x19.. In a stainless steel.<br /><br />I was just curious, 13x19 is available in stainless steel, so i could easily keep the exact same size, I was just curious what would be different if I changed Diameter...<br /><br />I havent taken the engine over 3500 RPM @ 25mph, I only drove the boat for about 10 minutes on the lake..<br /><br />Thanks,<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

Chad, the prop you will need will be determined by wot and performance needs..Generally when going up in diameter you lose RPM unless you are willing to raise the engine to get the Rpm back and lose some drag..this is maximizing the set-up. Smaller diameter in a given pitch is used mostly on non-surfacing applications, and tends to be (in most cases) a bit slower, except for very light boats, where you find small dia. and large pitch.
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

walleyehed: with a 13x19 Prop, at WOT trimmed up, I am at 5000 RPM.. According to Mercury, my 115HP 4-Stroke has a Redline of 5000-6000 RPM<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

It needs to be well broken in, but 5000 ain't enough...that 4-stroke needs to be near 6000 to develope the power it's rated at...well, actually, it's rated at 5500, but they do best above the 5500.<br />This is VERY typical of a dealer set-up.<br />If it were mine, I'd opt for 2" less pitch which will gain between 600-800 RPM due to the powerband, and then raise the engine a hole at a time until I got close to 6000RPM.<br />Load the boat with people and gear and you will be in engine destruction mode the way it's set up now.<br />Alot of dealers need to go in for some serious training....
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

You said raise the engine a hole at a time, but it's power trim....<br /><br />So you suggest a 13x17 prop?<br /><br />With 4 people and gear in the boat, it does take a little bit to get the boat up to speed and on plane, with 2 people, it jumps on plane in just a few seconds.<br /><br />The engine has only about 6 hours on it, so It's not even completely broke in yet...<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

When I say raise the engine, I mean on the transom, not trim-n-tilt.<br />I'm saying a 17 pitch yes, not a 13X17...don't get stuck on this diameter issue..it may be a 13-1/4X17...or maybe a 13-1/2X17...doesn't matter if it's made to fit your engine.
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

Is it possible that the engine is just to low on the transom now with the 13x19 prop?<br /><br />Is there a certain measurement as to how high/low the engine is suppose to sit on the transom?<br /><br />If all the sizes you mentioned are available to fit my engine, is there a pref as to which one?<br /><br /><br />Thanks,<br /><br />-TheChad
 

procraft180

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

FWIW...I have a 2003 Procraft 180 Combo with a 2004 115 4-Stroke. It came propped with the Black Max 13x19. At normal load, WOT, full trim I could only turn 5400RPM. I purchased a Turbo 2+2X, 13 1/4x18,my engine is mounted in the stock 2nd hole from the top. With this Turbo, I gained tremendous holeshot, WOT is now 5700RPM, but I lost about 3 MPH due to the 4th blade addition. After that test, I had the engine raised up one hole on the transom, now I am turning 5900RPM @ WOT, gained back my 3 MPH, plus 2, so now I am 50MPH, 5900RPM at WOT, gained a little more in holeshot, and improved my gas mileage. It is like a totally different boat now.
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

hmm... That's good to know.. Mine is only an aluminum boat, so if you are gettin 50Mph, I should be pulling more than that (Lighter)...<br /><br />I wonder if the transom adjustment is something that would be covered under the warrenty?!<br /><br />I Think I will start by just raising it up 1 hole on the transom, see what that does for me, then look into a different size prop...<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

Hear me chad...Raise the engine until it slips or blows out...then Lower 1 hole-THEN prop for the set-up if you're leaving the engine mounted to the transom.<br />The procraft has a pad and your aluminum will never get the performance...the weight isn't the issue...you have no pad, just like mine, it will be slower than those that do.
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

What do you mean by pad?<br /><br />Slips or blows out at what trim? all the way down?<br /><br />I am not really worried about the speed, I'd be happy with a better holeshot, and better fuel consumption, 42mph is plenty for me..<br /><br />Thanks,<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

Pad is a flat surface, usually narrow smack center of the hull that the boat gets up on at high-speed reducing drag even farther...you and I don't have that feature built-in to our boats.<br />The idea of raising the engine is for a couple of reasons..#1, we get the gearcase up some, eliminating a bit of drag, and by reducing drag we pick up a bit of speed. #2, we get the thrust-line closer to the bottom of the hull (the distance of parallel between the 2 becomes less) and this usually aids in hole-shot and acceleration. If we increase in all of these areas, we've increased the over-all efficiency, which means less effort from the engine at the same speed which increases fuel economy...it's a win-win.<br />Proper set-up is the only way we can maximize efficiency...I know you'd like the better fuel economy, hole-shot, AND speed just because it's there..
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

walleyehed: That was very informative, thanks for the explination..<br /><br />I am going to raise the engine as you suggested, I just need to know at what trim should the motor be when testing for slip out?<br /><br />The boat is in storage as my garage isn't big enough to store it, so i need to take a look at it and see where exactly this transom adjustment is and what setting its on..<br /><br />Its amazing that thease dealers don't set up brand new boats correctly... That just gets me...<br /><br />Thanks again,<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

As with prop pitch, there is no set std for trim angle, but as a general rule, on plane, at any given speed we trim to the best ride and speed for that throttle setting.<br />The trim angle changes with load, RPM, water conditions and even the prop used. Different props lift differently, and trim has no "standard" position.<br />The higher the engine is mounted, the less trim (positive) is needed.<br />As for the dealers not setting up "correctly"...I wouldn't say it exactly that way..it would be better fitting to say they don't set them up for the best efficiency, they just set them up to "go"...
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

The Engine is mounted on the 2nd hold from the Top.<br /><br />I did not relyize by moving the motor up, we were talking about completely unmounting the engine from the transom to do this... I don't know that this will be an option for me, I will have to contact a dealer to find out what they would charge to do this...<br /><br />-TheChad
 

TheChad

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

When selecting a new prop, Should I stick with the 3 blade? Or should I change to a 4 or 5 blade prop?<br /><br />This boat is used about 90% for fishing, and 10% for tubing/sking. Right now the hole shot sucks. But hopefully raising the engine will help with that....<br /><br />If I understand it correctly by droping to the 17" pitch prop will give me about 400rpm, which would put me at about 5600 RPM, instead of the 5200 RPM i am getting now with my 19" prop, but by lowering the pitch I will also loose holeshot, which would be bad since it sucks already!<br /><br />Thanks,<br /><br />-TheChad
 

walleyehed

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Re: Prop Diameter & Pitch Questions - 115hp EFI 4-Stroke

When you lower pitch, your hole-shot is faster (better).<br />I would not go to 4-5 blade unless I had a jackplate and was looking for the very top performance, and, of course, the 4-5 is best for ski-tube, but not top-end in this case.<br />Don't spend the money if you're not going to use the technology.
 
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