Re-pitching my prop

[Alaska viking]

Well, my 0540 is running well, but I max out at 2500rpm.
I have a 73" water walker, and can run dry ground, to a point.
My question is, if I try to achieve 2650 rpm, how little should I reduce pitch?
I am currently set on the detente marks on the prop. Should I flatten it out maybe 1/8", from the marks?

 

[Slidin Gator]

An 1/8” on marks sounds about right, maybe a hair less for 150 rpm gain.

You can try 2,650, But I suggest taking it to 2,800 rpm. Sure it’s a hair past peak on power, but the snap more than makes up for it.

 

[John Fenner]

Do yourself a favor, go to Home Depot, buy a digital level, it makes for setting pitch with great accuracy, you can drop a degree at a time till you find the sweet spot, plus both blades will match, I can guarantee using the pitch marks, one is off a bit from the other, they are or "were" just under $50.00

 

[Gary S]

You can also download a app for your phone that seems to work well.

 

[Alaska viking]

I don't mind getting a digital level. Can you explain how to use it on the prop?
As a professional carpenter, I know my way around quality levels, but I use them on buildings.
What position should the prop be in? And where should I take the reading?

 

[John Fenner]

I don't mind getting a digital level. Can you explain how to use it on the prop?
As a professional carpenter, I know my way around quality levels, but I use them on buildings.
What position should the prop be in? And where should I take the reading?

Plumb the crankshaft fore and aft, lowering or raising landing gear on trailer tounge, once zeroed out, with prop hub horizontal, measure the angle of each blade at the tips, I usually note on the nickle leading edge with a sharpie, gather the base per side, note it down.
Ok, now, dump a degree of pitch out per blade, evenly, do a static run up on trailer "even before checking pitch" for reference, you can compare the RPM difference per degree adjustment, noting each change in RPM and degree.
Usually a degree less is roughly 100 RPM more depending on the prop design.

 

[BobBrack]

I second the 2800 RPM. You will not believe the difference in performance.

 

[Slidin Gator]

I try to use 3 different measurements and settle if 2 out of 3 agree. I use a phone app that measures to 0.1 degree vs. a digital level. Same scenario at John describes, except I ignore making level on the crankshaft and just rotate 180 for each blade measurement. My second measurement is off the cage, I fix a point on the cage and find the shortest distance (while rocking prop) to the Nickle edge. My third measurement is the hub marks/labels. I find the marks accurate vs. the other methods, as long as one of the marks lines up good with the engine side hub split line.

In all cases, a rubber mallet makes for quick work. None of these are perfect, no 2 blades are identical, the next step is dynamic balancing.

 

[Alaska viking]

.well, these suggestions, while enlightening, bring new challenges!
My boat literally "lives" in the bush. It stays in a remote slough, and I have to take a skiff, or 24' boat across a bay to reach it. It stays parked on a high bank, well above tide line, covered with a tarp.
Finding true level ground ain't happening.
Guess I will try using the marks, and start with about 1/8" flatter.
Sound like a plan?

 

[Slidin Gator]

Finding true level ground ain't happening.

That’s the point of the methods I described, all work in the bush at any angle. Just make sure the mags are grounded and carb leaned out before turning the prop.

 

[Alaska viking]

You bet. Thank you.
Keep hoping to get out there, but weather here keeps saying, "Acess Denied".
Supposed to blow 60 mph for the next couple of days.

 

[Deano]

My boat literally "lives" in the bush. It stays in a remote slough . . . . Finding true level ground ain't happening.

Like you, my boat is only on the trailer if it needs something beyond regular maintenance.
This is exactly what you need:
iGaging Angle Cube Digital Protractor Gauge Magnetic Angle & Level Sensor Bevel | eBay

 

[Alaska viking]

Like you, my boat is only on the trailer if it needs something beyond regular maintenance.
This is exactly what you need:
iGaging Angle Cube Digital Protractor Gauge Magnetic Angle & Level Sensor Bevel | eBay

Well, I ordered one. Now how do I use it?

 

[Slidin Gator]

Mark spot on cage as close to horizontal as you can get. Measure blade angle on stern side using protractor at/near tip.. Rotate 180 and measure the other blade, same way.

Use prop hub marks for rough in, use protractor to get them to match. Same concept as matching mags.

 

[Alaska viking]

Got it, I think.
My instinct tells me to get the prop horizontal, set the level on the tip in a near vertical position, set to zero, then rotate the blade a degree.
Then turn the prop 180, and do the same to the other blade.
Re-tighten the hub, and have a lash.
Does that make sense?

 

[digginfool]

One of the tricks I use when I'm adjusting pitch is I adjust one blade with the digital level, pull it to a point where I can clamp a straight edge from either the transom on my open boat or part of the cage if it's my sled, adjust it until it just touches the trailing edge, then pull the other blade(s) to that point and turn them to just touch the flat edge. It's particularly useful if you have multiple blades (my open boat has a four blade prop and I run either a two blade or five blade prop on my sled). The advantage with this method is you end up with all the blades pitched exactly the same. Makes for a much smoother run. Using the level on all the blades I've found I have been as much as 3/4 a degree off from blade to blade when I check after everything is tightened back up, even though I was as diligent as possible using the same spot on each blade when measuring with the level. The blades tend to have a curved surface so it can definitely have an affect. As Slidin said, it really isn't that important to have the boat perfectly level as it's all relative; a degree will be a degree regardless what reading you start with.

 

[Deano]

Well, I ordered one. Now how do I use it?

My apologies, I didn't mean to leave you hanging.
You didn't state otherwise so I guess you are running a two blade Signature Series. Those hubs have a flat surface on the top and bottom when the blades are in a horizontal position. Start by setting your angle cube on the top of hub, facing fore and aft and then press the 'ZERO' button on the face. You now have the plane marked where your crankshaft is level (whether it really is or not makes no difference).

How you proceed is likely more a matter of preference than importance. There have been a number of methods described already that all will work. What is most important is consistency between blades no matter how you actually arrive at that end.

To position each blade before measurement, it is IMO, faster, easier and most accurate to put a straight edge on the top of blade and then turn the blade so the straight edge contacts a given horizontal brace on the cage. This ensures each blade is in the same physical position when measured. I have a piece of 1" square aluminum tubing about three feet long that works perfectly for this and is light in the boat.

With the Signature blades, the best spot to place the cube will be between two and three inches from the end of the blade. (I don't remember exactly.) Now, put the top edge of the cube flush with/on the bottom of the blade's leading edge. If you slide it back and forth (left to right) you will find a sweet spot where all four corners of the cube contact the blade surface, this is your spot. Measure that spot from the end of the blade so you can mark each blade in the same spot. I generally put a piece of masking tape vertically on each blade before I start, such that the leading edge and tape make a 90 degree mark where the corner of the cube can be placed on each blade.
If that sounds like a time consuming PIA, consider that after you've done it twice you will be able to do it as fast as it took to read this. Remember the bottom line is consistency, which is why I like this method.

With that, and everything else that's been said, I expect the rest should be self-explanatory.

 

[Slidin Gator]

You can also download a app for your phone that seems to work well.

Gary turned me onto this in a post a while back. Any of the electronic levels work fine too, but only carpenters carry a level on a Airboat, everyone (that can afford a Airboat) has a phone in their pocket. My son came by today to help re-install my engine, rigging and prop. I had a good opportunity to document.

At first I let him set it, he nailed the marks on #2 first try. But then I whipped out the phone for a double check and found the pitch off by 0.9 degree. So we loosened up the bolts and added a bit of pitch to one blade with the rubber mallet without breaking the press on the blades.

First, no need to set the crankshaft level, or even a need to calibrate the level. All that matters is the difference between the readings.

First thing is to level the prop hub. Honestly, boat cocked sideways on the side of a levee, no problem. Use a 30-degree reading on the hub as long as each blade is measured on the same hub reading. In my case, it is easy to remember 0.0 degrees.




Measure Blade #1. The key is finding a way for your measuring device to find the same spot on each blade. In my case the phone itself fit's the blade tip well. You can also measure off a point from the center of the hub on each blade and lay a larger straight edge.



Rotate to the next blade, repeat setting hub to the same "Level" setting and check the next blade.





So that is as good as it get's. For reference, note the difference between the two prop hub marks. I'm not sure which one is more accurate, but the blade tips run the fastest, so since I'm trying to eliminate vibrations I gonna try it.

 

[Gary S]

Not sure what your measuring but I measure pitch on the face of the blade. In I think it is 2 inches.