Prop Wear (No Beanies Invovled)

N

NORO LIM

Member
I have two new (less than 50 hours) props on my Yamaha F50's. The port side is wearing badly, but the starboard looks brand new.

There is no apparent difference in performance between the two - no vibration or slippage that I can detect. Cursory examination reveals no obvious defect in the port side prop, but I'm assuming there must be some. Previous props had 100's of hours and showed no wear like this on either engine. The Permatrims were installed well before the new props. I haven't run aground (recently!) or hit anything I know of since the new props were installed.

I'm about to experiment by swapping props between the two engines, but I'd hate to mess up the good one if the problem is not the prop itself. Any thoughts?


09_09_Prop_wear_005.sized.jpg
 
Bill – the wear spots on the port side prop is too uniform to be normal wear. All three blades have identical markings in the same spot on each blade. Something caused it other than normal wear. I don’t have any idea what caused it other than a wild guess and I am not going to do that. Are there any markings on the other side of the prop? Or any on the edge of the blades? I can’t tell from the photo.
_______
Dave dlt.gif
 
Interesting problem. Let’s assume that the two units are identical: same props, same bolt heads on the permatrim, etc., etc., etc. In other words, forget about “mechanical” factors, and assume that if you were to swap motors port and starboard, you’d still have the same problem. You can check that out pretty well by eyeballing the lower units, and the permatrim installations.

If they’re essentially identical, I’d assume that the props aren’t cutting the same water stream. Without getting into a discussion of ventilation vs. cavitation, or of all the things which affect the water the props encounter (hull design, the permatrim itself, the two rows of bolt heads mounting the prematrim, the lower unit, etc., etc.), I’d look at things that could result in different water at the props, and most of them come from how the boat is balanced and trimmed.

Get a “level gauge”, “incline-o-meter”, or whatever they’re called, and mount it at the helm. Until you do that, you don’t have any idea if the boat is tilting to one side or the other. Then, check out your level at the dock, with you at the helm, and everything else in place. If you’re level there, you’re probably going to have the motors titled equally while underway, at least until you burn fuel or catch a really big fish. Every now and then, while underway, repeat the test by stopping dead in the water, and rebalance your load as much as possible to reflect fuel burn, water consumption, etc.

Once the boat is as balanced as possible, and only then, use the motor trim to keep the boat level, side-to-side, while underway. What I’d try to avoid is having one motor tilted down more than the other, except to the extent necessary to trim the boat.

I’d also keep the paint on the problem prop retouched, so that I could tell if I was making progress in fixing the problem.

Let us know what happens.
 
I have to agree with Jack.

Poor paint job.

Because the pattern is similar on every blade, there must have been some grease or oil on the dies when that prop was stamped into shape.

My 2 cents.

Easy fix though.... a can of spray paint!

Capt Dan
 
Thanks for the input everyone.

I don't believe there is any wear on the forward side of the prop or on the edge, but I haven't inspected them that closely yet. (The boat's in the water. Just taking the picture was an Olympic event - at least in the geriatric class.)

I do have a level gauge, and I am fairly careful, some might say obsessive, about keeping side to side balance with weight loading. (In fact, ironically, I just spouted off, again, about balancing with weight distribution in another post a few minutes ago.) However, Almas Only's comments just got me thinking about the recent stickiness of the port engine trim sending unit. I got it moving again with some lubrication, and it seems to be operating normally, but now I'm suspicious about the accuracy of the gauge reading. Maybe it's time to replace the unit.

The first thing that struck me about the wear was the peculiar symmetry of the pattern - the same three shapes on each of the three blades. I've seen prop wear in spots before on other boats, but I don't remember anything like this. Maybe it's not that uncommon.[/i]
 
NORO LIM

This may be a long shot, but easy to check, anyway.

Measure the angle of attack of the torque trim tabs on the two motors and their clearances with the props, and, as well, check to make sure that their shapes are the same in profile and thickness, etc.

I'm wondering if one is closer or somehow differently positioned than the other to the prop blades and causing some true cavitation issues which is resulting in very low pressure areas on the rear prop sides, pulling the paint off by true cavitation, where molecules/atoms are removed by low pressure and other forces.

Usually real cavitation issues become problematic at higher force situations, such as encountered in racing boats, but .....you never know!

Joe. :teeth :thup
 
...verry interesting Grasshopper.

After reading the initial posts, I spent about an hour reading up on things like "prop burn" and signs of cavitation. Some folks really get into this with negative pressure readings, vaporization effect and other esoteric stuff; all of which is Beyond me. Ooh well.

The fact that you have two props and can replicate certain issues is valuable. (Slightly) etch and repaint the offending (port) prop and subject it to some standard usage, then (re)inspect. I'm hard pressed to think this is an oil-blob-on-the-stamping-die problem; I think it's an effect of the prop spinning, but I'll be damned if I know the answer.

Bottomline: I don't think this is something that should disrupt your boating in any way. From my experience, a lot of props show distinct wear patterns after being worn-in over hours of use. A minute variation of a micron or two in the manufacturing process may be the culprit. But in this case the "culprit" might not be worth chasing down. A similar situation might be in the standard manufactured engine versus a "blueprinted" engine. If you're looking for the absolute peak in performance, go for perfection; if not, just cruise along in the pack with the rest of us. It's comfortable, and we'll leave the light-on for ya.

...I gotta learn to make shorter replies.

Best,
Casey
 
Hi Bill, Consider the possibility that the scars might be from different sources. Could the longer ones have been inflicted on the port prop by something you hit when that prop was going astern? Their symmetry is greatest from the leading edge of each vane if they spinning CCW. Perhaps if you were spinning the boat to port at low speed, you hit something that struck each blade before it broke off. It might have inflicted a little more damage, again starting at the 10 o'clock vane, with those smaller pecks that get progressively bigger, and then it was gone. Faulty coating seems an unlikely cause to me.
Don't you love a good mystery? :cat
Rod
 
rjmcnabb":1vjmfuhp said:
. . . the scars might be from different sources. . .
Click to expand...

Hey! I'm trying to narrow the field here! OTOH, I was always telling my kids, "Never forget, two things can go wrong at the same time."

So far, it could be:
  • Bad paint job
    Bad paint job due to grease on die
    Engines running at different trim angles
    Undisclosed wild guess
    Torque trim tab angle
    Torque trim tab clearance
    Torque trim tab shape
    Striking something with port prop while going astern

Seriously, thanks again for all the ideas. I'm a glutton for punishment - anyone else have a theory?

Bill
 
I've seen this before on a couple of props I have run on a 90 ETEC. It's the result of a cavitation type erosion. I showed one of the props to a shop that specializes in marine propellers and they indicated it was was the result of turbulence at that point on the prop generating cavitation bubbles. I think Joe hit on it with the low pressure point on the back of the prop. I don't understand fluid dynamics that well, but I would suspect if you swapped props right and left the problem wouldn't move as it endemic to the prop and not the motor.
 
Looks like prop burn. If you do not have a nick on the motor or the prop its self then the problem may be forward of the motor. Where is the sending unit for the depth finder? do you have a raw water pick up? where is it. And dont be fooled to thing that it has to be right in front of the motor. When you turn the boat water comes from different angles. switch the props and see what happens. is this a problem with other twins.?
 
Well, I sure do not have an answer about the cause.
What I do know is doing nothing will cause the rapid decline of the prop. In salt water and with the metals being used in props, paint is critical. I ran my prop on the Honda 90 for less than a season with some non gouging paint penetrations and when I again inspected it closely the metal was corroded 70% through two blades near the base. All of my zincs were and are new. I was shocked. Now the prop is a spare that I hope will get me home should the need ever arise.
 
Look HERE regarding prop cavitation and burn! Note the pattern of burn areas on the prop!

Normal_Cavitaion_Burn[1].jpg

normal cavitation erosion after one year on a 65 Viking.



Joe. :teeth :thup
 
Hey Joe,
You done done it now....ole buddy. I went out and bought a 20" widescreen....Flat Display the other day
and here you go an post a picture the I still have to scroll to the right to see the other side of...and down
40 clicks to get to the bottom.

If you don't pratice some resizing controls...you will force me to spend good boat money on a whole new home
Theater to vew your post in the future..

And if you don't want to watch a grown man cry...please...think of me the next time.

PS: or was that a prop off of the Queen Mary?
 
Mike-

I just copied the image "as is" and figured the site would re-size it.

Will try to reduce it somewhat, if I can before the 30 minute "dead zone" sets in!

Joe. :lol:
 
Papillon":n49hms2u said:
Hey Joe, . . . was that a prop off of the Queen Mary?
Click to expand...

Man, that thing scared me!

Joe, if you do get it reduced to manageable size, compare the wear areas shown on this shot of just the damaged prop:
09_09_Prop_wear_006.sized.jpg

I have assumed all along this is a cavitation/ventilation problem, but remain mystified as to the cause in light of:
1. No problem with prior props on either engine;
2. No known changes other than two new props; and
3. No damage on starboard prop.

Bill
 
Thanks for the reduction and comparison, Dave!

While the Viking 65 prop and the one in question both show cavitation burn, what's more striking is that the pattern of bubbles on the prop in the video and the one in question are much more alike than the ones in the side by side photos of the C-Dory's prop and the Viking.

I think we've established that we have a cavitation burn problem, but the question is why is it on one prop and not the other?

Is there any reason that the water speed across the port side prop would be any higher than the one on the starboard side? In turns with a right handed prop on the outside of the curve? Downside vs upside movement?

If not, perhaps there is something ahead of the prop causing this?

Time to switch props and test?

Joe. :teeth :thup
 
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