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Old 01-05-2016, 08:56 PM   #1
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Prop Wear

The trailing edges of my prop are sharp, almost knife sharp. Is this normal? Is it a problem or will it cause an inefficiency?

We're talking a 7 knot boat here. Prop is somewhere near 21X21.
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Old 01-05-2016, 09:35 PM   #2
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Do you have prop singing?
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Old 01-06-2016, 08:02 AM   #3
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Do you have prop singing?
Not that I know of.
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Old 01-06-2016, 08:11 AM   #4
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How old is the prop and how many times has it been reconditioned?

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Old 01-06-2016, 09:49 AM   #5
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I am not the original owner so I don't know the answer. The original owners put 2800 hours on the boat cruising the US east coast.


The boat is a 2000 and I have owned it since 2008. In the pre-purchase survey, the surveyor commented that the edges (of the prop) were "thin due to electrolysis".

The boat came with an extra prop. The writing on the box leads me to believe that this spare has been reconditioned or reworked. I've thought about exchanging the two but there's no point unless the one that's on the boat is less efficient than it could be.

The boat is out of the water being bottom painted so now would be the time if I'm going to do it.
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Old 01-06-2016, 09:56 AM   #6
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A knife edge trailing edge is almost certainly due to corrosion. That corrosion makes the entire prop blade weak. If it is driven by a low power engine then you shouldn't be in much danger of throwing a blade. But if you have a couple of hundred hp and you sometimes use it....


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Old 01-06-2016, 04:27 PM   #7
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Over 150 responses arguing about the definition of the term "trawler".


Six (now seven) responding to an actual boat issue and four of these are mine.


Sad.
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Old 01-06-2016, 04:40 PM   #8
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Old 01-06-2016, 04:41 PM   #9
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Corrosion very suspect when you replace props and you may well have to make sure the new props don't go the way of the old. Check for stay electricity your boat dock or neighbor-keep active zincs proper # and size-check to see if shaft needs grounding. If you are not comfortable with this stuff get a professional to check it out props are expensive as you will soon know.
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Old 01-06-2016, 04:52 PM   #10
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Over 150 responses arguing about the definition of the term "trawler".


.
Yes something should be done about that. Certainly if there is a realistic definition all the second poster would have to do is display it for all to see. Don't you think that on a form called Trawler Form where people sometimes talk about a "Trawler" there should exist a definition of what the thing is? Actually there has been little arguing about the definition since hardly a word trying to define the term has been said. It is not unusual for specific topics to get higher response look at the anchoring posts. Here where we are talking props which are very important since that is what makes a boat go there may only be moderate interest. Props may not be a emotionally charged subject.
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Old 01-06-2016, 05:44 PM   #11
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My best performing prop is like that. Thin and a tad pink. Bought a new prop but I'd really like to have the old one back on. Since we run less than 40hp (16 - 18 at cruise) the old one was probably fine but throwing a blade would be a shakey experience. But the new one has a tad too much pitch and next time i'm out I'll have some blade edge ground off.
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Old 01-06-2016, 06:40 PM   #12
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I went down earlier today and got the spare out of the lazzarette. To the untrained eye, there's little difference. It was cold and windy and I've had a very bad cold so I didn't spend a lot of time comparing the two.


I called a local prop shop but they declined to visit the boat and give advice or change the prop. They only repair them, they don't install or remove them.


The boat looks like it will be out of the water for a few more days so I'll go back and check a little more.
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Old 01-06-2016, 10:03 PM   #13
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FWIW, some years ago during a routine haulout it was discovered that we needed a cutless bearing replaced on one of the shafts. Since the shaft had to be pulled to do this the yard went ahead and sent the shaft and its prop to the shop they use for evaluating these components. Turned out the shaft was slightly bent so they straightened it and installed a far more robust coupler than the original.

When they looked at the prop (a Michigan) they said it had been "worn down" and needed to be replaced. The evidence, according to them, was that the trailing edges were very sharp. There was no corrosion, galvanic or otherwise, on the prop.

They said that over time the surface of a prop can be worn down particularly if the boat is operated in water that has a lot of particulates suspended in it. The boat had spent the first 25 years of its life in SFO Bay before we bought it and trucked it north, much of it in the delta and river area which we assumed could be pretty muddy at times. We were skeptical of the shop's explanation but at the time knew very little about this stuff so it seemed more or less plausible.

The other prop was in the same condition as the one the shop looked at. The yard manager said he didn't think we needed to take any action at the moment so the shaft and prop were replaced and we boated for another season or so.

Fast forward to the following year when we decided to pursue the notion of replacing the props. Research had showed us that the best prop shop in the area was not the one that had examined our prop before, so we took both props to the shop that had been highly recommended by friends in the marine industry. We called this shop first and they told us the kind of performance information they needed to determine the best props for our specific boat.

We obtained the information and a few weeks later walked in with our two props fully expecting to have to buy new ones, which would have at the time cost about $2,000 each.

The fellow who received us when we walked into the shop took one of our props and went into the shop to check it. When he came back he said our props were physically just fine but they had been horribly set up by whoever did it last, which would have been someone in the SFO Bay area.

So insead of buying new props we had the ones that came with the boat completely reconditioned, tuned, and balanced for about $350 each as I recall. This included smoothing and rounding off the sharp trailing edges.

These props (four blade) are still on the boat 17+ years after we bought it and probably some 10 or 12 years after the prop shop reworked them. The sharp trailing edges have never reappeared.

So I would suggest that someone with a questionable prop take it to a reputable prop shop-- there seem to be plenty of the other kind--- and have it evaluated by people who know what they're doing. Sharp trailing edges can be the result of several things, it seems, but what we learned is that it does NOT automatically indicate a fundamental problem with the prop that would require its replacement.
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Old 01-07-2016, 08:10 AM   #14
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"take it to a reputable prop shop"


That can be a problem. How do you decide which shop is "reputable"?
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Old 01-07-2016, 09:01 AM   #15
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"take it to a reputable prop shop"


That can be a problem. How do you decide which shop is "reputable"?
I guess you will have to ask around. There are only two in the Houston area(Baumann and Hood). And this is an area that has a huge recreational boating population and an even hugER commercial boating population to support the oil industry.

I am with Marin here. I have seen these guys perform miracles. The boat I have now I had to buy a new prop because one fell off because the shaft broke!!! Yeah, you heard that right. The electrolytic corrosion was so bad that the shaft broke in half during the sea trial. Imagine what the props looked like. They were literally half gone and beat to hell. Well I had to buy the one because it had departed. But they managed to revive the other one. I do not know how they ADD metal to the prop but that is the only way that they could have don it. They must weld it on and then machine it back down. All I am saying here is that even if there is metal that is missing from the prop, it can be added back to it. I have no clue how....but they did it in this case.

There are no other prop shops in this area that I know of. These guys do amazing work. It is not uncommon for people to ship their props out of town for work. You may look into that. You can also call Hood Propellor in Houston and talk to the owner himself(Mike Hood) or his wife. At the very least they can give you an idea of what you are in for and maybe they will be able to direct you to a reputable shop in your area.
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Old 01-07-2016, 09:10 AM   #16
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Knife edges on the assistance boat prop every year. NO corrosion issue.

EROSION issue from sand, mud and sediment was my problem.

Hopefully no recreational boat is trudging through the same soup as what I used to do...but in a high sediment area and enough years...sure the edges can sharpen up is my best guess having done so repeatedly for years.

Could it be something else? Sure... but if it is perfectly smooth like it was ground to an edge and not significantly discolored pink......I will vote erosion.

When back from the reconditioning place...they would just grind a tiny, flat trailing edge and no issues. As long as the metal is good, a shop can add back if there is more than a little worn off.
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Old 01-07-2016, 09:13 AM   #17
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I looked at both Baumann and Hood websites. They both mention they are members of the National Marine Propeller Association. Maybe that would be a start as to finding a reputable shop.
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Old 01-07-2016, 09:22 AM   #18
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Not sure who determines which shop is good or bad.

The one often used where I am is a father and son working out of a residential garage.

They have the latest in computer measuring even though when you walk in it remids you of a 1950s one bay auto repair shop where the old guy in overalls wiping his hands with a red bandana walks up to you.

the props are mostly still just hammered back into shape as far as I have been told so don't think anything more sophisticated than a hammer and pitch block is being used no mattter where you go.

And like doctors...a little research and a second opinion if the first sounds out of place.
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Old 01-07-2016, 09:37 AM   #19
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I mentioned that I have a "spare" prop that was on the boat when I bought it. This spare seems to have been worked on by a shop (the box indicates a shop in Norfolk, VA but I have no proof that the prop and box go together).


My guess is that the PO damaged the original prop while cruising, bought another and had the original repaired and kept it as a spare. That's just a guess. I may call him if he is still around and ask.


What I can do is try to compare the two as best I can with a tape measure and a micrometer. I've had no issues that could be traced to the prop but of course wear would mean a gradual loss of efficiency.


When I had a small I/O, I could swap props at will for testing. Not with this boat.
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Old 01-07-2016, 10:21 AM   #20
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If all you have is a sharp edge...probably not much loss in efficiency...

I am guessing the reason they are usually a little thicker and flat is just so they aren't easily damages where even small variations would start causing vibes and loss of efficiency.

If you can call that prop shop or check in the boats papers if any, they may have a copy of the final computer readout of that spare prop. That way if you put it on and you notice anything different, you/the shop can compare it to the prop you are taking them and adjust if necessary.
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