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Old 11-26-2019, 08:56 AM
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Originally Posted by Tom W Clark View Post
Look at the photo closely. That is exactly what we see there, each blade is progressively less imbedded in the stump.

Doesn’t take much to snap an aluminum blade off of an outboard prop.
I'm not questioning the authenticity of the photo, I am wondering why the hub did not slip before all three blades snapped off? Aren't hubs designed to slip to help prevent catastrophic damage? Seems to me that the lower unit would have been severely damaged considering the forces involved? This is just my uneducated guess....
Old 11-26-2019, 09:01 AM
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I rented Searay I/O boats for a bit on my lake. The rental place has stacks and piles of old props with missing blades. Our lake is mud and sand with a lot of shallows, I grew up running all sort of boats aground here, and never found rocks. The old marinas full of deadheads are all cleared out and modernized. I talked with the owner of the rental place, no idea how people are destroying props, but they come back with a single blade and say they didn't notice anything.
Old 11-26-2019, 09:16 AM
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Originally Posted by jbacc View Post
I'm not questioning the authenticity of the photo, I am wondering why the hub did not slip before all three blades snapped off? Aren't hubs designed to slip to help prevent catastrophic damage? Seems to me that the lower unit would have been severely damaged considering the forces involved? This is just my uneducated guess....
Excellent question. I think the answer lies in the nature of the obstruction: the stump. It is not just a solid object, but a wooden one with the grain aligned vertically. Anybody who has spent time splitting firewood on a chopping block knows how that end grain will often receive the blade of the axe or splitting maul quite nicely and hold it there.

In the case of this propeller, I suspect the blades inbedded themselves as the boat was passing at high speed and that the forward momentum of the boat just pulled it forward after each blade struck putting an instantaneous bending force on each blade. The hub has nothing to prevent that highly unusual force.

This all would have happened virtually instantaneously. A boat cruising at 4000 RPM with a 2:1 gear ratio means the prop itself is spinning at 2000 RPM. In other words, it spins over 33 times each second, so the impact would have happened in 1/33rd of a second.
Old 11-26-2019, 09:27 AM
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Thank you for taking the time to explain/educate me, Tom, much appreciated.
Old 11-26-2019, 10:40 AM
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in other words, is the motion forward that snapped each blade off, instead of the vertical force that lodged them in the stump. Gives you an idea how to make art of old props!!
Cool
Old 11-26-2019, 10:57 AM
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I saw this on the qualified captain, and really do not know what make of it.

Using the example above, a boat with a 17 pitch prop would be running at about 30 mph (lets just assume 0% slip for now). Each 1/33 of a second of full rotation, the prop is moving the boat forward 17 inches. The blades in the stump are stacked way tighter than that.

If a boat is running at speed, to do this, it would need to have roughly a 3” pitch prop...and I don’t think those exist.

If the photo is real, then perhaps a boat was running at a much lower speed where slip is very high to be able to stack the blades and the forward momentum did in fact break them off.

But I don’t think I am buying this as legit.
Old 11-26-2019, 11:15 AM
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Originally Posted by Timeless View Post

Using the example above, a boat with a 17 pitch prop would be running at about 30 mph (lets just assume 0% slip for now). Each 1/33 of a second of full rotation, the prop is moving the boat forward 17 inches. The blades in the stump are stacked way tighter than that.
I don’t think so. The photo angle makes them look much closer than they are. I would expect a 17” pitch prop with about 10 percent prop slip to have the blade spacing of about 5”

17” pitch, less 10 percent = 15.3”

5” x 3 = 15”
Old 11-26-2019, 11:39 AM
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Derp, 17” divided by 3 blades. I still think it’s too tight to happen at speed, but running under a condition of high slip, e.g. getting on plane, I could see this being possible now.
Old 11-26-2019, 11:57 AM
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I would cut the stump off as low as I could, clean it up, and encapsulate the top in bartop epoxy and make an end table out of it.
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Old 11-26-2019, 12:30 PM
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Originally Posted by xlr8ngn View Post
I would cut the stump off as low as I could, clean it up, and encapsulate the top in bartop epoxy and make an end table out of it.
Thinking same .
Old 11-26-2019, 12:56 PM
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Originally Posted by Tom W Clark View Post
I don’t think so. The photo angle makes them look much closer than they are. I would expect a 17” pitch prop with about 10 percent prop slip to have the blade spacing of about 5”

17” pitch, less 10 percent = 15.3”

5” x 3 = 15”
Do you think any contact with the skeg, maybe even the leg starting to kick up, might have some effect on any calculations?
Old 11-26-2019, 01:42 PM
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Originally Posted by SeaCat22 View Post
Somewhere, there is a dude laughing his arse off, thinking, "Wait 'till they find these 3 prop blades I hammered into this stump". "Someone will probably try and calculate the speed by the separation of the blades". Lol
I agree. Looks phony. Too perfect.
Old 11-26-2019, 01:47 PM
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Originally Posted by Locke N Load View Post
I agree. Looks phony. Too perfect.

This ^^^
Old 11-26-2019, 01:59 PM
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Originally Posted by SeaCat22 View Post
Somewhere, there is a dude laughing his arse off, thinking, "Wait 'till they find these 3 prop blades I hammered into this stump". "Someone will probably try and calculate the speed by the separation of the blades". Lol
There's a dude right here laughing his arse off at your comment.
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Old 11-26-2019, 02:01 PM
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Originally Posted by Tom W Clark View Post
Look at the photo closely. That is exactly what we see there, each blade is progressively less imbedded in the stump.

Doesn’t take much to snap an aluminum blade off of an outboard prop.
The next question is what hole was the outboard mounted, assuming it was an outboard. And if an I/O, what hp?
Old 11-26-2019, 03:37 PM
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it's a good one, but... photo shop. The horizontal stump surface behind the first blade impact (direction of travel) is far wider than the distance between blades. How did this area avoid contact with a blade? It would have been struck first. And the vertical area of the stump in front of the third blade avoided any impact with the lower unit??? Not a chance. At least it got my long repressed math brain working again

Last edited by lydoniablock; 11-26-2019 at 03:56 PM.
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Old 11-26-2019, 04:50 PM
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Originally Posted by jg109 View Post
So, you are calling "photo shop"?
i'm calling fake no matter how they did it...almost looks like each blade is in an age ring...

Originally Posted by Gullpt View Post
unless it was a deisel.
and you honestly believe it would have sheared three blades off identically without any hub slip and deposit them so perfectly in the log?...

Originally Posted by Tom W Clark View Post
Look at the photo closely. That is exactly what we see there, each blade is progressively less imbedded in the stump.

Doesn’t take much to snap an aluminum blade off of an outboard prop.
i dont buy it...

doesnt take much to snap aluminum blades off...but what are the chances of perfect spacing and identical breaks as the prop loses speed and is deflected...time or distance arent factors here unless they are attached to a prop on a fixed object...there is a lot more going on in a prop strike than just snapping them off and leaving them evenly spaced in a log...

Last edited by bladenbullet; 11-27-2019 at 06:19 AM.
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Old 11-26-2019, 04:54 PM
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Cool thing for the den
Old 11-26-2019, 07:12 PM
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These blades were a little stronger.
Old 11-26-2019, 09:12 PM
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Wow

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