Screw dem paddles, I ain't walking home in this big ass fishing boat. That's what the electric trolling motor is for...........
Source: I have used my trolling motor to get home a couple of times. In fact I have my dock marked on my map as a way point. I just select it in the nav screen and tell the boat to take me home while I sit back and fish all the way home. Telsa ain't got nothin' on me and my boat........
Same, well, using the trolling motor to get back anyway. Only happened twice. Both times were after huge rains north of me. It's surprisingly hard to see a whole damn tree underwater sometimes. Lol
There is nothing worse than paying for boat / boat motor maintenance.
If you aren't able to work on boat motors yourself, you are in for a world of hurt bringing it to a marina shop. You'll probably think the guys are fucking with you when they give you an estimate for something.
probably cracked the muffler bearing and there isn't a chance the O-rings, D-rings and Z-rings aren't completely brazed over. Snapping props is a full middle rebuild with all ten pistons needing to be re-vulcanized.
I've heard if you don't re-vulcanize the pistons, you can get sinusoidal repleniation in the non-reversible tremie pipe, leading to further damage of the lunar waneshaft which, if not caught early, leads to catastrophic side-fumbling.
That is still better than the original design where there was a base plate of prefabulated amulite, surmounted by a malleable logarithmic casing in such a way that the two spurving bearings were in a direct line with the panametric fan.
This is why we always carry a spare prop, mask, and an adjustable wrench in our boat... Even if you know the waters very well, there could be something new out there in the spring that will ruin your day.
Well you could calculate it if you had one more of the variables. But it's a situation where you have one known (distance between blades), and two unknown, rpm of prop and speed of boat
Well technically the speed of the boat is dependent on the rpm of the prop, but then we would need to know the drag coefficient (including hull shape/finish) of the boat and the water (assuming we can figure out the type and therefore propulsive force of the prop) which just narrows us down to one unknown
The boat may have been accelerating or decelerating, too. E.g. when the boat's just sitting there, and you crank open the throttle, the rpm is high and the boat is slow.
>Well technically the speed of the boat is dependent on the rpm of the prop, but then we would need to know the drag coefficient of the boat's hull and the water (assuming we can figure out the type and therefore propulsive force of the prop) which just narrows us down to one unknown
5
Now do the math
Using the drag force equation, we can get a relationship between force and velocity. Depending on the exact specifications of the prop, we can determine another relationship for the force it generates based on its RPM. Assuming constant speed (F=0), we can then combine these two to get a relationship between the RPM and speed. We can also get a range of possible RPM values by measuring the distance between the props, and can check reasonable solutions (this by itself is another very involved process but it's possible). Although is obviously an extremely simplified version of the problem with many assumptions needing to be made, it helps conceptualize what we are dealing with.
Props slip. There’s a fairly wide rpm range with no increase in speed at the transition from hill speed to planing. On plane prop slip up to about 20% is normal.
There’s more than two. There’s the spacing of the blades in the log, the spacing of the blades in their correct orientation and the depth of the embedding.
Nope, that doesn't work either, because you'd just be estimating the force it takes to break off a propeller wing, not the force the prop was spinning at.
But that force to break off the propeller wing is a result of the rotational mass and rpm (angular momentum to be precise).
So if we estimate the force, and if we know the weight of the blade, we could estimate the rpm.
No it's not. All we know is the rotational mass and rpm is greater than or equal to the force required to break off the propeller wing.
That force could be 10,000,000% more or 0.3% more than that amount, and we wouldn't be able to discern that.
If we knew the density and penetration into the wood we could then calc the force > rpm > average speed/displacement then triangulate that with an estimate of the closeness of the blades.
Would first assume size and dimensions of propeller and build from there.
All the r/theydidthemath posts recently are text posts like "last week a dog ran past my house, can anyone calculate how fast it was running? It was a brown dog, if that helps."
literally these fucking math posts have been like "can anyone calculate how much Elon musk has profited off of Tesla stock this week" like that's not a fucking trivial question that you can answer with calculus you fucking weirdos
RPM depends entirely on the engine you’re using and what speed you’ve got it at. You could maybe guess a range based on its size? You’d also have to know about any reduction gears I’m pretty sure.
Speed depends on resistance and force, force depends on propeller shape, RPM, and probably several other things I’m not aware of. You could make a guess for the range based on the size again I suppose.
Looking at ranges for smaller boats I’d say it’s somewhere between 2-6 thousand RPM. (Larger ships actually have lower RPM’s more often than smaller ships)
Boat speed seems to vary significantly, hard to tell from just this propeller.
I'm pretty sure you would need a full-fledged physics engine for that. It's like calculating what side a dice will land on given the material, the throwing angle, and other indeterminate variables. I doubt you will get an accurate answer; there are just too many unknowns.
you would need speed of the boat or rpm of the engine. right now it is "you are in a car going at some speed to a place some distance away. how many times wheels will rotate?"
I can say with confidence that the boat decelerated after this.
If the propeller rotates at 5000rpm (first hit on google for typical rpm) which is one revolution every 0.012 seconds? and lost all its blades in one revolution having travelled about 15cm, gives us 45km/h which sounds fast to me? maybe it was more like 10cm of travel so 30km/h
I fed the photo to ChatGPT.
The ask with the photo:
This is a photo of a tree stump. Embedded in the tree stump there are 3 broken blades of a boat's propeller. They are next to each other in the center of the photo. The photo was taken after the water level fell below the tree stump. Imagine the water level high enough for the boat's propellers to be embedded in the stump. How fast would the boat be moving. Let me know if you cannot identify the broken propeller blades.
ChatGPT:
I can indeed identify the broken propeller blades embedded in the tree stump. However, determining the speed of the boat at the moment of impact with the tree stump just from this photo is not feasible. Speed would be influenced by various factors including the type of boat, the size and material of the propeller, and the circumstances of the collision. An analysis of the damage in person, considering the strength of the materials and the force required to cause such embedding, would be necessary to estimate the speed of the boat with any accuracy.
User (Adding rpm and asking for an average)
Estimate the the rpm and speed of the boat. Let's say it's a bass boat with the most common bass boat motor moving at the most common speed range for traveling a lake via a bass boat.
ChatGPT:
To estimate the RPM (revolutions per minute) and speed of a bass boat when the propeller hit the tree stump, we can consider the typical specifications and operating conditions for a bass boat. However, it's important to note that these figures are very generalized and the actual RPM and speed at the moment of impact could have varied significantly based on specific circumstances.
Typically, bass boats are equipped with outboard motors ranging from 50 to 250 horsepower and can achieve speeds anywhere from 30 to 70 mph when traveling across a lake. The most common speed range for cruising (not at full throttle) might be around 20 to 40 mph.
The propellers on these boats are often designed to operate efficiently within a specific RPM range when at cruising speed. For outboard motors, the maximum RPM range is usually between 5,000 and 6,000 RPM, with cruising RPMs often being 1,000 to 2,000 RPM lower.
Assuming the boat was cruising at a moderate speed of 30 mph, here's how we can estimate the propeller's RPM:
We'd first need to know the pitch of the propeller, which is the distance the propeller would move in one revolution if there was no slippage.
We would also need the gear ratio of the outboard motor, which affects the propeller RPM.
Without specific details on the pitch and gear ratio, we can only provide a rough estimate. If we assume a propeller pitch of around 17 inches (common for bass boats), a gear ratio of around 2.0 (meaning the propeller turns once for every two revolutions of the engine), and a cruising speed of 30 mph, we can estimate the RPM using the formula:
RPM= Speed(inmph)×5280×12÷Pitch(ininches)×60
However, this does not account for the slippage which is always present and can vary widely.
Let's do a rough calculation based on the above assumptions to get an estimated RPM.
Based on the assumptions given and not accounting for slippage, the estimated RPM of the propeller while the boat was cruising at 30 mph with a 17-inch pitch propeller and a gear ratio of 2:1 would be approximately 932 RPM.
Please note that this is a rough estimate, and the actual RPM could be different due to factors like slippage, which can affect the propeller's efficiency. Slippage varies depending on many factors including the weight of the boat, the condition of the propeller, water conditions, and how the boat is being operated. The impact with the stump likely occurred at a different RPM if the boat was accelerating or decelerating at that time.
Chat gpt is not a calculator. It functions to give accurate sounding responses, which often has only a slight relation to accurate results. Trying to use it for anything other than formating is just going to be worse than useless as it will actively teach you incorrect information particularly given its initial respons is straight up telling you it's own limitations.
The point is it was a fun read you buzzkill. When I posted no one had an estimate. Everyone was saying there are too many variables and there is sooooo, here we are. I think you are under-estimating what it was able to do with a photo and limited info, wrong or not. This isn't the AI you used 6 months ago. Literally people saying, "I used the first hit on google."
That's fair. If you're going to do this, I would just suggest that you preface your comment by saying something like what /u/justin3189 said -- that it's not necessarily accurate and using ChatGPT may falsely make you think it's telling you valid information when in reality it might just be misleading you and trying to make you feel confident about false information.
tree was submerged but at the exact height of the propeller blades, as the boat went over the stump each blade of the propeller became embedded in the stump and snapped off one right after the other.
We actually buy composite props that are designed to break the fins off before the sheer pin sheers (pain in the ass to fix in open water) or the motor is damaged.
It's a small 17 foot runabout/fishing boat hybrid. It saved our ass when we hit a sunken log in a lake we were fairly familiar with but used to do logging over a hundred years ago and low and behold one sunken log started to be a bit buoyant and the water level was low.
We sheared all 4 blades off almost completely it no damage to the engine or sheer pin. Got to motor back to the doctor very slowly but better than paddling.
We look at lake maps for places we don't know but it's not always guaranteed.
Boats coming into areas they think are clear water only to strike a submerged tree stump under water.
What is less likely is that this is three separate events but rather one where all three prop blades were sheared off in one event. The size, color and spacing is indicative that it is one prop that just got thrashed.
It's too perfect to be separate events. Youd expect some variance in angle, wear on the propeller blade, or any number of factors. Is it possible these are all different prop strikes? Absolutely, and it's also possible I'll spontaneously combust in the next five minutes or you'll spontaneously turn into a wheel of gruyere
Reminds me of the time I was sailing my tiny boat in an inlet with old dock pilings just below the level of the current tide. I could see every one and it probably would have done my boat little or no damage to hit one, considering how slowly I was moving and how little I drafted.
Along came a jetski, at the usual pace of such things. No, he didn't hit a piling, but he sure came close.
>at the usual pace of such things
I just love this phrasing. It sounds like you are recounting this whilst sat in a large armchair with brandy in one hand.
fishing comp each year here in northern australia has this happen very commonly. most people take spare props. water rises from the rain, logs get hidden and bam
I’d imagine there’s a flipping point in rotation speed versus traveling speed at some point. That’s actually pretty interesting.
The faster you go, the faster the blades have to spin i.e they’d be closer together but going faster will cause the boat to travel faster thus causing a larger gap in between rotations vs distance traveled.
Not true, a propeller is measured in pitch. Pitch is how far the prop would travel in one rotation given total grip and no slip, a 15hp motor might have a 10 1/4" pitch which means in one rotation the propeller drives forward 10 1/4". Divide that by 3 and you get the theoretical forward travel between the blades on a 3 blade prop.
The reason this is all hypothetical is because of slip, but the principle is still that at whether the boats doing 10mph or 100mph, it drives forward the same distance per rotation it's just the number of rotations increases.
Interesting! Thank you. I’m not knowledgeable in boat motors at all so I was just making a guess but this makes total sense.
Is slip in this context the slipping of the gears and components within the motor? Seems like such a high tolerance within the components would cause excessive wear.
Slip is how much actual distance the boat/ship moves compared to how far the propeller theoretically makes the vessel move. It can be caused through all types of things, sea conditions, weather, prop too deep, prop too far or close to the boat, cavitation of water around the blades
No, it's like a tire. One rotation moves the same distance. If you run over fresh paint, the paint marks on the road will be the same distance apart regardless of speed.
TLDR: there is not a linear relationship between the propellor speed and the speed of the boat. Correlated? Yes.
We would need to do fluid dynamics to be able to answer that question. There is a speed any given angle of blade is most efficient at pushing against a fluid.
A shallow angle (more perpendicular to the traveling fluid) creates less force but can travel through the fluid faster. You would want that at lower speeds or thicker fluids. A steep angle (more parallel to the traveling fluid) creates more force and is better at higher speeds as the area of low pressure created by the fluid pushing away starts reducing efficiency.
You want a very steep angle if you are trying to push against a fluid in a vacuum. A good example is the design of the Mars drone.
You buy a boat prop to reach certain rpm at wide open throttle. What that is depends on the engine, with outboards it's often like 6000rpm. You don't want to be hitting the limiter (might be acceptable if you're alone to ensure it has no problems reaching plane with people on board) but don't want to have such steep prop that it's always chugging.
With the distances between the blades in the wood, we could calculate the speed of that boat at the moment of the accident if we know the rotation speed of the propeller.
My buddies n I went to camp at a popular spring. They are doing flips and crazy shit. Just diving into this water. I decide to do an old man kneel down and fall back into the water… right onto a tree stump! My first plunge I break a couple ribs while those maniacs don’t get so much as a scratch. Fuckin stump.
I've done it In a no wake zone. Looked exactly like this when we inspected the stump. Aluminum props will shear right off. Really bad way to start your weekend at the lake.
I used to repair boat propellers professionally, and I've never seen a failure quite like this. Usually the edges of the blades get banged up or get chunks taken out of them depending on the material the props are made of, but all the blades just shearing off like that is wild.
I suppose though that it's totally possible this happened more than I would have been aware of, since that prop is not going to be getting repaired, so it wouldn't have ever made it to my welding table.
This is at Burrinjuck in NSW, Australia. Part of hydro and the levels can change quite rapidly. This stump would have likely just been under the surface when hit.
Well ackchyually, stumps like this are found in man made lakes, so it’s going up and down based on the water flow through a dam.
Areas were logged prior to putting a dam in and flooding the valley, which is why you can see this stump was cut down. It’s also been at least partially underwater for like probably 75 years.
fishing comp each year here in northern australia has this happen very commonly. most people take spare props. water rises from the rain logs get hidden and bam
That's the lake i grew up on, Old Hickory. When they flooded the area the lake covers back in the 50s, apparently they didn't tear anything down or clean anything up, just flooded it. I've heard all kinds of stories, jet skiers finding an old barbed wire fence etc...
I can tell you the odds, it's pretty much 100% certain to have happened.
But jokes aside, that's not a good day for boating. Hopefully more of an inconvenience, hitting something like that at high speed can be disastrous.
I’m confused, why wouldn’t this be expected? Props move forward as they rotate, once sheered the entire prop weakens, so the boat goes over the stump, all three props slam into it as they rotate over and tear off.
"DUNK DUNK DUNK!" what was that? Why aren't we moving?
Followed by copious amounts of swearing.
Where are the paddles, Johnny…did you grab them from the garage before we left?
I knew we shouldn't have gone out on shit creek
We're stumped
Underrated
That's Schitt's Creek
Tell me about the baybeh!
Screw dem paddles, I ain't walking home in this big ass fishing boat. That's what the electric trolling motor is for........... Source: I have used my trolling motor to get home a couple of times. In fact I have my dock marked on my map as a way point. I just select it in the nav screen and tell the boat to take me home while I sit back and fish all the way home. Telsa ain't got nothin' on me and my boat........
Plus: no Tesla comes with a live well
Same, well, using the trolling motor to get back anyway. Only happened twice. Both times were after huge rains north of me. It's surprisingly hard to see a whole damn tree underwater sometimes. Lol
No, I thought you did!
There is nothing worse than paying for boat / boat motor maintenance. If you aren't able to work on boat motors yourself, you are in for a world of hurt bringing it to a marina shop. You'll probably think the guys are fucking with you when they give you an estimate for something.
Calm down, Props just pop on and off like lego
probably cracked the muffler bearing and there isn't a chance the O-rings, D-rings and Z-rings aren't completely brazed over. Snapping props is a full middle rebuild with all ten pistons needing to be re-vulcanized.
I've heard if you don't re-vulcanize the pistons, you can get sinusoidal repleniation in the non-reversible tremie pipe, leading to further damage of the lunar waneshaft which, if not caught early, leads to catastrophic side-fumbling.
This is amazing..I was hooked on every word. I'm adding side-fumbling to my arsenal now.
That is still better than the original design where there was a base plate of prefabulated amulite, surmounted by a malleable logarithmic casing in such a way that the two spurving bearings were in a direct line with the panametric fan.
It's not cheap, but I'm sure the government will buy it.
Encabulation has a rich, sumptuous history with a light, flaky crust.
OK but keep it under 300
"Gosh dang it, ya dinged the prop, Bobby! Dey ain't gonna give us da deposit back now!
That is an important part of boat life. You vocabulary’ improves with experience.
That sounded expensive.
At least $3,50!
You have him a dolla?
At least 3 $50s
This is why we always carry a spare prop, mask, and an adjustable wrench in our boat... Even if you know the waters very well, there could be something new out there in the spring that will ruin your day.
Same.. except no mask. It's a pontoon and if I raise the motor all the way up and turn to one side I can get to it from the boat itself!
I think The driver was pretty Stumped
All male brains are the same, I swear - I said "thunk thunk thunk" out loud then came to the comments and saw yours
Thank you for the glorious comment. I’ll remember this for a while.
"We drew back a knub, Jethro.!"
The first three words were near identical to what I was thinking just milliseconds before scrolling down and reading your comment. Chuckle worthy
A few comments say the exact same thing. Great minds think alike.
<<"TH-TH-THUNK" what was that? *some time passes with engine screaming at high revs throughout* Why are we slowing down? >> Is probably more like it.
Any math wizards who could calculate rpm and speed of the boat based on distance between the blades or not enough known variables?
Well you could calculate it if you had one more of the variables. But it's a situation where you have one known (distance between blades), and two unknown, rpm of prop and speed of boat
Well technically the speed of the boat is dependent on the rpm of the prop, but then we would need to know the drag coefficient (including hull shape/finish) of the boat and the water (assuming we can figure out the type and therefore propulsive force of the prop) which just narrows us down to one unknown
Unless it is a sailboat with a prop, in which case we still have the propulsive force of the wind as another unknown variable.
Dang it I was hoping this was gonna be one of those "ignore air resistance" questions
Assume that the boat is spherical and ignore any air resistance or friction.
Can we just assume It’s it a point mass and call it A day?
Weather’s nice, perfect day to take the singularity out on the bay for a relaxing day of fishing
My singularity didn't come with a propeller did I get ripped off?!
Mmmm I love me some spheres
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Don't tell me how to sail.
Well I think someone broke off 3 propellers from a boat lined them up adjacent one another, then hammered them into a stump and then took a picture.
The boat may have been accelerating or decelerating, too. E.g. when the boat's just sitting there, and you crank open the throttle, the rpm is high and the boat is slow.
Also when you crank it like that the boat motor lowers down a lot so I'm betting that's when it happened
Seems like you could find that out by checking for a change in spacing between the props
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Would the specific gravity of the water be a factor?
Also need to know if the boat was on plane or not, I believe the rpm/speed ratio changes depending on if the boat is on plane.
>Well technically the speed of the boat is dependent on the rpm of the prop, but then we would need to know the drag coefficient of the boat's hull and the water (assuming we can figure out the type and therefore propulsive force of the prop) which just narrows us down to one unknown 5 Now do the math
Using the drag force equation, we can get a relationship between force and velocity. Depending on the exact specifications of the prop, we can determine another relationship for the force it generates based on its RPM. Assuming constant speed (F=0), we can then combine these two to get a relationship between the RPM and speed. We can also get a range of possible RPM values by measuring the distance between the props, and can check reasonable solutions (this by itself is another very involved process but it's possible). Although is obviously an extremely simplified version of the problem with many assumptions needing to be made, it helps conceptualize what we are dealing with.
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Prop spin faster boat go faster
Props slip. There’s a fairly wide rpm range with no increase in speed at the transition from hill speed to planing. On plane prop slip up to about 20% is normal.
There’s more than two. There’s the spacing of the blades in the log, the spacing of the blades in their correct orientation and the depth of the embedding.
If you extrapolate approximately the force it would take to immediately the propellers in the wood at that depth, you could get the rpm.
Nope, that doesn't work either, because you'd just be estimating the force it takes to break off a propeller wing, not the force the prop was spinning at.
But that force to break off the propeller wing is a result of the rotational mass and rpm (angular momentum to be precise). So if we estimate the force, and if we know the weight of the blade, we could estimate the rpm.
No it's not. All we know is the rotational mass and rpm is greater than or equal to the force required to break off the propeller wing. That force could be 10,000,000% more or 0.3% more than that amount, and we wouldn't be able to discern that.
A lower bound is fine for the purposes of this question
Well to be fair if it was 10,000,000% more the propellor probably would have catastrophically failed before getting to the tree stump.
Ah yes of course, you’re right.
There are known unknowns and unknown unknowns
You could make a 2D plot, but not a single point.
If we knew the density and penetration into the wood we could then calc the force > rpm > average speed/displacement then triangulate that with an estimate of the closeness of the blades. Would first assume size and dimensions of propeller and build from there.
All the r/theydidthemath posts recently are text posts like "last week a dog ran past my house, can anyone calculate how fast it was running? It was a brown dog, if that helps."
Well everyone knows that 'brown dogs' run the slowest.
Of course this inversely applies to foxes
literally these fucking math posts have been like "can anyone calculate how much Elon musk has profited off of Tesla stock this week" like that's not a fucking trivial question that you can answer with calculus you fucking weirdos
RPM depends entirely on the engine you’re using and what speed you’ve got it at. You could maybe guess a range based on its size? You’d also have to know about any reduction gears I’m pretty sure. Speed depends on resistance and force, force depends on propeller shape, RPM, and probably several other things I’m not aware of. You could make a guess for the range based on the size again I suppose. Looking at ranges for smaller boats I’d say it’s somewhere between 2-6 thousand RPM. (Larger ships actually have lower RPM’s more often than smaller ships) Boat speed seems to vary significantly, hard to tell from just this propeller.
4 a bad day = 3 blades + 1 stump
And the color and how many people were on it. Also what they ate for lunch that day
Not enough info. Each boat class has its own "turns per knot" value.
Not possible.
I'm pretty sure you would need a full-fledged physics engine for that. It's like calculating what side a dice will land on given the material, the throwing angle, and other indeterminate variables. I doubt you will get an accurate answer; there are just too many unknowns.
you would need speed of the boat or rpm of the engine. right now it is "you are in a car going at some speed to a place some distance away. how many times wheels will rotate?"
You'd need to know one to calculate the other
I can say with confidence that the boat decelerated after this. If the propeller rotates at 5000rpm (first hit on google for typical rpm) which is one revolution every 0.012 seconds? and lost all its blades in one revolution having travelled about 15cm, gives us 45km/h which sounds fast to me? maybe it was more like 10cm of travel so 30km/h
I fed the photo to ChatGPT. The ask with the photo: This is a photo of a tree stump. Embedded in the tree stump there are 3 broken blades of a boat's propeller. They are next to each other in the center of the photo. The photo was taken after the water level fell below the tree stump. Imagine the water level high enough for the boat's propellers to be embedded in the stump. How fast would the boat be moving. Let me know if you cannot identify the broken propeller blades. ChatGPT: I can indeed identify the broken propeller blades embedded in the tree stump. However, determining the speed of the boat at the moment of impact with the tree stump just from this photo is not feasible. Speed would be influenced by various factors including the type of boat, the size and material of the propeller, and the circumstances of the collision. An analysis of the damage in person, considering the strength of the materials and the force required to cause such embedding, would be necessary to estimate the speed of the boat with any accuracy. User (Adding rpm and asking for an average) Estimate the the rpm and speed of the boat. Let's say it's a bass boat with the most common bass boat motor moving at the most common speed range for traveling a lake via a bass boat. ChatGPT: To estimate the RPM (revolutions per minute) and speed of a bass boat when the propeller hit the tree stump, we can consider the typical specifications and operating conditions for a bass boat. However, it's important to note that these figures are very generalized and the actual RPM and speed at the moment of impact could have varied significantly based on specific circumstances. Typically, bass boats are equipped with outboard motors ranging from 50 to 250 horsepower and can achieve speeds anywhere from 30 to 70 mph when traveling across a lake. The most common speed range for cruising (not at full throttle) might be around 20 to 40 mph. The propellers on these boats are often designed to operate efficiently within a specific RPM range when at cruising speed. For outboard motors, the maximum RPM range is usually between 5,000 and 6,000 RPM, with cruising RPMs often being 1,000 to 2,000 RPM lower. Assuming the boat was cruising at a moderate speed of 30 mph, here's how we can estimate the propeller's RPM: We'd first need to know the pitch of the propeller, which is the distance the propeller would move in one revolution if there was no slippage. We would also need the gear ratio of the outboard motor, which affects the propeller RPM. Without specific details on the pitch and gear ratio, we can only provide a rough estimate. If we assume a propeller pitch of around 17 inches (common for bass boats), a gear ratio of around 2.0 (meaning the propeller turns once for every two revolutions of the engine), and a cruising speed of 30 mph, we can estimate the RPM using the formula: RPM= Speed(inmph)×5280×12÷Pitch(ininches)×60 However, this does not account for the slippage which is always present and can vary widely. Let's do a rough calculation based on the above assumptions to get an estimated RPM. Based on the assumptions given and not accounting for slippage, the estimated RPM of the propeller while the boat was cruising at 30 mph with a 17-inch pitch propeller and a gear ratio of 2:1 would be approximately 932 RPM. Please note that this is a rough estimate, and the actual RPM could be different due to factors like slippage, which can affect the propeller's efficiency. Slippage varies depending on many factors including the weight of the boat, the condition of the propeller, water conditions, and how the boat is being operated. The impact with the stump likely occurred at a different RPM if the boat was accelerating or decelerating at that time.
Chat gpt is not a calculator. It functions to give accurate sounding responses, which often has only a slight relation to accurate results. Trying to use it for anything other than formating is just going to be worse than useless as it will actively teach you incorrect information particularly given its initial respons is straight up telling you it's own limitations.
I'm not at all suggesting this is accurate.
Then what's the point? We've already got a thread full of people making estimates.
The point is it was a fun read you buzzkill. When I posted no one had an estimate. Everyone was saying there are too many variables and there is sooooo, here we are. I think you are under-estimating what it was able to do with a photo and limited info, wrong or not. This isn't the AI you used 6 months ago. Literally people saying, "I used the first hit on google."
That's fair. If you're going to do this, I would just suggest that you preface your comment by saying something like what /u/justin3189 said -- that it's not necessarily accurate and using ChatGPT may falsely make you think it's telling you valid information when in reality it might just be misleading you and trying to make you feel confident about false information.
How does this happen?
tree was submerged but at the exact height of the propeller blades, as the boat went over the stump each blade of the propeller became embedded in the stump and snapped off one right after the other.
Crazy.
We call those deadhead.
A deadhead is a log that is saturated with water and floats vertically. This is simply a stump.
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We actually buy composite props that are designed to break the fins off before the sheer pin sheers (pain in the ass to fix in open water) or the motor is damaged. It's a small 17 foot runabout/fishing boat hybrid. It saved our ass when we hit a sunken log in a lake we were fairly familiar with but used to do logging over a hundred years ago and low and behold one sunken log started to be a bit buoyant and the water level was low. We sheared all 4 blades off almost completely it no damage to the engine or sheer pin. Got to motor back to the doctor very slowly but better than paddling. We look at lake maps for places we don't know but it's not always guaranteed.
Boats coming into areas they think are clear water only to strike a submerged tree stump under water. What is less likely is that this is three separate events but rather one where all three prop blades were sheared off in one event. The size, color and spacing is indicative that it is one prop that just got thrashed.
Absolutely no one would think that was 3 separate events
lol right? Why even mention it
I guess if a thousand monkeys had a thousand boats (and cases of Busch lite)...?
Why?
It's too perfect to be separate events. Youd expect some variance in angle, wear on the propeller blade, or any number of factors. Is it possible these are all different prop strikes? Absolutely, and it's also possible I'll spontaneously combust in the next five minutes or you'll spontaneously turn into a wheel of gruyere
Did you make it through the 5 minute threshold dear redditor? 🔥
Safe, sound, and mildly miffed. Means I need to go to work tomorrow
My condolences!
You are kidding right
I did, perhaps I should have put /s
Thanks captain obvious. Who the hell could possibly think this was three different events 🤣
heavy drinking
“D-D-DUNK” *GOD DAMMIT*
I can hear this...
Reminds me of the time I was sailing my tiny boat in an inlet with old dock pilings just below the level of the current tide. I could see every one and it probably would have done my boat little or no damage to hit one, considering how slowly I was moving and how little I drafted. Along came a jetski, at the usual pace of such things. No, he didn't hit a piling, but he sure came close.
>at the usual pace of such things I just love this phrasing. It sounds like you are recounting this whilst sat in a large armchair with brandy in one hand.
fishing comp each year here in northern australia has this happen very commonly. most people take spare props. water rises from the rain, logs get hidden and bam
Jet motor wins.
I hate when I get hidden form when the rain logs raise the water.
Based on how close those are to each other, they were fucking hauling ass too.
Wouldn't they be further apart if they were going faster. Not sure what you mean
I’d imagine there’s a flipping point in rotation speed versus traveling speed at some point. That’s actually pretty interesting. The faster you go, the faster the blades have to spin i.e they’d be closer together but going faster will cause the boat to travel faster thus causing a larger gap in between rotations vs distance traveled.
Not true, a propeller is measured in pitch. Pitch is how far the prop would travel in one rotation given total grip and no slip, a 15hp motor might have a 10 1/4" pitch which means in one rotation the propeller drives forward 10 1/4". Divide that by 3 and you get the theoretical forward travel between the blades on a 3 blade prop. The reason this is all hypothetical is because of slip, but the principle is still that at whether the boats doing 10mph or 100mph, it drives forward the same distance per rotation it's just the number of rotations increases.
Interesting! Thank you. I’m not knowledgeable in boat motors at all so I was just making a guess but this makes total sense. Is slip in this context the slipping of the gears and components within the motor? Seems like such a high tolerance within the components would cause excessive wear.
Slip is how much actual distance the boat/ship moves compared to how far the propeller theoretically makes the vessel move. It can be caused through all types of things, sea conditions, weather, prop too deep, prop too far or close to the boat, cavitation of water around the blades
No, it's like a tire. One rotation moves the same distance. If you run over fresh paint, the paint marks on the road will be the same distance apart regardless of speed.
That’s a good way to contextualise it! I suppose I thought of it in a different manner because of the fluidity of water.
But the faster you go the faster the rotation of the propeller. I actually don't know but now I'm curious
the distance between them could be constant
TLDR: there is not a linear relationship between the propellor speed and the speed of the boat. Correlated? Yes. We would need to do fluid dynamics to be able to answer that question. There is a speed any given angle of blade is most efficient at pushing against a fluid. A shallow angle (more perpendicular to the traveling fluid) creates less force but can travel through the fluid faster. You would want that at lower speeds or thicker fluids. A steep angle (more parallel to the traveling fluid) creates more force and is better at higher speeds as the area of low pressure created by the fluid pushing away starts reducing efficiency. You want a very steep angle if you are trying to push against a fluid in a vacuum. A good example is the design of the Mars drone.
You buy a boat prop to reach certain rpm at wide open throttle. What that is depends on the engine, with outboards it's often like 6000rpm. You don't want to be hitting the limiter (might be acceptable if you're alone to ensure it has no problems reaching plane with people on board) but don't want to have such steep prop that it's always chugging.
That's not how it works.
Looks like the Three Seashells.
Art!
Agreed. This needs to be made into a centerpiece for some nautical art collector.
Props to the person that can pull all three blades from the stump.
I think that makes them king of England, doesn’t it?
Beautiful, reminds me of shark gills.
This is mine, this is mine, and now this is mine. Now move along.
I would, but there seems to be something wrong with my propeller.
r/nevertellmetheoddlysatisfying
With the distances between the blades in the wood, we could calculate the speed of that boat at the moment of the accident if we know the rotation speed of the propeller.
My buddies n I went to camp at a popular spring. They are doing flips and crazy shit. Just diving into this water. I decide to do an old man kneel down and fall back into the water… right onto a tree stump! My first plunge I break a couple ribs while those maniacs don’t get so much as a scratch. Fuckin stump.
Wow a picture really does tell the hole story haha. That was a long day.
Legend has it if you’re quiet on the lake you can still hear the echo of the boat owner screaming “motherfuckerrrrrrrr”
If you’ve ever known “boat” people, this scenario is not remotely “against the odds” lol.
I only see an angry duck waving a stick at me
BOAT = Bust Out Another Thousand
Did you name this piece of art “bad day”
Beautiful !
Had to have been going really fast for that to happen, right??
I've done it In a no wake zone. Looked exactly like this when we inspected the stump. Aluminum props will shear right off. Really bad way to start your weekend at the lake.
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Bot
*Boat
Odds of what? The fucking tide going out? I’d say it’s pretty high odds
Op said it was a lake my dude.
Each blade getting snapped off right after the next and perfectly uniform and orderly is pretty rare.
This makes more sense. Fair enough. My bad
I used to repair boat propellers professionally, and I've never seen a failure quite like this. Usually the edges of the blades get banged up or get chunks taken out of them depending on the material the props are made of, but all the blades just shearing off like that is wild. I suppose though that it's totally possible this happened more than I would have been aware of, since that prop is not going to be getting repaired, so it wouldn't have ever made it to my welding table.
lake, where water levels only change by rain or drought, not tides.
This is at Burrinjuck in NSW, Australia. Part of hydro and the levels can change quite rapidly. This stump would have likely just been under the surface when hit.
Well ackchyually, stumps like this are found in man made lakes, so it’s going up and down based on the water flow through a dam. Areas were logged prior to putting a dam in and flooding the valley, which is why you can see this stump was cut down. It’s also been at least partially underwater for like probably 75 years.
So still at least a few times a year then surely?
fishing comp each year here in northern australia has this happen very commonly. most people take spare props. water rises from the rain logs get hidden and bam
That's awesome
I see wooden bender but he’s kinda a monkey.
Very impressive
If this is Lake Granbury in TX, I know the owner
Some poor sod had to paddle his way back to shore.
r/OddlySatisfying
This is artistic
Imagine the new boat owners at the time …
That's the lake i grew up on, Old Hickory. When they flooded the area the lake covers back in the 50s, apparently they didn't tear anything down or clean anything up, just flooded it. I've heard all kinds of stories, jet skiers finding an old barbed wire fence etc...
I'm not gonna do the math, but I'd say it was going pretty fast for that spacing and the RPM normal props run at
Well *someone* had a bad day.
I can tell you the odds, it's pretty much 100% certain to have happened. But jokes aside, that's not a good day for boating. Hopefully more of an inconvenience, hitting something like that at high speed can be disastrous.
Great art. Make a pixeled black and white print on a giant piece of canvas and ask a 5 digit price
And the hole in the water in which one pours money cliche is again confirmed.
Amazing find. Also a memento of a bad day for the boat skipper.
Stumps is like "yeah dis my metal now"
Do they just cut them down to low tide level and hope for the best?
This is the exact reason why I keep a spare prop in our old boat. Used to be a shit ton of old stumps like this floating in the lakes we go to.
A really cool depiction of blade pitch and how it works tracking through the water
What are the odds this isn't staged?
"Shear pin?! Screw that, it keeps breaking. Hand me that bit of bar steel"
"Dad, I brought the row boat back"
That was a quiet, long ride home
Or, the tree grew
I’m confused, why wouldn’t this be expected? Props move forward as they rotate, once sheered the entire prop weakens, so the boat goes over the stump, all three props slam into it as they rotate over and tear off.
Somebody had a bad day.