Why go easy on it when coming on plane?
12-01-2012, 11:01 PM
#31
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I bet this theory could actually be tested. I'm not an engineer but I see it like this, it's not just the torque that the motor makes that would hurt the drive but also what's going on at the other end. So factors like weight of boat, drag coefficients on the hull at the time of planing, and bite of props would be equally as important.
I bet if you had enough time with a prop shaft Dyno that you could adjust the amount of load on the shaft you could simulate planing and find out which way was easier on parts. But more importantly exactly what amount of force begins to cause fatigue on drives. Now it's late and I might be a little delirious, but Let's say you could figure out this magic number for each drive and take it one step further. Why not design a shear pin setup on either the input or output shaft of the drive, you hit your max load amount the pin shears you replace the pin but save the drive? So it ruins your day, but anyone who's grenaded a drive knows by the time you get parts or somebody to fix it it's always at least a week or more.
I wonder if that would actually work?
I bet if you had enough time with a prop shaft Dyno that you could adjust the amount of load on the shaft you could simulate planing and find out which way was easier on parts. But more importantly exactly what amount of force begins to cause fatigue on drives. Now it's late and I might be a little delirious, but Let's say you could figure out this magic number for each drive and take it one step further. Why not design a shear pin setup on either the input or output shaft of the drive, you hit your max load amount the pin shears you replace the pin but save the drive? So it ruins your day, but anyone who's grenaded a drive knows by the time you get parts or somebody to fix it it's always at least a week or more.
I wonder if that would actually work?
12-01-2012, 11:05 PM
#32
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If I mash the gas in the cat it will dig a hole and not come up u have to come up slow or it will not plan with the big props , the small props u can mash them and lett it eat! Like a drag boat
12-02-2012, 12:49 AM
#33
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For me I don`t need a scientific explanation, its just common sense. There is no doubt a drive is under a ton of stress trying to get a boat on plane with the throttles mashed.
I`ve blown up enough rear ends at the track to know if i throw on a pair of drag radials and hot lap it ..it`s going to fail a HELL of a lot faster than taking off easy from a stop light.
I`ve blown up enough rear ends at the track to know if i throw on a pair of drag radials and hot lap it ..it`s going to fail a HELL of a lot faster than taking off easy from a stop light.
12-02-2012, 04:24 AM
#34
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For me I don`t need a scientific explanation, its just common sense. There is no doubt a drive is under a ton of stress trying to get a boat on plane with the throttles mashed.
I`ve blown up enough rear ends at the track to know if i throw on a pair of drag radials and hot lap it ..it`s going to fail a HELL of a lot faster than taking off easy from a stop light.
I`ve blown up enough rear ends at the track to know if i throw on a pair of drag radials and hot lap it ..it`s going to fail a HELL of a lot faster than taking off easy from a stop light.
12-02-2012, 06:55 AM
#35
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For the sake of conversation:
It seems to be gospel that bringing a boat up on to plane at WOT is one of the most abusive things that can be done to a drive. While this makes sense on a street car, where the transmission multiplies the torque to the final drive gear, virtually all boats are top-gear-only. Add in that most engines develop peak torque well into their rpm range (let's say 4000-4800 rpm in general) and that prop slip rate is much higher at low speeds, and it seems to me that peak drive stress is more likely to occur at speed when the engine is at peak torque and the prop is hooked up.
My engines develop little torque below 2500 rpm, so full-throttle starts are pretty much mandatory if I ever plan to get up on plane.
Am I missing something in the physics here?
It seems to be gospel that bringing a boat up on to plane at WOT is one of the most abusive things that can be done to a drive. While this makes sense on a street car, where the transmission multiplies the torque to the final drive gear, virtually all boats are top-gear-only. Add in that most engines develop peak torque well into their rpm range (let's say 4000-4800 rpm in general) and that prop slip rate is much higher at low speeds, and it seems to me that peak drive stress is more likely to occur at speed when the engine is at peak torque and the prop is hooked up.
My engines develop little torque below 2500 rpm, so full-throttle starts are pretty much mandatory if I ever plan to get up on plane.
Am I missing something in the physics here?
Even if your peak torque is in the 4000-4800 range of your engine is freewheeling (in neutral) there is no resistance to it, thus it is not developing torque then. Only under load can torque come in. The most resistance you drivetrain experiences is when there is the most resistance which happens at the point your trying to get on plane or at top speed if your propped right and don't overspin your engines.
Before I ran #6's (which are a godsend after you are use to any Bravo's) EVERY time I poped a drive was on getting on plane, I'm taking gears breaking lower/upper, casing blowing up, top cap detonating, shaft breaking...M-O-U-S-E... get it, So that is enough for me to take it easy on take-off if you want to limit your wear...
My very humble opinion.
PS: I'm surprised you ask that CSpray you know the answer unless your just bored and figured rightfully that it is a good educational discussion to further mankind in broadening the knowledge base as a whole,,, to a population that makes it so the Kardashians (however you spell those fat chicks name...) are marketable...
Last edited by GLH; 12-02-2012 at 06:59 AM.
12-02-2012, 07:06 AM
#36
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[YOUTUBE]http://www.youtube.com/watch?v=FaYSDK4FXj4[/YOUTUBE]
...It even happens to the best of us...
Originally Posted by Wikipedia
...In Toronto however, Unser's engine blew off...
12-02-2012, 07:25 AM
#37
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Anything put to the ultimate will fail. Some faster than others. Take a boat with 350/260 and an alpha. Not very fast but that alpha will last a very long time even after repeated hole shots. We used to use ours to ski all te time when I was a kid.
Ultimately the more you beat on it the faster an more likely failure is.
12-02-2012, 08:28 AM
#38
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Great post! Everytime i look at my broken one sitting in the garage i think this very thing. Another thing is why the hell are they so expensive? Is the marine "tax" really that high? I look at any of these drives and i just dont see the money sitting there.
12-02-2012, 09:46 AM
#39
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Not all of us who wonder if getting on plane slow feel to get on plane fast you have to MASH the throttles all the way hard and fast.
YES< if you slam your sticks you will break something
But what about just SMOOTHLY accelerating but to a higher point so the boat gets on plane a little faster without dragging Azz forever?
Guess thats where I am at.
SLOW is bad
SLAM the throttle fast and hard bad
There prob is a "sweet" spot for every boat, and i don't feel super slow is correct for my boat because it still just plain WEARS out the XR gears no matter what. Might as well just get up on plane and enjoy your day.
YES< if you slam your sticks you will break something
But what about just SMOOTHLY accelerating but to a higher point so the boat gets on plane a little faster without dragging Azz forever?
Guess thats where I am at.
SLOW is bad
SLAM the throttle fast and hard bad
There prob is a "sweet" spot for every boat, and i don't feel super slow is correct for my boat because it still just plain WEARS out the XR gears no matter what. Might as well just get up on plane and enjoy your day.
12-02-2012, 12:38 PM
#40
Gold Member
Gold Member
Let me take another whack at this one. If one plots a graph of force (vertical axis) vs. time (horizontal axis), it’s generally the shape of the curve that makes or breaks (literally) driveline parts. “Spiking” the curve – which is what happens when you sail majestically off of a 6 foot swell with the sticks pasted all the way forward while you steal a smooch from your sweetie – and then land in flat water, will almost always break something. And it was either the magnitude and / or short duration of the peak load achieved that did the damage.
On the other hand, even more gentle applications of more power than a particular component was designed for – over time – will eventually lead to failure. Said another way, everything will break at some point.
The same goes for the human body. For instance, when they test humans in a centrifuge to see how they react to g forces, they build up the g forces up slowly. Sure, everybody will pass out at some point, but they generally just pass out – without any long term damage. Now, if the human body is subjected to a sudden shock (g loading), one can really get hurt. (Remember concussions?) And the peak force involved may actually be less that what was applied in the centrifuge.
So back to the original question of why some stuff (drives, props, etc.) don’t always hold up to what some folks throw at them, the answer is actually pretty simple. Much of the stuff we’re breaking is stressed – or worn – past its breaking point. Why don’t manufacturers just build stuff strong enough so we can’t break it? Again, simple. The cost would be prohibitive and folks would just keep adding more power until it broke anyway. In fact if you look at what the Mercury Bravo drive was originally designed to handle and compare it to what some folks are throwing at it today, you’ll find it’s actually a pretty good drive.
On the other hand, even more gentle applications of more power than a particular component was designed for – over time – will eventually lead to failure. Said another way, everything will break at some point.
The same goes for the human body. For instance, when they test humans in a centrifuge to see how they react to g forces, they build up the g forces up slowly. Sure, everybody will pass out at some point, but they generally just pass out – without any long term damage. Now, if the human body is subjected to a sudden shock (g loading), one can really get hurt. (Remember concussions?) And the peak force involved may actually be less that what was applied in the centrifuge.
So back to the original question of why some stuff (drives, props, etc.) don’t always hold up to what some folks throw at them, the answer is actually pretty simple. Much of the stuff we’re breaking is stressed – or worn – past its breaking point. Why don’t manufacturers just build stuff strong enough so we can’t break it? Again, simple. The cost would be prohibitive and folks would just keep adding more power until it broke anyway. In fact if you look at what the Mercury Bravo drive was originally designed to handle and compare it to what some folks are throwing at it today, you’ll find it’s actually a pretty good drive.
