Notice when ya let off the gas instantly the hull instantly rolls right back level, thats the stored energy dissipating back through the prop, engine, hull and air.
Now we have inertia of motion which is now stored energy or kinetic energy. When intertia of rest is overcome then the only torque being extracted is that required to move the hull forward at whatever speed is being traveled. Roll is induced by inertia yes, but it is inertia of rest not motin. Overlooking hull dynamics here, just energy dissipation. As the boat moves forward the torque being extracted from, the power sourse decreases and the hull will begin to roll back up in proportion to the energy being dissipated. When that volume and value equal the roll ceases. When a hull rolls it has to displace a quantity of water proportional to the value of applied torque. Torque roll in an airboat is related to several things and no one thing. Lot of good aircraft talk here and I like it. More air moved (doesn't matter what direction) per unit travel of prop = more roll. The force that you use to beat the air into submission and accelerate out the back is counteracted as thrust so the boat moves forward.
The force you apply to accelerate the prop through the uncooperative air is felt by you as torque roll in the opposite direction. So, torque roll is due to the inertia of the prop and the surrounding air. Now, if you spun up a prop with no mass in a vaccuum you wouldn't be doing anything with the prop but torque roll would still exist due to the inertia of the rotating assembly inside the engine. As Felber alluded to earlier, if your prop weighed nothing you'd still be acting upon the ambient air and if you spun up a prop in a vacuum you'd still be accelerating the mass of the prop. You are also changing the speed of the propeller. When you nail the throttle on your boat you are changing the direction and speed of the surrounding air. In real life, gravity and friction start to affect its speed and direction the instant it leaves your hand so it slows down and at some point begins to arc down. The baseball would forever and ever travel in the exact direction it left your hand at 100 mph if no other forces acted upon it. Let's say you wind up and throw a baseball with an initial velocity of 100 mph. If no external force exsists, the object will continue both its exact speed and its exact direction to infinity. I just put into two paragraphs, what I think Dave did in one sentence.Īn object, be it an aircraft carrier or an atom will do whatever it's doing at first glimpse unless and until it's acted upon by an external force. And if you need a big boat that has to be heavy.Ya better get it as wide as possible, If I run a small diameter prop that snaps quicker, I'll find myself using more pitch which will roll more, if I run a larger diameter prop with less pitch the leverage of the prop will equal things out.So yeah, weight of the prop is definitely a factor, but weight of the boat and if provided adequate power to overcome it is applied the rotational force/torque on the boat will go up accordingly, and I think the #1 reason light light light matters so much in a boat's overall package. If I could run a prop that weighed absolutely nothing, I would still have substancial torque-roll to counter just based on the aggresiveness of the prop and the air it's diggin into. It's an invisible screw that is moving "X" amount of weight of air. But the #1 inertia you're trying to overcome is the air you're moving in itself. In racing applications or a light/nimble boat it's WAY more of a factor. I for one put less emphasis on the weight of the prop (inertia) in HD applications. And I like the way Dave puts it in simple form.
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