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Uninformed

A

Anonymous

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I have two questions............

Why do airboats run faster in "no water" than deep water?

Does anyone have any experience with the CHE3 Long belt drive. It would seem to add a lot of stability to the boat?

Any comments?
 
They run faster in (skinny) water or less water because induced drag is reduced. In water deeper than the hull floats at the more induced drag occurs because more surface area of the hull is contacting the water thus increasing drag. When a hull is floating in water you must displace the weight of the boat in the water so when less water is available you do not have to displace it. Thus reducing drag. That’s why the step hulls are so fast their just like that hockey puck on a airhocky table turn the air off and the puck drags on the table now turn on the air and there is almost no drag because it’s ridding on a cushion of air.


Oh yea I think belt drives are no good unless you run a barge tour boat and don't care anything about performance. Now if your boat is so large it needs a 502 big block to push it and it's cargo. And you don't care aboat running dry with ease then their fine.
 
An airboat runs faster in shallow water because when the boat pushes the water down, it has no where to go. This creates sort of a pillow effect that keeps the boat on the surface instead of letting it ride low in the water so there is almost no drag. It is the same effect caused when an airplane is landing and gets within five or ten feet of the ground, the air that is being pushed down by the wing is squished between the wing and the ground and the plane floats on this pillow. It is called "ground effect".
 
We said the same thing but in two different ways. Boats can't disperse ground and a pilot pray's they never disperse ground. An airplane always fights the same drag it always pushes against (air). So their induced drag only depends on speed. Boats on the other hand loose drag when they get up on top of the water because the drag coefficient of air is much lower than water. The less a boat runs in the water the lower its drag coefficient is. So the more air a hull runs on the lower the drag coefficient. The ground effect your talking about comes from an increase in air pressure from the air being compacted and accelerated under the wing at landing because the air under the wing during landing is compacted between the wing and the ground thus increasing air pressure. Everybody laughs at us redneck airboaters but I have found very few things that utilize more physics than an airboat.
 
An airboat has several sources of drag.
The most significant in deep water and lower speeds is the energy required to move the water out of the way of the hull ie; wave generation. This wave generation energy decreases significantly in shallow water because there is so much less of a wave created because the ground effect has raised the boat.

Skin friction and air resistance are fairly insignificant compared to this wave generation drag. Consider the difference in wetted surface between running on plane in deep water versus scooting along in an inch of water. Maybe the difference is a factor of 2:1, but I would guess the difference in drag is significantly higher.

I found an article that discusses boat drag, but it doesn't address ground effect for planing hulls (only displacement).http://members.iinet.net.au/~bluep/wavedrag.html
http://members.iinet.net.au/~bluep/wavedrag.html
 
Oh yea I think belt drives are no good unless you run a barge tour boat and don't care anything about performance. Now if your boat is so large it needs a 502 big block to push it and it's cargo. And you don't care aboat running dry with ease then their fine.
Click to expand...


Water Thunder, I am not doubting you but i would like to know your theory about this. I am ignorant to the gear boxs because we rarely see them in these parts of the south. Do you lose that much usable power through the belt compaired to a gear drive or is it a weight issue? Around here everyone is running the 2:1 CH3 belt drive with a 454 or 502 and they seem to perform well. Even the ZZ4's and 5's handle themselves well with the belt drives.

Wondering minds want to know, Kevin
 
That’s what I mean the wave is caused by the hull dispersing it’s weight or pushing against the water. The bigger wave means there is more drag and more energy being consumed from pushing the water. It’s all the same we are just interpreting in different way’s.
 
It’s mostly a weight issue were talking over a hundred pounds of weight in the worst possible location plus the 100 lbs is up high off the bottom of the boat. Another smaller factor is on a belt drive the prop and motor all torque in the same direction. On a gear box some of the prop torque offset’s the engine torque this causes the boat to roll on its side less when you accelerate. Don’t get me wrong belt drives are fine but I would never run one on a hull less than 14ft.
 
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