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my airboat is pushing water

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my airboat is pushing water

Old 03-16-2015, 07:37 AM
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keithcitra
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Default my airboat is pushing water

i have 2 airboats one runs great 24 by 12 the other one is 31 by 18 balance point now is 8" from back and it still will not get up on plain it pushes water like a dozer any one no what i need to do
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Old 03-16-2015, 10:08 PM
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crispyspa
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It almost looks as though the rake has a definite angle to it and not a curve. That could be creating a vacuum at the bow. Also it looks as though you have the back of the motor jacked up with chunks of wood. That faces the prop down creating lift at the stern and, in turn, making downforce at the bow. Try removing the shims and see what happens.
Old 03-18-2015, 04:58 AM
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will try was told to put the blocks there but will remove have close to a pound and a half of weight in the back amtaking that out two
Old 03-19-2015, 10:04 AM
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wellipulled the blocks i had on the back and pulled all the excess weight out sanded the front down still pushing water as soon as i give it throttle the thrust pushes the front down should i put blocks by the prop and lift the front of the motor
Old 03-20-2015, 02:37 AM
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yes raise rear of engine, the prop wants to travel in a strait line, so raiseing the stearn end will lift the bow and lower the stearn
Old 03-24-2015, 12:52 PM
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keithcitra
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well i have shimmed the engine both ways no help as soon as i hit the throttle the nose goes down if i remeber right the motor is a viago 36 -74 1800 kv i am running 4s 5000 mah 65 c
Old 03-26-2015, 02:52 AM
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That is a pretty high Kv for a boat that size, it's twice the size of you smaller hull. What prop are you using? I suspect that you just don't have enough thrust for that large hull.


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Old 03-26-2015, 03:15 AM
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1QwkSport2.5r
 
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So what are the dimensions, weight, and CG of the boat in question? Post #1 talks about two boats of two different sizes and one runs good. I'm suspecting either the CG is off, or the boat is too heavy for the power train being used (as what Got RPM said).
Old 03-26-2015, 10:38 AM
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keithcitra
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the boat is only about 4 lbs the motor runs about 26,000 rpm the prop is a 10 6
Old 03-26-2015, 01:14 PM
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Originally Posted by keithcitra View Post
the boat is only about 4 lbs the motor runs about 26,000 rpm the prop is a 10 6
Well, the motor isn't going to turn a 10x6 at 26,000rpm unless you're running like 12 cells and a ridiculously huge motor and even then you'll likely lose a prop blade at that rpm. If that's actually correct because the safe rotational limit of a 10" (APC for example) is around 19,000rpm. If your actual motor RPM on a 10x6 is even 14k, that's a fair amount of thrust to make 4lbs move good and get on plane.

What attitude does the boat take if you hold it up by the prop? The CG should be at the prop and the bow should be slightly heavy (hang low). My flatbottom boat is about 7lbs and hangs pretty level when held up by the prop. Mine are in a tractor configuration with the prop in front of the engine. In a pusher prop configuration, you should still be balancing close to the prop. If your bow is way too heavy and if the power plant is underpowered, it might be pushing water no matter what. I'm gonna guess you need to move your motor forward some to take the weight off the bow.

Do you have a video of the boat plowing water or can you make a video? May help find a solution better/quicker that way.
Old 03-31-2015, 12:22 PM
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keithcitra
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the cg is at one third when you are going slow it runs good but as soon as you hit the throttle it pushes the front down i wish i had a video i was told to try a smaller prop and lower the motor down
Old 03-31-2015, 04:23 PM
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Originally Posted by keithcitra View Post
the cg is at one third when you are going slow it runs good but as soon as you hit the throttle it pushes the front down i wish i had a video i was told to try a smaller prop and lower the motor down
You probably need to move the motor forward.
Old 04-01-2015, 01:19 PM
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keithcitra
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i do no both air boats can not use a wood prop the fly apart the boat is running about 20 pushing water i had the motor in my 36 " shovel nose hydro it ran about 45

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