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Center of Gravity

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Old 09-10-2007, 11:32 PM
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Default Center of Gravity

I'm trying to find out how to check the center of gravity on a stepped bottom boat, most specific a multi-stepped hull??? Please help, Thanks
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Old 09-10-2007, 11:44 PM
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eerrr..I am probably wrong but I think it is right under your feet when on plane.
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Old 09-11-2007, 12:09 AM
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How specific do you want to get? To find the exact point you would need some type of a three axis machine. I don't know that one exists. In aircrafts I think you have pitch, yawl,and roll.
You can determine the center forward and back with jack stands or slings. The others are harder to measure. The way a boat is rigged can help lower the cg. Staggered engines help to lower it. Adding ballast can move it. I hope this is of some use to you.
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Old 09-11-2007, 02:47 AM
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Originally Posted by TSUNAMIRACING View Post
I'm trying to find out how to check the center of gravity on a stepped bottom boat, most specific a multi-stepped hull??? Please help, Thanks
You need a Travel Lift or similar machine (large forklift) that can support the entire boat. With a SINGLE sling/strap, begin with it where you think the COG exists. Try to lift the boat off the trailer VERY slowly. One end of the boat is going to go up. Lower the boat, and move the strap fore/aft until you get it right. You may have to begin by lifting the boat up off of the bunks so you can get the strap under the boat. You may have to put a couple short 2x4s on top of the bunks to lift the boat away from them so you can slide the strap.

I'd make sure the trailer is still attached to the truck, and make sure the boat is still tied to the trailer at the bow and transom, with a foot or so of slack for lifting away from the trailer, (think using some ratchet straps, but leave them about 12" slack). This will alleviate any potential for the boat to slip out of the single sling, fore or aft; off of the trailer.



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eerrr..I am probably wrong but I think it is right under your feet when on plane.
On a few boats, this may be true, but this is not a rule.

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Old 09-11-2007, 07:50 AM
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Gotta' ask...

What are you going to do once you see where the balance point is?
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Old 09-11-2007, 08:10 AM
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If you can get your trailer on a trucker's weigh scale empty and tell me the load on the wheels and at the tongue, and then repeat that with the boat on it, I can do the math. Other than that, I don't know.
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Old 09-11-2007, 09:09 AM
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If you can get your trailer on a trucker's weigh scale empty and tell me the load on the wheels and at the tongue, and then repeat that with the boat on it, I can do the math. Other than that, I don't know.
What he said.

Weigh the trailer empty, wheels only then tongue jack only, then repeat the measurement with the boat on the trailer. Measure the distance between the wheels and the tongue jack. Then you can determine where the CG is mathematically, relative to the trailer, then measure out the CG location with the boat on the trailer and you'll know where it is on the boat. Not too tough, you just have to measure carefully.

Might be more accurate if you measure each axle individually, and measure center to center of each axle then front axle to tongue jack. Try to do this with the trailer as level as possible, any angle will screw up the measurement.
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Old 09-11-2007, 09:19 AM
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Drop it off a building and see what hits the ground first.
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Old 09-11-2007, 09:46 AM
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I'm trying to find out how to check the center of gravity on a stepped bottom boat, most specific a multi-stepped hull??? Please help, Thanks
A lot of the racers that know this are the ones who win and they may NOT be willing to tell you...
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Old 09-11-2007, 10:22 AM
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Thanks for the input thus far;

Second part of my question, I would like to check and set the balance on my Cigarette Gladiator TS with side by side engines.

Rule of thumb, where should the balance point be, I've heard at the front step, in between the two steps, center of the boat, or is there no answer and it's all based on ride characteristics?

Also, should center of gravity be measured with the boat at rest or does that really have no bearing and it needs to be set with the boat in motion?
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