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Any Boat Builders in the house? 30 O/B Cat CG Question.

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Old 03-29-2011, 02:41 PM
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Default Any Boat Builders in the house? 30 O/B Cat CG Question.

I removed my F16 2 Man inline canopy and I'm in the process of replacing it with a 4 man side by side canopy and have a C.G. question.

My CG was just in front of the "redline" on my drawing. With the weight being added equal (maybe less than) what was removed everything is about the same except I'm moving the throttle man forward "next to the driver"

Thats approx. 300lbs person, seat, brackets, throttle box..etc.. moved up 36-38" to the front of the boat.

Will this cause any issues? I have to figure its nothing worse than having someone sitting in the back seat of your 30 O/B spectre cat and moving to the front seat.. right?

The Cockpit area is a fixed point so that never moved, just the driver was moved over to allow room for the throttlemans seat to be placed next to it..

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Old 03-29-2011, 03:17 PM
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you should be fine as a rule the fuel tanks are the cg in a cat nice drawing should be nice i see your in mich
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Old 03-29-2011, 03:30 PM
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you should be fine as a rule the fuel tanks are the cg in a cat nice drawing should be nice i see your in mich
The fuel tanks are were the redline is placed.



Yes, In Chesterfield Twp. I have a thread started last Feb. when I cut off the F16 Canopy and started the job on Sunsations site seeing as Wayne and Joe have been helping me out with Material and info.
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Old 03-29-2011, 08:24 PM
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if you do a search there are some CG calculators out there. I have one on a disc from years ago. it is for a small airplane for figuring luggage, etc. you would need to know certain weights at different points but it will tell you what happens when you add or move weight.
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Old 03-29-2011, 08:52 PM
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I think you'll find it a much better rough water boat with the cg forward like that. Remember the Alcone Boats in rough water? Jerry wasn't a fan of the far aft smooth water cg, his boats always flew level and really excelled in the rough. On smooth days just lower your motors an inch or two and get it to carry the nose better and feel like your right back where you started.
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Old 03-29-2011, 09:05 PM
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I remember the Alcone boats pretty well, I built them and maintained them and yes we ran with a slightly forward CG compared to many. depending on the water the CG was about 12 to 18" forward of the last step. we also had the advantage of a ballast tank so if it got really snotty water you could weigh down the nose a little. I was never a big fan of rear CG and really "flying" the boat nose up as you cant go forward if you spend all your time going up and down.
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Old 03-29-2011, 11:08 PM
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If I understand correctly you are adding frontal area in front of the CG. The added weight of the Throttle Man forward, in addition to a full front windscreen might change the static CG a bit. I think the dynamic Cg will move quite a bit forward of the tanks due to the downforce created by the new windscreen at speed.
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Old 03-29-2011, 11:11 PM
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By the way....the guy driving the bottom boat looks very relaxed
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Old 03-30-2011, 08:28 AM
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By the way....the guy driving the bottom boat looks very relaxed
Yes, he was taken from a chair clip art site. I'm guessing he was in a recliner.



Couple more numbers that I took last night..

F16 Canopy is much heavier than the 4 person canopy I built, so over all I'm removing weight from the boat and not adding any (yet)

The original throttle mans seat was closer to the front bulk head than it is now. I moved it back 12" to acomidate your legs seeing as I rolled the seat back so your not sitting up like a car.

The rear seat was moved 20" forward next to the seat, not 36" like I previously thought.

Overall I dont thing I effected the CG
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Old 03-30-2011, 09:01 AM
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This question appears best answered by the boat manufacturer.
CG is a number/location. It does not mean that this IS where the weight should be.
Each hull has different characteristics in how "it" likes to run and carry weight.
I would have recommended running the boat with some sand bags in the area where you intend to relocate the weight to....prior to disassembly.
In this situation, given that the project is underway, finish it. (I would think that the total seat/control position needs to back up if the prior weight location was considered correct) Run it as you planned it, then drop weight in the old location and test again. Given that this appears to be a race boat, I would expect that you will be able to tell the difference at that point...
You may need to reposition the seats and /or the dash/controls back a bit.... In the center area between where the front and rear seat were prior....
The boat manufacturer may be able to tell you if adding rocker at the back of the hull can be a safe way to compensate for moving weight forward (it usually is, but some hull bottoms are more sensitive than others)

Regardless, Very cool boat, and great project.
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