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-   -   Battery Placement/CG on 44" 12lb. Hydro (https://www.rcuniverse.com/forum/speed-electric-109/11674701-battery-placement-cg-44-12lb-hydro.html)

jhrobins 01-29-2020 06:26 PM

Battery Placement/CG on 44" 12lb. Hydro
I am converting a scale model of a 1976 Gold Cup winning Hydroplane (Miss US) that is 44" L x 20"-14"W at total weight of 12-13 lbs. with a Leopord 4092 electric motor, 200A ESC, and 2 - 5000 mAh 4S 70C batteries. I need advice and experience as to where to place these for balance on the CG of the boat. Where is the CG on such a hydro? Is it at 33% aft of the sponson tips? Your help would be much appreciated. Thanks.

Jim Robins
Belllingham, WA

Hydro Junkie 01-30-2020 08:06 AM

The CG should be somewhere between the sponson transom and roughly 1-2" aft of the sponson. The reason I say "somewhere" is that all boats are slightly different and there is no hard and fast rule. One thing to be aware of is that your boat has a 9" picklefork depth if built scale(can be plus or minus up to 10%), meaning that your center of lift will be well aft. This is just as important as where the CG is located
Just did a little figuring and, going off of the MHR, I found the following:
1) If your sponson transom is at the scale location(it may not be and still be legal), it will be 25.125" from the transom or 18.875" from the sponson tips
2) The sponson transom can be moved forward to 27.64" from the transom or 16.36" from the sponson tips
3) Your 33% figure would have the CG at 14.52", well in front of the sponson transoms, even at the furthest forward location. While this will probably prevent a blow over, it will also make the boat difficult to get up on plane.

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