Oberto gas set up- need help! A

[Craig Degotardi]

I am fairly new to the sport in Australia. I have a gas powered Oboy Oberto boat. I think it is 1/8 scale. I have modified it with a Toxic marine engine & a decent tuned pipe. I got it running well with a 6717 prop. It got up on its tail & barrel rolled down the river last weekend, leaving a trail of destruction. I am wondering if I have mounted the engine too far to the back of the boat. Can anyone help me with the centre of gravity when mounting the engine? I heard something about 29-30% from the rear of the hull for tunnel boats. Is there a corresponding C.G. figure for these unlimited hydroplane hulls? The other fault may be the prop angle, causing the nose of the boat to sit too high at speed. I had it basically horizontal & suspect some negative trim may have kept me out of the fiberglass workshop for the next 3 weekends! The other issue I have with this boat is turning. It doesn't like to turn, unless at almost idle, and even then it's a very wide turn. I know photos help, so I'll try to get some up soon. All advice is greatly appreciated. Thanks guys.

 

[Hydro Junkie]

That percentage deal is for vee, cat and maybe tunnels. A scale hydro needs to be balanced at roughly 1" behind the sponsons, some closer and some slightly further depending on the hull and set up. If you're running a modded gas motor, it's probably too much for a scale sized hull. Here in Western Washington, a club was started using gas engines. It was found that the hull really needed to be about 20% larger than a nitro powered scale hull to make it able to handle the torque of the gas engines. For more info on that, Marty is the one to talk to here in the forum