Design help and insight.....
 

I am gonna jump into the hobby feet first. I have had my AirForce for about a month. Just built my first baot a couple weeks ago. I figured I would try to build a dual engine boat. Plan on using 2-OS .25's. swinging 7" props. Now onto the questions.....can you have both props turning the same way and still be stable? Would you go with two seperate engine pylons or one big one? How can you blance out teh rear biased weight? Is there any other major factors I need to look into? How will the linkage work? Can you run 2 servos off one channel? What is the maximum distnace a fuel tank can be from teh carb? I may try to use this to balance out the weight. I know this is very basic questions. As I get more into it....I KNOW I will have more. That being said. Here is what I have drawn up so far.....Will it work?

RE: Design help and insight.....
 

Looks and sounds good, there is nothing like the sound of twins revving together. My boat uses a separate servo for each throttle. They are each on their own channel but are mixed so that the master (throttle channel) drives the slave (elevator channel). You can of course just use a Y harness but then tuning is all mechanical instead of tuning each channel like i do. I use 3 pylons to hold my engines up, as the nacelles are connected together. I have noticed that my boat will turn much sharper to the right than to the left, but this may be due to the engines being off centered, i dunno. I run a 1 inch clearance between props, both of the deck and each other, my weight balance is about centered on the hull, this is because of how long my nacelles are and the length of my hull (36" ) My original hull was 14" wide with the engines swinging 11 inch props, so the weight was higher, plus each engine carries 8 oz of fuel, this hull was very easy to roll. Mind you my hull edges are 90 degrees opposed to your beveled edges so your might slide a bit before rolling, plus your engines are smaller, and lower and probably less fuel. So I am not promising it should work the way you want it to, but it looks good.

RE: Design help and insight.....
 

I think CJ is the only one here with the experience of twin engined airboats. His advice and comments so far are good.

I've flown twin powered aircraft before, but that's a different story.

But your gonna love the sound:D

Throttle control would be simple with dual servos and a 'y' harness, but like stated, would require manual adjustments. But the only way to do it unless you have more than a 2ch radio.

Props turning opposite directions would require one of the engines running a reverse crankshaft, which may or may not be available for that particular engine. In the airplane field, canting them towards or away from each other helps the torque issue.