First, I don't understand what plane you are talking about. You say a 50% Arrow. To me that is a plane that would mean this is a scale plane that is 50%, or one half the size of the full size plane. That would be huge. Then you say you are using a 1200 mah battery which is pretty small. So I can't provide any specific advice since I have no idea what plane you are flying.

As far as flying over water, unless you make the plane 100% water tight, you are going to get water inside, so plan for it. I am not experienced with water airplanes but I would presume you would have drain holes of some kind in the fuselage anyway.

Cooling is critical to the safe operation of any electric plane. This is especially true of foam planes as foam is an insulator. But regardless of the material, we have to account for heat.

Let's look at the affect of not providing adequate cooling.

ESC overheats - ESC Fails, you lose control of the motor.

BEC Overheats - If you are using the BEC feature of the ESC, and you don't provide adequate cooling, then your BEC will go through thermal shutdown to protect against fire. You lose all radio control.

Battery Overheates - Short life, or immediate damage. In extreame cases, this can lead to fire.

Motor overheats - housing expands, bearings fail, insulation on windings fail, motor shorts out, in extreme cases, fire.


So, how do I feel about cooling? I think it is important.