4-5hp electric outboard

Hi
I have plans to put in an electric motor in a 6hp outboard motor.
Is there anyone who can help me with what kind of motor and speed controller to choose?
The engine will be used by my 6 year old son on a small 9 feet inflatable boat. The engine should provide about 4-5hp
Will any of these engines fit?

http://hobbyking.com/hobbyking/store/__17987__Turnigy_RotoMax_50cc_Size_Brushless_Outrunner_Motor.html

http://alienpowersystem.com/shop/80mm/c80110-sensored-outrunner-brushless-motor-80kv-6000w-2/

http://www.ebay.com/itm/BRUSHLESS-MID-AXIAL-MOTOR-48V-1500W-CONTROLLER-E-SCOOTER-E-BIKE-QUAD-BIKE-CAR-/201060585451?pt=LH_DefaultDomain_0&hash=item2ed0250feb

Hope someone can help me

The main problem is high enough efficiency at the right RPM fitting the gearing of your outboard.
You need to find a motor that is at least 92% efficient at these power levels.

5hp x 746W = 3720W output
3720W / 0.92 = 4043W input neded
4043W - 3720W = 323W in loss.

323W might not seem very high but the fact is that heat accumulates and the motor
will burn or the magnets demagnetize at these loss levels if not properly cooled.
Then imagine a less efficient motor....it will crash even faster.

I'd like to recommend a 94% efficient motor. That will only produce 237W in loss
compared to 323W in the 92% motor. As you can see efficiency rules.

Your choise of motor shall have low enough phase resistance and low no-load current to get you high efficency.
Perhaps you can ask this question in the forum Motor section.
I think there's more people with great motor suggestions hanging around there.

Built an electric outboard for my 26ft sailboat using an old 5hp outboard lower unit.
The motor was a surplus hydraulic pump motor, rated at 2hp at 12vdc, which I ran at 36vdc.

I still have this outboard motor. The gears of the outboard are not particularly efficient, but it does work.

I am planning to use a 5hp winch motor for the next project, they are quite cheap at $100 new.
These are series DC motors, a bit heavy, but tough.