Originally Posted by canabus

Your boat from internet search is length 20.5" (520mm) beam 8.8"(190mm) solid drive shaft.

The motor looks to be a 540 brush motor (approx. 90watts) can diameter for these is 36mm.

Your easy and cheap option is a bit of bits from Hobbyking.

Radio 2.4G 2-6 channel (the 6 channel Turnigy TGY-iA6 AFHDS can handle up to 20 models on the one Transmitter(so all you require is a stack of receivers).

You can setup for each model and name them, also software reverse servos.

Brushless motor Trackstar 13.0T 3000kv(3s(11.1 volt)=33300rpm, 4s(14.8 volt)=44400rpm) 550 watts.
This motor will fit straight into your motor mount if the old motor is a 540 motor.

ESC use a car 60A with reverse one because the motor and ESC can take the two battery types.

Battery Turnigy 2650mah 3S 30C(250grams) about the same size and weight as the old NiCad battery.
Second battery Turnigy 2650mah 4S 40C (289grams).
This is a small boat so weight and size of your upgrade bits is important.
You have not the room to move bits around a lot, the battery is the biggest problem to get the balance of the boat right.
Prop start with the same prop but look at Hobby king's prop selection and may be get a few around the same size and pitch to test(the plastic ones are cheap).

Note:- ESC to BRUSHLESS MOTOR connection 3 wires the centre one to the centre one and cross over connect the other two and the motor will run the correct way(ye it sounds Irish but it works on all my boats and cars).