One I built many years ago, and still use regularly. The fire jets all work, powered by a car windscreen washer pump in the bow with an intake through the side of the hull. Jets shoot water about 6 feet, so can have fun when youngsters are watching and get a quick shoot of water. Motor is 12v, so same battery can power pump, which means a small extra battery for the receiver. The big problem with this model is access to main hatch under superstructure, so battery access is very tight. Main stern hatch has easier access, but the weight of the 12 v battery is too much aft. The contacts on the rudder servo, energise the pump, by swinging the transmitter to maximum swing with trim tab maximum. This was built with only 2 channel radio, so had to dream up a switch solution for the pump.

Finally got a video of the firejets working.