Very nice model Larry well built i would say going by the images, you say its underpowered, could it possible be that the builder of the electronics did it as a scale speed?, or it is a total 'bodge' job with motors too small for the boat combined with possible prop size?
Understandably that if the guy who installed the electronics is an Aircraft modeller he may be assuming that his normal activity's with electronics will be good enough for boats, that would come down to a bit of inexperience (with boats) on his part rather then his technical knowledge.
I can't imaging that it would to too difficult to incress boat performance with a simple motor change, possible esc as well should the currents not be appropriate with larger or more powerful motors, What motors are installed in the boat and what size are the prop?
Its a fair size i would like to imagine it has at least 555/600size motors in, im not sure if its single or twin screw ( can't tell by the photos)
However,.. if your 'lad's' happy with it and it runs then it may be worth leaving it as is and just enjoy the model for what it is as a nice example of a model fire boat