Could be right there Glyn, its hard to see the actual size of the boat compared to a toddler so i used best guess ( between 36 and 40 inches)
However the motor suggestions would still be fine, if the model is over powered ( which i do think is unlikely since GRP hulls tend to be heavier then Wooden ones) then its a simple case of not using full throttle, although i expect single a 1400KV compared to your duel motor setup will be enough.
That said a brush less motor would be better run from a lipo then a NHMI battery in any case as those size motors can take a range of between 2 and 4 s lipos which in turn will control the no load RPM.
2s Lipo is 7.4 v running a 1400kv motor is 1400x7.4 = 10,360 RPM < this is as close as u can get with a NHMI
3s lipo is 11.1v running a 1400kv motor is 1400x11.1 = 15,540 RPM
4s lipo is 14.8v running a 1400kv motor is 1400x14.8 = 20,720 RPM
4s would be over powered but 3s would be a perfect power supply for a 1400kv motor giving you a decent turn of speed .