Hi Westlink;
So nice to have your questions on my Najade and sorry having been so late in replying.
As for batteries layout, see following pics.
Steering servo set in the pics was Japanese-brand Futaba S3003 standard servo as I am a Japanese.
This level of servo is I think suitable and sufficient to steer Najade even when she runs the motor at 24000RPM
on the water.,,,,
But I make it a practise to sail at much more lower RPM on the water to enjoy the scale like atmosphere
to suit her appearance.
Attention to a digital V meter seen in the Pic No2.
This is to check the voltage at a glance after each run which is indispensable for my operation of RC models.
Please enjoy building your Najade spending a lot of time to get the best result.
The beautiful "Najade" will surely respond to your efforts.!!