Basically, there is a maximum of 255 engine points, after which the game's variable wraps back around to zero and counts up again.
Battlemoons need 200 engine points per movement.
A maximum speed of one is quite reasonable, IMO.
The same thing happens with the Baseships.
If you want full speed, go with the real "ship" hulls. They should all be able to reach 15+
The fastest possible ship IIRC is the light cruiser. It has the best ratio of C&C to free space without hitting the 255 limit before getting to 30 speed.