Double engines and double cannons need power. Each time you have to calculate the strength of your engines or cannons, you must decide which double engines or cannons you will power and spend batteries for them.
1) Does this mean that double cannons can only be used as strength 2 or 0.
2) Or does it mean you can power them for 2 or not use energy and count them as 1.
The emphasis here I believe is on "NEED POWER". I'm thinking no power and they do not work. It would also make the game much more strategic if number 1 is correct.