Mon plaisir! 😉 Let us know how it goes 😎

Thanks Doug

Strangely no one has answered an important part of your original question !? 🤔 How to calculate running time!
Simply put; divide the capacity of the battery in amp-hours (AH) by the current in amps (A) drawn by the load. AH/A = H !!
Step 1; measure the max current drawn A(max) by the motor under load; i.e. full speed ahead in water - hang on tight!. if not possible then use the max current data of the motor at the voltage you intend to use.
Step 2; check the capacity of your battery; usually given in mAH for some peculiar reason! Divide by 1000 to get AH.
Divide the capacity in AH by the max current in A =A(max). Result is the theoretical time that the fully charged battery can deliver the current required; i.e. runtime at full speed. Theoretical because in practise the usable capacity will be a bit less than nominal depending on the age and condition of the battery, ambient temperature etc. Also you won't want to completely discharge the battery; it won't like it 😡
Step 3; measure current at a mid-range throttle setting 'cruising' - A(cruise). Again divide capacity AH by A(cruise). result is 'cruising time in hours. if measuring not possible use the motor current data given at maximum efficiency. Should give a reasonable approximation.
Example: motor current at full speed = 10A.
Battery capacity 7000mAH = 7AH.
Max theoretical runtime at full speed = 7/10Hr. Approx 42 minutes.
Cruising current; 5A.
Cruising time = 7/5Hr = 1.4Hr. Approx. 84 minutes.
Use the highest capacity batt. you can get in without upsetting stability etc.!
If you need ballast use a bigger battery; then you have 'payload ballast' instead of JUST ballast.
Minimise current drain by; ensuring drive train is perfectly inline, well lubricated, prop is as small as possible for the desired performance (trial and error!).
Hope this lot helps, not space science but a few basic rules! 😉
Happy sailing and lots o' fun. Cheers Doug 😎

The esc has a max top end input voltage.
So an esc that runs between 6 volts and 11.1 volts
will blow up if using 24 volts.or any battery over 11.1 volts

The same with a motor that runs from 6 volts to 12 volts
Again 24 volts is a problem or any battery over 12 volts

So how does that relate to the ESC please?

My esc is rated at 24 volts My motors and there are two them them are rated at 12 volts to 30 volts so I use 2 x 12 volt batteries.

The size of the batteries depend on the size of the boat.

Another model has a 7.2 motor and the esc can run up to 11.1 volts so I use a 7.2 battery for this as the model is small the battery is also small..

The larger the boat the larger the battery that can be used.

Mine are also used as part of the ballast..
so the large batteries have a dual purpose for my tug...