To calculate that, readers will need to know the battery type and capacity, and the current drawn by the motor. If you haven't a way to measure the current, tell us the battery, motor and prop type and size.

Many people buy a low voltage alarm, this is ( in my view) essential with lipo batteries, and useful for other types.

Charles

The 400 brushless covers quite a range of motors with different kv values and current draw. That said, we can guestimate a bit, typically 6 to 10 amps drawn for many of these motors. Your 3 amp hour battery, presumably a nimh pack would run approximately 30 mins at 6 amps, and 17 mins at 9 amps. This is only ball park, it will vary if you change the running speed, as most of us do, and vary with the efficiency of the pack, as well as other more subtle electrical issues.

I presume you're just trying to get some idea of what to expect from the model, so maybe that will help a bit. In practice, running a quick model with nimh batteries is more forgiving than lipos, just come straight in to the bank as soon as the model starts to slow down a bit. Never run the model untill it's going a lot slower than normal, it knxxxxs the battery.

I hope you enjoy the model, it's a great looking boat.

Charles.

With NiMH, you note how much of the boat rides out of the water on a full charge at full throttle. When less of the boat rides out, its time to come in.

Doing it that way with LiPo is a bit fraught. There is very little between "yes I can go flat out" and "no, I ain't going nowhere". An alarm helps, but alarms are generally just for tone particular type of battery.