First off, I've never heard of this ESC but, in common with most high-current ones, it probably has a Battery Eliminator Circuit (BEC). If so, the problem may well be that the battery is flat. I shall attempt to explain:
Some ESCs will shut-down ("fail-safe") if they don't receive a valid signal from the Rx. Yours may be firing up but the sudden drain on the battery from the motors is dropping the battery voltage to below that at which the regulator in the BEC works, so the receiver stops sending signals out, so the ESC shuts down. As soon as that happens, the battery load reduces and the voltage to the regulator rises; the receiver then starts up again and sends a signal to the ESC; the motors fire up; the battery voltage goes through the floor again etc etc ad infinitum. Great fun for a few minutes but after that I'd sooner watch Graham Norton...........
Try charging your battery and/or using a separate receiver battery pack. I personally reckon that BEC-equipped ESCs in boats (except for fast-electrics) are more trouble than they are worth , especially for newbies - but I know I'm in the minority there!
Make sure that you're not "swamping" the receiver when you bench-test the system. Don't extend the aerial on the transmitter, although it's not a good idea to leave the Tx switched ON for more than a few minutes without the full aerial or you can damage the RF output stage through allowing it to overheat. Stand back from the model while you wiggle the sticks, and don't allow the Tx aerial to ground itself by touching anything on the bench.
If that doesn't cure it throw the ESC away and buy a proper one.........or two
Motors shouldn't be wired in series for all sorts of reasons; wire them in parallel or, better still, use a separate ESC and battery for each motor. You can always couple the ESCs with a Y-Lead if you only have two channels on your radio, or fit a mixer.
"545" can cover a multitude of different motors, from those which would rip your hand off on 6v to others which would shy away from the skin on a rice pudding. If they are direct-drive (no gearbox) then they might be too small for the model anyway. More info would be required (e.g. voltage, prop size, actual no-load current and RPM) before a conclusion could be drawn.
(Of course none of this is set in stone - just a couple of things to try, based on a heap of personal experience. Like I always say, suit yourself.)
Good luck.
FLJ