Just a note, 1 depends on the water temperature with 30 degrees being the top of the workable range. The strobes don't appear to shut down when overheating - they simply burn out the flash tubes and then you need a new strobe. If you are shooting in warm water (22 degrees +) I would allow time between full dumps for the strobe to cool down.
For no pre-flash press the button in. The strobe doesn't sense preflash or otherwise.