I'm guessing the "Heavo Ho" means "get to work". or maybe more, "OK... pull now!" Like a particular task at hand, maybe pulling on any particular line on a square rigger. If you and your dad were lifting a
trailer tongue to put on the
trailer ball, you might say... "Ready....Heave HO!" instead of "1, 2, 3 lift!" That's always been my interpretation of it anyway...