Re: Back-up motors
Does this charter boat include a dinghy? Does it have a motor? If so, problem solved.
You could either lash the dinghy alongside and lock the OB so that it does not pivot and steer from the cockpit (although you will find that the boat tends to "pull" to one side), or you could tow the 45' (or did you really mean a circa 1945?) Dufor with the dink. If you choose the latter option, someone will have to be the tow boat skipper, and that person better take a waterproof handheld VHF to stay in touch with the mothership...
Personally, I would simply use the auxiliary if the SOG drops below 3 kts. Plan your trip around your ability to make 6 kts (assuming that you meant a 45' boat), and all will be good.