These engines also act as generators, saving us the purchase cost, maintenance, and weight of a separate generator. Normally, it is not a good idea to run your diesel motors without having them under a load, but the electric motors act as the load as it produces power to charge the batteries.
If needed, the second engine may also run as a generator and be used to power the boat (A/C, etc.) while the other is charging the batteries.
If we go with the Beta Marine engine, we will have two 53 hp engines plus two 10 kw (13 hp) electric motors, which can produce a combined 116 to 132 hp when needed! She should fly under power as well as sail. Since we would not need to add a generator, we save around 600 pounds, more than making up for the weight of the electric motors and gear boxes (300 lbs). There is also less maintenance since we have two diesels instead of three to service.