Re: Running twin 350's
A someone with a twin engine boat, it is better to run them both vs. just one engine. I have read a great deal about this on manufacturer's web site and they go into great detail regarding the efficiency of the engines and fuel burn per ton and hull design, etc.
Can you run it on just one? Yes, but the engine will work twice as hard pushing the boat. The fuel burn can be greater with the single engine (depending on speed and conditions) than with both. There is relatively zero fuel savings by running just one, and it may actually burn more.
Is maintenance more? Yes. Twice the cost. Twice the impellers, distributer caps, rotors, plugs, etc. But the engines work half as hard at most given speeds (barring WTFO) and the maintenance may be performed less often.
Is it harder to steer? Yes. The boat has a tendancy to push toward the opposite side and counter steering is a full time job.
A twin engine boat offers the mindset of a redundant back-up power supply to get you home and as mentioned, it much more maneuverable in close quarters.