Re: mileage
Since twin outboards are generally less speedy than a single equal horsepower outboard and since there is more drag from two lower units in the water and since it takes roughly the same horsepower to go the same speed, thus using the same amount of fuel, Accounting for extra weight and extra drag, I suspect that twin outboards use slightly more fuel to go the same MPH---assuming the twins equal a single in horsepower.
There are all sorts of variables, like twin 18 vs. a 125 on the same hull, assuming both set-ups will get the hull to the same speed--20 MPH. So, Specific set ups would need to be compared.
