Twins = Complete set spare parts for the one that did not breakdown.
Unless, of course... same part fails on the still running engine!
Kidding aside... I had singles, they are OK too. But, I love having twins!
In our Tolly (planing hull - another thing I love):
Used correctly -
Twins can deliver good speeds [16/17 knots] at mid range rpm with a relatively reasonable 1 gph. And, we can do 21+ knots if need be
They can cruise us slowly [6.5 to 7 knots] at lower rpm for a pretty good 2 mpg.
And, to go even slower with darn good mpg one can being shut down... as we putts along at 5 +/- knots on the other = 2.75 to 3 mpg
Similar to singles... If you keep the twins in good repair there is not much breakdown that occurs, so major-repair expense can be pretty much avoided. Of course; oil changes, new impellers and things like that are double up cost. But how much we talking about here... a couple hundred bucks extra per year to service twins. Well worth what twins offer in capabilities... with a planning hull that is!!
Happy Motor-Boat Daze - Art