"Sorry guys, this one is going
"Sorry guys, this one is going to be long
I'm primarily an outboard guy, so can't really comment on reliability or exact service costs between the two fuel choices for motors not hangin' off the back of a boat.
Likewise, I have never looked as deep to see whether a high torque diesel is (better) than a high horsepower gas model.
I take the perspective of a rigger kitting out a particular boat for a specific client.
Bob and Tom may both want boat "X", but the way they will use it will ultimately determine what is the best way to rig it out - and the two boats, aside from the hull itself, may be nothing alike.
If you plan on keeping the boat for many, many years, than resale is not of prime concern - annual maintenace costs, rebuild/repower cost etc may be higher on the list. And vice versa for a boat you only plan on using for say 5 years and then trading in.
Regardless of how long you keep the boat, operating costs are going to dictate to a large extent, how often you actually get out and enjoy it.
Around the Great Lakes there are thousands of boats that never leave the slip - they are simply a "camper" sitting on the water.
Why? because after the owner bought more boat than they needed (and could afford) and paid the mooring costs for the year their wallet was empty and couldn't spring for the 20 gallons per hour (at 4 bucks a gallon last summer) to take the boat out for even a 1 hour cruise around the bay.
You can't buy a boat "backwards" - you determine what your needs are and then from that point, figure what you require.
Rollie is correct, diesel is safer and all else being equal, it will (normally) consume less fuel and commands a higher price in the used market. But that may not be an important factor for "you".
But if you are a "weekend cruiser" how long will it take you to break even with a diesel option.
A brand new 5.7 Merc with a Bravo drive from a reputable shop can be obtained for somewhat under 8K - a comparable diesel could run you 15-20K.
At the low end 7000 bucks worth of gas could be the equavalent of 4 or 5 seasons of running on the water for the "average boater". How do you tell "that boater" that they are better off with a diesel? Where's the economic's?
Yes, if you are doing regular runs down to the Carribean an IPS or Zeus powerplant (that costs more than a couple of my previous homes) may be exactly what you need, but you can cruise Lake Erie for a few hours each weekend, and one week a year with a gas powered I/O that you could totally replace 4 times or more before you equal the cost of that single Diesel powerplant....
Diesels are not really designed for "stop and go" boating. A diesel likes to get up to operating temperture and stay their - not idling along - not a hop in, fire it up, tear accross the lake and then shut down.
So fit your boat and it's powerplant to "your" style.
Lot's of us can give all kinds of advice and all of it is "right" and all of it is "wrong" depending on how you are going to play with your toy..."