I looked long and hard at the inboard diesel vs outboard. But there were several factors that pushed me to the outboard. I will try to list several but not necessarily in the order of importance.
1. Complexity - Hands down the outboard for me was a much simpler install
2. Odor - I hate the smell of diesel and I have been in far too many enclosed boats that reek of diesel on the inside.
3. Availability - I live in the Midwest. Here you will find 200 I/Os or O/Bs for every one diesel I/B. This means the dealer network for diesels is very small and local knowledge is almost non-existent. The engine – new or used – would have to be shipped or brought in from many miles away and I would then be on my own to sort out the install and any problems. I personally have zero knowledge of diesels.
4. Cost - Diesels I/B do operate more efficiently than O/B but if buying a new one it is almost impossible to recoup the cost difference in savings. May have been different in the day when diesel fuel was 1/3 cheaper than gas but now that is not the case. I guess buying used is a possibility but for me still a problem – see #3.
5. Noise – With an enclosed boat the noise created by an inboard diesel will be substantially louder than an O/B mounted behind and in my case outside the boat. We plan to take long cruises someday (yes, the Loop is a goal) and listening to the drone of the diesel hours on end is not something we wanted to endure if it could be avoided. With the O/B the cabin is extremely quiet. We can talk at normal levels, listen to music or audio books as we run at cruise speed. My hearing is already very poor (and getting worse) so this was a major consideration.
6. Lost Storage – For long cruises in a boat of this size storage space comes a at a premium. The diesel and transmission would have used a good bit of space we now have available for stuff. And trust me, my wife needs LOTS of stuff to keep her happy.
7. Probably more but these are the one that come quickly to mind.
On the downside we did give up a few things.
1. As mentioned free and abundant hot water. We installed a 6 gallon electric water heater and so far it has proved workable. It does require shore power or use of our Honda 2000 generator. But once heated the water tends to stay warm enough to shower for about 8 hours.
2. High amperage house battery charging. Our 60 HP Honda does have 25 amps available for charging. This a good bit more than other outboards in it’s class but still not near what you can get from an alternator on a diesel. I will say we have found the O/B will recover our evening /night usage (lights and TV for several hours) after about six hours running time. When on the move it should work out OK. If hanging on the hook for a few days the generator will be needed to run the 40 amp onboard charger.
3. Fuel Tank Location - If you are wanting a good amount of fuel capacity the placement of the weight within the hull is a big factor. With diesel the tanks can be placed more or less where ever you like with little fuss. But it gets more complex with gas tanks because of the need to isolate them from any electrical devices - above or below the deck - as well as vent the tank area well with outside air. My tanks are under the saloon floor which is less than I deal for gasoline (although totally acceptable and common for diesel) but needed to keep the weight forward. They are in a sealed vented chamber. This took a good bit more work to sort out and construct and it does appear to meet the Coastguard standards. Still, in other designs gas tanks are usually not placed below enclosed cabin areas.
Some people would probably want to add “dependability” to the items sacrificed but I am not one of them. I feel the new modern 4 stroke O/B’s are very dependable and I dare say I have as much confidence in my Honda as I would a new modern compact diesel. The new diesels like the Yanmars are very sweet and excellent power plants. But to my thinking they are fairly complex pieces of equipment not the big heavy almost indestructible diesels of yesterday. If I understand correctly a major benefit of the “old” style diesels were once started they would run even if all electrical power were lost. Is that still the case with the new electronically controlled engines? If not it nullifies a good part of the diesel dependability advantage.
I must add when I comes to dependability the biggest engine problem I have had in my river travels is with the props not the motors. I can't tell you how many times I have damaged a prop hitting logs, rocks, stumps - you name it. Some of them my fault some of them not but the end result is the same. With the O/B I can just trim up the engine and change the prop from the swim platform in less than 5 minutes. Want to try to change a prop on an I/B while drifting helplessly down the river? I didn't even consider this in the original logic but it is a factor I would weigh now.
All this is not to say in a different situation or location I might have ended up with a diesel I/B and been very happy but in this case the above is the thought processes that lead me to the gas O/B for my True Grit.
Also, might want to look at this link. It is a little dated now but still interesting.http://www.yachtsurvey.com/GasDiesel.htm