Re: Inboards vs I/O--long term reliability and maintenance costs
The initial post asks about TWIN engine boats only, so lets go there....
A few years ago I was faced with the same dilemma- I had a 23' go-fast and wanted to move to a larger, more comfortable cruiser. Here's what my research uncovered:
As noted earlier, I/O's (or sterndrives) are a lot more complicated and therefore need more maintenance. Personally, I've ALWAYS found them to be less reliable than inboards.
On the other hand, I/O's have 2 BIG advantages- they can be trimmed/ tilted for shallow water operation or prop replacement, and (due to the fact that there's less hardware below the waterline and the shaft angle can be trimmed) they will perform much better than an identical vessel with inboards. That means faster top end and increased fuel efficiency.
Now, true inboards come in 2 flavors- straight shaft and V drive. It's easy to tell the difference because V drive boats have their engines mounted "backwards" (with the engine cooling pump at the rear). Both types will move the boat thru the water with the same relative efficiency BUT the nature of V drives require their driveline to reverse direction, therefore reducing power and efficiency at the prop- by as much as 10%. And remember, the V drive is another part to maintain and repair. In addition, the shaft packing glands can be almost impossible to service on a V drive, sometimes requiring engine and/ or transmission removal because of their location directly under the mechanicals.
As you can probably guess, I bought a straight shaft inboard. 4 years later and I couldn't be happier. Maintenance is easy enough to do myself and I'm not worried about leaving her wet all year. I could never say that about an I/O.
