"Jim and Becky" wrote in message
...
Same engines yet the I/O had a top speed 10 mph higher than the straight
inboard.

Is this difference in speeds common and why?


Due to the prop angle an inboard will always be directing a portion of its
thrust down instead of back. The bigger the boat the shallower that angle
can be, but for a small boat the angle is pretty severe.

If top speed is your only concern then go with I/Os. On a 28 foot boat,
however, I would be much more concerned with maintenance and long term value
than I would top speed.

For a runabout, which lives most its life sitting on a trailer, an I/O is
great. You can't beat them for maneuverability and overall utility. Since
the boat isn't in the water much you don't have to worry as much about the
outdrive deteriorating or the boot seals failing.

For a serious ski boat, the extra pulling power and better weight
distribution favor the inboard. There is nothing like a tournament ski boat
for pulling skiers, as long as you don't mind the fact that they have no
steering in reverse.

For a single engine cruiser I would be torn between inboard and I/O.
Maintenance is a major issue, but trying to dock a single engine inboard can
be a real bitch.

For a twin engine cruiser, inboard, no question about it. With two engines
you can maneuver nicely and the system is very trouble free.

The problem with I/Os on a boat that sits in the water all the time is that
the outdrives deteriorate. Electrolysis does very bad things to aluminum,
and you can have your entire outdrive eaten away in a few years. It can
also be hard to check the outdrives to be sure that they are okay. If a
seal leaks and the oil leaks out or water leaks in you can have a major
outdrive failure. There is also the issue of the large rubber boot that
seals the large hole in the transom. If that seal fails, your boat could
sink!

There is also the issue of the outdrives are simply in the way for swimmers.
The first time you swim to the back of your boat and kick the prop with your
foot you will be cursing having I/Os.

So, to summarize: General purpose runabout should have an I/O. Twin engine
cruiser should have inboard. Boats in between, well, you need to decide.


Rod