On Apr 24, 9:22*am, wrote:
"jamesgangnc" wrote:
I think you
are confused about how inboard engine boat cooling systems work.

No, I'm not confused. I've owned and maintained a number of inboards.
Moreso than I/Os. Both gasoline and diesel. *I'm apparently just not
communicating my thoughts very well.

All of them have a pump that supplies water from the outside.

And you can maintain them without hauling the boat in half the time
and half the effort of an I/O.

On the rest it's
usually mounted on the front lower side of the engine.

Good idea. No impeller in the leg at all? All of mine had an impeller
in the lower outdrive except one with it on the top.

As to the reason, it let them
build a boat with some of the advantages of an outboards but without the
finicky, easily damaged, aluminum 2 stroke engines.

And with a lot more power to push much larger boats. Outboards didn't
have nearly the HP back then as they have now. I think the basic idea
for the I/O was valid and sound. I just don't think the designers put
enough thought outside their box. They could have built a much less
complex and more maintenace free system. One with something more than
rubber boots between it and sinking. But they didn't and the market
responded by demanding huge outboards. Which it now has.
I'm not saying I/Os are a bad idea. I'm saying they could have been
less complex which usually means better.

Rick

Your earlier post "Whether or not they use a standard automotive pump
or a special marine design that's self priming, I'm not sure." lead me
to think you didn't understand. Because they all use both pumps. The
difference between the alphas and the bravo/volvo/trs/etc drives is
that the alphas continue to use the raw water pump in the leg while
the others used a belt driven raw water pump on the engine.

And you'll get no arguement out of me that the raw water pump in the
engine compartment is way better and much easier to service. I was
only discussing how it got where it is. The orginal merc drive went
through several minor design improvements to give us the 2nd
generation alpha we have today. And engineering wise it is still not
even close to state of the art. But it works and has proven to be a
pretty reliable platform. Volume made it extremely cheap at the bulk
level. That kept it around. Merc as well as others have designed
much better outdrives. They simply cost more and many consumers don't
appreciate the difference therefore consumers don't want to pay the
difference. That volume is changing and more modern i/os are a bigger
part of the market now.

I'm not saying the i/o is "better" that the other two propulsion
solutions. All 3 have their pros and cons. How those factor in also
depends on the application. In some situations the i/o pros make it
attractive.

And there really isn't a real higher risk of sinking because the i/o
has a rubber boot coupling the drive to the exterior prop assembly.
The i/o is far more likely to survive a high speed hard strike to the
drive train without compromising the hull integrity that a
conventional inboard. The i/o absorbes most of the force in the gear
train and typically destroys props, gears, and couplings. The i/o
physical unit is typically kicked up rather than sheared off the
transom. On a conventional inboard usually the prop shaft is ripped
out or severely bent and there is frequently compromise to the rear
lower hull or stuffing box. Of course the outboard installation will
also kick up and often can stand anything up to and including being
ripped clean off the back without compromising hull integrity.

I don't think the hp difference was all that great, merc had some
pretty big inline 4s and 6s early in the outboard game. While they
did not match the hp of the early small block v8 engines if you factor
in the weight difference they were pretty powerful engines. Inboards
with automotive engines already predated i/os. So the larger boats
did not need i/os. Outboards simply don't attract a significant part
of the consumer base. Never have. It's all about what sells first
and engineering is always second to that. That's not unique to boats,
that is true in everything.