I/O speed > Inboard speed
 

I saw a comparison in a boating magazine last fall.
I didn't get a chance to read it all but essentially a new boat was offered
in Inboard or I/O configurations.
It was perhaps a 28 foot Regal or Rinker twin screw.
Same engines yet the I/O had a top speed 10 mph higher than the straight
inboard.
Does anyone remember this aricle? I believe it was on the front page.
Is this difference in speeds common and why?

I/O speed > Inboard speed
 

On Thu, 18 Mar 2004 23:25:23 -0500, "Jim and Becky"
wrote:

I saw a comparison in a boating magazine last fall.
I didn't get a chance to read it all but essentially a new boat was offered
in Inboard or I/O configurations.
It was perhaps a 28 foot Regal or Rinker twin screw.
Same engines yet the I/O had a top speed 10 mph higher than the straight
inboard.
Does anyone remember this aricle? I believe it was on the front page.
Is this difference in speeds common and why?


For one thing, the thrust angle of the I/O is parallel to the bottom
of the hull. The inboard is at an angle, so some of the thrust is
directed upward instead of forward.

Dan

I/O speed > Inboard speed
 

"Jim and Becky" wrote in message
...
I saw a comparison in a boating magazine last fall.
I didn't get a chance to read it all but essentially a new boat was
offered
in Inboard or I/O configurations.
It was perhaps a 28 foot Regal or Rinker twin screw.
Same engines yet the I/O had a top speed 10 mph higher than the straight
inboard.
Does anyone remember this aricle? I believe it was on the front page.
Is this difference in speeds common and why?

The inboard has a untrimable fixed prop, pointing about 13 degrees downward.
This causes stern lift, which pushes the bow down, resulting in a higher
wetted surface, hence the lower speeds.

The I/O is trimable. Once on plane, the out drive can be trimmed up, which
pushes the stern down and the bow up, resulting in less wetted
surface...which means higher speeds.

The advantages of an inboard is that they are much less complex, and have
many fewer moving parts verses an I/O. They also (because they run flat in
the water) generate very small wakes...perfect for a slalom ski boat. Big
disadvantage...single screw inboards do not back well.

The advantages of an I/O is that it is trimable, and backs like a car. You
can even use the trim to alleviate a rough ride in choppy water. But even
though it has less wetted surface, the propulsion system has more drag than
an inboard.

--
-Netsock

"It's just about going fast...that's all..."
http://home.insight.rr.com/cgreen/

I/O speed > Inboard speed
 

FYI. It was the 342 Rinker.

http://www.pmyvoyaging.com/boattests/0403rinker342/

--
Keith & Laura Koether
Pleasure Island
Blue Ribbon Marina, Hogan's Creek
Ohio River Mi. 497 RDB
http://thebayguide.com/rec.boats/koether.html

"Jim and Becky" wrote in message
...
I saw a comparison in a boating magazine last fall.
I didn't get a chance to read it all but essentially a new boat was
offered
in Inboard or I/O configurations.
It was perhaps a 28 foot Regal or Rinker twin screw.
Same engines yet the I/O had a top speed 10 mph higher than the straight
inboard.
Does anyone remember this aricle? I believe it was on the front page.
Is this difference in speeds common and why?

I/O speed > Inboard speed
 

Cantide wrote in message . ..
On Thu, 18 Mar 2004 23:25:23 -0500, "Jim and Becky"
wrote:

I saw a comparison in a boating magazine last fall.
I didn't get a chance to read it all but essentially a new boat was offered
in Inboard or I/O configurations.
It was perhaps a 28 foot Regal or Rinker twin screw.
Same engines yet the I/O had a top speed 10 mph higher than the straight
inboard.
Does anyone remember this aricle? I believe it was on the front page.
Is this difference in speeds common and why?


For one thing, the thrust angle of the I/O is parallel to the bottom
of the hull. The inboard is at an angle, so some of the thrust is
directed upward instead of forward.

Dan

Dan, your correct, it does have to do with shaft angle. But the one
thing not mentioned is operating cost and ride. The I/O, because of
it's greater complexity, and because it made of aluminum (except the
new Volvo units that are "plastic") will cost more to own over the
long term. Also, the straight inboard will have a much better ride,
they tend to stay in the water when going over most waves, rather than
jumping like I/O's and outboards.

I/O speed > Inboard speed
 

"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

I/O speed > Inboard speed
 

Also Sprach John :

For one thing, the thrust angle of the I/O is parallel to the bottom
of the hull. The inboard is at an angle, so some of the thrust is
directed upward instead of forward.

Dan, your correct, it does have to do with shaft angle. But the one
thing not mentioned is operating cost and ride. The I/O, because of
it's greater complexity, and because it made of aluminum (except the
new Volvo units that are "plastic") will cost more to own over the
long term. Also, the straight inboard will have a much better ride,
they tend to stay in the water when going over most waves, rather than
jumping like I/O's and outboards.

Oh, absolutely. I would NEVER own an I/O because of the mechanical issues
relating to the outdrive. But I don't deny that they are more more
mechanically efficient than an inboard.

Dan

--
Barbie says, Take quaaludes in gin and go to a disco right away!
But Ken says, WOO-WOO!! No credit at "Mr. Liquor"!!

-- Zippy the Pinhead

I/O speed > Inboard speed
 

On 23 Mar 2004 11:34:47 GMT, Marshall Banana wrote:

Also Sprach John :

For one thing, the thrust angle of the I/O is parallel to the bottom
of the hull. The inboard is at an angle, so some of the thrust is
directed upward instead of forward.

Dan, your correct, it does have to do with shaft angle. But the one
thing not mentioned is operating cost and ride. The I/O, because of
it's greater complexity, and because it made of aluminum (except the
new Volvo units that are "plastic") will cost more to own over the
long term. Also, the straight inboard will have a much better ride,
they tend to stay in the water when going over most waves, rather than
jumping like I/O's and outboards.

Oh, absolutely. I would NEVER own an I/O because of the mechanical issues
relating to the outdrive. But I don't deny that they are more more
mechanically efficient than an inboard.

I/O are ok if you maintain them properly.

However, I agree with the complexity problems with I/Os. That's why I
prefer outboards - a lot easier to work on too.

Later,

Tom
S. Woodstock, CT
-----------
"Angling may be said to be so
like the mathematics that it
can never be fully learnt..."

Izaak Walton "The Compleat Angler", 1653