From: wwalker@qualcomm.com (Bill Walker)
Subject: Re: Inboard VS. Outboard
Followup-To: rec.boats
Organization: Qualcomm, Inc.
Date: Tue, 18 Aug 1992 19:46:49 GMT

In article <1992Aug18.122316.7043@trantor.harris-atd.com>,
eriseman@dw3f.ess.harris.com (Eric Riseman) wrote:
> 
> I know this topic has probably been beaten to death, but what the hey!
> 
> Which is better, Inboard or Outboard?  Is it because of cost?
> Maintainability? Power? (or anything
> else that I may have missed).
> 
> Which type requires less Maintenance?  Breaks down less? Is easier and
> cheaper to repair/rebuild?
> 
> This I/O or Outboard will be used for Ocean diving/fishing on a boat who
> size will range between
> 20 - 24 feet (deep "V" of course)
> 
> Thanks in advance..........
> 
> ESR

First, the caveat:  I'm neither a diver nor a fisherman.  I use my boat
almost entirely for water skiing.  However, I have lived with an I/O for
many years, and I've been around outboards a fair amount.

First, terminology.  First you say "Inboard or Outboard", and later you say
"I/O or Outboard".  I've noticed boat dealers starting to call I/Os
"inboards" lately, and I decry this practice.  An inboard has a separate
propellor and rudder mounted on the bottom of the hull, with a straight
shaft to the prop.  What you're talking about is an inboard/outboard or
stern drive, which has an inboard, automotive-type engine, with an outdrive
that looks like the bottom of an outboard motor sticking out of the
transom.

Assuming we're comparing I/Os and outboards, each type has advantages and
disadvantages which you must weight according to your own priorities.  As I
see them, the items are, in no particular order:

Outboard advantages:

1) Motor designed for marine use - frequent use of wide open throttle, long
periods at constant throttle, etc.

2) Compact.  An outboard will give you more cockpit space, which is a
particular issue for diving and fishing use, I would think.  The
compactness also makes multiple engine installations a bit easier and more
prevalent, which is worth considering for offshore use, I would think.

3) Assuming a trailerable boat, the outboards can be easier to work on,
simply because they're easier to get at (although the powerheads tend to be
pretty densely packed, from what I've seen.  At least you can work standing
up).

4) At one time, outboards were cheaper, but I'm not sure this is still the
case.

5) Power/weight ratio.  An outboard engine is much lighter than a stern
drive of comparable power, which make the boat lighter, which in turn means
you need even less power, etc.  You can get the same performance from a
lighter, easier-to-trailer package.

Outboard disadvantages:

1) Motors stick up behind the transom, blocking your view aft, access to
the transom, etc.  It's tough to find room for more than the most minimal
boarding platform.  I/Os are only a little bit better in this regard,
though (although some of the newer ones have full-width boarding platforms
above the stern drive, but I don't think that'd be desirable for offshore
use).

2) Noise.  Outboards may in many cases be quieter than I/Os, but I find the
character of outboard noise to be extremely annoying even when it's not
very loud.

3) Smoke.  Even the newer outboards, with variable-ratio oil injection,
seem to smoke pretty badly when you're in neutral.

4) Oil.  With only a few exceptions, outboards use 2-stroke engines, which
requires that oil be mixed with the gas.  Most newer outboards have
automatic oil injection systems, which means you just have to make sure the
oil tank is full, provided they work.  There's been some discussion in this
forum about the reliability of oil injection systems.  Folks have been
known to disable them and go back to mixing oil into the gas by hand.

5) Parts.  I may be mistaken, not having owned one, but I'd guess outboard
motor parts are more expensive, because of advantage (1) above.  The basic
rule is that if it says "boat" on it, it costs at least twice as much, and
since outboards were designed for boats, I'd expect them to follow the
rule.  Perhaps an outboard owner can correct me on this.

6) Limited power.  The most powerful outboard you can buy is 300 hp, and
those are pretty rare.  I doubt this will be an issue for your 24-footer,
particularly if you go with a dual-engine installation (but remember you'll
have twice the maintenance).

7) Fuel consumption.  Outboards typically are thirstier, though I
understand they've improved in the last few years.


I/O advantages:

1) Plain old automotive-type powerplant that any mechanic can understand
(well, OK, nowadays I have to say any old mechanic who understands
electronic ignitions systems, and maybe electronic engine management
systems).

1a) Many parts can be bought at your local auto parts store, provided
they're not specific to the marine adaptation of your engine, thus avoiding
the aforementioned "boat" surcharge.

1b) Maintenance items are easily understood by the home mechanic, since the
engine is basically the same as what's in your car (it may even have
interchangable parts!).

2) No motor sticking up to block your view or access aft, but you do have
to remember there's a stern drive sticking out back there.  Perhaps this is
a disadvantage for fishing?  I don't know.

3) Power.  How much do you want?  Offshore racing powerboats run stern
drives, in many cases (they all used to, but surface drives have taken over
at the top levels).  Mild, off-the-shelf I/Os can go up to about 365 hp
(using the GM 7.4 liter {454 cubic inch} V-8 block).  Again, this is
probably not an issue for your 24-footer.

4) Fuel consumption.  I/Os tend to be more economical, even though they
might be pushing more weight (but perhaps outboards are better when
trolling?).

5) That good old automotive motor sound.

I/O disadvantages:

1) More complication in the drive system.  Compared to an outboard, you've
got a set of universal joints, a 90-degree bevel gear, more complicated
shift linkage, rubber bellows, water hoses, non-self-contained trim & tilt
mechanism, etc.  So the outdrive is probably less reliable than an
outboard, and all those things are expensive to fix.  I think the motor is
probably more reliable, though, and cheaper to fix, so perhaps it balances
out!  Over the 25 years my boat has been in our family, we've had a lot
more trouble with the outdrive than with the motor.

2) Space.  The motor takes up a lot of space inside the boat, and the more
horsepower you need, the more space it takes.  And it's typically harder to
get at to work on, too.  Twin engine installations can be especially
cramped, and I'd be surprised to see twin I/Os available on a 24-footer
(but I've seen lots of 24-foot fishing boats with twin outboards).

3) Weight.  Again, the I/O will be heavier for a given hp, making the whole
rig heavier and requiring more hp.  Put another way, for the same
performance level, with an I/O the rig will be heavier and have more
horsepower than the outboard.


I can't comment on the reliability of modern outboards (or really of modern
I/Os, I suppose), but my father owned an outboard before he bought the boat
I now have, and I recall we had problems with it constantly.  But that was
25 years ago.  The I/O has had few problems that could not be attributed to
its advanced age.


----------
Bill Walker - WWalker@qualcomm.com - QUALCOMM, Inc., San Diego, CA
All opinions expressed are mine, and do not reflect those of my employer.
"First thing we do, we kill all the lawyers." - Shakespeare
Newsgroups: rec.boats