I, too, am in a quandry about replacing the 1989 Mariner 9.9 kicker on
my Mac25. I've named the engine "Sybil" due to its several
personalities, one of which involves dying in order to test my
seamanship at the most intersting moments imaginable.

Anyway, I'm interested in a 4-cycle for quiet operation, and I want the
smallest, lightest engine that will push my boat at its hull speed of
6.7mph reliably and safely under varied conditions. You would think
that there would be some scientific way to figure this out, but nobody
seems to know for sure.

SZ


Sherwin Dubren wrote:
Chris,

You mention that you could always get your boat up to hull speed
before
you hit maximum throttle rpm's. Now, was that in calm waters or going
downwind. I think you will find trying to make headway into a strong
wind and sea puts more demand on the engine. It's for those unusual
conditions that I would be willing to put up the extra cash to get the
reserve power. My only regret is that they have not come up with a
four stroke engine with a reasonable weight. I could heist my 65 pound
Chrysler Sailor over the transom into the boat, at sea. I cannot do
that
with my 4 stroke 99 pound Yamaha. I would have gotten a 2 stroke but I
am tired of mixing the oil with the gas, the loud noises from the
engine,
plus the worry that the government is going to put some kind of
restrictions on 2 stroke engines.
There are places to economize in boating, but for anyone doing
serious cruising (not day sailing), the added expense of a strong engine
is worth it. As I mentioned before, the higher gear ratio gives you
more leeway to increase your thrust, beyond what changing the propellor
can do.
It's true that high gear ratio engines are getting harder to find,
but not impossible.
Two years ago, while on a vacation to the Florida Keys, I found that my
Chrysler had
frozen up in storage beyond repair. I had to hustle to get a Yamaha
dealer to truck
one down from Miami since there were none available locally. I'm sure
that if people
are not pressed for time like me, they can order any engine they want.
If people were
more knowlegable about sailboat engines, they would not get stuck with
these motor boat
engines, and wouldn't have to change props as an afterthought.

Sherwin

Chris Edmonson wrote:

Sherwin;

True enough that gear ratio is of import but I think in the dollar range I
have seen people willing to spend a $150 propeller change will get more for
the expense than the $700 to $1500 sometimes charged for gear change. The
retail marine motor business is spotty at best. Often someone looking for a
particular motor will find that particular motor difficult to obtain. I
have even had people look into changing a short shaft motor into a long
shaft motor along with a gear change... just not cost effective. I guess I
was thinking more of someone wanting to correct a situation with an existing
motor than getting a new one.

Motors are set up for the different kinds of jobs they do. A work boat will
typically have the "high thrust" version whereas a sport fishing boat often
goes for speed / troll trade-offs. A sailboat that cannot plane does not
need a high pitch prop (equates to higher end speed in a planing hull).


Assuming that their gear ratio will allow them to get enough thrust
with
more conventional pitch props.

The

rule of thumb is that for every inch of pitch change you will increase or
decrease your max rpm's by 150 tp 200 rpm (a fact that is written on the
Mercury propeller box). For fuel economy you might choose a lower pitch
that will make power at a lower rpm... in a way this IS a gear change. On
my own sailboats I have gotten hull speed long before I ever get to max
thrust of the motor. It has allowed a smaller motor to be used and saved on
the expense and wieght of the larger motor and the fuel savings on a long
use of the motor. This last is relatively unimportant because in a season's
use I can count the tanks used on one hand!

Because the high thrust option is needed to extend even further the range of
useful power generated by the engine it is reasonable to make a motor with a
MUCH higher gear ratio... so in terms of designing a workboat or sailboat
motor it is understandable that the gear ratios are offered. It is just
that they are not readily available everywhere. There are charts at almost
all marine motor dealers that match pitch to a variety of motors so there
isn't really much experimenting to do to get the power you are seeking.
Overall I have to agree with pretty much everything you say BUT in terms of
expense and availability I would look at my motor with the idea that unless
I were replacing the whole thing I would opt for a pitch change before I
would get hung up on getting a motor that may not be obtainable at the
moment. Your points are very well taken though and if you can find the gear
ratio option it is an easy cure for the thrust question.


There are no easy cures. Changing the pitch to overcome a design
deficiency
is asking for trouble down the line.


Best;
Chris

"Sherwin Dubren" wrote in message
...

Hi Chris,
Your point about the 4-strokes developing power (or torque) at lower
rpm's
than 2-strokes is correct, but I'm not sure that leaves the gear ratio's
out
of the picture entirely. First of all, why would Yamaha and Mercury go
to higher
gear ratio's on their 'high thrust' engines, if it would be simpler to
just change
the propellor pitch to achieve the same result? Secondly, I would be a
little
nervous about experimenting with a propellor's pitch to match it
optimally to
the engine. The bottom line is will a 4-stroke engine with a low gear
ratio
and a compensating pitch propellor run as well as a 4-stroke with a
higher
gear ratio engine with it's appropriate propellor (I don't think so).
Actually,
both the higher gear ratio and the propellor can each contribute to the
higher
thrust. However, given a choice, I would go with the higher gear ratio
which
would allow me to get even more thrust by decreasing the propellor
pitch. With
the lower gear ratio engines, I can only lower the pitch of the
propellor which
has obvious limits as to how much this can be done.

Sherwin Dubren

Chris Edmonson wrote:

All good points being made here. If the wieght maximum you have in mind

is

clear to you then go with a smaller four stroke. I have found it

difficult

to move much more than fifty or sixty pounds of bulky motor around so

would

tend to go with a smaller motor than a lot of folks might choose. The

other

thing is that the four strokes make power at a lower RPM so may be best

on

fuel economy over the long run. The gear ratio is perhaps not as large

an

issue as it was when almost all of the motors were two strokes that

needed

the higher RPM's to get you going. The propeller's pitch can give you

some

of the pushing power that the old gear ratio change would give. If you
don't have enough umph move down a couple of inches in pitch and gain

power

earlier in the curve. The four strokes definitely handle this change

very

well.

Best;
Chris

"Bruce" wrote in message
...

I need to buy an outboard for my San Juan 21 and not quite sure about

how

big to go. I would like a 4 stroke and I am thinking that about 5 HP

would

be a good size. Any comments about the different brands would be
appreciated.
Also, do I really need a "long shaft" motor. With the motor mount

currently

on the boat, it seems to me that any motor would easily bury the prop.

Regards,
Bruce