hi all,
Im trying to compare a couple of yamaha 4 strokes, both long shaft, both
electric start. the 15 and the 9.9 seem to share a common block, but with a
different carb and prop? they have exactly the same weight (50kg), same
displacement (323cm3), same compression (9.19:1), different gear ration
(2.92 for the 9.9, 2.08 for the 15).

is the 15 just a 9.9 with a different carb? are they just as reliable as the
9.9? Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

thanks for any and all info,

Shaun

Shaun,
Basically Yes....

The only reason to market a 9.9 is for the "less than 10" market (like
Canada).

Is there any difference in reliability? I very much doubt that it will
ever show up and will very user dependent.

Which you choose is your bet. What are going to do with it? Do you
want to spend the extra money for the 15?

The High Thrust versions are for things that take a great deal of effort
to get going through the water. It is like holding a car in second gear.

If you are going to push a less than 2 ton sloop, you don't even need
the high thrust version (the new Honda HT backs much better than the
standard). I push a 4800# centerboard sloop with the board halfway down
a 6.0k at just over half throttle at about 1/2g/hr with a Honda 9.9. WOT
gets me to 6.2 and empties the tank way faster. A friend bought the new
TH and you can tell the difference just as he cranks up, but his cruise
is at a higher engine speed and his fuel rate is not as good as mine and
on flat water I can be at cruise at the same time.

What do I know? Well apart from being a lifelong waterman, I'm also a
naval architect and a marine engineer (licensed).

Your bet from here.

Matt Colie



Shaun Van Poecke wrote:
hi all,
Im trying to compare a couple of yamaha 4 strokes, both long shaft, both
electric start. the 15 and the 9.9 seem to share a common block, but with a
different carb and prop? they have exactly the same weight (50kg), same
displacement (323cm3), same compression (9.19:1), different gear ration
(2.92 for the 9.9, 2.08 for the 15).

is the 15 just a 9.9 with a different carb? are they just as reliable as the
9.9? Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

thanks for any and all info,

Shaun



--
target of diversity
victim of affirmative action
refugee from the war on poverty
minimized by political correctness

On Mon, 12 Mar 07, Matt Colie wrote:
I push a 4800# centerboard sloop with the board halfway down
a 6.0k at just over half throttle at about 1/2g/hr with a Honda 9.9. WOT
gets me to 6.2 and empties the tank way faster. A friend bought the new
TH and you can tell the difference just as he cranks up, but his cruise
is at a higher engine speed and his fuel rate is not as good as mine and
on flat water I can be at cruise at the same time.

Just looking at your friend's Honda HT gearcase, can you tell a
difference between it and yours? I'm wondering if the distance between
the prop shaft and the cavitation plate is greater on his HT.... or if
Honda just sticks a larger diameter prop and lower ratio gears on the
same case.

Rick

On Mon, 12 Mar 07, "Shaun Van Poecke" wrote:
Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

Shaun, as you can tell from the replies so far, we need to know your
intended use ....
a) pushing a displacement hull
b) pushing a planing hull
c) combination of both "a" & "b"
d) none of the above

Rick

Maybe I'm looking at a different spec sheet or different year model
but.....

On Mon, 12 Mar 07, "Shaun Van Poecke" wrote:
the 15 and the 9.9 seem to share a common block, but with a
different carb and prop? they have exactly the same weight (50kg),

I'm seeing a heavier 15hp than 9.9hp (granted, I'm looking at specs on
short shafts).

same
displacement (323cm3),

I'm seeing 362cc for the 15hp, and 323cc for the 9.9hp

same compression (9.19:1),

9.3:1 for 15hp, and 9.19:1 for 9.9hp

different gear ration
(2.92 for the 9.9, 2.08 for the 15).

Yep

but different RPM ranges. 5000-6000 for 15hp and 4500-5500 for the
9.9hp.

is the 15 just a 9.9 with a different carb?

My guess...... no.

are they just as reliable as the
9.9?

My guess.... yes.

Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

Depends.... (see my multiple choice post).

thanks for any and all info,

Good questions. Glad you asked.

BTW, here are the spec sheets I'm looking at:
http://www.yamaha-motor.com/outboard...s/4/specs.aspx
http://www.yamaha-motor.com/outboard...s/5/specs.aspx

Rick

CW,
(I used to live next door to a boat by that name.)

I fully respect right and desire to disagree, but the facts are that a
two ton sloop (that can actually sail) regardless of hull dynamics does
not even need the 10Hp to make hull speed in most weather you would
actually ever be in and if it is too rough for that, an outboard will be
out of the water half the time.

My boat came to me with a 7.5 and the only reason that I changed it to
the 9.9xles was for the electric start. The 28" transom height was just
nice to have in spite of the small additional weight. (I think nobody
make that 28" anymore.)

Yes, the high thrust version will always produce more thrust, but always
at the expense of crankshaft speed at cruise and always at the expense
of top speed (again this may not matter as you have achieved hull speed
at less than WOT). That additional engine speed must cause additional
fuel consumption (just like running in second gear).

By the by, since the Ford B block went away (1968?) all the trucks built
in this country have had engines that were common with the passenger
automobile production.

Matt Colie
Lifelong Waterman, Licensed Mariner and Pathological sailor


Charlie Morgan wrote:
On Mon, 12 Mar 2007 10:16:52 -0400, Matt Colie
wrote:

Shaun,
Basically Yes....
Your bet from here.
snip

Matt Colie

I respectfully disagree with this assessment. For a displacement hull,
the high thrust version is so much more suitable that I would not
consider a standard thrust model, even if it cost $1000 less. I would
not put a car engine in a dump truck, either.

You'll find out a Major difference when you need to motor against a 4
or 5 knot current. We can motor (Yamaha High Thrust 9.9) at hull speed
in calm waters, and carry on a conversation at normal levels in the
cockpit. At idle, it's almost completely silent. There's a big comfort
benefit. It also stops the boat very quickly. When people ask me how I
like my motor, I tell them it's like having my own personal tugboat
along.

Another factor is that the 9.9 High Thrust is available with a Xtra
long 25 inch shaft. For transom mounting on a lift bracket, that's a
big advantage.

CWM

Shaun Van Poecke wrote:
hi all,
Im trying to compare a couple of yamaha 4 strokes, both long shaft, both
electric start. the 15 and the 9.9 seem to share a common block, but with a
different carb and prop? they have exactly the same weight (50kg), same
displacement (323cm3), same compression (9.19:1), different gear ration
(2.92 for the 9.9, 2.08 for the 15).

is the 15 just a 9.9 with a different carb? are they just as reliable as the
9.9? Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

thanks for any and all info,

Shaun




--
target of diversity
victim of affirmative action
refugee from the war on poverty
minimized by political correctness

CW,
Responses are in line (I don't like to do that but we are getting a
little long here.

Charlie Morgan wrote:
On Mon, 12 Mar 2007 16:40:35 -0400, Matt Colie wrote:

CW,
(I used to live next door to a boat by that name.)


Yes, I know. Your mother was the "dog lady" of Mystic.
Right and I still miss her.

I fully respect right and desire to disagree, but the facts are that a
two ton sloop (that can actually sail) regardless of hull dynamics does
not even need the 10Hp to make hull speed in most weather you would
actually ever be in and if it is too rough for that, an outboard will be
out of the water half the time.

Sorry, but my actual experience conflicts with that assertion.
My sample is based on experience with a fleet of S2-7.9 hulls 1, 67, 86,
153, 224?, 346, 415 and 505. This has been a serious discussion in the
area as the weeds preclude the effective operation of an inboard
version. Several of these have been repurposed as cruisers so engine
weight is less critical that all around performance.

What class/builder is your experience based on? We have have an
interesting data point here.

Yamaha makes a 25 inch shaft, but it is not available in the standard F series
engines. It is only available in the High Thrust motors which are made
specifically for propelling sailboats.
Actually, I was just at Yamaha's site. The specifications for the HT
and STD are very different and unlike Honda they do not give any
propeller information. If the page is correct, the 9.9TH is using less
displacement and turning the propshaft way slower (2.08 vs 2.92). So,
the engine is running faster.

Yes, the high thrust version will always produce more thrust, but always
at the expense of crankshaft speed at cruise and always at the expense
of top speed (again this may not matter as you have achieved hull speed
at less than WOT). That additional engine speed must cause additional
fuel consumption (just like running in second gear).

What?!? The high thrust version propels the boat at hull speed at LOWER RPM's
than the standard motors. Significantly lower. For sailboats, what you need is
GRUNT.
The propeller shaft is turning less fast, but the engine is running
faster (trust me - we had a tach on them) and this is just what you want
for maximum thrust at zero speed. All the High Thrust engines I have
messed with these days are capable of reaching rated engine speed with
the boat stationary (tied to a dock in most cases). The standard
configuration engines will not get to rated crankshaft speed at zero
boat speed. Yamaha apparently does this with gears, Honda does it with
a larger D and smaller pitch on the prop with the same gears (this year
was different two years ago).

My Honda is actually terrible at this, it won't get to within 500RPM of
the torque peak and that is still 1k below the the HP peak. I
frequently have to go to WOT when maneuvering just to back it off as
soon as the boat is actually moving, but I have to be there anyway. It
is quieter underway and does burn less fuel than #346 Jus Ducky (but Lee
won't tell me how much).

This is the same thing that tugboats do - the don't pull fast, they do
pull like hell.

The big engines don't turn so slowly because they need to to produce the
high torque you keep hearing about, they do so because the physics of
moving a piston get in the way. That is why the little VW engine that
is the same class as your Volvo 2xxx or Yanmar XGM runs up to 4800 or
5200 redline - it is to make horsepower. Their specific torque is about
the same as the little marine engines that you know, but they make a
good deal more power - only for about 2500 hrs - a Volvo will do twice
that.

I think you know and understand EXACTLY what I meant, Matt.
I was trying to stick to a single category, but the GM 4500 is a truck
can come with a 7yard box and is available with the 8.1 that is the
current big block.


Matt Colie
Lifelong Waterman, Licensed Mariner and Pathological sailor


Charlie Morgan wrote:
On Mon, 12 Mar 2007 10:16:52 -0400, Matt Colie
wrote:

Shaun,
Basically Yes....
Your bet from here.
snip

Matt Colie

CWM

Shaun Van Poecke wrote:
hi all,
snip
thanks for any and all info,

Shaun

wrote in message
...
On Mon, 12 Mar 07, "Shaun Van Poecke" wrote:
Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

Shaun, as you can tell from the replies so far, we need to know your
intended use ....
a) pushing a displacement hull
b) pushing a planing hull
c) combination of both "a" & "b"
d) none of the above

Rick

Its intended as the main engine on a thunderbird 26. i am planning to buy
second hand, and have seen more of the 15's come up for sale than 9.9's
which is what i was hoping for. will be used for general harbour docking as
well as motoring longer distances when becalmed.

Shaun

interesting how you got a different spec page from what i did... i got mine
from here

http://www.yamaha-motor.com.au/marin...htm?marine.asp

click on protable 4 strokes, and the two models im comparing are the
FT9.9DEL and theF15AEHL. they have the specs i gave before, wondering why
the page you've given me shows different specs?


Shaun

wrote in message
...
Maybe I'm looking at a different spec sheet or different year model
but.....

On Mon, 12 Mar 07, "Shaun Van Poecke" wrote:
the 15 and the 9.9 seem to share a common block, but with a
different carb and prop? they have exactly the same weight (50kg),

I'm seeing a heavier 15hp than 9.9hp (granted, I'm looking at specs on
short shafts).

same

displacement (323cm3),

I'm seeing 362cc for the 15hp, and 323cc for the 9.9hp

same compression (9.19:1),

9.3:1 for 15hp, and 9.19:1 for 9.9hp

different gear ration
(2.92 for the 9.9, 2.08 for the 15).

Yep

but different RPM ranges. 5000-6000 for 15hp and 4500-5500 for the
9.9hp.

is the 15 just a 9.9 with a different carb?

My guess...... no.

are they just as reliable as the
9.9?

My guess.... yes.

Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

Depends.... (see my multiple choice post).

thanks for any and all info,

Good questions. Glad you asked.

BTW, here are the spec sheets I'm looking at:
http://www.yamaha-motor.com/outboard...s/4/specs.aspx
http://www.yamaha-motor.com/outboard...s/5/specs.aspx

Rick

"Shaun Van Poecke" wrote:
interesting how you got a different spec page from what i did... i got mine
from here
http://www.yamaha-motor.com.au/marin...htm?marine.asp

Charlie Morgan wrote:
You are comparing an "F" series 9.9 to the "F" series 15. The sailboat
motor (high thrust) is a "T" series motor.

Actually, the spec sheets are calling both the "F" and the "T" 9.9s
"High Thrust" motors. One site is American, the other is Australian.
Shaun.... you wouldn't happen to be Australian would you?
Either way, methinks you'll need to speak with a product expert with
the company. This is gettin' a little too confusing for moi.

Rick ----- Gulf Coast MS, USA