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