[Public-list] diesel engine

[5thseason at canada.com]

On Thu, 03 Feb 2005 10:29:21 -0500, Don Campbell wrote:
Don
How right you are, on my trip south last winter I was
averaging 0.75 gallons per hour of motoring for the
whole trip.  Depending on wind and current S.O.G varied
between 2 and 7knots.  Increasing RPM from my optimum
of 1500 caused the prop to cavitate reduced boat speed
and increase consumtion to 1 gal per hour. Having extra
horsepower available does not help  In regard to RPM
(1500) to charge amps, at cruising speed my 100amp
alterator would only put out 40amps at 1800 RPM I would
get 75amps (max at temp).  Had I had a smaller pitch
prop my rev would have increasd to max charge amps. 
Extra fuel was carried on deck in 6 gal tanks and I
carried enough fuel for 3 days motoring (about 30gal
total).  As a final thought a diesal motor tends to be
noisey than a gas engine and vibrates a lot more, on a
short trip out of harbour this is no problem but after
7-9 hours even a smooth gas engine is intolerable some
thing to think about.
John Boor
MAHSEER #380
> 
> We are back to power and props . There is an optimum
> prop for every motor and
> the rules of thumb for this is 1" of diameter is 2.5"
> of pitch and 2" of pitch
> will change the RPM by 450. Match the prop to the
> performance curves - Torque,
> HP and fuel consumption - to fit the motor not the
boat
> or skipper. The hull
> speed of an Alberg 30 is about 10.5 feet per second.
>     A more recent comment talked about having more HP
> in reserve for times when
> needed. This is pointless if the power cannot be
> transferred to the prop. You
> need to consider effective thrust on the prop not HP
in
> reserve. And the boat
> will still only go at 10.5 feet per second. (The spec
> on the A4 from dynomometer
> tests is that the motor will put out 36 HP at 3600
RPM.
> Effectively we can only
> get to 2000 RPM in our application. We have power in
> reserve but of no use.)
> 

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