"Wayne.B" wrote in message
...
On Wed, 23 Feb 2005 20:41:51 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

I run a 1985 Perkins 85 HP 4 cylinder pushing a 43'
boat. I consistantly burn 1 GPH.

==================================

If so, you are only using about 20 hp out of your 85 available. At
85% of full RPMs it should be burning about 3 gph unless you are way
under propped.

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.

On Wed, 23 Feb 2005 23:51:31 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:
==================================

If so, you are only using about 20 hp out of your 85 available. At
85% of full RPMs it should be burning about 3 gph unless you are way
under propped.

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.

========================================

You obviously have plenty of reserve power which is nice for those
occasions where you are motoring into head winds and seas.

Actually, the original owner repowered the boat from a Perkins 4-108 to
a 4-236. The boat lived in Newfoundland. Fighting currents was
definitely his goal.

Doug
s/v Callista

"Wayne.B" wrote in message
...
On Wed, 23 Feb 2005 23:51:31 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:
==================================

If so, you are only using about 20 hp out of your 85 available. At
85% of full RPMs it should be burning about 3 gph unless you are way
under propped.

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.

========================================

You obviously have plenty of reserve power which is nice for those
occasions where you are motoring into head winds and seas.

"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in
:

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.



What RPM are you turning on that Perkins, Doug. Lionheart has a 4-108 I
got from a guy on this newsgroup in NC for $1200. In spite of the
boatyard's screwup flooding her exhaust and crankcase with seawater with a
dripless packing water injection line, she's a great engine. Our
econocruise is also very easy to get near hull speed on the Amel Sharki 41
ketch at around 2200 RPM, but she's nearly as fast at 1800. There's a 120A
house alternator mounted to port and the engine has a 90A alternator on its
bracket for the starting battery for some silly reason I have yet to figure
out. The new fridge is 12/120V so we took away all the car air conditioner
parts of the old French fridge/freezer combo.

The original Perkins that came with the boat ran just fine, even though the
hourmeter read over 7000 hours! Engine shop said it was still usable so
it's in the captain's garage in Atlanta, our spares repository of used
parts. Simply an amazing engine.....by anyone's standards.

"Larry W4CSC" wrote in message
...
"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in
:

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.



What RPM are you turning on that Perkins, Doug. Lionheart has a 4-108 I
got from a guy on this newsgroup in NC for $1200. In spite of the
boatyard's screwup flooding her exhaust and crankcase with seawater with a
dripless packing water injection line, she's a great engine. Our
econocruise is also very easy to get near hull speed on the Amel Sharki 41
ketch at around 2200 RPM, but she's nearly as fast at 1800. There's a
120A
house alternator mounted to port and the engine has a 90A alternator on
its
bracket for the starting battery for some silly reason I have yet to
figure
out. The new fridge is 12/120V so we took away all the car air
conditioner
parts of the old French fridge/freezer combo.

The original Perkins that came with the boat ran just fine, even though
the
hourmeter read over 7000 hours! Engine shop said it was still usable so
it's in the captain's garage in Atlanta, our spares repository of used
parts. Simply an amazing engine.....by anyone's standards.

I don;t actually know. The calibration of the tach is off because the
alternator is
not stock. When we first bought the boat I measured the actual RPM and made
a graph to convert from indicated to actual. Converting the proper cruising
RPM
to the indicated gives 2500 so that is where we run unless we need some
extra. I've forgotten what the actuals are. 1800 sems to stick in my mind
but
I'd have to go look it up.

Doug

On Wed, 23 Feb 2005 23:51:31 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

"Wayne.B" wrote in message
.. .
On Wed, 23 Feb 2005 20:41:51 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

I run a 1985 Perkins 85 HP 4 cylinder pushing a 43'
boat. I consistantly burn 1 GPH.

==================================

If so, you are only using about 20 hp out of your 85 available. At
85% of full RPMs it should be burning about 3 gph unless you are way
under propped.

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.

I do 5.8 knots at 1/2 throttle on a direct drive Atomic 4 with a 12" x
6" "standard" two-blade prop pushing a 10,000 lb boat with a 27' LWL.
Hull speed is just under seven knots. RPM is around 1,500-1,600.

I can get to 6.6 knots SOG at 3/4 throttle, but the noise is
unpleasant and I start burning a lot more gas...it's not worth it.

I can sail in heavy air favourably angled slightly above hull speed
(7.3 knots SOG) for sustained periods, or about 1.5 knots

I have logged a pretty consistent gas usage of 0.73 Imp. gal/hr. which
is about .825 U.S. gal, I think. That's at a typical cruise speed of
1/3 throttle or 5 to 5.2 knots. A 12 gallon tank gives me a range of
about 84-90 NM or just under two round trip Toronto-Niagara River
crossings. Motorsailing increases this significantly, of course.

If I drop it to 4 knots, I burn one half gallon an hour. This means 24
hours of constant use and nearly 100 NM of range. (It's a
racer-cruiser, not a passagemaker).

I only use full throttle in reverse, actually...if ever.

The point? You pay hugely in fuel consumption and engine wear getting
that last knot.

R.

Here's the scoop on fuel efficiency. It's an engine parameter called
specific fuel consumption. The most efficient aero recips use
0.45 lb per HP hour.

A diesel could be 50% more fuel efficient, let's say.
So 0.3 lb diesel fuel per HP.hr would need 26 lb fuel per hour
to produce 85HP
That's 4 gallons or more....for 84HP

I guess this means Doug is using full revs at 1/4 throttle,
or full throttle at 1/4 max revs....

Regards

Brian Whatcott Altus OK

On Wed, 23 Feb 2005 20:41:51 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

Something must be wrong with your figures or your engine/prop
situation. I run a 1985 Perkins 85 HP 4 cylinder pushing a 43'
boat. I consistantly burn 1 GPH.

Doug
s/v Callista

wrote in message
oups.com...
Another thread discusses sailboats motoring "too much" but I think most
sailboats will use their engines to supplement sail but we still worry
about fuel economy. Even motoring alone, my yanmar 2GM seems to burn
only about 1-1.5 gals/hr at 6 kts in my 28' S2 but still I wonder about
the best way to conserve fuel in very light air.
Normally, in light air, I start with sails and no engine and eventually
get impatient with going only 3 kts and start the engine and put us up
to 5 and then eventually 6 kts or more. It is this last little bit
that I think burns the most fuel because she is most efficient at
slower speeds but as we get closer to hull speed fuel use rises
sharply.
An alternative strategy that would burn less fuel but would go a little
slower might to be ALWAYS run the engine at sufficient rpm to get to
3.5 kts and then use the sails to supplement that.

The number I've used for marine engines is 0.055 Gallons per HP per
hour. For gas engines, use 0.1.


Brian Whatcott wrote:
Here's the scoop on fuel efficiency. It's an engine parameter called
specific fuel consumption. The most efficient aero recips use
0.45 lb per HP hour.

A diesel could be 50% more fuel efficient, let's say.
So 0.3 lb diesel fuel per HP.hr would need 26 lb fuel per hour
to produce 85HP
That's 4 gallons or more....for 84HP

I guess this means Doug is using full revs at 1/4 throttle,
or full throttle at 1/4 max revs....

Regards

Brian Whatcott Altus OK

On Wed, 23 Feb 2005 20:41:51 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:


Something must be wrong with your figures or your engine/prop
situation. I run a 1985 Perkins 85 HP 4 cylinder pushing a 43'
boat. I consistantly burn 1 GPH.

Doug
s/v Callista

wrote in message
roups.com...

Another thread discusses sailboats motoring "too much" but I think most
sailboats will use their engines to supplement sail but we still worry
about fuel economy. Even motoring alone, my yanmar 2GM seems to burn
only about 1-1.5 gals/hr at 6 kts in my 28' S2 but still I wonder about
the best way to conserve fuel in very light air.
Normally, in light air, I start with sails and no engine and eventually
get impatient with going only 3 kts and start the engine and put us up
to 5 and then eventually 6 kts or more. It is this last little bit
that I think burns the most fuel because she is most efficient at
slower speeds but as we get closer to hull speed fuel use rises
sharply.
An alternative strategy that would burn less fuel but would go a little
slower might to be ALWAYS run the engine at sufficient rpm to get to
3.5 kts and then use the sails to supplement that.

Brian Whatcott wrote in
:

A diesel could be 50% more fuel efficient, let's say.
So 0.3 lb diesel fuel per HP.hr would need 26 lb fuel per hour
to produce 85HP
That's 4 gallons or more....for 84HP



That should be about right, even for the biggest diesel engine in the world
over 108,000 HP
http://www.bath.ac.uk/~ccsshb/12cyl/

" Fuel consumption at maximum power is 0.278 lbs per hp per hour (Brake
Specific Fuel Consumption). Fuel consumption at maximum economy is 0.260
lbs/hp/hour. At maximum economy the engine exceeds 50% thermal efficiency.
That is, more than 50% of the energy in the fuel in converted to motion.
For comparison, most automotive and small aircraft engines have BSFC
figures in the 0.40-0.60 lbs/hp/hr range and 25-30% thermal efficiency
range.

Even at it's most efficient power setting, the big 14 consumes 1,660
gallons of heavy fuel oil per hour."

Do bunker oil barges take VISA?....(c;

I just want to be in the engine room for the sea trials....

Definitely somethingw WRONG here ... A 2Gm should be using 1/2 GPH
Blocked exhaust pipe at the water injection elbow will do this....

Make chart of actual boatspeed vs. rpm. Plot various points of
operation in kts. vs. rpm ... from slow to wide open throttle
operation.
The data points (well below hull speed) will describe a straight line
..... then as the bow begins to rise, the data points will 'knuckle' and
the straight line will begin to curve upwards.
If you operate anywhere in the range of the straight line the fuel
economy will be at its best, if you operate in the curved portions, the
fuel economy will be worse, if you operate where the tha curve starts
to go straight up ..... all you're doing is using energy to lift the
bow and develop huge bow and stern waves .... and you wont go any
faster than being down the flat section of the plot.

Go to your engine manual and look at the power curve HP vs. rpm. vs.
GPH.

In article . com,
wrote:

Another thread discusses sailboats motoring "too much" but I think most
sailboats will use their engines to supplement sail but we still worry
about fuel economy. Even motoring alone, my yanmar 2GM seems to burn
only about 1-1.5 gals/hr at 6 kts in my 28' S2 but still I wonder about
the best way to conserve fuel in very light air.
Normally, in light air, I start with sails and no engine and eventually
get impatient with going only 3 kts and start the engine and put us up
to 5 and then eventually 6 kts or more. It is this last little bit
that I think burns the most fuel because she is most efficient at
slower speeds but as we get closer to hull speed fuel use rises
sharply.
An alternative strategy that would burn less fuel but would go a little
slower might to be ALWAYS run the engine at sufficient rpm to get to
3.5 kts and then use the sails to supplement that.