"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.

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.

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.

"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

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.

You have a problem. A 2GM20 shouldn't use over one gallon an hour
even running at full rated power.

At 6 knots, however, you're at 95% of hull speed, so you're well up
the curve, but since your displacement is under 8000 pounds, you
should only need about 14 HP which means about .77 gallons per hour.

Diesel use = 0.055 gallons/hp/hour

OK Jeff,
What do you estimate my usage should be with 4-108, 30' LWL, 20,000
displacement, two blade 16 x 14 prop.
krj

Jeff Morris wrote:
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.

You have a problem. A 2GM20 shouldn't use over one gallon an hour even
running at full rated power.

At 6 knots, however, you're at 95% of hull speed, so you're well up the
curve, but since your displacement is under 8000 pounds, you should only
need about 14 HP which means about .77 gallons per hour.

Diesel use = 0.055 gallons/hp/hour

My 3GM30F in my previous 36' boat only burned 3/4 to 1 GPH.

"Jeff Morris" wrote in message
...
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.

You have a problem. A 2GM20 shouldn't use over one gallon an hour even
running at full rated power.

At 6 knots, however, you're at 95% of hull speed, so you're well up the
curve, but since your displacement is under 8000 pounds, you should only
need about 14 HP which means about .77 gallons per hour.

Diesel use = 0.055 gallons/hp/hour

krj wrote:
OK Jeff,
What do you estimate my usage should be with 4-108, 30' LWL, 20,000
displacement, two blade 16 x 14 prop.

To drive a boat at a Speed-Length ratio of 1.2 requires about 1 HP for
every 700 pounds. So to push 20,000 at 6.6 knots requires 28 HP,
which should burn about 1.5 gallons per hour. It would seem that the
4-108 is overkill for this boat, but you have plenty of reserve. If
you push to hull speed, the requirement goes up to 1 HP for every 500
pounds, or 40 HP or around 2.2 gals/hours. If you back off to under 6
knots, then you only need one HP per 1000 pounds, or 1.1 gals/hour.

So how close did I come to your experience?

A prop calculation will cost you an extra 50 cents, but your goal
there should be to have a large enough prop to handle the power, and
the engine reving at a sweet part of its power curve. My rough guess
(and admit this is one area I never really understood) is that the
blade area your prop is small for the horse power you may be putting
through it - this would cause cavitation.

"Steven Shelikoff" wrote in message
...
On Thu, 24 Feb 2005 14:41:58 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

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.

If the 4-108 can push the boat at it's theoretical hull speed without
too much effort, adding the little extra power of a 4-236 isn't going to
make it go all that much faster in smooth calm water. Maybe what, a
half knot at best? Probably less. The extra "over" power is very
useful at fighting wind and waves. Currents? No, not much help at all.

Steve

I've never met the gentleman so I can't tell what he really had in mind.

Doug

"Steven Shelikoff" wrote in message
...
On Thu, 24 Feb 2005 18:05:12 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

My 3GM30F in my previous 36' boat only burned 3/4 to 1 GPH.

That's what my 4-108 burns in my 37' boat. The OP definitely has a
problem.

Steve

Agreed.