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Fuel economy while motorsailing
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GYXU > Boats > Fuel economy while motorsailing 8 March 2005 11:09:45

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Fuel economy while motorsailing

Guest 23 February 2005 22:04:20
 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.

Add comment
Leanne 23 February 2005 23:46:29 permanent link ]
 
<dbohara@mindspring­.com> wrote in message
news:1109181860.227­648.46240@o13g2000cw­o.googlegroups.com..­.
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.

I use 5 kts for the target speed and adjust sails and engine to
try to maintain that.

Leanne


Add comment
Guest 24 February 2005 00:08:23 permanent link ]
 I truly do not know how much fuel it uses but am saying 1-1.5 gal/hr as
a maximum. I have major problems filling it as the fuel backs up and
tries to backflow even though I have unclogged the breather line.

As far as finding time to sail, I am blessed with loving my work and
really cannot decide if I would ever really want to go sailing for long
periods.

Add comment
Doug Dotson 24 February 2005 05:41:51 permanent link ]
 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

<dbohara@mindspring­.com> wrote in message
news:1109181860.227­648.46240@o13g2000cw­o.googlegroups.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.>


Add comment
Wayne . B 24 February 2005 08:01:16 permanent link ]
 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.

Add comment
Wayne . B 24 February 2005 11:45:42 permanent link ]
 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.
Add comment
Steven Shelikoff 25 February 2005 05:19:38 permanent link ]
 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
Add comment
Steven Shelikoff 25 February 2005 05:20:58 permanent link ]
 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
Add comment
Doug Dotson 25 February 2005 06:25:15 permanent link ]
 
"Steven Shelikoff" <shelikoff@yawho.co­m> wrote in message
news:qavs1194hpqvfk­rv4ro765aombl9br57b2­@4ax.com...> 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.


Add comment
Wayne . B 25 February 2005 07:48:23 permanent link ]
 On Thu, 24 Feb 2005 20:26:42 -0500, Jeff Morris
<jeffmo@nospam-at-a­ll-sv-loki.com> wrote:
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.

===================­================

Propping a sailboat is always a big tradeoff between sailing
efficiency and motoring. For motoring a big 3 or 4 bladed pop is
ideal for a displacement hull but that is deadly to sailing
performance unless you got a feathering prop, and that is another
level of compromise and expense.

Add comment
Skipper 25 February 2005 09:22:37 permanent link ]
 On 23 Feb 2005 12:08:23 -0800, dbohara@mindspring.­com wrote:
I truly do not know how much fuel it uses but am saying 1-1.5 gal/hr as>a maximum. I have major problems filling it as the fuel backs up and>tries to backflow even though I have unclogged the breather line.>
As far as finding time to sail, I am blessed with loving my work and>really cannot decide if I would ever really want to go sailing for long>periods.

It seems you are well passed the speed you want for fuel economy.
My boat is about 36,000 lbs (46') and my big 85 hp burns between 1 and
1 1/2 gph at 6 knts.
You might try a self-pitching prop like the Auto-Prop. You can
still use sail power and the prop will self-pitch to still give speed
at slower rpm. Take a look at their web site. Over time, the fuel
economy will pay for the prop. You'll also get a real prop in reverse.


Add comment
Larry W4CSC 26 February 2005 05:17:15 permanent link ]
 "Doug Dotson" <dougdotson@NOSPAMc­ablespeedNOSPAMcom> wrote in
news:Ap6dnW55mNtus4­PfRVn-vA@cablespeedm­d.com:
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>

Thanks. The 4-108 just seems to lazily cruise along in the 1800-2000 RPM
range. Lionheart has 90 gallons of diesel in the tank that's the starboard
seat in the center cockpit. It's amazing how long that lasts under power.

Add comment
Larry W4CSC 26 February 2005 05:23:14 permanent link ]
 Wayne.B <waynebatrecdotboat­s@hotmail.com> wrote in
news:nq7t111dehhq2k­9qb5k481vb41u4ue19jc­@4ax.com:
Propping a sailboat is always a big tradeoff between sailing> efficiency and motoring. For motoring a big 3 or 4 bladed pop is> ideal for a displacement hull but that is deadly to sailing> performance unless you got a feathering prop, and that is another> level of compromise and expense.>

Lionheart's 3-bladed prop freewheels to operate the shaft alternator on its
4-108 diesel setup. For this reason, it has the "hydraulic transmission",
not the straight one. When the engine was swapped out, the transmission
was inspected but not changed to the other type. The mechanic said it
wouldn't be good to freewheel that shaft all the time, but I've forgotten
the "why" he told us. An extra 15-20A of 12V is easily worth the drag of
the turning screw.....

Add comment
Peter Bennett 26 February 2005 22:41:04 permanent link ]
 On 23 Feb 2005 10:04:20 -0800, dbohara@mindspring.­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.

I had a Yamaha 30 with a 2GM, and I'm sure I got about 1.5 _litres_
per hour. I normally cruised around 2500 rpm, if I recall correctly.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-we­bpages.com/nnq
GPS and NMEA info: http://vancouver-we­bpages.com/peter
Vancouver Power Squadron: http://vancouver.po­wersquadron.ca
Add comment
Brian Whatcott 27 February 2005 00:53:51 permanent link ]
 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>
<dbohara@mindsprin­g.com> wrote in message >news:1109181860.22­7648.46240@o13g2000c­wo.googlegroups.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.>>

Add comment
Rhys 27 February 2005 07:17:06 permanent link ]
 On Wed, 23 Feb 2005 23:51:31 -0500, "Doug Dotson"
<dougdotson@NOSPAMc­ablespeedNOSPAMcom> wrote:
"Wayne.B" <waynebatrecdotboat­s@hotmail.com> wrote in message >news:i6kq11hh2qp1s­qhejgfdfqlk60nh0apig­v@4ax.com...>> 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.

Add comment
Wayne . B 27 February 2005 10:39:27 permanent link ]
 On Fri, 25 Feb 2005 20:23:14 -0500, Larry W4CSC <noone@home.com>
wrote:
The mechanic said it >wouldn't be good to freewheel that shaft all the time, but I've forgotten >the "why" he told us.

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

The reason is that the tranny depends on being powered by the engine
to receive proper lubrication. You will definitely shorten the life
of the transmission if you allow the prop to free wheel for long
periods of time.

Add comment
Larry W4CSC 27 February 2005 17:29:59 permanent link ]
 Brian Whatcott <betwys1@sbcglobal.­net> wrote in
news:l1o121hlub4e80­2dbcs9ielnp777ps2p19­@4ax.com:
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....

Add comment
Jere Lull 8 March 2005 11:09:45 permanent link ]
 In article <1109181860.227648.­46240@o13g2000cwo.go­oglegroups.com>,
dbohara@mindspring.­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.>

You've got it, I think, but I suspect the 1.5 GPH. We don't burn 1 GPH
until we're at max throttle, which gives us a solid 7 knots.

Xan's numbers are similar to yours; I've been tracking our usage over
1200 hours and a dozen or so years. Ours is a 2GM20F; best prop we used
was a 15x11" 2 blade. They recommend 16x10, which I'd prefer.

At 6+, we burn about 0.6; 5.6 = ~.33; 5.3= ~.25; 5=~.20. Below 5, no
noticable improvement as we're only turning about 1500.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.­net/jerelull/X-Main.­html
Our BVI FAQs (290+ pics) http://homepage.mac­.com/jerelull/BVI/
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GYXU > Boats > Fuel economy while motorsailing 8 March 2005 11:09:45

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