Fuel economy while motorsailing
 

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.

wrote in message
ups.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

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.

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.

There are a couple of simple things you can do that will help you better
understand what the optimum RPM range is for your boat for fuel
conservation/consumption.

What you need a

a. a chart showing your engine's RPM vs. fuel consumption/hr. - this is
available in the Yanmar shop manual. If you don't have this, it's a
great resource and worth buying from your local Yanmar dealer. The
charts you're interested in should be somewhere in the front of the
manual (if memory serves me).

b. another chart showing engine RPM vs. boat speed through the water -
this is something you can easily create on your own. "Chapman's"
describes how to do this, but essentially you'll run a measured mile on
a calm day at various RPM's, clean bottom, clean prop, full tanks.

Armed with these two charts, you'll soon see that there is an optimum
range of RPM's (where both curves start to "flatten out") for fuel
consumption vs. speed made good.

The next step is to compare what the charts say "should be" versus what
your boat actually does by maintaining a log, monitoring your fuel
consumption, and comparing this information with designer specs and what
other similar boats are getting.

In our case (an Express 37 with a 3GM) a quick call to the designer and
a few fellow E37 owners revealed that although our fuel consumption was
about right, our boat speed was about 1.5 knots less than norm. We
later tracked this down to the prop which had been replaced by a
previous owner and the pitch was not as recommended.

Hope this helps,

--

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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
ups.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.

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.

"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.