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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. |
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#3
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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. |
#4
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#6
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On Thu, 24 Feb 2005 21:22:37 -0800, Skipper
wrote: 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. A friend has a 35 hp Volvo from the late '70s pushing an 18 ton ketch with an AutoProp. He loves it and says the efficiency is huge as is his control. His heavy displacement full keeler now docks like a minivan parks, and he's getting more knots from the same revs. He says that investing in the Autoprop (around $4K Cdn.) saved him from repowering to 55 or 85 HP ($20K-$35K). Yes, he's a liveaboard and knows he's got too heavy a load, but he was sailing here in Toronto yesterday and today...in February...so overbuilt steel has an upside. His one caveat is that he feels he should install both an AquaDrive and a shaft lock to better protect his transmission. As I may buy his boat one day, I keep track of all his mods. R. |
#7
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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 |
#8
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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, -- =-------------------------------------------------= Renewontime A FREE email reminder service for licensed mariners http://www.renewontime.com =-------------------------------------------------= |
#9
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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. |
#10
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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. |
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