|
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, -- =-------------------------------------------------= Renewontime A FREE email reminder service for licensed mariners http://www.renewontime.com =-------------------------------------------------= |
|
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. |
"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 |
|
|
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. |
On Thu, 24 Feb 2005 20:26:42 -0500, Jeff Morris
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. |
In article ,
Jeff Morris wrote: 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. The analogy is driving a Viper with skinny tires that light up every time you try to apply throttle. KeS |
|
Rich Hampel wrote:
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. Do this in calm conditions, and do not use a gps, you want water speed, here. -TK The data points (well below hull speed) will describe a straight line The faster you go in that range, the more fuel it takes to cover a given distance, on a more or less linear scale. .... 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. Well, you will actually, but the extra fuel will knot buy much. (ouch!) Hmm, sounds like a fore and aft inclinometer might be calibrated to read efficiency. My old Omni had an efficiency indicator on the dash. -TK Go to your engine manual and look at the power curve HP vs. rpm. vs. GPH. The height (or depth) of the wake might also serve as a rough economy guide. A 4" high wake means you have depressed an equal amount of water downward, and it rebounds. The amount may be taken as the displacing weight, the length, shape and speed of the boat and possibly the depth and width of any canal will determine the frequency of vertical oscillation of the water. The speed will be indicated by the height of wake behind the boat in calm water. That could be indicated with a calibrated laser indicator illuminator. Anyone got math enough to calculate resonance effects of a mass of water in water, Q of the tank, and energy input efficiency for a wave making machine? There comes a longer hull bulb bow shape and wave mechanic where the bustle is patted along by the wake, like pushing a child on a swing, and a hull is designed for one most fuel efficient speed. Exhaust bubbles underwater may lubricate the hull, or ameliorate water acceleration dynamics in a lumpy hull, gas being compressible. Skin friction is different from displacement resistance, which equates partly with the amount of wake left behind. Or Would the speed of the wake oscillation be determined only by the length of the wave, or height of the oscillation, akin to a pendulum's length in some way? The Q may have an effect, if you consider the shape of the tank. A hemispherical bowl barely bigger than the boat will be one limit, open ocean the other. A tennis ball in such a bowl of water on a vertical motion table might give some data, but might it all just sit still while being externally agitated? How about dropping a blob of cream into a cup of still coffee, or coloured water into clear? Somewhere therein lie the secrets of hull efficiency when in displacement mode, for all hull shapes including those that get narrower. I think it boils down to skin friction, cavitation constants and force applied to the water, moving it around the hull as it passes. Since water cannot be compressed, it can only move out of the way in an essentially vertical direction, like water pushing up and down in a convoluted pipe. How slippery is a pressure wave in water? The bigger the wake, the more energy input required for the inefficient wave maker machinery. Sounds like a fun project for a math student and a couple of laser pointers, or an array, calibrated to measure wave height, a la dam busters' spotlights. All we need now is a calm day, a boat, some notepads and a case for buddies to argue over. A sextant might measure certain angles. Oh, and a research grant and credentials to request funding for such a question about steamboats, like it's never been done already. The question about bucking currents and fuel efficiency is a different one, related slightly to the silly train collision question, recalled below, with a hint to an outside the box solution. (If you were making a low budget movie about a train collision, how would you minimize fuel requirements for the locomotive if plenty of track was available, but a certain speed was required to propel shrapnel impressively? It too boils down to Delta-vee, time and acceleration, all rocket science, vs accountants' hourly wages.) The best fuel economy for a motorsailer is to sail. If you have to ask about the price of the fuel, you can't afford to sail. I used about 3 gallons of gas last year, how long would it take for me to recoup the conversion to diesel? Please include the cost of a new knot meter, since I don't have one, and testing requirements to calibrate present fuel consumption documentation and financing cost, including lost income. Cruising means sailing nowhere special, at economical speed, including the mental effort. Why do you think sailors cruise? Terry K 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. |
"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in
: 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. |
Wayne.B wrote in
: 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..... |
"Larry W4CSC" wrote in message ... "Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in : 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. We have 2 95 gallon tanks. Great cruising range but having that much fuel when one only consumes 1 GPH has it drawbacks. Doug |
On 23 Feb 2005 10:04:20 -0800, 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 |
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. |
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. |
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. |
On Fri, 25 Feb 2005 20:23:14 -0500, Larry W4CSC
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. |
"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in
: We have 2 95 gallon tanks. Great cruising range but having that much fuel when one only consumes 1 GPH has it drawbacks. Doug Fuel polishing is probably an issue, mostly ignored by sailors until it's clogged the injectors or at least the filters. It always disturbs me how so many sailors will just leave the tanks half empty all the time, instead of topping them off before docking. Being down a gallon or two is probably ok, but the condensation in a half-empty fuel tank of any size is just awful here in Charleston. It's just laziness. All those that have half empty fuel tanks all have plenty of money to fill them. http://www.gulfcoastfilters.com/fuel_polishing.htm |
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.... |
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. 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/ |
| All times are GMT +1. The time now is 10:26 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 BoatBanter.com