I was wondering if anyone knew approximately how many nautical miles 3 gallons of gas will take you for a 2-stroke engine?
dlankow@babson.edu
Gas Mileage
Moderator: Jim Walsh
-
Ken Coit
Re: Gas Mileage
Doug,
We would need more info to give you anything close to a correct answer.
For example, my 150 HP Yamaha fitted to my Grady White 204c, can gulp 15 gallons an hour at 35 MPH. In that case, 3 gallons would take us about 7 miles. It does better at slower speeds. I think that at hull speed, about 5.5 MPH, she drinks 2 gallons an hour; that would give us a trip of about 8.3 miles.
I would guess that a 2 HP 2-stroke on a 16 ft. john boat, might push her at 5 MPH or so and drink maybe 3/4 gal an hour, for a 3 gallon trip of 20 miles.
Then there's the questions of weather, water conditions, engine tuning, etc.
I suggest you check an outboard specification to get some idea of the appetite of a well-tuned engine. That is probably your best gauge.
Ken Coit
Raleigh, NC
parfaitNOSPAM@nc.rr.com
We would need more info to give you anything close to a correct answer.
For example, my 150 HP Yamaha fitted to my Grady White 204c, can gulp 15 gallons an hour at 35 MPH. In that case, 3 gallons would take us about 7 miles. It does better at slower speeds. I think that at hull speed, about 5.5 MPH, she drinks 2 gallons an hour; that would give us a trip of about 8.3 miles.
I would guess that a 2 HP 2-stroke on a 16 ft. john boat, might push her at 5 MPH or so and drink maybe 3/4 gal an hour, for a 3 gallon trip of 20 miles.
Then there's the questions of weather, water conditions, engine tuning, etc.
I suggest you check an outboard specification to get some idea of the appetite of a well-tuned engine. That is probably your best gauge.
Ken Coit
Raleigh, NC
Doug Lankow wrote: I was wondering if anyone knew approximately how many nautical miles 3 gallons of gas will take you for a 2-stroke engine?
parfaitNOSPAM@nc.rr.com
-
Larry M
Re: Gas Mileage
As Ken mentioned there are many factors but the link below should give you a starting pointDoug Lankow wrote: I was wondering if anyone knew approximately how many nautical miles 3 gallons of gas will take you for a 2-stroke engine?
-
JimL
Funny you ask that, I ran a few tests....
Cruising my CD25 in near zero wind, swell 2-3 feet, speed 3.3-3.6 knots, I calculated my mileage using the GPS and running the engine mounted tank dry (repeatedly). I have a NISSAN 5HP 2-stroke, and it gave me between 9 to 11 mpg (nautical miles). I did about the same test, 25 years ago, with a Coronado 23 and Johnson 9.9. It gave me 8-10 mpg at about 3.5 knots.
I also had a Sea Ray 205 Cuddy with Mercruiser 305 V8. At about 4 knots, it gave me 8-9 mpg (barely above idle)while at wide-open it gave less than 2 mpg. Notice the similarity in fuel burn? You'll see very similar numbers in boat tests, down through the years, in many different magazines. Only the 4-strokes and/or fuel injection make much difference.
The key is throttle opening. Once I ask my 5HP for more than about 1/2 hull speed, the engine really starts taking fuel. At continuous 4-4.5 knots I get about 5 mpg.
I hope this gives you a feel for fuel burn. Remember, if the engine and prop (!) are in decent shape, the fuel consumption will be a function of speed until you get up closer to hull speed. At that point the larger engine can really waste fuel.
Below that, "energy required" is "energy required". Internal engine friction is not a big deal between a 5HP or a 10HP two-stroke.
Also, these carbs are really not tuneable, so the only way you'll do better is switch to a 4-stroke or slow down. One caution: If the carb is dirty, or has a little water in it, the engine will be lean. With a lean condition, you'll add throttle to get the same engine speed, and wind up burning a little more fuel. Ported vacuum over the atomizer jet is too low, when the throttle is opened, without corresponding engine RPM increase (pumping capacity). That results in poorly vaporized fuel, so less fuel can be "more fuel burned" as the engine runs less efficiently to deliver your requested power.
Many carbs have brass jets, which water has a strong affinity for, meaning fuel can't get through the jets. I ALWAYS add a water trap type in-line fuel filter on my outboards. My favorite is the plastic units found on Toyotas from the 80's. The Trucks and Celicas had small fittings (about 1/4") while the Land Cruiser (FJ60 model) had larger tube size fittings and a very deep water trap bowl. These filters will work with up to 6 psi positive pressure or 10-15" hg vacuum. Pay attention to the direction arrow, or it'll pass the water through.
Regards, JimL
leinfam@earthlink.net
I also had a Sea Ray 205 Cuddy with Mercruiser 305 V8. At about 4 knots, it gave me 8-9 mpg (barely above idle)while at wide-open it gave less than 2 mpg. Notice the similarity in fuel burn? You'll see very similar numbers in boat tests, down through the years, in many different magazines. Only the 4-strokes and/or fuel injection make much difference.
The key is throttle opening. Once I ask my 5HP for more than about 1/2 hull speed, the engine really starts taking fuel. At continuous 4-4.5 knots I get about 5 mpg.
I hope this gives you a feel for fuel burn. Remember, if the engine and prop (!) are in decent shape, the fuel consumption will be a function of speed until you get up closer to hull speed. At that point the larger engine can really waste fuel.
Below that, "energy required" is "energy required". Internal engine friction is not a big deal between a 5HP or a 10HP two-stroke.
Also, these carbs are really not tuneable, so the only way you'll do better is switch to a 4-stroke or slow down. One caution: If the carb is dirty, or has a little water in it, the engine will be lean. With a lean condition, you'll add throttle to get the same engine speed, and wind up burning a little more fuel. Ported vacuum over the atomizer jet is too low, when the throttle is opened, without corresponding engine RPM increase (pumping capacity). That results in poorly vaporized fuel, so less fuel can be "more fuel burned" as the engine runs less efficiently to deliver your requested power.
Many carbs have brass jets, which water has a strong affinity for, meaning fuel can't get through the jets. I ALWAYS add a water trap type in-line fuel filter on my outboards. My favorite is the plastic units found on Toyotas from the 80's. The Trucks and Celicas had small fittings (about 1/4") while the Land Cruiser (FJ60 model) had larger tube size fittings and a very deep water trap bowl. These filters will work with up to 6 psi positive pressure or 10-15" hg vacuum. Pay attention to the direction arrow, or it'll pass the water through.
Regards, JimL
leinfam@earthlink.net
-
JimL
One more note about carbs....
I've struggled with many carbs, over the years, on engines that were running poorly. An easily overlooked area is air bleed passages into the atomizing port from the mainjet. The aluminum will slowly corrode shut (these passages are not submerged in gasoline) resulting in insufficient air for the fuel being lifted from the jets. The droplets of fuel are too large to completely vaporize so the engine runs lean with a wet, oily exhaust and not enough power.
Exhaust cooler plates get hotter, and you may see paint baked off around the exhaust port area of the engine. This is occurring due to late and slow burn of the gasoline (still burning when it gets pushed out the exhaust port). It'll really coke up a lower unit, as well.
The only way I've found to clean these is phosporic acid solutilons such as naval jelly or some aluminum wheel cleaners. Some carbs have enough room to stick small stiff wire (from paper label tags) through the passages.
Some very basic carbs don't have these passages.
Regards, JimL
leinfam@earthlink.net
Exhaust cooler plates get hotter, and you may see paint baked off around the exhaust port area of the engine. This is occurring due to late and slow burn of the gasoline (still burning when it gets pushed out the exhaust port). It'll really coke up a lower unit, as well.
The only way I've found to clean these is phosporic acid solutilons such as naval jelly or some aluminum wheel cleaners. Some carbs have enough room to stick small stiff wire (from paper label tags) through the passages.
Some very basic carbs don't have these passages.
Regards, JimL
leinfam@earthlink.net
-
Doug Lankow
Re: Gas Mileage
Ken et al,
This provides a good starting point. My engine is an 1984 Evinrude 6 H.P. and it moves pretty slowly (I would guess maybe 3 knots or so on average). I am planning to go a distance of 15 - 20 nm and may rely extensively upon the engine as it is not a pleasure sail but a delivery of sorts (for winter storage). I have a 3-gallon tank and then an auxillary I will bring which holds 2 gallons. I am thinking I will have enough with the 5 gallon total.
Thanks for the information,
Doug
This provides a good starting point. My engine is an 1984 Evinrude 6 H.P. and it moves pretty slowly (I would guess maybe 3 knots or so on average). I am planning to go a distance of 15 - 20 nm and may rely extensively upon the engine as it is not a pleasure sail but a delivery of sorts (for winter storage). I have a 3-gallon tank and then an auxillary I will bring which holds 2 gallons. I am thinking I will have enough with the 5 gallon total.
Thanks for the information,
Doug
Ken Coit wrote: Doug,
We would need more info to give you anything close to a correct answer.
For example, my 150 HP Yamaha fitted to my Grady White 204c, can gulp 15 gallons an hour at 35 MPH. In that case, 3 gallons would take us about 7 miles. It does better at slower speeds. I think that at hull speed, about 5.5 MPH, she drinks 2 gallons an hour; that would give us a trip of about 8.3 miles.
I would guess that a 2 HP 2-stroke on a 16 ft. john boat, might push her at 5 MPH or so and drink maybe 3/4 gal an hour, for a 3 gallon trip of 20 miles.
Then there's the questions of weather, water conditions, engine tuning, etc.
I suggest you check an outboard specification to get some idea of the appetite of a well-tuned engine. That is probably your best gauge.
Ken Coit
Raleigh, NC
Doug Lankow wrote: I was wondering if anyone knew approximately how many nautical miles 3 gallons of gas will take you for a 2-stroke engine?