Endurance vs. Range

[rlb2252]

Fuel burn at idle and low speed. A question of endurance versus range.

I put a deposit down on my first boat--at long last. I?m taking it on a river trial tomorrow. If I close the deal, I?ll be spending a lot of time learning the boat and boating in general.

I?m not going anywhere in particular, I'll likely just putter around the harbor in circles. I just want to keep the engine running for the longest period of time for the least amount of gas?while I practice.

Manuals give the best rpm for cruise fuel economy. But what about at low speed, say 10-15 mph in a cruiser capable of 30 or 40 mph.

I understand that from a distance stand point you?ll cover more ground at the ideal cruise speed. But what about endurance. For maximum endurance must you operate at a much lower rpm than best cruise.

 

[Bifflefan]

Re: Endurance vs. Range

Thats something your going to have to learn with your boat. depends alot on alot of things. wieght, prop pitch, wind, load, and so on.
As a general rule for all engines of this style, less is more until you go to low.
That means low rpms but not to low. id guess that below 1200ish the fuel consumption is more then just above 1200. Cruise is a happy medium between speed and fuel cons.

 

[Numlaar]

Re: Endurance vs. Range

well the best fuel economy will obviously be at idle, but you won't get very far...

Wide Open Throttle (WOT) will obviously be the worst, thats why there is an "optimum" cruising RPM. It should be the lowest hull speed of the boat that will keep it on place without over revving the RPM's..

If you were to try and go 10-15mph in a cruiser rated for 30, I doubt you would actually be up on "plane" and more "plowing" the water with the bow sticking up in the air... This actually burns a ton of fuel because it is making the engine work very hard to keep forcing the boat to go against the water, when it wants to get up on plane.

When the boat is up on plane, you'll get less hull resistance, and better fuel economy than if you were plowing along.

typically you go 3/4 to full throttle to get the boat up on plane as quickly as possible, than back off the throttle till your optimal cruising speed, and you'll be where you need to be for fuel economy... unless you just want to putter around at idle/no-wake.

Hope that makes sense.

Num

 

[rlb2252]

Re: Endurance vs. Range

typically you go 3/4 to full throttle to get the boat up on plane as quickly as possible, than back off the throttle till your optimal cruising speed, and you'll be where you need to be for fuel economy... unless you just want to putter around at idle/no-wake.


Num

Puttering around at idle with no wake will probably be part of my day as well. I'm really just trying to learn how to handle the boat, especially docking and low speed maneuvering.

Sounds as if plowing around at 10 or 15 guzzles gas. But put-putting around at 5 or less would give you max endurance.

 

[Numlaar]

Re: Endurance vs. Range

Puttering around at idle with no wake will probably be part of my day as well. I'm really just trying to learn how to handle the boat, especially docking and low speed maneuvering.

Sounds as if plowing around at 10 or 15 guzzles gas. But put-putting around at 5 or less would give you max endurance.

Yeah... its hard to say really because every boat is different, as bifflefan mentioned, its just something you'll have to get used to with your particular boat, through trial and error..

There is a optimal "off plane" speed you can run for idling around, then the optimal planing speed, so the curve for it is more like an a sideways S i would imagine...

Basically, you'll be able to tell when your idling around, just keep bumping up the throttle a bit to go a little faster... once you see the bow start to raise up, and you start kicking out a decent wake, the boat is starting to "plow" and you'll you know you need to back it off a bit for slow moving around.

Then of course when you want to go fast, you have to get over that "hump" and get the boat up on plane, then as I mentioned above, you find a nice cruising RPM where the speed is good for you, motor isn't over working, and the boat will stay up on plane for you. If you back off too much, it'll break plane and start to plow again.

 

[dmccaffrey]

Re: Endurance vs. Range

Fuel burn at idle and low speed. A question of endurance versus range.

I put a deposit down on my first boat--at long last. I?m taking it on a river trial tomorrow. If I close the deal, I?ll be spending a lot of time learning the boat and boating in general.

I?m not going anywhere in particular, I'll likely just putter around the harbor in circles. I just want to keep the engine running for the longest period of time for the least amount of gas?while I practice.

Manuals give the best rpm for cruise fuel economy. But what about at low speed, say 10-15 mph in a cruiser capable of 30 or 40 mph.

I understand that from a distance stand point you?ll cover more ground at the ideal cruise speed. But what about endurance. For maximum endurance must you operate at a much lower rpm than best cruise.

Take a look at this performance report from Yamaha. Granted, it's for an outboard motor and a completely different type of boat but the principles shown are the same for any planing hull.

http://www.yamaha-motor.com/assets/...in_4stroke_hpv6_sws2_sct-222abaco-f225txr.pdf

As you can see, the best MPG is achieved at almost dead idle (1000 rpms). Of course you are only going 5 mph but you are getting 4.4 mpg. The second best MPG is at the slowest planing speed - in this case about 25. It's a little worse than dead idle (3.5 mpg) but you are going 5 times faster.

The worst milage will be when you are in between the two, such as your requested 10-15 mph. At that speed, the boat is pushing a big hill of water in front of it and the milage plumets to a low of 1.9 mpg at 10 mph.

 

[tboltmike]

Re: Endurance vs. Range

Good points on fuel consumption.

However, slow operation leads to carbon build up. Carbon has a way of sticking rings and result in piston/cylinder scuffing. There are some de-carboning discussions on this site.
May affect the heat of the plugs you should choose.
May want to consult on this for your engine.
Mike

 

[rp23g7]

Re: Endurance vs. Range

I just tested this on my boat.

We have a 17 ft Starcraft I/O Bowrider with a 24 gallon tank and a 3.0.

Last friday, we went out tubing for 3 hrs. 5 people, 3 in the tube and two in the boat. So, lots of time at 3000 rpm, and some plowing.

Filled up before, and the next day, used 8 gallons.

The next day, Seafair saturday for you seattle people. We spent the day at 1800 rmp, going to the airshow in Lake Washington, around Lake Union, and out the Locks to downtown and back. It was to rough in the sound for 7 people in the boat to plane comforatbly so we went there are back at 1800 rpm too. Fun.

Probably a distance of 30 miles total, used 16 gallons.

 

[tboltmike]

Re: Endurance vs. Range

Several of the GPS companies have fuel flow meters that connect the display and with the GPS data will calculate mpg, gph, tank level, etc.

 

[Lion hunter]

Re: Endurance vs. Range

Alot is going to depend on the type of motor you have as well (i/o, 2 stroke or 4). 2 strokes are not made to idle all day, they need to be hot enough to burn off the oil used for lubrication. That's not to say they can't do it, but you need to oopen them up at least before you put them away for the day. 4 strokes can idle all day with no ill effects. As far as the most effecient speed that will get you some where, every boat is going to be different based on how it planes. At idle the boat is flat in the water, it will continue to be that way up to a certain speed at which time the bow raises and the stearn sucks down. At that point you are pushing at wall and fuel economy is going to suffer. The next step up puts the boat on plane, this is probably the best point in speed vs economy. Next is WOT. You have to find out what your consumption is at those 3 points to optimize your fuel. Say it's a 100hp and the theorectical fuel use is 10 gal/ per hour at WOT which also correlates to 30 mph. You can 1/2 your fuel use by going 10 mph using only 5 gal/hr. You need to go 30 miles down the lake. At 30 mph you'll be there in 1 hour and use 10 gal of fuel. At 10 mph it will take 3 hours to get there and use 15 gal of fuel. Better fuel consumption doesn't always = using less.