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Thread: Fuel Consumption

  1. #1
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    Default Fuel Consumption

    I'm sure this is an old group of questions from a newer boat owner, but here it goes. I'm running a 2006 24' north river with the OS bracket with twin Suzuki 140's. The boat is over 7000 pounds dry.

    We just ran 160 miles this weekend and burned 90 gallons of gas. I ran at 4500 RPM's and was cruising around 20 to 22 knots. The boat seemed bow heavy and acted like it wanted more power.

    Here are some of my questions:

    Does running at higher RPM's at a faster speed balance out with the distance traveled?
    Can you recommend a fuel management system, or do i even need one?
    What should be the range on this boat with 100 gallons of fuel?
    Do most guys carry extra fuel when going out to the blue water?


    I guess I'm a little concerned because a friend of mind is running a 24 foot kingfisher with a single 200 HP Honda and he runs at 30 knots with less RPM's and burns have the gas. Why?

    I'd appreciate any advise or suggestions that you have.

  2. #2
    Member spoiled one's Avatar
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    Lots of variables here. Those 140s are light motors, but have a great reputation. You mentioned that you were bow heavy. Do you have trim tabs and were they trimmed down at all? At what level do you keep your motors trimmed? What is your WOT rpms? ( you want to be in the upper half of the manufacturers recommended rpms) What size props are you running? Fuel management gauges really make a difference and will pay for themselves over a season. Pretty cool tool.

    A big single will get better mileage than a set of twins with a combined, similar horsepower. Nice boat by the way.
    Spending my kids' inheritance with them, one adventure at a time.

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    I'm not sure what the WOT really is? Here is a link to the DF140 -http://suzukimarine.com/df140-115-100/features/. It saying that Operating range is 5600 to 6200. Isn't that going to really eat the gas? Thanks for your help by the way.

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    Member jrogers's Avatar
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    WOT is Wide Open Throttle. It is important to make sure you are getting the correct RPM's at full throttle so that you are propped correctly. Being propped correctly will effect both fuel mileage and engine life.
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    Kasuun....what Spoiled One is trying to say it that at full throttle (or in boat speak wide open throttle) you should be hitting the upper half of 5600-6200rpm. I'd prefer you be close to 6200rpm and that's running with a normal operating load (it appears JRodgers already covered this ) . What that's telling you is that your motors aren't lugging down from being over propped and over loaded. Also, as he said fuel management gauges are one of the more important gauges on my boat. Ohhh and he's right that a single big main is more effecient than twins any day of the week.

    From what you descibed I don't think your setup is too far off. I have a 26ft Pacific Cruiser with twin 150hp Yamahas. I burn 14-15gph at 30mph. Basically I average just over 2mpg. I could be propped better but I'd bet if I was propped right we'd still get 2.25mph at best. I'm not much heavier than 7000lbs running weight with a full load of gear, 2 adults, 1 young kid, 3 dogs, and enough stuff for a 3 day weekend. If you're lucky you should get 225 miles to a tank and that's if you're doing nothing but cruising. Factor in screwing around and such and I'd say 200 miles is your effective range.

    Get a good set of gauges, figure our the right prop and learn how to maximize your mileage. That way you'll feel confident about staying out for long trips. As Spoiled One said, nice boat. I used to love those NR boats. Nice lines...and tight lines! Look me up if you ever want a running partner.

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    General rule of thumb is if you run your boat with the motor close to wide open is it will burn 10% of the HP rating in gallons. For example, a 200 hp motor will burn 20 gallons per hour WOT, a 250 hp would burn about 25 gallons per hour.

    WOT you should burn about 28 gallons per hour, maybe 16-22 while cruising (using both 140 hp motors). For a 7,000 pound dry boat weight with 280 hp you are about average for power.

    It is amazing how much weight your boat will gain as you own it as you add this, that, etc. Personal opinion is you are close to having the minimum power you need to operate that boat safely. Less than 250 hp and you would most likely hate it. But twin 175's would be about perfect and allow you to cruise at lower rpm's and maybe better fuel economy.

    I bet with full fuel tanks, water, gear, and a couple of people your boat weight is close to 8,500 pounds. Like others mentioned, if you don't have trim tabs installed, add them.
    Tennessee

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    Member SkinnyRaven's Avatar
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    If you felt bow heavy I suspect you were not trimmed correctly (always depends on the water conditions) more boat in the water = more drag = lower speed = more fuel consumption. Once on step slowly trim the engines up, notice the rpm and speed change, when you get to a point where you have an rpm increase with no speed increase (or loss of speed) you have gone too far, ease back on the trim. This will be your optimum trim for the current conditions, you will feel the difference, better handling and fuel economy. You also need to be able to reach the manufactures maximum rpm range whether you run there or not. You are overloading the engine at all rpm if you can not reach the maximum. Check for performance bulletins on your setup, confirm proper engine mounting height before changing props, most dealers use a conservative mount and more than likely they are mounted as low as they will go.

    I had the local dealer mount mine per the Yamaha performance bulletin and saw an increase of 300 rpms.

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    Question on the note of trimming, rpms, and fuel consumption. I have a 27' seasport with a volvo diesel. WOT running about 3700 to 3800, and about 24kts. i have messed around with triming up the od, and bringing the trim tabs all the way up and back down as little as possible to even out the ride. I have no idea of fuel consumption, but would always like to get a little better, any ideas. In kodiak, i don't run more than 5 or 10 miles for a whole day of fishing, but somedays more.

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    I think the best part of getting our boat has been learning how to operate it and the willingingnes of other boaters to help out. I'll look for you on the water. Thanks.

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    Member JR2's Avatar
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    I am with the others and say you need to trim out your boat a bit better. I adjust the trim all the time to keep the fuel consumption and ride were I want it. When I first got my boat I was running across the water and watching the fuel consumption numbers on my gauge. I was showing 1.8 mpg and going 25 mph... I tipped the motors up about 5 inches and went to 2.2 mpg and 28 mph... faster and better economy... I have factory gauges that show fuel consumption on my Honda's but you can get a flo-scan gauge and hook it up and see what is really going on.
    2007 Kingfisher 2825 - Stor Fisk

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    I have a single suzuki 140, at cruise it burns 6gph, wide open 12 gph. Depending on how heavy I'm loaded and the prop, cruise is 4000-4400 rpm @ 22 knot, wot is ~6000 rpm @ 30 knots. For fuel management I'm using a lowrance lmf-400, it communicates directly with the engines computer and get's fuel burn from the engine, it's been spot on. It also works as an accurate fuel gauge, you enter the size of your tank and tell it when you've filled up, and then it subtracts fuel as you burn it.

    If your gps is NMEA 2000, you can hook it up the lmf-400 and it will calculate your mileage. For me the mileage doesn't change too much between a fuel burn of 6-9 gph, but that last bit of throttle doesn't gain me much speed, but burns alot more gas.
    Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

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  12. #12

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    One of the best purchases (maybe THE best purchase) was a fuel flow meter. Once installed, and it's easy, you can play with the trim tabs and engine trim to find the best trim and fuel usage. My fuel flow meter also tells me how many gallons I've used which is important since my fuel gauge is not something that I trust.

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    When I got my current boat, I also was not happy with my fuel burn, RPM, etc... One I learned how to adjust my trim and watch the bar meter for the tilt, watch my fuel flow meter, I found out my WOT was at 6000 RPM and I was cruising at 5100 RPM burning 12-14 GPH at 30 mph with twin 115's with a 15 pitch prop. I got few 17 pitch props both 3 and 4 blade solas ss props. With the 4 blade 17 pitch my RPM's running 4300 rpm at 30 mph burning 11-12 mph. My WOT was 5700 rpm. This set up along with learning how to trim my motors has reduced my RPM, Fuel Burn, and made me a happy camper. It took a little time playing with props, etc... but it was worth iti. Lots of help from this forum got me there. Good Luck

  14. #14

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    Quote Originally Posted by skydiver View Post
    One of the best purchases (maybe THE best purchase) was a fuel flow meter. Once installed, and it's easy, you can play with the trim tabs and engine trim to find the best trim and fuel usage. My fuel flow meter also tells me how many gallons I've used which is important since my fuel gauge is not something that I trust.
    Got to 100% agree, best thing along with my Wallas Stove was a FloCan meter.
    2800 rpm goes 8mph @ 3gph
    3200 rpm goes 9mph @ 4gph
    3900 rpm goes 12mph @ 7gph
    40 gallon tank over the 4th went 88 miles burned 28 gallons, which is the important part, If I had know how useful the meter was I would of yanked my fuel gauge and not made a new hole in the dash.

  15. #15

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    Been trying to guage my boats fuel consumption, 20 ft Koffler Bay Bee with twin Honda 45.s at 4500 RPM 22 MPH I used 6.78 Gallons. In 2 hrs 5 minutes. Sounds lo lo but started with a full tank and finished with a full tank both to over flow on gas tank.
    Lighty lowded with 3 peopl min. gear. Installed a remote fuel guage, had only a guage on belly tank. Guessing that high consumption with heavy loads should be under 5 GPH.

  16. #16
    Member HuntKodiak's Avatar
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    From what I've read, you can connect a NMEA 2000 network directly to your Suzuki outboards given the proper Suzuki pigtails. If you choose to do this, it will give you a wealth of additional information about your motors ON TOP OF real time fuel consumption rates measured by your outboard's computer.

    If you don't have a NMEA 2000 network on your boat, it's not a difficult thing to install once you buy the components. Then, you can connect all your electronics that are 2000 capable onto the network, and they will share data amongst them.

    I know this goes beyond your question, but I agree with what the others said. Consequently, if you choose to make the leap, direct connection to your motors is superior to installing an in-line flow sensor. Sensors don't fail often, but they do fail. I have a friend right now that suspects his is impeding his fuel flow, and this coincides with him noticing his fuel flow rates are varying. Could be his sensor is starting to fail.

    Just offering you the knowledge of other options, and your local Suzuki dealer would be a good place to start asking questions.

    For what it's worth, I installed a 2k network on my Kingfisher and directly connected it to my 250 Etec. Very glad I did. I display my fuel consumption info and other data (like my engine trim numbers.....another valuable tidbit to repeat the engine trim setting on each outing) on an LMF-200 meter I installed in my dash.

    Good luck, safe boating, and have a blast!

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    Member M Gho's Avatar
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    Hi Kasuun,
    I was in the same boat as you (pun intended) - I have a NR OS 24' with a single Yamaha 225 and after nearly running out of gas from Seward back to Valdez in heavy seas, I bought a fuel flow meter. Like Spoiled One said; it will pay for itself in a season when adjusting speed for long distances. I usually average about 2.2 mpg starting out with a full load, but get around 2.5mpg when 1/2 the fuel is gone. I got a few props- one for light loads and one for heavy loads or heavy seas. Kind of like a downriver and upriver prop. It was pretty easy to add to the Garmin network. As you mess around with your trim tabs the mpg changes, kind of like a video game. It was pretty bumpy last week, and the super steep deadrise of the NR really sticks making an easy ride, but at certain angles in the waves, it just doesn't spin around in the waves like the Wooldridge Sport I used to have. Also, I was suprised to learn with the NR and the fuel gauge, I got better mileage at higher rpms to a point; around 4800-5000 rpms. Also, at slower speeds the fuel meter goes up to 9-13mpg. But who wants to go slow ??

  18. #18
    Member Cliffhanger's Avatar
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    My Honda 225 is one year and a couple of months old. My top end rpm is right are 6000. I started out with a cruising speed of 22mph @4200 rpm and got 2.4 mpg. In the last month that has changed to 1.3 mpg, and my cruising speed is now 26 mph, at 4700 rpm, getting 1.9 mpg.

    What changed?

  19. #19

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    Sell me your bike. I'll pay you a years worth of fuel for my boat! You can use the $$ at Shoreside.

  20. #20

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    My Honda 225 is one year and a couple of months old. My top end rpm is right are 6000. I started out with a cruising speed of 22mph @4200 rpm and got 2.4 mpg. In the last month that has changed to 1.3 mpg, and my cruising speed is now 26 mph, at 4700 rpm, getting 1.9 mpg.

    What changed?
    Jim,

    What type of fuel monitor are you using - information from the motor's computer or the fuel line paddle wheel type? My fuel monitor system from Yamaha uses the paddle wheel type sensor. The number's displayed will bounce around on the low side every now and then. I will have to cycle through the different modes to get back to accurate numbers. Recently I loss the display for mpg and had to reseat the connection from the GPS.

    Just a thought.

    Doug

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