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Thread: Jet Boat Fuel Consumption - Need Impeller Rebuild?

  1. #1
    Member AK_Kid's Avatar
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    Default Jet Boat Fuel Consumption - Need Impeller Rebuild?

    Hey guys,

    I'm running a 21' 2003 North River Commander. It has a 330 HP, 5.7 L 350 with just over 300 hours and a Hamilton 212 jet. We bought it in the spring and ran it on the Yukon/Nowitna this fall. We were really pleased with how it performed with two exceptions. First, it tends to porpoise before you get to WOT, particularly under load. We installed trim tabs over the summer, so that's not the end of the world.

    More concerning was the fuel consumption. We were hunting moose and running pretty heavy (both ways, fortunately ). WOT is about 4100-4200 RPM. We ran at about 3800 RPM. Ended up running about 29 MPH on average and burning about 14.5 GPH. We were hoping to get between 3 & 5 MPG, but only ended up getting 2 GPH. That was disappointing.

    Questions for those of you with more experience than I have: Am I correct that should have been getting a bit better mileage? Any idea how much better? We had two guys, TONS of food and gear, an extra 115 gallons of gas, Zodiac, generator, etc.). Somebody suggested that we probably need to have our impeller rebuilt considering the hours on it, RPMs, and fuel consumption. How do I know if that's legit? Other ideas about why our fuel economy might not be great or what we can do to improve it?

    Thanks.

  2. #2
    Member Music Man's Avatar
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    In glacier fed rivers you will probably need to have the impeller rebuilt every 3 years. or every 100 hours to maintain peak performance. Take it to Greatland welding, they can evaluate it for you.
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

  3. #3
    Member Dupont Spinner's Avatar
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    I have pretty close to the same boat.I have a '97 NR w/ the Big Block. WOT throttle I burn 14 to 16 gallons per hour and the boat will reach 57 mph (GPS) on Big Lake with a new sleeve and a perfect impeller. We run about the same rpm's but I have a little more pitch. So I will run a little faster at the same rpm's. My normal cruise is 3,000 rpms. So here is a couple of things.

    You said it porpoises at speed. Your are most likely running bow high. Does the trim tabs fix it? If not you can turn your nozzle over 180*, this helps a bunch. Or you need to put more load on the bow. How much more you ask....on an empty boat (full fuel, some gear and one other guy) I need to load a 150 qt cooler full with water. So roughly figuring about 300 pounds on the nose to be able to run WOT.

    I have my boat setup to run bow high which allows me to run faster at lower rpms. It also will run a little shallower water. Turning the nozzle the other way allows me to carry a heavier load and gets on step easier.

    Now to your impeller question. Look thru the nozzle if you DO NOT see a lot of heavy gouges or nicks then impeller is most likely fine. Probably a little file cleanup at home. BUT>>>>>your sleeve is most likely in need of a change.

    I bet if you add everything up that you took on your trip you were most likely at and maybe even a little over weight. Funny thing is boats over 20 feet do not require capacity plates. So what is over weight???? Just in extra fuel alone you have 800 pounds. Guessing at the rest for gear another 1500 to 2000 lbs in gear. So you roughly doubled the weight of your boat empty. Turning 3800 rpms is pretty much WOT. A difference of 300 to 400 r's means very little in fuel consumption.

    You want to get out and run together to compare notes before freeze up let me know. Or someone to look over your 212. I do all my own impellers and sleeves.

  4. #4
    Member alaskabliss's Avatar
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    With the same boat for the most part, 21' Tjet 330hp 350 with a 212, you are running a little more fuel than normal but not much. From the factory mine would max out at 4150 rpm's. Fuel burn at wot with a flow meter was 19gph. Running super heavy, as in very hard to get on step, I burn about 12 gph at 3600 rpm and about 28-30mph. I would definitely think about a new sleeve and rebuild but I don't think it is a must at this point. The one variable to throw in is your trim tabs. If you have them below the water line while cruising you are creating drag and that will kill fuel consumption numbers.
    I have never had a porposing issue unless I loaded it poorly. Easy to do sometimes. On big load trips on the Sue I put what I can in the bow like propane tanks or fuel cans. I like the water line under the boat to start right about under my feet. There are times I would like trim tabs but would mostly use them to get on step and then retract them for a smooth clean hull.
    Ignorance is not Bliss, it's insanity

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    Member DanielApplin's Avatar
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    I don't think 5 mpg is possible even if your boat was empty, wot seems dead on and if your not cavitating your impeller is fine. 2-2.5 mpg is accurate for your boat loaded down, dont sweat it

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    Member Music Man's Avatar
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    Quote Originally Posted by DanielApplin View Post
    I don't think 5 mpg is possible even if your boat was empty, wot seems dead on and if your not cavitating your impeller is fine. 2-2.5 mpg is accurate for your boat loaded down, dont sweat it

    Just because it doesn't cavitate doesn't mean that the tolerances are good.
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

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    Member DanielApplin's Avatar
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    Quote Originally Posted by Music Man View Post
    Just because it doesn't cavitate doesn't mean that the tolerances are good.
    Of course, I agree but is a good warning sign, and with no mention of the issue with a really heavy load and listed fuel numbers I don't think there is an issue

  8. #8
    Member Music Man's Avatar
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    300 hours without a rebuild of the impeller is to long unless it is all clear water running. Take it to Greatland and have them check the tolerances!
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

  9. #9
    Member Yukoner's Avatar
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    2 MPG loaded would be on the mark, maybe a bit low, but you did say 3800 RPM. My 350/212 in a 20' Wooldridge will run at 3200 RPM, 4 adults, gear, full fuel and a moose, and. 3200 gives me 3.125 MPG. 260 hours on the engine and pump.
    Never wrestle with a pig.
    you both get dirty;
    the Pig likes it.

  10. #10
    Member alaskabliss's Avatar
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    Mine never cavitated really, it was an increase of RPM at WOT that showed I needed a rebuild. After 300 hours I am sure it is due. $500 rebuild can pay off in a hurry.
    Ignorance is not Bliss, it's insanity

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    Member AK_Kid's Avatar
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    Many thanks to all of you for sharing some knowledge with a newbie. I swear, I don't know what guys did to get good AK outdoor advice before the forum.

  12. #12

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    A 212 rarely needs a new sleeve so at most you'll probably just need an impeller rebuild. You should have the 2.4 turbo impeller which should hold the engine back at ~4200 @wot so you don't sound to far out of spec. If you bring the impeller by Ak Frontier Fab we can measure it to see how far out it is from spec. Diameter and blade length are what's critical.

  13. #13
    Member Yukoner's Avatar
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    Thought I would share some new data.
    Since my hull mod that I posted on the modifications forum, I have two longer trips under my belt, and my new MPG data is 4.0 MPG, up from 3.125. That's derived from distance covered and USG consumed. Cruising at 2900 RPM, 3 guys, full fuel, camping gear, but no Moose (sadly).
    Obviously it's not accurate to compare between boats, but it gives an idea of what similar set ups are getting.
    Never wrestle with a pig.
    you both get dirty;
    the Pig likes it.

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    Member Akgramps's Avatar
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    Quote Originally Posted by Yukoner View Post
    my new MPG data is 4.0 MPG, up from 3.125.
    WOW, thats a substantial improvement....!
    “Nothing worth doing is easy”
    TR

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