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Thread: How much gas?

  1. #1
    Member LungShot's Avatar
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    Default How much gas?

    Ok I just bought an 18ft tracker with a 90/65 merc jet (brand new). after breaking it in Im going about 120 miles up a fairly slow moving river with about 500lbs (not including weight of gas) then Im coming back up river with about 1200lbs (not including weight of gas which should be half of the original trip up river). I know this is broad but approx how many gallons of gas am I going to need to bring?

    The max weight of the boat reads 1500 lbs or 7 persons - thats in addition to the motor weight. (1700lbs without motor).

  2. #2
    New member fishnhuntr's Avatar
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    Default Too hard to tell

    Lungshot,
    Too many variables, my .02$, load your boat up similar to what your going to do, make sure she's topped off good, and take an hour trip on your river at what you want your crusing speed to be. See what your burn off for fuel after that and compare with how far you got with a gps if you can. Run the numbers. I would guess a 65 jet w/ 18ft might be ugly consumption wise, but hope I'm wrong. Oh, and then take a little extra for the trip. Luck
    fishn

  3. #3
    Member Erik in AK's Avatar
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    Boats are pigs when it comes to fuel...no way around it

    Mileage with boats is generally a function of RPMs and hull design. Flat bottoms plane with less power than Vee's and light loads take less RPMs to get on and maintain step. With heavier loads more etc. and on rivers you have variables such as current and wind.

    fishnhuntr's advice is right on....test run. But I recommed you run a half hour each way so you average out the upstream and downstream runs. It's totally worth the effort if you're planning a major trip. My guess is at 3/4 throttle you will average 10 gallons per hour under the light load and 12-13 under the heavy.

    Assuming you average 25 MPH on the way up thats just under 5 hours or 50 gallons. Running with the current on the return you will prolly average 27-28 MPH so about 4 hours 20 min...call it another 55 gallons. 105 gallons just to get there and home--granted these numbers are hypothetical and intended to get you thinking the right ballpark--a trip of this length is a major logistical undertaking.

    105 gallons of fuel weighs 631.5 lbs. (6.25 x 105) The weight of all this fuel will impact your fuel economy.

    If your serious about going this far then you NEED to know how much fuel you need. You may want to consider doing some scouting trips and staging fuel along the way or arrange for fuel drop offs if that's an economical choice.

  4. #4
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    Default

    The best investment I made when I bought my boat was a fuel flow gauge. Using that, a GPS for speed, and various props, I was able to find the prop and rpm's that gave the best speed for fuel consumption. It would work the same for your jet.

  5. #5
    New member fishnhuntr's Avatar
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    Default concur

    with nitro, if you really want to get serious about it. I've heard those fuel flow gauges are great, I personally have the smartcraft in my boat that works with my merc optimax and love it, lets me know exactly how much fuel I'm using. Might be a good investment for you, especially if you're taking those long trips. luck

  6. #6
    Member AKBighorn's Avatar
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    Default

    I have never run that size outboard with a jet but my boat with a 175hp sportjet is burning 8.3 gph at 26mph. I thought that was a little high, 10-13 gal. for a 90hp motor just seems a little excessive but like I said, I have never run one.

  7. #7
    Member AKBassking's Avatar
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    Thumbs down $3.00 a gallon

    At these prices or more this summer, I may consider fewer trips and winterizing my boat this summer. Hard to justify filling an 80 gallon tank for a weekend on the water! Sucks!

    ALASKAN SEA-DUCTION
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  8. #8
    Member AKBighorn's Avatar
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    Quote Originally Posted by AKBassking View Post
    At these prices or more this summer, I may consider fewer trips and winterizing my boat this summer. Hard to justify filling an 80 gallon tank for a weekend on the water! Sucks!
    Unfortunately it isn't going to ever get any cheaper.

  9. #9
    Member skybust's Avatar
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    Ya the gas prices do suck but a boat is like a sports car when you get one you realy cant worry about the gas mileage. But I too will be taking less trips

  10. #10

    Default No way to tell

    Even if you and I had the same boat the way we operate it would make a diff. Water conditions, one time it will us 6 gallons next time 8 because of wind and water.
    One thing is change out prop for weight and speeds you want. Jet boats nope, I guess. But there is a ideal RPM / HP range where you can get the best mileage, need to find that sweet spot.
    For prop info look at piranha propellers web site, lots of info. In the bush they go down river with on and change to go up river.

  11. #11
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    Lungshot
    I have a 90/65 merc jet on a 18 foot alumacraft and I always figure about 10 gallons per hour on average.

  12. #12
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    Thumbs up Similar setup

    Lungshot

    ..... about 120 miles up a fairly slow moving river with about 500lbs (not including weight of gas) then Im coming back up river with about 1200lbs ......
    Up and then up farther....? Also 2 or 4 stroke?

    I'm running a Merc 90/65 2-stroke on an 1860 Alumacraft. Averaged out fuel over over 5 days in a row on the Talkeetna and Big Su/Deshka last summer. We ran with 5 big guys, fishing gear, 20 gal gas most days. I would say around 3/4 to 2/3 throttle most of the time (put tach on at end of season). I got around 4.5gph. If you add my weight we were around 1800lbs (w/ mtr) some days....and never had a problem. Of course those are all pretty short runs - 10mi one way, but ran them more than once a day some days.

    I would say we average 21-23 mph up and 28-30 down. So, using those #'s, I'd guesstimate....

    (figuring running up and then back down)
    -5.5 hrs up and 4.5 hrs down
    -@ 5gph you'd need 50gal (but always use 1/3 out, 1/3 back, 1/3 in reserve) - so est. 75gal
    -@ 8lbs/gal that's 600lb fuel up and around 380 coming down
    - which would make total wt approx 1100 up and 1550 down

    Best advise on here has been to make a test run to get an idea how your rig will perform, take a load so you get a feel for that. For me, mine rides rough with much under 1000lbs. Much smoother ride and bettter handling with a load. Also play with positioning your load, good balance will affect your ride, handling and gph. I use moveable seats for my front passengers so I can push them farther forward when needed.

    Congrats on the new boat! Good luck and have fun! Let us know how your #'s come out so we can compare notes. (If that comes close, PM me your e-mail and I'll send you an excel sheet I use to estimate my fuel needs.)

    AK_BigO

  13. #13
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    Talking fuel weights

    Sorry my fuel wts were off...(6.25 vs 8)....that just accounts for the case of beer and all the mud that gets tracked into the boat...

    Or for those of us who weighed ourselves at 200 before winter and are well over that after a good hibernation but are waiting til after hunting season to get on the scales again.....lol

    (That'd leave my 75 gal estimate closer to 460 & 290)

  14. #14
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    Default

    Wow BigO, 4.5 gph is good. I have the same boat and motor as you and I dont get near that. Running with no gear and one other person I'm lucky to get 6 gph. Put some weight in the boat and I run 8 gph on a good day.
    I wonder what the difference is.

  15. #15
    Member LungShot's Avatar
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    Default thanx

    Thanx for all the info. Im glad a couple of you have the same motor so I really can relate with your #'s. I wont be going till late august so I'll let you all know how it went. Thanx again.

  16. #16

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    The 1/3 ,1/3, 1/3 rule is what you want to do for sure it is always better to have extra than to run out 10 mile out.

    I knew I bought the Mokai for a good reason with gas going up I can still play and not kill my wallet, at $3.00 it is only $9.00 to run 8 hours

  17. #17
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    Default How Old is your Motor/Impeller?

    TonyH,

    That was on a brand new motor/impeller last summer. I'm curious to see how my #'s hold up as it gets more broke in. I''ll be logging all my trips this year to get good "over time" estimates.

    I'm thinking on buying a stainless impeller, but haven't seen the need yet. I'm pulling mine next week to check it, so I'll have a good idea how bad it got chewed up in the creeks....

    AK_BigO

  18. #18
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    BigO
    I put a stainless steal impellor in mine and really like it. I run the Tanana river alot so it doesn't dull as fast and my performance last longer.

  19. #19
    Member AKRoadkill's Avatar
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    Default

    So far it looks like my SportJon 210 is getting around 8gph. Meter said alittle over 2 hours and I put in a little over 16 gallons. I'll be trying to keep better track of it for awhile, although it'll probably just disgust me.

    I never figured it out with the Roughneck 1960 with 90/65 I had, but I'm pretty sure it did a lot better than I'm getting now.

  20. #20
    Member LungShot's Avatar
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    Default Good fuel economy

    I finally got out to run my boat around. I filled up one of the 12 gallon tanks thinking I would burn it up in a couple hrs. I had a little gear, and one other guy with me. We trolled for about 5 hrs at 900 to 1100 rpms, then we went from half to three quarter throttle for 5 minutes here 10 minutes there probably a half hour total at higher speeds. When we got back I looked at the tank, and we figure we used maybe 1 - 2 gallons. Thats for almost 6 hrs of putting around! I wasn't expecting that good of fuel economy.

    Im sure that running a river with more weight, and at three quarters throttle will change the amount of fuel used but I really am starting to think I will be more in the 3 to 4 gal per hr range.

    I will do more running to see, and I'll report.

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