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Thread: Thunder Jet load testing

  1. #1
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    Default Thunder Jet load testing

    Today we finally got a chance to see how much our 25 foot Thunderjet Maxim would carry in preparation for our upcoming moose hunt. Boat has the 496 HO connected to a Hamilton 212.

    Filled up 6 - 55, and 3 - 15 gallon barrels with water (calculated weight 3,127). Had about 100 pounds of misc gear on the boat and a full fuel tank (110 gallons). Two adults on board as well. She managed to get on step but it took awhile. Once on step getting to low 30's was pretty easy. Would get on step at about 17 mph. Motor was revving up to 4,400 rpms which surprised me as I was told this motor would not go above 4,200.

    Replacing the water in the barrels with gasoline will reduce the weight by about 850 pounds which we will make up in food and camping gear. Considering we will only have full fuel barrels when we leave the boat launch and Galena and will be going down stream for the first hour after that we will be in good shape. Still, I was expecting the boat to do a little better getting on step but guess it does not matter as we are carrying all the gas we should.

    Is it is the middle of September yet ?
    Tennessee

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    Have you calculated your fuel burn rate (gph) when maxed out like that? Running WOT or close to it with heavy loads seriously sucks the fuel so be prepared for that - I'm sure you already considered this. Good luck with that moose and enjoy!

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    Member f0zzy2's Avatar
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    So what are you calculating your MPG at?

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    Quote Originally Posted by f0zzy2 View Post
    So what are you calculating your MPG at?
    I have no idea, lol. She will stay on step if we back off to 3,200 rpms. Am guessing it will be around 15 gallons per hour when running down the Yukon at about 3,200 rpms. This will put our speed in the low 30's. When we hit the mouth of the Koyukuk with most barrels full and running upstream am estimating 18 GPH.

    Maybe someone with more experience than myself runnning inboard jet boats can chime in to tell me if I am in the ball park. The nice thing about it is she gets lighter every mile we travel (so does my wallet!).
    Tennessee

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    Seems pretty high to me. I bet you get alot better GPH than that. I'm guessing 11-12 going DS and 13-15 going up I'm not a big block guy though. Are you telling me you dont have a fuel flow meter in that new boat yet.

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    Why would you get better GPH burn going down river?

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    No flow scan, maybe next year, maybe not. Sweet spot for the 496 seems to be at 3,200 rpms so will try to keep her around there and see what happens.
    Your GPH is better going down the river because you are not fighting the current. I remember last trip we could run 40 down stream (different boat) yet barely hit 30 running back up.
    Tennessee

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    Hey Randy,
    I did my water test this weekend as well with my 24' SeaArk. Basically the same baseline, although I over loaded with 320 gal of water, 4 adults, 2 kids and gear. Couldn't get on step with all this though. So redid it some and got on step. For me WOT was burning about 15 GPH so I need to back it off some.

    It's not September yet, but you can smell it...
    Tony

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    GPH pretty misleading unless you know how fast the river is flowing. I calculate my fuel buy 2.5 MPG. Last year on the Yukon I ran 27mph going up at 13 GPH and on the way back down I was running 36mph at 8 GPH.

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    f0zzy2,

    What type of boat and power plant are you running?

    If I average 2 MPG in the Thunder Jet I'll be happy. This is a heavy, big boat. 25 feet long with a 9 foot beam and metal roof and fish deck. 9.9 kicker hanging off the swim step as well, 1/4 inch bottom. My gut tells me it is all about RPM's. Get the boat on step and run close to 3,200 and she will do fine.
    Tennessee

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    Quote Originally Posted by tzieli22 View Post
    Hey Randy,
    I did my water test this weekend as well with my 24' SeaArk. Basically the same baseline, although I over loaded with 320 gal of water, 4 adults, 2 kids and gear. Couldn't get on step with all this though. So redid it some and got on step. For me WOT was burning about 15 GPH so I need to back it off some.

    It's not September yet, but you can smell it...
    How mush gas do you plan on carrying? Your boat is pretty light and long so it should carry a fair amount of weight easily. What speeds could you reach?
    Tennessee

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    Member f0zzy2's Avatar
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    I have a Willie Predator with the 200 SJ. I dont carry near the wieght you do only close to 2500 lbs

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    Quote Originally Posted by Snowwolfe View Post
    How mush gas do you plan on carrying? Your boat is pretty light and long so it should carry a fair amount of weight easily. What speeds could you reach?
    No more than 300 gal. I want to focus on my burn rate as well but with my gear and such I want to minimize as much as I can. I figured with what I tested with, I was able to get on step and go about 28 mph down river at 4600 rpm's vs my normal 4400. This will give me another 300 or 400 rpm's left if needed. My goal is to get back up river at 20mph at 4400 or 4600 and I should have enough gas to do it. But I need to sit down and go over that pretty close. What I do know is at 4400 rpm's my burn rate is about 6 gph at 27'ish mph, but same load going WOT at 4900/5000 I burned just under 15 gph at 24 mph, so it's not too far from one to the other to double my gph.

    I also haven't confirmed this but I am told that Koyukuk has the cheapest gas right now, not sure it'll stay that way but something else to consider. Was also a bit concerned about the weight going back but found a nice deal with an airline that will back haul for less that I can carry it back, so if I can work out the logistics of this trip, I would be able to cruise back to the bridge almost empty minus the fuel I need to get back. That is of course if all the stars line up and I hold my mouth right.
    Tony

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    Where along the Koyukuk were you told has the cheapest gas? I am not aware of a village called Koyukuk that sales gas.

    Along the Yukon you can buy gas in Tanana, sometimes Ruby (last time I was updated their fuel hose didnt go to the river so labor was involved), Galena, and on a good day in Huslia.

    If anyone knows the price of gas for these places be nice if you can post them.
    Tennessee

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    Randy,
    A few months ago the price was 6.5 in Galena; http://www.crowley.com/What-We-Do/Al...tion/Locations

    Just click on the location (dot) for contact data

    Galena, AK 99741
    Tel: 907-656-1852
    Hours are Monday-Friday 8 a.m. 5 p.m.
    (Closed 1 hour for lunch)


    Tony E.





    Quote Originally Posted by Snowwolfe View Post
    Where along the Koyukuk were you told has the cheapest gas? I am not aware of a village called Koyukuk that sales gas.

    Along the Yukon you can buy gas in Tanana, sometimes Ruby (last time I was updated their fuel hose didnt go to the river so labor was involved), Galena, and on a good day in Huslia.

    If anyone knows the price of gas for these places be nice if you can post them.

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    We bought some fuel in Koyukuk one year - Had to find someone with a 4 wheeler to haul it. Not sure how readily available it is.

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    A friend of mine just said at the mouth. Haven't been there yet so I assumed right at the mouth... There I go again, assuming something. I'll need to double check.
    Tony

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    Quote Originally Posted by f0zzy2 View Post
    GPH pretty misleading unless you know how fast the river is flowing. I calculate my fuel buy 2.5 MPG. Last year on the Yukon I ran 27mph going up at 13 GPH and on the way back down I was running 36mph at 8 gph.
    But there was less weight in the boat coming back down right? I do all my fuel calculations based on gph. I've found that my boat will burn so much fuel an hour depending on the rpm. While the mpg will change with the water levels and current at the same rpm.
    06 custom weld storm 6 liter 212 and other stuff
    05 1000X with some little thing's done

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    Yes, I agree all engines will run the same GPH at a set RPM, but the two variables are load and current speed. At 4900 RPM I was at 10 GPH, which is where I usually run. But was only running about 20 MPH. So I kicked it up to 5200RPM and 13 GPH and increased to 27 MPH. Coming DS I was able to pull my RPMís back and only burn 8 GPH because the current was running about 9 mph. I was not lighter on the trip home; I have found moose weighs more than fuel. I have just found in my boat if I base my trip around 2.5MPG I always make it back to the landing with a little fuel to spare. And I did lie about the variables, shallow water =faster running, worn impeller =less speed and Iím sure the list goes on. Iím not saying my method is right or the best, just the way I do it. I would love to hear how others do it.

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    f0zzy2,
    I try to keep decent records when we run the Yukon from and to each place that sells fuel. What I have found is I generally will use approximately 40% more fuel running from Galena to the bridge with 2 moose on board than we did when running from the bridge to Galena. Our speed generally falls off 6-8 mph as well.
    Think of the current as a tail wind. It is either helping to push you, or you need to push against it.
    Still, we keep 2 or 3, 15 gallon containers full in the bow for insurance on the way back.
    Tennessee

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