Page 1 of 2 12 LastLast
Results 1 to 20 of 24

Thread: Short trip

  1. #1

    Default Short trip

    I just got back from a trip in mine (I'm new to jet boating) and was dissapointed to find I only got about 1.6MPG!! We were very loaded and much of the trip was upriver but I had to cut it short because of the fuel consumption. What kind of fuel do you all burn that have Jet boats?

  2. #2

    Default 20ft Wooldridge Sport - 150 HP 2 stroke OB jet

    After carefully analyzing 6 trips: Hidden Lake, Skilak Lake, Kenai Lake, Resurrection Bay, Whittier, & 20-mile river..................2 mpg average.
    I bought and installed a fuel meter to help optimize mileage & prevent running out of fuel. The future of pleasure boating could very well be numbered if you consider that gas could easilly become $4.00 to $5.00 a gallon. Trips are either infrequent or you got to find some paying riders...........I think a general rule of thumb is 1.0 gallons/hour for every 10 HP of motor head.

  3. #3
    Member broncoformudv's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage, Alaska
    Posts
    4,670

    Default

    What size boat, what engine, what jet unit do you have? New or used? What rpm's were you running at cruise? max rpm's?

    Your fuel consumption seems a bit high to say the least.

  4. #4
    Member
    Join Date
    Jun 2006
    Location
    Fairbanks
    Posts
    106

    Cool GAS

    Typical measure of consumption in a boat is Gallon Per Hour (GPH). You can more accurately optimize your motor using this measure. If you are running upstream in a 20mph current doing 30mph ground speed, your effective speed is ~ 10mph. Obviously your mpg will be greatly reduced as opposed to running the same current downstream.
    So you can see where GPH would be a better measure.

  5. #5
    Member
    Join Date
    Oct 2006
    Location
    Fairbanks
    Posts
    973

    Default

    Welcome to the world of jet boating! With a heavily loaded boat your mileage does not sound unreasonable.

    The gallons per hour is frequently referred to but is BS - without the speed traveled it does not matter how may gallons per hour you are burning - The only measure that matters at the end of the day is miles per gallon.

    The miles you can travel matters much more than the hours the motor will run.

  6. #6

    Default mph / gph = mpg

    That of course is the basic formula. I use GPS speed in my calculation so river speed is irrelevant to the desired result of how much real estate you can cover before you run out of gas. A real world example from my boat on lake water is as follows:

    25 mph / 14 gph = 1.78 mpg

    Heavier loads take more rpm to push to same speed so of course it depends on your load, but in my experience so far I plan based on 2 mpg and use the 1/3 1/3 1/3 rule and now also have a fuel meter to cover any error in the 2 mpg planning estimate.

    My 2 mpg general average is for a 20ft Wooldridge Sport with a 2003 150HP Mercury XR6 oil injected, carburetored, outboard jet, with about 125 hours of typical use without much bottom bashing, an in impeller that looks to be in reasonable tolerances but not recently sharpened. It runs around 4000 rpm. to stay on slow step at 24 mph.

    The Marita lead mechanic told me this engine will burn up to 16 gph if you run it wide open at 5500 rpm, and that I should expect around 12 to 14 gph at 4000 rpm.

    Thus I believe the 2 mpg average is very real for my setup. It is also very painful? The range on the in-hull 45 gallon tank is not that good & the gas not be cheap. Unfortunately Marita apparently advocates for the low end torque, lighter weight, and better hole shot with the 2-stroke. All things considered............I wish I had 150HP 4 stroke that supposedly would burn about 70% of the gas the 2 stroke does!

    The 2 mpg seems to even get me close if you are going very slow trolling, or going up (and usually then back down a stretch of river).

  7. #7
    Member MARV1's Avatar
    Join Date
    Jul 2006
    Location
    Kotlik
    Posts
    640

    Default

    Heck we pay $5-6 here in the bush, yes it is expensive. Everyone here, most everyone uses a 4-stroke now which is the only way to go. Unless you go DI.
    The emphasis is on accuracy, not power!

  8. #8

    Default

    Quote Originally Posted by rambling raven View Post
    The gallons per hour is frequently referred to but is BS - without the speed traveled it does not matter how may gallons per hour you are burning - The only measure that matters at the end of the day is miles per gallon.
    Take any boat, run it upstream at a certain rpm and weight for an hour, then log the miles. Turn around and run downstream at the same rpm and weight, log the miles. (The point will become clear, when you pass your launching site.)

    Are the mileage figures the same? Nope.

    Would you have burnt the same amount of fuel each hour? Yep.

    Take that 'the only measurement that matters' you got going down stream (mpg), and use it to figure out how much fuel you'll need going back upstream, and your hunting partners are going to be pissed.

    Both measurements have their place in navigation.

  9. #9

    Default upriver v.s downriver mileage

    Of course there is better mpg downstream than upstream. With literally infinite mpg if you kill the engine & drift with oars!

    But I have found that if you go up and down (or down and up) the same stretch of stream the overall mileage for me is still about 2 mpg. The river stream works for you one way and against you the other and the end result seems to basically cancel out when considering the round trip distance.

  10. #10

    Default Jet Boat

    Am I missing something? Wouldn't half of the trip be up river and the other half down river? Or vice-versa?

  11. #11

    Default

    Quote Originally Posted by 4whlr View Post
    Am I missing something? Wouldn't half of the trip be up river and the other half down river? Or vice-versa?
    Sure!

    Say ya travel 100 miles down river with 80 gallons of fuel. It takes 4 hours and 40 gallons of fuel to get there. That's 2.5mpg as 100 miles divided by 40 gallons equals 2.5mpg. Everything is cool because you've still got 40 gallons of fuel, and you now know, thanks to the miracle of the magic mpg figure, that you can make it back upstream because 2.5mpg time 40 gallons equals 100 miles.

  12. #12
    Member
    Join Date
    Oct 2006
    Location
    Fairbanks
    Posts
    973

    Default

    Quote Originally Posted by BrianW View Post
    Take any boat, run it upstream at a certain rpm and weight for an hour, then log the miles. Turn around and run downstream at the same rpm and weight, log the miles. (The point will become clear, when you pass your launching site.)

    Are the mileage figures the same? Nope.

    Would you have burnt the same amount of fuel each hour? Yep.

    Take that 'the only measurement that matters' you got going down stream (mpg), and use it to figure out how much fuel you'll need going back upstream, and your hunting partners are going to be pissed.

    Both measurements have their place in navigation.
    "Miles per Gallon" uses the "Gallons per Hour" figure in its calculation there fore gives you more information in one figure. Everyone boating should realize that while operating a jet boat fuel consumption is a constantly changing variable dependant on a lot of factors - water flow, weight of the load you are carrying, wind speed, etc. Proper planning includes each segment of the trip taking into consideration all the variables and worst case scenarios. Take the original post figure of 1.6 miles per gallon and travel 100 miles you have burned 62.5 gallons of fuel and you are now roughly 400 pounds lighter and getting better fuel consumption. Now add in a large bull moose and that 1.6 miles per gallon would look good. It is all in planning and knowledge of the equipment you are using.

  13. #13

    Default

    Quote Originally Posted by rambling raven View Post
    "Miles per Gallon" uses the "Gallons per Hour" figure in its calculation there fore gives you more information in one figure.
    Really?

    When I fill my truck I like to reset the trip odometer. Then when I fill it up again I check the miles traveled, divide by gallons added, and come up with a mpg figure. At no point was time (hours) a factor.

    Quote Originally Posted by rambling raven View Post
    Everyone boating should realize that while operating a jet boat fuel consumption is a constantly changing variable dependant on a lot of factors - water flow, weight of the load you are carrying, wind speed, etc. Proper planning includes each segment of the trip taking into consideration all the variables and worst case scenarios.
    Very true!

  14. #14
    Member
    Join Date
    Oct 2006
    Location
    Fairbanks
    Posts
    973

    Default

    [QUOTE=BrianW;146020]Really?

    When I fill my truck I like to reset the trip odometer. Then when I fill it up again I check the miles traveled, divide by gallons added, and come up with a mpg figure. At no point was time (hours) a factor.

    Brian - Yes Really! - My statements were about the original post of Jet boats not my truck, while your calculation is correct for your truck I find it irrelevant for the boating I do. My boat has 5 built in tanks and we carry many gallons more in drums and I do not have an odometer (other than my GPS) that accounts for miles traveled on step as opposed to drifting, running the kicker, etc.

    Miles per hour divided by Gallons per hour equals miles per gallon -

    OR

    Traveling down the river and the GPS reads 30 MPH, Fuel flow meter reads 20 GPH - 30MPH / 20GPH = 1.5 Miles per Gallon

    (A lot of the new fuel flow gauges will do this calculation)

    This calculation done in real time and frequently gives you the miles you are getting per gallon at all times not an average you got over the entire tank of gas. This mileage will change frequently and keep you up to date at every turn and every change in condition and let you optimize your throttle setting to nurse every last foot out of the tank. As I originally stated this is much more relevant to a long trip than GPH. If you are going out for a day trip fishing who cares you have lots of fuel - don't worry about it.

    There is always more than one way to do everything. I typically travel 1200 to 1500 miles a trip for hunting each fall and have found a method that works quite well for me as I have yet to be longing for fuel short of the boat ramp.

  15. #15

    Default

    Miles per gallon need only two factors. Miles traveled, and fuel burned. If you need to add a third dimension, time, then go for it. I find it ironic that you now claim that gallons per hour is crucial to figuring miles per gallon, yet called it BS earlier. Can't debate that logic, it changes too much.

  16. #16
    Member
    Join Date
    Oct 2006
    Location
    Fairbanks
    Posts
    973

    Default

    Brian - I believe I clarified in my original statement that GPH wasn't enough information without adding the speed element in "without the speed traveled it does not matter how may gallons per hour you are burning".

    I wasn't trying to start a pissing contest with you and I don't believe I was even replying to a post you made with that statement. You are obviously the authority on this topic and I apologize for having an opinion counter to yours.

    Deuce - sorry if I somehow sidetracked your post

  17. #17

    Default

    The reason GPH is used in marine applications is because not to long ago there was no GPS to accurately get your speed over land so all you could go by was the amount of fuel burned and the number of hours ran unless you had a flow meter then you had instant GPH calculated and total flow since the last reset.

  18. #18

    Smile Stop!!

    Wow. I really started something here. thanks for all the good info. I think a combination of GPH and MPG is the way to go. By the way we saw 0 biggame but the weather was great and we caught a slew of monster Pike!!
    Attached Images Attached Images

  19. #19
    Member
    Join Date
    Apr 2006
    Location
    Anchorage, AK
    Posts
    273

    Default Miles Per Gallon vs. GPH

    They both have their uses, but GPH is is somewhat difficult to deal with without a flow meter, unless you want to bring a few small gas tanks along and check them methodically at different RPM's and loads, make a chart, and pin it to your dashboard. It also is hard to plan with GPH unless you know exactly what the weather and load factors for the trip are going to be like. I know for fact that my worst case scenerio is 2mpg, that's running hard, heavily loaded, combined with sight seeing, trolling, and nasty weather the earliest I have run 35 gallons dry is in 72 miles. This is best when figuring that your going to take dad over to ailik glacier, then off to the chiswells for rockfish, then over to pony cove to troll for about two hours for silvers then head back in. I like knowing that if I take 90 gallons for this trip, I will have 1/3 fuel when I return and conditions were perfect, or somewhere between 1/4 and 1/8 fuel left if the weather goes to hell, someones boat breaks, I have to respond to a distress call that's within 15 miles, or any number of other things that could happen out on the water. It's just plain embarassing to run out of fuel. For me, it just seems best that worst case scenerio mpg is the most useful tool for trip planning. Plus, knowing how much I burn per hour makes me cry.

    Chris

  20. #20
    Member AKBassking's Avatar
    Join Date
    Oct 2006
    Location
    SE Alaska-Summer Columbia River-Winter
    Posts
    2,007

    Default

    I get about 2.9 MPG with my 250 Evinrude Jet. I keep the trottle at 4200 RPMs though.

    ALASKAN SEA-DUCTION
    1988 M/Y Camargue YachtFisher
    MMSI# 338131469
    Blog: http://alaskanseaduction.blogspot.com/

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •