pontoon / ferry design

Discussion in 'Stability' started by jklos2002, Feb 9, 2010.

  1. nukisen
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    nukisen Senior Member

    jklos!!!
    I think this will be quite easy as I think the cog is very low on a macine like this.
     
  2. sharpii2
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    sharpii2 Senior Member

    The real problem I see is reserve buoyancy.

    If all your floats are completely submerged, there is no buoyancy left on the low side to right the boat, once the boat heels. This could lead to a runaway capsize provoked by a sharp turn or a powerboat wake.

    The frightening thing is that you would never see it coming.

    What you need is more displacement. Adding a third pontoon the same size as the large two would help a lot.
     
  3. Asleep Helmsman
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    Asleep Helmsman Senior Member

    Danger Will Robbins

    You're better off hauling it across the lake in a roll off dumpster.
     
  4. nukisen
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    nukisen Senior Member

    First of all this seems to be tight.
    :idea: Are you able to make the platform attached in the bottom of the pontoons?
    If it is salt water maybe it is not very good for the machine to stand a little bit under the waterline. If it is sweetwater as it seems to be in an inland lake then it should not be any problem as this types of machines often works in mud. The stability would be increased a lot.
    With this arrangement and with about 4500 kilos (Sorry I have much easier to calc in metric as I feel more comfortable with the metric scale.)
    The metacentric hight will be about 5.521 ft. I you place the help pontoons center at hight 1.6 ft. This will be just a little bit under the waterline and the floating craft will increase faster if heel a little bit. It will also be easy to load the machine as you dont need ramps.

    Remember if one pontoon will carry 2.4 this doesnt mean that two of them carry 3,5 tons in the middle and 650kilo at the reel, this is caused by if you move the weight from the center towards starboard then portside will float higher.

    I have worked out a crosscurve regarding your arr. Remember this isn´t exact numbers. I have attached pictures of the crosscurve. By using freeship.
    And as I don´t have enough money yet, I am not able to buy the delft ship pro. Wich would calculate more exact.

    Also please let somebody who have more experiance with hydrostatic data take a look before launching this. I think you are able to do this but I feel like it is quite tight. I feel like I have done a part of the job and we need someone confirm the calculations. As about a 100 or 150 kilos on the reel will make the ferry tip. The weight of the machine is about 30 times more. Hmmm!
     

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  5. jklos2002
    Joined: Feb 2010
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    jklos2002 Junior Member

    Nukisen - Thanks for your input.

    Could you comment on this new design which takes an existing 24' long pontoon boat and secures the two rectangular pontoons in between the two round pontoons?

    I've attached a sketch of the new design.

    The center of gravity of the tractor is very low, approx. 18" from ground.

    The two round pontoons about double the displaced capacity of the 2 rectangular pontoons.

    My concern remains stability... thanks again.
     

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  6. nukisen
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    nukisen Senior Member

    Are you able to turn this one upside down. And then place the tractor in the bottom. Place the other Pontoons at the side of this one then you definately do have a functional boat to transfer the tractor.

    Other wise I will take a look at this tomorow if I am not running out of time.
    Here it is great past midnight by now and need to sleep for a few minutes. :D
     
  7. jklos2002
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    jklos2002 Junior Member

    could someone comment on the stability of this design?

    Boat is shown with 10,000# total load inc. boat weight.
    Total submerged bouyancy is approx. 20,000#
     

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  8. nukisen
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    nukisen Senior Member

    Good practice!

    Hi again!
    I have made a new model for you.
    I still think this is fun and want to do it in matter of time.

    Please I don´t want to be mean, but i will honestly let you participate my mind. I am an amateur in stability calculation. And think this is fun. :)

    Maybe you should try to explain a reward for anyone of the experts to help you read the crosscurves. So they see that you not only get the answer for your projekt and then just disappears from this forum. With some kind of freerun.

    As this is a forum for those who are interested boatbuilders. Not a free engineer calculation society. I think thats why you do have less expert anwers. Some of the members have this calculations for living in the same way as you do live for others hires your sevices by machines I supose.

    Well, back to the model.
    If your machine is weat when arrives to the shore, then my calculation is correct!:eek:

    Kind regard!
    Janne
     

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  9. nukisen
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    nukisen Senior Member

    The solution!

    For me the solution by floatation looks like this!
    Remember I am still a happy amateur to this.:confused:

    If you do separate the pontoons so you do have 1400mm between And if you are able to hold the center of grav under 1100mm for the whole ferry + load weight. Then the transportation is safe. (for me!);)

    I did made a sketch. Attached!
    A new table Attached!
    ssd and dsd Attached!

    Secure the machine!
    Try if the machine is weat when arrives the shore. My calculation failed.:eek:
    :p
    Use Life jacket!:cool:
     

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  10. nukisen
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    nukisen Senior Member

    How is the transportation going?
     
  11. Marco1
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    Marco1 Senior Member

    Well Nukisen...how do you expect?

    You suggested to the guy to split his pontoon in half to make it wider, attach the other two floaters, bang a couple of drums on the top for decoration, join the lot with saliva or similar, and hope not to get wet. :)
     
  12. nukisen
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    nukisen Senior Member

    Hahahaha! :eek:
    Forgot to tell that the drums you are talking about is a substitute for his machines center of gravity. So these are only for weight calculation.

    Hahaha!
    Sometimes I am just stupid.:confused:

    Actually I thought this man should make a post about this.

    Anyway I feel for now, I have done enough.

    A very good exersice though. But it would be fun to how he solves the problem.

    //mr curious
     
  13. Asleep Helmsman
    Joined: Jul 2008
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    Asleep Helmsman Senior Member

    I was kidding earlier about the dumpster, but why don't you have a local welder build you a flat bottom barge.

    It will be stronger, lower, draw less water, and all around safer to use.

    If you build it 12' x 16' with flared sides 30" high
    1. 1/4 plate for the hull
    2. Square 2"x5"x 1/8" tube 4' O.C. Ribs
    3. 2" Pipe or Square tube welded around sheer line (top of sides)
    4. Stringers between ribs to hold 2x12s or 11 7/8" X 1 3/4" LVL runners to drive the loader on.

    Total weight around 1100 lbs. total displacement 11900 lbs per foot of draw, plus however much flair you add to sides.
    You would need to have have some kind of hinge in the bow to create a ramp.

    You might even be able to use 3/16 plate or 1/8. Hopefully a steel boat guy will have an answer for you.


    This is just an idea.

    Also some one needs to check my calculation on the weight, please.
     
  14. jklos2002
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    jklos2002 Junior Member

    Problem is i already purchased the pontoons, so I can't switch gears to a flat bottom barge.

    New design is 12' wide but with slightly smaller inner pontoons.

    total displaced water weight is about 15,000#
    Max load would be 9,500# including 2,000# boat weight.

    That would leave about 5,500# reserve bouyancy.

    The max load would be seen 1 or 2 times per year. Usually, less than 4,000# would be hauled to the island. I'd wait for calm water for max. load.

    Current design is to weld together 12' aluminum i-beams & cover with tread plate, then bolt to top of pontoons.
     

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  15. nukisen
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    nukisen Senior Member

    Wow!
    Good luck then!

    Hope you post some photoes then.

    Would be great to see it work!
    :)
    //Janne
     
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