A better idea for Congo - a speedy tug and a plastic bag

Discussion in 'Boat Design' started by congoriver, Jul 14, 2010.

  1. liki
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    liki Senior Member

    Should you use fuel, say 2l/km, the fuel costs for a 500km round-trip would be 1 200 000, assuming all the required 2000l can be bunkered at the lower cost.

    If you can afford 500/kg for fuel costs of the freight, and still make profit, this means that you must get atleast 2400kg payload for one-way commerce. 2000l fuel plus 2400kg payload at 2l/km sounds doable. To be more competitive than the air cargo, you must get lower costs, 6000kg would get 200/kg at the same consumption. How large are the supply & demand?

    Someone else with a better understanding may continue from here, but I think you could well meet these or better limits with a vessel travelling at, say 10kn. 10kn at 2l/km would require achieving it with something like 100-120hp, which seems to start setting limits for the types of vessels with which this is achievable.
     
  2. pedalingbiped
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    pedalingbiped Junior Member

    A boat that can travel 10km/hr + current speed of 5km/hr = 15km/hr
    You will travel 500km in 33hrs. Divide that by 2 days and you will travel 16 hrs/day.

    Your bag is completely immersed in the water which causes it to high drag. It would take alot of power to over come the drag. You would essentially move with the currant. 500k / 10k =50 hrs or 500k / 5k = 100 hrs

    No need of a hovercraft.
    Though if you want one:
    This one goes 50mph or 80kph - less then 10 hrs.
    http://www.hovercraft.com/content/index.php?main_page=index&cPath=55

    Your profit is 1300fc/kg - 350fc/kg = 950fc/kg
    Fuel consumption is based on 600fc per liter

    1l/1k = 500l = 300,000fc which needs 316kg to break even.
    1l/2k = 250l = 150,000fc 158kg
    1l/3k = 165l = 99,000fc 105kg
    1l/4k = 125l = 75,000fc 79kg

    5 miles per gallon = 1l / 2k

    if you only have 1 cubic meter then:
    316kg looses money
    158kg leaves 42kg = 39,990fc profit = 18gals of gas = $54 at $3/gal
    105kg leaves 95kg = 90,000fc profit = 40gals = $120
    79kg leaves 121kg= 114,950fc profit = 51gals = $156

    If you haul empty back up the river then divide all profit numbers by half.

    With a hovercraft hauling 1m/3 you would make a minimum of 20,000fc/day or 60,000fc a week for 3 days work.

    If using price of gas for conversion then $25/day for a profit of $75 a week for 3 days work.

    I would think that a modern hovercraft moving at high speed would attract a lot of attention. Good way to get robbed.
     
  3. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    As an added data point:

    I was on an aluminum boat the other day, a large planing plate boat. The boat was approximately 25 feet long and 10 feet wide with a slight deadrise and a modern 200hp 4-stroke Merc outboard. Loaded with 2500lbs of cargo, the boat easily went 40mph while getting around 3mpg. There was plenty of power left in reserve, and I believe that boat could easily carry two tons of cargo and still perform well, at least get you that 500km in a day, although at a cost of 100gal petrol.

    Biggest problem I see with the bag (other than drag in the water) is that the leaves will be quite wilted by the end of the trip. You can combat the drag with water skis. :D
     
  4. congoriver
    Joined: Jun 2007
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    congoriver Junior Member

    Wow, wouldn't a jetski be able to function as a tug?

    I read that some of these machines have over 300 horsepower engines.

    I've seen some pull banana floats with 8 people on them at a reasonable speed, at sea... :idea:

    Video of one pulling 5 people on a banana float at sea; impressive speed:

    http://www.thoughtequity.com/video/clip/990129_004.do

    (How fast would that be?)


    -Speed up with plastic baggie folded up (weighs about 100kg), at 60km/h
    -Speed down with plastic baggie filled up, at 20km/h

    Fuel consumption on those things? I have no clue, but I bet it's a bit high.
     
  5. mmd
    Joined: Mar 2002
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    mmd Senior Member

    I agree that the semi-immersed plastic bag would create a lot of drag, especially if it were towed at anything close to a decent speed.

    A hovercraft is too expensive to operate as a cargo vessel - the maintenance costs will be daunting.

    Keep it simple - a steel (easy maintenance & repair) low-deadrise planing hull can haul the five tons of cargo at 20 knots (24-hr delivery time) with a 450-hp Caterpillar C7 diesel (easily maintained, good parts availability, lower cost fuel) installed.
     
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  6. Reason
    Joined: Jan 2010
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    Reason New Member

    Interesting. I would also be concerned that putting leaves in a sealed plastic bag could result in premature spoilage. MMD's idea might give more flexability in how the leaves are packaged for transport.
     
  7. uncookedlentil
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    uncookedlentil Junior Member

  8. bearflag
    Joined: May 2010
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    bearflag Inventor/Fabricator

    That is sort of what I was saying. The cargo he wants to ship isn't heavy. But it is voluminous. No need for a deep hold, with the associated drag penalty. Similarly barges aren't made for going fast.

    If he wants to go fast. The least drag/weight etc is a multihull with a fine waterline, probably a catamaran. Make the guy out of local strip-planked wood and have a broad open deck or ad-hoc bimini-ish cover.

    Just make a Really long, fairly wide boat with some pretty heavy duty diesels in it, and some big props.

    Motor it up and down the river. You could probably easily build something to do 20-30 knots much more efficiently than you could do a hovercraft with.
     
  9. hoytedow
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    hoytedow Wood Butcher

    Is there no way to preserve the leaves, such as brine or something?
     
  10. bearflag
    Joined: May 2010
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    bearflag Inventor/Fabricator

    I think if you filled the bag up with some air, and you were towing it from the front it would achieve a sort of reverse raindrop shape, which isn't that bad. If it was mostly air by volume and pretty lightweight to begin with , it'd float pretty high. The drag wouldn't be optimal, but it wouldn't be that bad.

    Instead of having a fully closed "balloon" you could have it be a "fan" inflatable like we use for events. By doing so you or constantly cycling in fresh air... If you needed to, you could even refrigerate it a little.

    The bag is probably more suited for transporting fuel etc. But not a terrible idea.

    I still thing something like a large motor cat is much more economical though.
     
  11. pedalingbiped
    Joined: Jun 2010
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    pedalingbiped Junior Member

    KISS
    Keep it simple, stupid or
    Keep it stupid simple.

    The FOA boat is 8.5 M (32ft) it travels at 7kt or 13km/hr
    The river currant as an estimate is 5km/hr
    500/18 = 27.7 hrs. or travel 14hrs/day while it is light.
    Upriver 13 - 5k/hr = 8k/hr or 62 hrs or 5 days to get back if traveling 12hrs.

    The payload of this boat is 500kg
    Your profit is 1300fc/kg - 350fc/kg = 950fc/kg

    950fc X 500 = 475,000 fc
    Your post use 1000fc = $1
    So that is $475 for one trip.
    The FAO boat calls for a 8hp motor. I tried to find an exact figure but in my quick seach I got a formula that comes out at 4.5k per liter.
    A trip both ways averages the current so 1000/4.5 = 222 liters per round trip.
    At 600fc/liter = 133,000
    So income = 475,000 - fuel or 133,000 = 341,666fc net.
    The figures you give for annual income means you could pay a guy 10,000fc a week for an equivalent of $520/yr
    This would still be 341,666 - 10000 = 331,66fc profit. or $331/wk or $17,212/yr

    Ten boats would give you $170,000/yr
    and pay 10 guys enormous salaries of $520/ yr

    You say there are boat graveyards or beached that you can use.
    When you start building a boat let us know and those that can will help.
    I just like to crunch numbers.

    "success is 10 percent inspiration and 90 percent Perspiration"
     
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  12. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    I agree with pedaling biped that simple is the answer.
    Long narrow boat or a catamaran can keep decent speed with fraction of power (fuel) needed compared to planing boats.

    Forget jetskis they are very inefficient and not rated to last in full power duty of 12h per day.

    Also forget the plastic bag - the longer the boat (other dimensions not changing) the faster and with less wave resistance it will travel. So makes much more sense to make a long skinny boat with enough cargo space. It will travel upstream empty faster too. The bag will introduce huge drag and will not travel fast unless it can be made to have boat like shape.

    If single long hull is not good enough then opt for catamaran for more cargo volume. And this kind of boats should definitely built locally out of wood. Really.

    If speed is 20 knots or more then full speed boating should probably be limited to daylight hours to avoid accidents. A log or another boat with no lights can get you in the dark I would assume.

    Can fuel be bought on the way or does the boat have to carry all the fuel needed for the whole trip?

    Congoriver - you should get copy of "Nature of Boats" by Gerr. It will give you a good basic understanding of what kind of factors result into a compromise called boat. It is not overly technical and very well written - easy to read. Unfortunately it is not in Amazon Kindle so you have to find a hard copy.
     
  13. bearflag
    Joined: May 2010
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    bearflag Inventor/Fabricator

    Yeah, this is what I was saying...


    I still think buying and selling something like kerosene, gasoline, and diesel in Kinshasa or other big ports and selling it or storing it in the "sticks" (probbaly to the same peopel who are providing your leaves) makes a lot of sense too for the return leg.

    You don't need to be a major oil tanker. If you just supply to the most remotest villages. They could have their small boats bring you leaves. You give them a barrel of kerosine. I am sure you could sell it for much less than they are paying. And that way you are making money on both legs, and your fuel prices will be cheaper than buying in the expensive ports.

    Just something to consider.
     
  14. RAraujo
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    RAraujo Senior Member - Naval Architect


  15. congoriver
    Joined: Jun 2007
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    congoriver Junior Member

    Guys, you are great!

    I just dropped in an "exotic" idea to get a discussion going (but we know: bag = drag). And it seems that things are chrystalising out, a bit.

    -a narrow, long boat will be efficient [Kerosene, Pedallingbiped], and can easily be made out of wood or steel

    -in fact, there are these sturdy, very long (30ft) pirogues here, made out of 1 tree; they're very low cost (less than $500), and could perhaps serve as the basis for some kind of a catamaran

    -even at low quantities [Pedallingbiped crunched the numbers] of 500 kg and at current fuel prices, one can turn a profit

    -the time limit (3 days for 500km) doesn't seem to be a major problem

    -most rational option: carry leaves downstream, but carry something upstream (e.g. fuel) to avoid going empty

    -a remaining problem: fuel -- if you carry it upstream for the roundtrip, you lose some time; if you don't, you lose some money; we'll have to calculate a bit [Pedallingbiped: fuel 500 km upstream costs almost double]


    In any case, it seems like this idea might actually be feasible, and with a small investment, it could be implemented rather rapidly. I will certainly try it, but I'll go have a look at the dead boats in Kinshasa first.


    By the way: prices of Gnetum africanum in Nigeria (the largest market) are 3000CFA (that is: 5235 FC). I understand why people export it from Cameroon and Gabon all the way up. Perhaps there's even an opportunity in this for Congo.
     
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