Reaction Ferry Design?

Discussion in 'Boat Design' started by C-2iinc, Jul 16, 2010.

  1. C-2iinc
    Joined: Jul 2010
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    Location: ma

    C-2iinc New Member

    Hello everybody, I was hoping to get some insight/direction on how to build the most efficient hull for a reaction ferry with a slight twist.

    My company has been asked to develop a drifting reaction ferry, one that instead of floating across a single plane of the river, moves back and forth the river as it drifts down it as well. We plan to use a propeller to provide the reaction force to allow for the ferrying action (opposed to a cable, etc), however I'm interested in understanding what parameters are necessary in creating the most "efficient" ferrying action.

    I understand that any shape will technically "ferry" given the correct design but I'm trying to gain insight on which hull shape creates the largest force vector in the direction we want to travel, while requiring the least amount of energy to do so.

    I've begun reading up on overall boat designs, have got some design books on the way as well. I've also poked around with Delftship and Michlet but all of the information I've come across currently is in relation to straight line motion and efficiency.

    If anybody gain lend some knowledge on this topic, or point me in the right direction to somebody (a company?) who might be able to help, that would be much appreciated. I've looked at the page of consultants, does anybody have recommendations on who might be a good one to work with?

    Thanks for your time

    C-2iinc
     
  2. C-2iinc
    Joined: Jul 2010
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    C-2iinc New Member

    Nobody?
     
  3. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Perhaps the reason you aren't getting any response is your question is nonsensical. A reaction ferry without a cable is not reaction ferry - it is a conventional boat.

    The ferry will crab into the current to follow the desired path, just like any boat would do. If the current is swift, it will mostly be motoring upstream, and only a comparatively small heading change will be required to traverse from one side of the river to the other. A small adjustment in speed will allow it to drift downstream or make progress upstream.

    You don't want to create large forces. You want to have a boat that is very efficient at speeds a little faster than the maximum current - a minimum drag design for the required loadings. The side force on the boat will be zero - work out the vector diagram for a boat following a given path over the bottom with a cross current. You don't want the boat generating side forces when tying up to the dock if the dock isn't perfectly aligned with the direction of the current.

    The boat needs to be stable and operate in the shallow water of a river - leading to a flat bottom with possibly rounded bilges. If you want to generate side force to enhance the maneuvering of the boat, that is best done with a centerboard or bilge boards. Look in design texts for sailboats for sizing and designing such appendages.
     
  4. C-2iinc
    Joined: Jul 2010
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    C-2iinc New Member

    Fair enough. However the only thing the cable does is create a differential between the boat an the water correct (keeping it in place). The thought was to do the same thing with a propulsion system going against the water current. If we matched the speed exactly opposite the river, but was turned to one side we could "ferry" back and forth across the river like a normal cable ferry does without losing any ground. This is something kayaks do all the time, we are trying to mimic that action with a force just slightly less than the current speed so we continue to move down the waterway.

    Agreed. But clearly a sphere wouldn't ferry alone, and if you attached a rudder it won't be as efficient as a a more elongated shape, I was just looking for some insight on what factors play into creating an efficient shape to traverse. If one design needs the boat to turn 45* into the current to achieve a 1 mph traversing speed, and another design only requires a 2* heading change to do the same, once is clearly more efficient than the other.

    Not that it really matters but the boat is going to be unmanned and fairly small (under 2 feet long). Its going to be placed upstream in a river, drift back and forth down the river autonomously, and then be collected at some point down the river.


    OK i guess this is the type of information I was looking for. I understand wider=better for stability, but there are also certain Beam vs. LWL ratios for specific types of boats, round bilges vs. hard chines, I don't know exactly what I'm looking for yet.

    A flat bottom boat would also be most stable as mentioned, but if there is not enough wetted area then it won't "catch" the current to allow it to ferry efficiently. You then mention centerboards or bilge boards,what one is better? Are these better than a Deep V boat? Is a flat bottom boat with a large rudder better than a boat with a large keel and smaller rudder for maneuvering at low speeds? Since the boat is going to spend its life floating backwards does it need to be double ended? etc etc etc There are a million questions to be asked and I'm a little overwhelmed at where to start looking so i guess i was looking for a good starting "point" then work from there.

    I honestly don't know if I'm trying to over complicate this entire problem and appreciate your input so far, I have little to no experience with this type of design work so I'm just trying to absorb as much as I can from people who are wiser than myself.

    I have a few texts coming as mentioned, however wanted to try and pull the the community knowledge as much as I could as this is a much more dynamic way of learning. So again any and all insight would be appreciated, and any suggestions on design software would also be great.

    -C-2iinc
     

  5. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    You haven't thought the problem through properly. In order to traverse the river at a given rate, all boats will turn to the same angle.
     
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