Parasailing

Discussion in 'Boat Design' started by holdfast, Nov 21, 2013.

  1. holdfast
    Joined: Nov 2013
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    Location: Spain

    holdfast Junior Member

    Hi all,
    It has been difficult to choose a good idea for my final year engineering proyect. Finally, I have decided to study the loads on a parasailing boat and design the winch system and fitting reinforcements according to that, making it safe and simple.
    I have choosen this proyect because I think there is a big lack of knowledge about this in my country (Spain). And I'm more motivated if I can work on something that may be helpfull.

    I just wanted to share this idea with you because I know this activity is more common in other countries and you may have more information.

    I'm starting to calculate de loads due to the parachute pull in the worse case scenario. Later on, I will need to find a hull to start making stability numbers. I don't want to waste time designing a hull, because that is not the purpouse of the proyect and because I don't have a good knowledge about it. Do you know where can I get hull lines for a suitable boat? Looking at other boats in this business, I think it has to be around 28feet long and 11 feet width, two inboards with legs, deep vee but with low deadline angle...

    I'd apreciate any coments, thanks in advance.

    [​IMG]
     
  2. holdfast
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    holdfast Junior Member

    Does anybody know if there is any standar about safety factor in boat structures?
     
  3. holdfast
    Joined: Nov 2013
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    holdfast Junior Member

    [​IMG]

    Do you think it is necessary to reinforce the longitudinal frames from the boat?

    In the worse case scenario there would be a winch vertical force of 9000N.

    Thanks.
     
  4. lohring
    Joined: Nov 2006
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    Location: Eugene, OR

    lohring Junior Member

    These guys have spent a lot of time investigating kite sailing.

    Lohring Miller
     
  5. holdfast
    Joined: Nov 2013
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    holdfast Junior Member

    Thanks Lohring, it is very interesting.
    While I've been calculatine some loads related to the parachute pull force, I've been playing a bit with the FreeShip software. I need your opinion as this is my first hull design and I am pretty sure I have a lot of mistakes. Thanks.

    lh4.googleusercontent.com/-OifOUiQuVXA/UpZx8tDW80I/AAAAAAAAFmU/DMt1QKQ_RAY/w786-h568-no/Untitled.jpg
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    To start with, if you are planning on using sterndrives, the transom needs to have an angle of about 14 degrees.
     
  7. holdfast
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    holdfast Junior Member

    Thanks Gonzo, that is a good point. Actually, there is no transom yet, that is my next step to learn.
    By the way, I want to extend the deck about 2ft above the transom, for the oarasailing platform, should I do that with the FreeShip? I will have to design the deck later on with another program I gess. Thanks.
     
  8. holdfast
    Joined: Nov 2013
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    Location: Spain

    holdfast Junior Member

    Hi! it took me a while but I think I've got it, 14 degrees at the transom.
    What do you think about the bow, is it too high? I just want to keep 8-10 passengers dry waiting at the bow for its parasailing turn, but on the other hand I want the driver to have good visibility. It is not going to have any cabin, just a console I think...

    lh6.googleusercontent.com/-Rc44aPgvafk/UphgqmUHSkI/AAAAAAAAFnY/4MYvv-gNusA/w1010-h568-no/Untitled.png
     
  9. gonzo
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    gonzo Senior Member

    You can always build a step for the helmsman to have better visibliltiy. You may have problems with a deep vee bottom like that. A shallower vee should give a better overall performance. This design also shows curved buttock lines which will make it squat. That is usually a major problem with parasailing because of the drag backwards.
     
  10. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Listen to Gonzo. Flatten the lower sections and for sure flatten the buttock lines aft.

    Even a large parasail has limited capacity to produce thrust. Yes, we know that it is wind strength dependant. Nonetheless, the parasail force is not likely to rival the sheer thrust of a big outboard in which case you could have a deep vee.. In this case you must sacrifice some ride quality in favor of planing performance. Flatten the bottom to a very small deadrise figure.

    With a kite, there will be a vertical force vector about which you can make some SWAG estimates. Depends on the length of the tether line I suppose.
     
  11. holdfast
    Joined: Nov 2013
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    holdfast Junior Member

    Thanks Gonzo and Messabout for your coments. I have flattened the lower sections and the buttock lines aft. I have attached two options, one flattener than the other, in my opinion the second one is too flat, but I am not an expert so I look forward for your coments...
    I agree to sacrifice some ride quality in favor of planing performance and most of all, in favor of stability. I have to consider the worse case scenario where the Parasail pulls sideways. On the other hand, the boat has to be confortable for the people on board....
    A large parasail can pull up to 1100kg in high winds, in an angle of 25 degrees from the horizontal.

    [​IMG]

    [​IMG]
     

  12. holdfast
    Joined: Nov 2013
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    Location: Spain

    holdfast Junior Member

    Hello,

    I finally changed the shape a little bit more. This is the final prototype, I hope you like it and I look forward for some coments. The hull deadrise angle is 18,5 degrees. Thanks. How much do you think it would weigh with two inboards? it is 9.3 x 3.5 meters.

    [​IMG]

    [​IMG]
     
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