From flat-bottom boat to partial V-bottom boat

Discussion in 'Boat Design' started by Dieter51, Oct 17, 2023.

  1. Dieter51
    Joined: Aug 2022
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    Location: Munich

    Dieter51 Junior Member

    From flat-bottom boat to partial V-bottom boat. See thread 67268

    Has there ever been an attempt to convert a dinghy from flat bottom to V-bottom? My dinghy ict a flat-bottomed Paulownia boat, see thread 67268, and the pounding in short wave in medium wind is just too destructive for me in the long run.

    The reason for this is certainly that the boat is very light, with a length of around 4.5 m it now weighs just over 50 kg. If it were not made of 18 mm paulownia, but of other solid wood, as it used to be, it would weigh 150 kg. Then the boat would run much smoother, as it does with an extra 80 kg man on board.

    I would now like to glue the hull bottom on the outside with hard foam boards, shape it and then shape it with epoxy/fibreglass. It's not a big deal, we used to do it for our own surfboards. In the middle, the boat should remain as it is, but then with a V-bow at the front and a V-tail at the back with a soft transition. The boat has enough rocker to be able to do that. In the back that v only as a balance of displacement and for a long waterline.

    Has anything like this been done before and if so, what has been learned?

    By the way: The capsize problems of my boat disappeared with a classic spritsail. The first sail had no sprits, but was stretched on the inside by a support and smooth on the outside like a wing. It pulled only moderately, but sometimes, seemingly for no reason, it suddenly delivered more than twice the force. Then one capsized and the boat filled up. Unpleasant. At first I thought it was the narrow hull, but it was the sail.
     
    Last edited: Oct 17, 2023
  2. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    Will Gilmore and bajansailor like this.
  3. Dieter51
    Joined: Aug 2022
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    Location: Munich

    Dieter51 Junior Member

    I would like to avoid a new boat at the moment. And I have found that the rocker of the boat is probably not enough to foam-shape a V-hull that could do its job well. I was a bit too optimistic.

    So I'm going to try to solve the problem with a water cushion on the floor of the foreship that I can quickly fill with water and empty using an electric small pump. In the event of a capsize, this "trapped water" won't do any harm, because it loses its weight (not its inertia), it floats in the water.

    As said in the other thread, the problem disappears when the boat is as heavy as its ancestors (3 - plank boats) once were. So here, when my boat is sailed with 2 people.

    Doing something differently and achieving success is always a process. But I never wanted to build a stitch'n glue boat out of plywood again. So far the paulownia wood is doing its job as hoped. The next boat will have a different design.

    Thank you for your answer

    Dieter
     
  4. carbon_pirate
    Joined: Oct 2023
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    Location: Austria

    carbon_pirate Junior Member

    Hi Dieter,
    I am experimenting with different hull shapes on my development project. I am no expert, but my experience is, that adding a V to the bow will change the lateral plan of the boat. Depending on the angle of the V and depending on the heeling of the boat, you might need to adjust the mast inclination or position a bit.

    best,

    Marcus
    https://www.instagram.com/carbon_pirate/
     
  5. messabout
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    Location: Lakeland Fl USA

    messabout Senior Member

    If you convert the bottom to some sort of vee, it will slightly reduce the wetted area of the immersed surfaces. That is good for light air sailing. You could reduce wet area even more by using trapezoidal sections, and compromising planing velocity requirements less. The vee will need more driving force before it will achieve planing status, extent depending on vee angle. You will also lose some initial stability when converting from flat to vee....... A vee bottom does not gain stability at the same inclination rate that a flat bottom does.

    Your sweetheart little flattie boat will not pound much at all when it is heeled. When heeled, even to a small degree, it automatically becomes a vee bottomed boat. Make some sketches of inclined section views to see how that works.
     
    Will Gilmore likes this.
  6. Dieter51
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    Dieter51 Junior Member

    Hi carbon-pirate, yes, the v would alter the lateral plane, but I'm free to tilt the whole rigg some degrees to compensate for that.

    Hello messabout, I just wanted to find out with this thread whether there have been conversions in which a flat-bottomed boat with moderate rocker has only received a V at the bow. Seems not to be the case.it is interesting that the flat-bottom was initially changed from flat to V for the stern of the boats in the past. They were trying to reduce the drag that a stern causes when it is pulled through the water with a corner. I prevented this on my boat by giving it enough rocker (as in the past) to allow the transom to be carried above the water surface at all times. The VAURIEN from France, which is still sailed today (many boats) is such a flat-bottomed skiff with a V at the stern and reduced rocker.

    Then came conversions with V fore and aft because this allowed a better balance of displaced volume over the longitudinal axis of the boat. Only flat front to V was never changed to my knowledge. My knowledge comes from Chapelle, Parker and others, the books I have here. And yes, I know that a rectangle block rotated sits on a sharp edge. But: the initial stability of my boat, which is very light for its size, is so great that I have to slide to leeward in order to sail stably on the chine despite a good wind.

    Now I'm going back to the experience I've had, that with a second man, i.e. with more weight and mass, I have no problems at all with the boat in strong waves and strong winds One sits in lee, I like, the other upwind and so that the boat runs longitudinally horizontal. So next year I put an 80 litre flat ballast bag in the boat to imitate the second man. I fill it after the ramp in the water and let the water out there too. In case of a capsize, the water in the bag won't bother me because it loses its weight in the water.

    After that I can concentrate again on making the boat so that it can be built in one week - ready oiled. Without mast, sails, daggerboard and steering gear, of course. That takes at least the same amount of time, and it's better to buy the steering gear ready-made, just like the sail.

    Good health!
     
  7. Will Gilmore
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    Will Gilmore Senior Member

    How do you search for a thread by number?

    -Will
     
  8. Will Gilmore
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    Will Gilmore Senior Member

  9. Dieter51
    Joined: Aug 2022
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    Location: Munich

    Dieter51 Junior Member

  10. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Where did you find the number Dieter?
    I can't see any identifying numbers on threads.

    EDIT: I've enquired with the Moderator as to where thread numbers are located and how to search for them.
     
    Last edited: Oct 19, 2023
  11. Dieter51
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    Location: Munich

    Dieter51 Junior Member

  12. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    I think it is better to copy and paste the whole URL of the thread if possible.

    Every thread has a thread ID (and every post has a post ID) in order to maintain a unique index; it's not really meant to search by the number. But if the thread url is https://www.boatdesign.net/threads/thread-title.67268/ if you only have the thread ID you can actually bring up the thread manually by entering https://www.boatdesign.net/threads/67268/

    But I think it's better to share the actual link to the thread rather than just the number. Sharing the thread URL might take a second longer for the person posting if using a device where it takes an extra effort to paste, but with only the number, every person reading has to make more effort; with a quick copy and paste of the thread URL people reading can open the referenced thread more easily, and also the full thread URL gives an idea of the subject of the linked thread.
     

  13. Dieter51
    Joined: Aug 2022
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    Location: Munich

    Dieter51 Junior Member

    Thank you, I did not know that.
     
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