Why I'm Following Sven Yrvind

Discussion in 'Sailboats' started by sharpii2, May 7, 2020.

?

Do you believe Sven's latest Ex Lex will make it to New Zeeland.

  1. Nope.

    60.0%
  2. Probably.

    20.0%
  3. Almost certainly.

    20.0%
  1. skaraborgcraft
    Joined: Dec 2020
    Posts: 25
    Likes: 13, Points: 3
    Location: sweden

    skaraborgcraft Junior Member

    Im wondering if hes more likely to trip and roll in a broach with those keels he is thinking of? They might be shallow enough to stay in broken water under those circumstances.

    So he is going back to Porto Santo in May to float around in Ex Lex in the Atlantic for a few months. Why is he building another boat? He came to the realization once someone actually asked him, that going to NZ served little purpose. I will probably be quite mad if i ever get to his age. Good luck to him.

    Anyone else notice how shaky his hand was? Never saw that before he left.
     
  2. skyl4rk
    Joined: Aug 2006
    Posts: 51
    Likes: 9, Points: 8, Legacy Rep: 21
    Location: Lake Michigan

    skyl4rk Junior Member

    The thing about a narrow flat bottom boat is that it needs ballast to increase its stability. The the question becomes, is the ballast heavier than the flotation can keep above water, if the boat is flooded.
     
  3. sharpii2
    Joined: May 2004
    Posts: 2,016
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    Location: Michigan, USA

    sharpii2 Senior Member

    Probably not.

    The actual boat is going to be made of nearly two inch thick foam core. In metric terms, if I'm doing my math right, he will get about 50 kg/sm of hull, minus of course, the wt of the foam and the wt of the skins on either side. I wouldn't be surprised if he's netting maybe 30 kg/sm of hull. The new Ex Lex may swamp, but she probably won't sink, at least not from the weight of the new, deeper, 'vertical chine-runners'.
     
    bajansailor likes this.
  4. Will Gilmore
    Joined: Aug 2017
    Posts: 451
    Likes: 187, Points: 43
    Location: Littleton, nh

    Will Gilmore Senior Member

    Not really true. Narrow, as in length to width, shouldn't affect stability. The cross section proportions of width to height of CG are the important factors and a flat bottom, while may be more rolly, is actually the most stable. Think about a log floating in the water and a two by four. The log floats any old way, it rolls all over the place and is very unstable, but the two by four will only float on one of two 4" wide surfaces. The length has no affect.

    Now, cut the log down the middle lengthwise so you have a half round shape. It will only settle on the flat spot. Any attempt to float it on its round side will result in a slow turning over to settle back into its flat surface. Very stable.

    Ballast helps, of course.

    -Will (Dragonfly)
     
    Last edited: Mar 30, 2021
  5. skyl4rk
    Joined: Aug 2006
    Posts: 51
    Likes: 9, Points: 8, Legacy Rep: 21
    Location: Lake Michigan

    skyl4rk Junior Member

    Hmm, I didn't explain that very well. What I mean is:

    In open water with waves, the forces related to hull form will cause a flat bottom boat to keep its bottom parallel to the surface of the water, which is constantly changing. This causes rolling, following the wave surface.

    A round bottom boat is affected more by ballast, its low center of gravity has more force than the round hull form as it is affected by waves. So a ballasted round hull has less roll in waves.

    Initial stability vs. secondary stability.

    A flat bottom boat needs a relatively large amount of ballast to overcome the force of the hull form in waves, to reduce rolling.
     
    Will Gilmore likes this.
  6. Will Gilmore
    Joined: Aug 2017
    Posts: 451
    Likes: 187, Points: 43
    Location: Littleton, nh

    Will Gilmore Senior Member

    That is true.
     

  7. sharpii2
    Joined: May 2004
    Posts: 2,016
    Likes: 191, Points: 63, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    This is kinda, sorta true. I think it's more true if the flat and round sections are much wider than they are deep. But if the flat main section is deeper than the round one (accomplished by narrower WL beam) the round bottom boat will snap roll more.

    The type of keel matters too. If the round bottom boat has a deep keel, perhaps with a bulb on it, it will probably snap roll more than the flat bottom will, if it has a long, shallow keel (with much more area).

    This is because the long, shallow keel produces more roll dampening than the short, deep one does.

    In the case of Yrvind's new boat, it appears that the Beam WL is going to be relatively narrow compared to the over-all Beam.

    This will produce a more gentle roll, even without a keel. The ballast, as high placed as it is, probably does little to add sail carrying ability. It does add to ultimate stability.

    As usual, he intends a very modest sail plan. Not as modest as Ex Lex 2.0, but probably less than two thirds of what we would see on a more conventional sailboat.

    Even so, he may have to get used to a whole new slant on sailing.
     
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