Stabalizing a small steel boat

Discussion in 'Stability' started by mwatts, Sep 16, 2009.

  1. mwatts
    Joined: Jul 2009
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    Location: Netherlands

    mwatts Martin

    Someone I want to help, has a small problem with his steel boat. He's worried it's not stable enough, especially when he wants to take it out with his kids.

    Here are some pictures of the boat:

    [​IMG]
    [​IMG]

    LOA = 580 cm
    BOA = 180 cm (at the bottom it's 140 cm)
    Draft is approx. 20 cm.

    My first suggestion was to weld on a keel. But that's not an option, because the boat is operated in shallow waters (e.g. he has to use the outboard's shallow water drive to get home).

    So I thought I'dd ask here. Has anybody got any idea's to improve stability without increasing the draft of the boat?
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Add 'fenders' full length (just like you see on RIBs)....nice foam filled ones so they do no lose buoyancy when damaged. These can be glued or rivet/bolted on. Therefore when the boat heels, she has 1) increased buoyancy and 2) a greater righting moment.
     
  3. mwatts
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    mwatts Martin

    Won't fenders make her plough thru the water even more than she already does?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    mwatts

    I have no idea, since i have no idea what your boat is like when underway, no video or pic showing this. Bit difficult to ascertain the performance when non given in the original post!

    Just place the fender underneath the black rubber strip..or replace it with the fender.
     
  5. rwatson
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    rwatson Senior Member

    Surely the designer has done the stability calculations ?

    If he hasnt had stability calcuations done, I would suggest he doesnt even go out on his own.

    The easiest and cheapest ballast aid for a tippy boat of this size are four of five bags of sand in the bottom

    In fact, he could get sandbags with the equivalent weight of passengers, put them all on one side to test the stability. It would be a quick way to see how 'tender' the hull is.
     
  6. mwatts
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    mwatts Martin

    To be honest, I expect the designer of this boat to have started pushing up the daisies a good two hundred years ago. It's a traditional dutch "vlet" and has been copied a million of times.

    I think however this version has a higher L/B ratio than usual. It will go faster, but I guess the tradeoff is less stability than the beamier versions.
     
  7. rwatson
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    rwatson Senior Member

    So, basically its *not* a traditional design, despite the similarity in lines. There are heaps of comments all over these forums and the web about the dangers of "its just a little change"

    Practical experimentation with real weights is probably the easiest and cheapest way to prove stability.
     
  8. messabout
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    messabout Senior Member

    Looks like a nicely built boat, abit odd, and it is probably not entirely hopeless. Do as Rwatson says. Put several sandbags in the BOTTOM of the boat. Move 'em around to test righting moments. secure them at the centerline of the boat and then try it with passengers. Keeping the bulk of the weight very low will be useful. The alternative solution is to give the boat a decent burial.

    The boat looks like a Bolger Gypsy run amuck. The steel boat has too much angle on the sections that we might call the lower strake. Five piece boats like this can be designed to work very well but this does not appear to one of them.
     
  9. gonzo
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    gonzo Senior Member

    Nice looking boat. With that flare she should have a fair amount of reserve stability. What does the owner consider unsafe? Those boats tend to be a bit tender and then stiffer as a chine comes off the water
     
  10. nukisen
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    nukisen Senior Member

    As far as I can see this looks to become a stable boat.
    You did ask for a sugestion to make it more stable without increase te draft.
    Then take a look at Matt Laydens solution.
    One of the smartest things I have ever seen. Usually used for sailbots. And with a lot of different functions.
    http://www.microcruising.com/Sketch1.htm
    As you can see on this page, the boat does have a little list at the bottom.
    This list does increase the stability. Caused by the displacement increases at thae sides. The draft will even get smaller. And also works like a keel when you heel the boat at side. (specially for sailboats)
    Of course you can try this option.
     
  11. nukisen
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    nukisen Senior Member

    Ahhh also this lists does move the center of gravity downwards (cog).
    This will increase the stability a lot.
     
    Last edited: Nov 5, 2009
  12. mwatts
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    mwatts Martin

    Nukisen, you are referring to the "chine runners" in the pictures? I will forward the suggestion. Thanks.
     
  13. nukisen
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    nukisen Senior Member

    U r welcome Martin!
    Yes i did refer to chine runner.
    How can a simple solution make so big differents.
    Remember the resistance may rice a bit.
    But I am not sure because the draft will be a few millimeters lower. So the wetted surface increased by the lists you will get back at the waterline.
     
  14. yuyewuyuconan
    Joined: Nov 2009
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    yuyewuyuconan Junior Member

    make another one ,become twin hull boat.
     

  15. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    until we see some photos of it in the water with a few sandbags on the center line and someone hanging over the side how can we tell how big the problem is ??
     
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