Leeboards: professional or 'have a go'?

Discussion in 'Hydrodynamics and Aerodynamics' started by Graemecb1971, Jul 2, 2022.

  1. Graemecb1971
    Joined: Jul 2022
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    Graemecb1971 Junior Member

    I'm in a 19m liveaboard Steel Dutch barge replica c2010. Love it. Am adding railings along the top of the living area and, in the winter, a tarpaulin cover strung over the length of the living area ~15m . The additional mass and area/wind resistance is going to cause increased heeling (?). I was considering adding moveable leeboards. Is this a good idea? Are there downsides other than maintenence? Can I just add large surface area boards to my hearts content or should I follow a formula? Bear in mind this is for stationary use only to improve living quality. .. the railings, covers etc are demountable for when under power.
     
  2. DCockey
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    DCockey Senior Member

    Leeboards will have zero effect on static heel angle. Leeboards may help dampen rapid rolling, emphasis on rapid.
     
  3. Tiny Turnip
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    Tiny Turnip Senior Member

    I'd be surprised if the weight or windage of some rails and a tarp is going to have very much effect on a 19m steel barge, especially if moored to a bank or dock. If you are meaning a tarp arranged to provide shelter on deck, rather than just a cover over cabin/hold accommodation, then it may offer more windage. Leeboards are not going to help much with it rolling and not at all with it heeling either. Larger ships at sea sometimes have stabilisers that stick straight out from the hull, not downwards, which dampen the speed of rolling motion, but won't prevent heel under a constant force, just slow it. And you would get into all sorts of trouble sticking stabilisers out into UK waterways. If you're really concerned, you'll need to find out /work out the total tonnage of the barge, the weight of the tarp and rail additions, and then look at the cross section of the barge, the positions of the centre of gravity and centre of buoyancy, and the effect the additions have on the centre of gravity. If you share pictures of the barge and a sketch of what you intend, that would help commentators.
     
  4. Graemecb1971
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    Graemecb1971 Junior Member

    Will put sketches and photos up tomorrow.
    We are moored on a surprisingly windy hammerhead pontoon.
    The covering tarp would be a "tent" along the top, acting to the wind as a sail hence why I'm considering the rolling effect now. Even attaching a chair set, table, and an animal cage (1m x 2m side area..mesh) has had a huge effect in increasing roll during a breeze. I agree that mass isn't really a problem unless beyond the point of no return in the roll...and I would hope a 38t 12ft wide flat bottomed barge cannot easily be flipped by the wind .
    All topside additions need to be removable in order to move the barge so I am just looking at a method of damping the roll whilst stationary.
    My assumption was that leeboards act as a surface area in the water that, when a moment is applied through the CoM of the boat, has to "push" water out of the way in order to turn and that this would act as a dampening device; a method I use when kayaking. Am I incorrect? What would be a be a better solution?
     
  5. DCockey
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    DCockey Senior Member

    They will provide dampening, but probably an insignificant amount unless very large and/or able to extend to a substantial depth. What is the depth of water at your mooring site compared to the draft of the barge? (Added) Leeboards which are beside the hull will provide essentially no dampening.

    The dampening would be larger if the boat was moving through the water, not just rolling.

    If I'm reading the posts correctly the need to dampen rolling of the barge due to wind gusts is currently hypothetical.
     
  6. kapnD
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    kapnD Senior Member

    Perhaps an anchor or two deployed on the windward side would help?
    Photos of the boat and its situation would help.
     
  7. Graemecb1971
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    Graemecb1971 Junior Member

    I'm putting photos up tomorrow
     
  8. Skyak
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    Skyak Senior Member

    12 ft wide is not much. You want to present that 3.5M to the wind and waves and do anything in your power to NOT present the 19M side. That said, I don't think that vertical lee boards will do anything positive but will have the negative effect of countering the natural wind cocking. If it was me I would likely put an anchoring sail at the transom, a bridal at the bow and program an active system to manage them. That tent could be driven to harmonics by wind but you are so narrow and heavy that the key is stay bow to wind and waves. If you still rock too much you could add dampers on swing out booms.

    Edit -I just had an even better idea. Replace the sail on the transom with a windmill to power the active management.
     
  9. Graemecb1971
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    Graemecb1971 Junior Member

    'Currently' being for next 5 days . Even a 10mph breeze can cause excessive rolling. The gales a few months ago were great fun!

    Scientifically: why would a deployed leeboard not create damping? I was thinking of 1m x 1m approx below the line of the Hull. That's about 1/16 extra at a greater distance from CoM OK only 0.5m effective distance beyond.

    Water depth 5m draft 0.85m.

    I'm considering this due to basic physics btw. I'm really not close to a designer.

    Some people have suggested an anchor but I don't think they are permitted within the marina itself and I doubt would be effective unless dragged into position and tightened in at least three places - two places would only change the possible direction of the motion. Limit it through fraction of
    Thank you: will look up several of those terms tomorrow! . You've mentioned sail, we are MV ... although maybe sail was meant differently in this context... hence the 'look it up tomorrow'
     
  10. Graemecb1971
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    Graemecb1971 Junior Member

    Thank you: my physics is rusty... why would it not dampen a slower motion? I'm assuming fluid dynamics reasons such as (simplified) "the water has time to flow away from the surface thereby decreasing the effective force "
     
  11. Graemecb1971
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    Graemecb1971 Junior Member

    Thank you to everyone trying to help me. The discussion is amazing!

    As commenters may have guessed, I'm a newbie and I seriously appreciate everyone explanations. I have a background in science and IT but my physics is more than a little rusty and therefore my assumptions are just that but I love hearing your explanations. Thank you so much, again
     
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  12. kapnD
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    kapnD Senior Member

    Are there waves involved as well?
     
  13. Graemecb1971
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    Graemecb1971 Junior Member

    From the less 'speed aware' boats .
    We are living in a river based marina. The only waves are <0.2m from 'breeze' or a few other boats. Wavelength <1m so probably has the technical term "choppy" .
    I'm mainly trying to dampen rolling from the wind, but I can't move position and I'm about to increase the effective wind surface area by around 25% . Trying to find solutions before the anticipated problem. In a kayak I use a paddle like a leeboard or a weighted umbrella opened about 6ft underwater if I need 'perfectly stationary' (I assume that's similar to a term I've heard in novels 'sea anchor')... for sea fishing
     
  14. Skyak
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    Skyak Senior Member

    "anchor riding sail" would be the closest search phrase. It is just like the feathers on a dart. I like my active windmill concept -I am not sure anyone has ever done it so I will look.
     

  15. DCockey
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    DCockey Senior Member

    That sounds like tied up to a pier, wall, etc; not swinging at anchor.
     
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