Water Ballast for small boats

Discussion in 'Stability' started by Toot, Sep 24, 2006.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    Hey SuperPiper of P'boro; what's stopping you sailing? I only just got back from the lake! I was paddling not sailing as the sailing stuff is lying in an untidy heap I didn't feel like sorting thru. I enjoyed improving my best in-the-water date, previously Nov 30.

    No sign of any fish although the water was crystal clear but lots of breathing holes in the sand so there's something down there. I was treated with distain by a family of over-wintering geese who seem to be raising a second 2006 family; obviously they knew this was going to be a mild winter. The local heron no longer allows me within 50 yds because I surprised her during the Summer and caused her to attempt to fly thro rather than around a tree. Kayaks are quiet! Pity, she was becoming quite used to my green plastic UFO (undesirable floating object).

    No nasty remarks about the plastic from those who know me please, I'm not about to push my flimsy wood canoe thru ice even if it is only a half-inch thick.

    There were some walkers in the distance so I executed a flashy turn and cranked on the speed. Clearly impressed them; sound carries well over the water. I thought I heard an admiring comment or two but the only thing I heard for sure was "Stupid idiot".

    There's a surprising amount of ice around considering the recent mild temperatures.

    To add a few words to the thread subject: riding a kayak up on an ice floe does nothing good to its stability so freezing the water ballast doesn't help unless it's firmly attached to the boat. I read somewhere that ice-breakers ride up on top of the ice to break it by weight but it didn't work for me. Ice breakers are a shade heavier than 240 lb. Well, we learn by trying.

    A Happy New Year afloat to all!
     
  2. im412
    Joined: Jan 2005
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    Location: australia

    im412 Junior Member

    i found this traditional style "kattumaran" that uses water ballast

    http://mahasagarboats.com/kattumaran.htm

    [​IMG]

    [​IMG]



    It incorporates a unique water ballast system whereby once launched, just by turning some valves, the craft ballasts itself with the right weight in the right place to provide all the stability required. Back from the fishing trip, the craft is hauled a couple of metres out of water and the ballast tanks opened to let gravity drain out the water ballast and restore the craft to its original weight for easy hauling the rest of the way up the beach.
     
  3. Claus Riepe
    Joined: Sep 2006
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    Claus Riepe Junior Member

    Waterballast Boat Capsize Tests

    Waterballast in small boats at its best.:

    The new BayRaider is completed and capsize tested for CE /RCD.

    See some videos on Youtube, linked through

    http://www.swallowboats.co.uk/content/view/127/

    C.
     
  4. RonW
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    RonW Junior Member

  5. Guillermo
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    Guillermo Ingeniero Naval

    Another interesting feature of water ballasts is that they are useful to categorize motorboats under combined categories C and B within the RCD scope. You can get a light boat (so fast) for C category and a heavier boat for B category. It allows the designer to fulfill both requirements for some types of boats.
     
  6. Pericles
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    Location: The heights of High Wycombe, not too far from Rive

    Pericles Senior Member

    How about pumping out the water from the keel with compressed air from a scuba diving set or a cylinder of compressed air mounted on the boat trailer, or finally a paint sprayer compressor. It's pointless carrying the weight of batteries and a high capacity bilge pump, when you are only going to use them whilst retrieving the boat onto the trailer. C'mon guys. Think it out. Lateral thinking eh?

    Pericles
     
  7. Claus Riepe
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    Claus Riepe Junior Member

    That has been thought out. The air pressure would be very difficult to control, and could quite easily burst the structure, the surface areas of a large tank are so big.

    Swallowboats did some lateral thinking too: The ballast tank can be filled and be emptied 'on the fly' using self-bailers, and/or through using a standard bailing pump.

    C.
     
  8. Guillermo
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    Guillermo Ingeniero Naval

    Yes, airing a tank under pressure is dangerous. On top of that you have to carry the weight of the air cylinders, compressor or whatever, while still needing the batteries for other services.
     
  9. Pericles
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    Pericles Senior Member

    Dumping water ballast from sailboat keel.

    I have to disagree on two points Claus and Guillermo. Scuba diving regulators are extremely accurate in metering air flow to the mouth piece, plus they perform this task whilst operating at varying depths. Quality control is absolute. Controlling the top pressure on the water inside the keel, which is tall and thin, rather than a ballast tank, would mean a far safer situation. 15 lb per square inch would be sufficient, bearing in mind that the boat is still in the water and the outside pressure is equal to the inside pressure. As soon as air starts to bubble up, turn off the valve and haul the boat out.

    I also wrote that the compressed air is only required to pump out the ballast water when retrieving the sailboat onto its trailer. Therefore the pump apparatus stays with the trailer and does not accompany the boat to sea.

    Pericles
     
  10. Claus Riepe
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    Claus Riepe Junior Member

    Pericles,
    you will know that Scuba regulators need regular professional service to reliably work properly, once a year is the usual interval.

    But then, why would one need to airpressure-pump water out during retrieving? Before all else, I would let gravity do the job.

    C.
     
  11. Pericles
    Joined: Sep 2006
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    Pericles Senior Member

    Remember, the boat is in the water with the water ballast still in the keel. Pump out the water with the compressed air. The boat is lighter to retrieve. So what, if the regulator needs servicing once a year? As it happens, as the regulator is not going to be used underwater, it probably won't require so much servicing.

    Anyway, this is just an idea. It just needs refinement.

    Pericles
     
  12. Claus Riepe
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    Claus Riepe Junior Member

    Well you may wish to refine it so. We have long discarded it.
    C.
     
  13. Pericles
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    Pericles Senior Member

    Nope,

    Not interested in wind driven craft.

    Sorry about that.

    Pericles
     
  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    In most cases the water should flood the tank(s) without need for pumping following or during launch, and can drain out while the boat is being raised from the water. The lifting weight need not be much more than the empty weight of the boat to get the water to exit under gravity. Pumping out before lifting will get you reduced draft but not much reduced weight, since you would hardly remove the boat completely before opening the drain cocks since that would put unnecessary strain on the structure.

    Unless you need to reduce draft, why use a pump to raise the boat, when you can use something with serious power like a hoist or tow truck?
     

  15. Claus Riepe
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    Claus Riepe Junior Member

    Hand air-pump

    We actually have gone air-pumping. Found a big manual airpump with 5 ltrs. volume per full stroke, and with safety over-pressure indicator.

    We use it when the wind drops in mid-race. The crew then pumps a little air pressure into the tank in order to help the selfbailers drain out the water quicker.
    Also, when the boat has come home into the marina with full ballast tank, the airpump works more efficiently than the water bailing pump to get the tank completely dry.
    C.
     
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