Irwin 25 Floatation

Discussion in 'Sailboats' started by seasailor55, Nov 6, 2020.

  1. seasailor55
    Joined: Oct 2010
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    Location: Lake Charles, LA.

    seasailor55 Senior Member

    Got it out of the water today. 13,000 pound excavator tied onto it and dragged it ashore, Total loss.
     
  2. seasailor55
    Joined: Oct 2010
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    Location: Lake Charles, LA.

    seasailor55 Senior Member

    FCC61951-DC1C-4F0A-9762-319BB9E358F4.jpeg Not a happy ending, but it’s out of the slip. You can see the source of the sinking. A 2” split in the keel about 12 inches forward of the rudder.
     

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  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Oh dear, that is sad news. :(
    It looks like the mast was damaged / broken as well?
    I suppose the only positive aspect is that you managed to get her out of the water, such that she is no longer a liability to you there.
    However I wouldn't be surprised if it still costs a fair sum to properly scrap her now.
     
  4. seasailor55
    Joined: Oct 2010
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    seasailor55 Senior Member

    It would have been nice to have saved the mast and the stern pulpit, but unfortunately both were damaged. We saved the lead ballast (2200 lbs) and will recycle it to help cover the costs. The excavator reduced the rest to a pile of rubble and put it in a rolloff dumpster.
     
  5. seasailor55
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    seasailor55 Senior Member

    Never did get my question answered. How much flotation is required to get a 5500 pound to the surface? Someone that said a submerged boat weighs less, while someone said more is needed because of the suction of the mud. Had it been in 50' of water on a hard bottom what would it have required? Any naval architects out there?
     
  6. bajansailor
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    bajansailor Marine Surveyor

    The lead keel is very dense, hence we can assume that the reduction in buoyancy needed for it would be very little / negligible. so it will need 2,200 lbs.
    That leaves 3,300 lbs for the rest of the boat.
    However this is built of materials with different densities - fibreglass, plastic, aluminium...... their weight underwater will still be less than their weight out of the water. If it is say 2,800 lbs underwater (a wild guess), then the total weight underwater is approx 5,000 lbs / 2,270 kg.
    If you had floats on the surface, attached to ropes suspending the boat underneath the water, totally immersed, then if the boat is in fresh water, 2,270 litres of floatation would hold the boat in equilibrium, as one kg of fresh water has a volume of one litre.
    If the boat is 50' down, and you use scuba tanks to go down and attach airbags to her, you will need a lot more than 2,270 litres of air from the tanks used to fill the air bags, as the pressure at 50' is much greater than at the surface. In fact the pressure at 10 metres / 33' depth is double atmospheric pressure And at 20 metres / 66' depth the pressure is 3 times atmospheric.
    So at 33' depth you would need 4,540 litres of air to lift the boat, and at 66' you would need 6,810 litres of air.
    If you fill the airbag at depth, the air will expand as the boat rises - I think that lifting bags have valves on the top of them so that air can be released as required, to control the rate of ascent.
     
  7. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    As bajansailor says, there is no answer to your question. The weight of the boat is diminished by the buoyancy caused by the displaced water. To know how much water is displaced by a sunken boat you need to know the volume of every part of the boat (its weight divided by its density) and in addition to this the volumes of in some spaces, compartments or devices trapped air.
     

  8. seasailor55
    Joined: Oct 2010
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    seasailor55 Senior Member

    Excellent explanation gentlemen! I never knew there were so many variables in the equation. Having never dealt with a sunken boat and under pressure from the Harbormaster to raise it and get it out of the slip, I was looking for the quickest, simplest way to accomplish this, and wanted to have a plan in place before I started securing pumps, flotation, and divers.
    As stated, in the end floatation was unnecessary. We cut the stern lines, attached a 3" tow strap looped around the bow cleats and under the nose of the boat with a shackle, and led it to the bucket of the excavator. The Operator dropped the grader blade to hold the machine in place and slowly withdrew the bucket, sliding the boat across the slick mud. When he got it close enough to reach it with the machine he plunged the bucket though the cabin top into the keel and pulled it up over the broken concrete riprap breakwater. The water in the boat drained when the concrete punctured the hull and he slid it across the grass to the dumpster. The whole thing took less than an hour.
     
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