Boat weight increase due to the marine growth

Discussion in 'Stability' started by daiquiri, Aug 21, 2013.

  1. daiquiri
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    A simple question (for a probably no simple answer) for you guys:

    Does anyone have some reliable numbers about how much weight is added to the hull by the marine growth?
    Like kg/sq.meter per month (or per year) would be a great info, but even the real-life examples stating the total weight increase for a given boat type can be useful (I will then do the required calcs).

    This Norwegian report: http://www.diva-portal.org/smash/get/diva2:566182/FULLTEXT01.pdf gives (for the north seas) gives the following data:
    - Page 23: thickness of mussels fouling after 2 year period: 80 mm (0.08 m)
    - Page 26: mass density value of the biofouling: 13 kN/cu.m (1325 kg/cu.m)​
    which translates into 1325*0.08= 106 kg/sq.m of added weight over a 2-year period, which sounds like an enormity to me (though it might be true). In the southern seas I would expect the time period for the same weight increase to be much shorter, but how much - 4 months, 6 months, 1 year...?

    What do you guys say?

    Thanks in advance. Cheers!
     
  2. michael pierzga
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    michael pierzga Senior Member

    I guess a mussel is 90 water ? Need to know the weight of the shells in sea water.
     
  3. MikeJohns
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    MikeJohns Senior Member

    Slavi
    If you are looking for moored structures and the weight increase you should be working on (1325 - 1025) kg/m3 approx and 80mm seems like a reasonable level of fouling for an un-treated surface. No operational vessel would ever be allowed to get so fouled.

    I notice that moored hulks tend to shed their growth in sheltered bays as the mussel growth gets too heavy ( recursive mussels growing on mussels ) and falls off. But I'd say the average was probably closer to 120-150mm in those cases.
     
  4. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    Thanks Mike (and Michael). Your numbers give me approx. 35 kg/sq.m for 120 mm of mussels, which sounds like a reasonable upper value to take account of.

    Yes, it is about a permanently moored structure with an unknown hull cleaning schedule, so the upper boundary of the weight growth is what I needed.

    Thanks again. Cheers! :)
     
  5. michael pierzga
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    michael pierzga Senior Member

    The weight gain must be small. Antifoul paint is heaver than sea shells. Resistance to movement..waves, stream is obviuosly great if the vessel is forested with growth.
     
  6. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    I agree Michael. Regarding the resistance, as I said it is a permanently moored structure. Can move only towards the sea bottom, if something goes wrong. :p
    Cheers
     

  7. michael pierzga
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    michael pierzga Senior Member

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