# Boat weight increase due to the marine growth

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

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### daiquiriEngineering 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?

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### michael pierzgaSenior Member

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

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### MikeJohnsSenior 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.

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### daiquiriEngineering 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!

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### michael pierzgaSenior 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.

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### daiquiriEngineering 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.
Cheers

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### michael pierzgaSenior Member

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