I don't whether this is any use to you. The NORSOK Standard N-003 Actions and Action Effects states:

"The weight of marine growth is classified as a variable functional action. Unless more accurate data are available, the specific weight of the marine growth in air may be set equal to 13 kN/m^3"

http://www.standard.no/pronorm-3/data/f/0/01/39/9_10704_0/N-003.pdf

It must be noted that marine growth varies over depth and location.

Hi friend,

really very thankful....

but as you qouted:


the specific weight of the marine growth in air may be set equal to 13 kN/m^3"   <===== how can be marine growth is possible in air. It should be in sea...

what u say?

Thanks

I spoke with one of the Caesar modellers at my work to see how they deal with it.  Most of the work we do is at a water depth great enough so marine growth is not considered.

To my way of thinking if that is the density in air, the submerged density should be less than this. So you could argue its conservative.

I dont really know of anything else I'm afraid.  I checked API RP2A which covers it for US waters but it only covers thickness.

I've used in the past 110mm of marine growth within of a depth of 0 to 30m.  Density of 1400kg/m3 in air and 373kg/m3 in water.

This was project specific, reference from the DBM... but it appears to be inline with the Norsok referenc.

The marine growth in air question is easily solved.

There is marine growth above the low tide mark and in the splash zone, so depending on the tidal range and the wave height, marine growth in air is quite possible. Look on any rocky beach at low water.

Dear friends,

all thanks for ur valuable comments.

Thanks

Offshore Technology Conference paper 3386 "The effect of marine growth on the performance of fixed offshore platform in the north sea" give the density of marine growth as 1.3 .

1.3 x D  ???

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Post of Jul 20 should have stated SPECIFIC GRAVITY of marine growth is 1.3.

Well, shell may have a specific gravity of 1.3, but the "thickness" of marine growth is not "solid" by any means.  I am a scuba instructor that has had the opportunity to make many dives, some on pipelines that I had designed many years previously.  In the GOM, they are covered with barnacles, sponge, sea fans, and some spiney oysters to a thickness of 8 to 10 sometimes 12 inches or so at the extreme areas of growth.  If one were to take a solid thickness equivalent, I doubt that it would be more than 2 or 3 inches.  Additionally marine growth is much more near the surface than at lower levels.  Below 60 feet, there's perhaps 1/3 of what you will find at 10 to 20 feet.  What is really important is that a drag factor be chosen that is much higher than a normal cylinder.  Something like 1.3-1.5 might be a good approximation.

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Nothing major, just a technical correction to a vaule given by Tahmasbi.  The density used for seawater should be 1025 kg/m3 to 1030 kg/m3, not 1000 kg/m3 which is fresh water.

That's ok, we already guessed, but I do like conscienciousness!

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