Question

The marine growth weight has not been included in the member elements. The 7.5% self-weight factor was applied to the member elements' weight only. I have commented out the marine growth cards as well to check and the weights are the same. Please can you advise how to include the marine growth weight? 

Answer

By default, adding marine growth in the model input does not automatically increase member diameter or mass in subsequent Dynpac analyses. To ensure marine growth effects are included, you need to configure the analysis properly.

1. Enable Marine Growth in Seastate

Run Seastate with the DYN option specified in columns 56–58 of the LDOPT line. This step updates hydrodynamic properties and generates a structural data file (.oci) with marine growth applied. 

2. Use the Updated Model in Dynpac 

Run Dynpac using the .oci file created by Seastate. This ensures marine growth effects are carried forward into dynamic analysis.

3. Marine Growth Weight Assumptions 

By default, SACS assumes marine growth is neutrally buoyant (density = water density).

If the marine growth density field (columns 49–56) is left blank, the weight and buoyancy cancel each other out, and no additional weight is applied.

   

If you want to include the marine growth weight in the calculation, do the following:

a) Select the 'DYN' option in columns 56-58 in the LDOPT line.     

       

b) Run Seastate to output the seastate OCI file. The seaoci forces were reduced by taking into account the DELGRP, DELJNT, MEMOV, and GRPOV.

c) Make some modifications in the seaoci:

• Copy LDOPT from sacinp. and make sure to use the 'CMB' option to 'combine loads to basic option' as we will be creating a seainp. later, as in this seaoci the marine growth was not included.
• Activate the HYDRO line     

d) Run Dynamic - Extract Mode Shape Analysis. Use seaoci from the seastate analysis as the input and you will see below changes in the dynlst:

• MEMBER PROPERTIES IN DYNPAC 

       

       

•     The member elements now include Marine growth weight. 

       

For clarity,

1. Seastate run: 

   

2. Dynpac run including marine growth without 1.075 factor 

   

3. Dynpac run including marine growth with 1.075 factor 

   

Element weight (seastate) = 37944kN

Element weight + marine growth (dynpac) = 38400.906kN

(Element weight + marine growth) x 1.075 = 41280.973kN

If you notice no change in weight after adding marine growth, it's usually because:

• DYN wasn't specified in Seastate, or
• The marine growth density was left blank, making it effectively weightless.