I noticed there had not yet been any response after a few days to your inquiry.  It might be helpful to provide a little more or clarifying information to get better response.   e.g. it may not be clear to all exactly what you are referring to as some sort of intake pipeline (of whatever size? and somehow on some sort of "supports") "dipped in sea"?  Right or wrong I am envisioning (maybe reading between the lines a little based on the verbiage you have provided) that you are dealing with some length of some size fiberglass piping with some sort of joints residing more or less permanently on some sort of supports directly immersed in the water (and whatever is in it/actions of it?) above the seabed.  
I guess those who are advocating you instead bury the line some elevation below the seabed may be thinking the line may be more protected from various actions/impacts/exposures in so doing  (and less chance of damaging impacts from large somewhat floating piles. wrecks, anchors, hurricanes, tsunamis, or vessels/runaway vessels etc.??)  I think in areas this may even be required by regulatory bodies.  
Those who are advocating more supports or more uniform supports may be of a school of thought that "redundancy" is good in such an application (from the standpoints of the pipeline, supports and/or the anchorages by which they are fastened together etc. for long-term service, for perhaps these same and/or other reasons).  
I think plastic or polymer type pipes also have different short-term and long-term or creep moduli, and choice of longer term modulus for inexorable loadings could result in need for more supports.   Finally, if you insist on an essentially exposed line you may wish to consider impact resistance and effects of various exposures on the pipe you choose for normally some rigorous subaqueous service.      

Bury it unless there is some reason not to.

Am I right in thinking that you want to use the surface water or at least 5m off bottom for the intake to avoid silt intake etc. In which case a buried pipe still has to have an end section 5m up into the water column.

Is the whole pipe 26m long or only each individual pipe? What size is it? What size waves will attack it? Where is the 12000lb force coming from.

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