SASless,
Let me attempt to answer two of the questions you have asked - or more correctly put my previous answer into context.
A standard ‘touchdown marking’ (soon to be called the ‘touchdown/positioning marking’) is a circle with the inner diameter of half the ‘D’ value of the helideck; the line width should be 1m. That these circles are not 0.5D in Nigeria does not alter the fact that it is the de jure Standard, only that the Standard is not being applied - the same is true for survey boats.
I totally agree with ‘check’ that a non-standard marking should be reported (confidentially if necessary). Once it has been reported that the ‘touchdown marking’ is incorrectly marked/positioned, any accident/incident that results from the incorrect marking will then be the joint responsibility of the ‘duty holder’ and the ‘operator’; an extremely powerful way of achieving rectification.
The second question - what is a ‘standard helicopter’ was addressed in my first post; to expand further, the 0.5D appears to be a ‘magic circle’ - go to the Flight Manual of your offshore helicopter and measure from the end of the tail rotor to the pilot’s seat, it usually comes out extremely close to 0.75D. There is no such thing as a standard helicopter but, as a generic marking to assist the pilot with the positioning of any helicopter on a helideck, it is as good as it gets (without individual tailoring). The geometry of the undercarriage appears to have no relevance to this equation.
The geometry of the undercarriage does have relevance to the size of the required TLOF - required in the sense that it will work for any helicopter within the D limits of the helideck - which has to be as large as 0.83D.
I would not disagree with your contention “one simply has to know where to place the wheels/skids on each deck to ensure avoiding the ‘boinking noises’” - but it results in an individual exercise for each deck and for each specific helicopter; for that reason I fail to see why you regard the use of ‘D’ and the ‘0.5D’ touchdown marking as crap.
As an initiator of many a call for safer practices, surely you see the logic of the use of an existing, and safe, Standard.
Jim