Page 29 - Navigator 2021

to which it will be rolling beforehand.”
GATHERING AS MUCH DATA AS POSSIBLE
Reason for Blankenburgh to gather as much data as possible over the period 2012 – 2020 from the NMS equipment (Navigation Marginal Ships) in the Rotterdam-Rijnmond region, the fairway records kept
by fellow pilots and an overview of all the issued tidal windows by Protide in the Netherlands. The pilot next used all this as his starting point for in-depth analyses. “It was a very intensive process. The PC
at my house would regularly be running for hours on end to perform yet another run.” Blankenburgh’s ‘quest’ also involved what many laymen would consider complicated mathematical formulas, bar charts and point clouds in order to gain insight into the differences between specified, estimated and measured roll periods. On the basis of all the analysed data, the input provided by the ships themselves proved to be inaccurate in many cases.
NEW OPTIMAL ESTIMATION FORMULA
After months of intensive research and comparing data, the conclusions are clear for Blankenburgh. The outcome is a new calculation formula for optimally estimating the roll periods of large tankers and bulk carriers. He also recommends using a bandwidth that expresses the uncertainty of the actual roll periods. “The data show that comparable ships with comparable cargo also show comparable roll periods. This makes it possible to correctly estimate a roll
period. Using the IMO formula that every seafarer knows - including corrections for the so-called Free Surface Effect - leads to more inaccurate estimates, as my data confirms. Based on my research, it
is better to set this free surface effect correction to zero and to use a fixed inertia constant based on the statistics, both for tankers and bulk carriers.”
Of course, Blankenburgh hopes that his research will receive widespread acceptance and that the results will actually be used in practice for determining tidal windows in the future. He certainly has the backing of MARIN (Maritime Research Institute Netherlands). They validated Blankenburgh's research method and reviewed the final report. “If one wants to put this into practice in Protide, then research will first need to be conducted into the roll periods of other ship
types than the ones I have focused on. But in the end, the better this estimate, the more accurate the tidal window, the safer operations will be for all parties involved!”
50
45
40
35
30
25
20
15
10
5
Figuur 15: gemeten slingerperiodes per groep
scatterplot gemeten Tφ vs geschatte Tφ VLCC, 60m breed, N=344
0
12 13 14 15 16 17 18
Figuur 16: scatterplot VLCC,60m meting vs opgave en schattingen
Meting →
Tφ opg Tφ vlgn Tφ opti
ave schip
s [IMO,2009]
male schatting: C =
0.344; vvc = 0
‘The outcome is a new calculation formula for optimally estimating the roll periods of large tankers and bulk carriers’
29
Schatting →