Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

On-board trend analysis for cargo vessel hull monitoring systems
1)

Oleg Gaidai1), Gaute Storhaug2), Fang Wang1), Ping Yan1), Arvid Naess3), Yu Wu1), Yihan Xing4), Jiayao Sun5)

Shanghai Engineering Research Center of Marine Renewable Energy, College of Engineering Science and Technology, Shanghai Ocean
University, Shanghai, China2)
Det Norske Veritas, DNV Maritime, Oslo, Norway
3)
Norwegian University of Science and Technology, Norway
4)
University of Stavanger, Norway
5)
Jiangsu University of Science and Technology, Zhenjiang, China

decays slowly because of low damping, which results in whipping being
superimposed on both the wave sagging and wave hogging cycle. The
challenge is that the whipping may be of more freak nature than the moreconventional wave bending considered in design.
Predicted stress level obtained by extrapolation is focused on extreme
value for the sake of vessel hull safe navigation. Extrapolation by ACER
(averaged conditional exceedance rate) method was done, including
uncertainty bands.
Main motivation for this paper is to contribute to the development ofreliability assessment methods for decision support on board ships which
may facilitate an improved balance between safety and structural design.
Seamanship is already a factor in ship design but through digitalization
it may be enhanced allowing for some steel optimization withoutcompromising safety.

ABSTRACTWith the increased focus on sustainability, de-carbonization anddigitalization also the shipping industry is scrutinized. High steel weight
implies high initial CO2 footprint but also higher operational CO2footprint. With requirements to decreased emissions through IMO
indices EEDI and CII, it is beneficial to lower the steel weight but
without compromising safety. Utilizing sensor technology may enhance
the safety and potentially allow for a more optimized structural design.
For hull girder loading this is related to hull stress monitoring systems.
Container ships are becoming increasingly important in the shipping
industry. As manufactured goods are increasingly containerized, thecontainer ship fleet has expanded.
According to DNV’s hull monitoring rules, it is required to provide aforecast prediction based on recent measurement data to alarm thecaptain of potential extreme hull girder loading. If this forecast prediction
is too low then a false impression of safety is provided, and if theprediction is frequently too high the captain may lose confidence in thesystem. These results are not acceptable, and it is therefore necessary that
this prediction is reliable. This paper highlights modern challenges andideas, incorporating novel statistical method to serve safe navigation.
Trans-Atlantic voyages along with monitored onboard hull girder
response data are discussed.
Sequence of the latest data from each individual sensor shall be displayed
as a trend. Current rules states that 4-hour data sequence from eachindividual sensor shall form the basis for a forecast trend prediction of
the expected response for at least the next hour. Encountered maximum
stress may overshoot predictions by 50%, which is regarded unreliable.
If too high values are predicted all the time, captain lose confidence andtrust in the system trend analysis. If too low values are predicted thesystem provides false impression of safety. Both outcomes areunacceptable.
Special focus is paid to whipping, which is defined as a transient hullgirder vibration phenomenon caused by wave impacts. The vibration

KEYWORDS
ACER, ship hull, whipping, reliability, extreme stress, container vessel.

INTRODUCTION
The latest DNV rules “Hull monitoring systems - HMON”, (DNV rules
for classification Ships, 2021) clearly requires early warning from the onboard software tool to warn captain about potential incoming extreme
hull girder loading. Hull girder loading are of critical concern for vessel
safety, as extreme loads may cause not only rapid fatigue damage but animmediate local or global collapse of the hull girder. Guidance note
(DNV rules for classification Ships, 2021) DNV-RU-SHIP Pt.6 Ch.9
Sec.3 states: “It is recognized that no extrapolation method is regarded
perfect for all responses at any time. Extrapolation should focus on theextreme value. Extrapolation by a Weibull fit should be done as aminimum, but other methods can be used simultaneously to improve thereliability and include uncertainty bands”. With container vessels sizes

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