presentation - 4th International Symposium of Maritime
Transcript presentation - 4th International Symposium of Maritime
Sonar Technology as a Control Option
of Oil-Spill Risk due to Ship Groundings
Tzannatos, E. and Xirouchakis, A.
Department of Maritime Studies
University of Piraeus – Greece
4th International MASSEP Conference
30 & 31 May, 2013 - Athens - Greece
The Need: Why ?
Ship groundings have been historically responsible for the loss of life and property at sea, as well as for the
pollution of the marine environment.
Almost 25 years ago, on the 24th of March 1989, the “Exxon Valdez” grounded on Bligh Reef, a well known
navigation hazard, ruptured 8 of its 11 cargo tanks and spilled 11 million gallons of crude oil into the pristine
waters of Prince William Sound. The coast of south-east Alaska became the setting of an oil spill accident
which by the MARPOL amendment in 1992 brought about one of the most important regulatory changes in
ship design, the double-hulling of oil carriers. Being purely a technical pollution prevention measure, it did
not address the human error as the root cause of shipping accidents but aimed at the control of the
grounding consequences. However in October 1989, in response to the HFE accident of 1987, IMO adopted
the “Guidelines on Management for the Safe Operation of Ships and for Pollution Prevention” which became
the stepping stone for the most important operational regulation on shipping safety, that of the ISM Code,
which was introduced through the relevant SOLAS amendment in 1993.
Despite the effort to improve ship’s bridge performance over the years by implementing various technical
and operational measures, ship groundings continue to dominate the picture of shipping accidents. Amongst
them, the most recent of ‘M/S Costa Concordia’ in the Tyrrhenian Sea and ‘M/V Rena’ of the coast of New
Zealand have reiterated the importance of navigational errors and the need to maintain the impetus for
improved ship bridge control.
The Objective: What ?
In enhancing shipping safety, the application of Formal Safety Assessment (FSA) as “a rational and
systematic process for assessing the risks associated with the shipping activity and for evaluating the
costs and benefits of options for reducing these risks” has been institutionally (i.e. by IMO)
acknowledged to be a most appropriate course of action.
To this extent, the present work aims at submitting the hull mounted forward looking sonar (FLS)
technology to the FSA “test” for assessing its suitability as a Risk Control Option (RCO) of powered
groundings, whilst the case of oil carriers was considered to be of particular importance because of
the high contribution of groundings to the accidental (i.e. large scale) pollution of the marine
environment caused by these ships.
The Method: How ? An adaptation of:
Definition of Goals, Systems, Operations
Options to decrease
Cost Benefit Assessment
Options to mitigate
Oil Spill Risk Data
(oil carrier groundings & contacts in 2004-2007)
Sources: International Tanker Ownership Federation Limited database, Lloyd’s Casualty Database and Intertanko Casualty
Oil Spill Risk Data
(oil carrier hard groundings & contacts in 2004-2007)
Ship’s Obstacle Avoidance Capability
(as a function of FLS detection range)
A ship will avoid the obstacle ahead provided that within the FLS
detection range will be possible to accommodate: a) the circle
manoeuvre, b) the response of the bridge crew to the verified
obstacle detection and c) the obstacle detection verification,
RN ≥ (TM + TH + TN) x VS
RN = FLS detection range (m)
VS = ship’s speed (m/s)
TM = time for circle manoeuvre (s)
TH = time for bridge crew response (s)
TN = time for obstacle verification (s)
Assuming that the time, TM, required to sail the “advance” distance of
the circle manoeuvre is given by:
TM = k x (LS/VS)
K = circle monoeuvre coefficient (=4)
LS = ship’s length (m)
a ship will be able to avoid the obstacle ahead provided its length, LS ,
follows the expression:
LS ≤ ¼ x [RN – (TH x VS) – (TN x VS)]
For the maximum commercially available RN = 900 m and assuming TN
= 5.1 s, TH = 10 s and VS = 7.2 m/s (14 knots), the FLS is technically
effective for all oil carriers up to and including the handymax category.
For the Aframax (LS=250m), Panamax and Suezmax (LS=300m) and
VLCC (LS=340m), the minimum FLS detection range for obstacle
avoidance is 1108, 1295 and 1457 m, respectively.
Source: ABS (2006).
Ship’s Obstacle Avoidance Capability
(as a function of FLS System reliability)
% Reduction of Groundings
Criterion of FLS Acceptance
The difficult part of setting the environmental criterion for the acceptance of any RCO (incl. FLS) is to define and
evaluate the Cost of Averting a Ton of Spilled oil, CATS (MEPC 62; MSC 91). The work by Kontovas and Psaraftis
(2009) and Psaraftis (2008) is most informative on the challenges involved in this issue.
For the purposes of the current analysis, it is assumed that:
CATS ≤ F x Spill Cost
F = assurance factor reflecting society’s WTP for prevention rather than cure
= 1.5 (Skjong et al., 2007; Vanem et al., 2008).
Spill Cost = damage cost + clean-up cost
CATS = 80,000 $/ton (Psarros et al., 2011)
For FLS acceptance:
CATS ≤ ΔC / ΔR
ΔC = Cost of FLS ($/Ship)
ΔR = Oil Spill Risk Reduction offered by FLS (ton/ship)
Cost of FLS (detection range 900 m)
Initial ($) *
Operational ($/year) *
(for 6 persons)
IC = 172,000
Replacement & Repair
1112 + 1000
YC = 3812
* Based on manufacturer’s information.
ΔC (NPV) = FLS Cost in NPV
IC = Initial FLS Cost = 172,000 $
YC = Yearly FLS Cost = 3812 $
i = number of year
y = duration of investment = 25 years
r = discount rate = 5%
Oil Spill Risk Reduction (Handy Category)
ΔR (tons/ship) = ΔG (%) x Existing Risk (tons/ship-year) x remaining ship’s life (years)
= 0.703 x 0.084 x 24 = 1.48 tons/ship
Technical and Economic Effectiveness of FLS System
FLS Cost as a Function of Detection Range
FLS Cost (million $)
Minimum requirement for FLS Detection Range (m)
A technically and economically effective FLS for all ships will require an increase in
detection range by 62%, to be offered at a 25-fold increase in cost !!!!!!
For the maximum commercially available detection range of 900 m, the FLS is effective for
obstacle avoidance by all ships up to and including the HANDY category.
The minimum FLS detection range for obstacle avoidance by SUEZMAX and VLCC must be
43.9 and 61.9% higher than the maximum commercially available FLS range, respectively.
The FLS is economically ineffective for the reduction of oil spill risk associated with all ships
of the HANDY category. It would have been cost effective for this ship category if the cost
of FLS was 46.1% lower.
The FLS would have been economically effective for the reduction of oil spill risk
associated with SUEZMAX and VLCC provided its cost was lower than 1.33 and 5.58 million
$ per ship.
ABS (2006) Guide for vessel maneuverability. American Bureau of Shipping, ABS Plaza, 16855 Northchase Drive, Houston, TX
Kontovas, C. and Psaraftis, H. (2009) Formal Safety Assessment: A Critical Review, Marine Technology, 46:1, pp. 45–59
McGrecor, J., Moore, C., Downes, J. and Aksu, S. (2009) Evaluation of the Environmental Risk of Aframax Tankers, WMTC 2009,
Jan. 21-24, Mumbai, India.
Psaraftis, H. (2008) Environmental Risk Evaluation Criteria. WMU Journal of Maritime Affairs, 7:2, pp. 409–427.
Psarros, G., Skjong, R. And Vanem, E. (2011) Risk acceptance criterion for tanker oil spill risk reduction measures. Marine
Pollution Bulletin, 62:1, pp. 116–127.
Skjong, R., Vanem, E., Endresen, O. (2007) Risk Evaluation Criteria, SAFEDOR Report:, SAFEDOR-D-4.5.2-2007-10-24-DNVRiskEvaluationCriteria-rev-3.0.
Vanem, E., Endresen, O., Skjong, R. (2008) Cost effectiveness criteria for marine oil spill preventive measures. Reliability
Engineering and System Safety, 93:9, pp. 1354–1368.