1 The Effect of Tonnage Measurement Regulation on Ship Design and Safety Capt.Ahmed Hamdy Collage of Maritime Transport and Technology مستخلص الخر حولء الى ا ميناقل منلبحار تنة عبر التجار ا عالم و ت بع ا لذلكتحصيل هناك معيار موحد ل ان يكونفق المجتمع البحري اتلدولية نظام عشر اقرت المنظمة البحرية التاسعفي القرن اينة. ف لحمولة السفلسفن طبقادارية من االرسوم الميناء و رسوم اي اقرتلة والتلحمو الدولية للمعاهدةتج عن ذلك اغاتها ونن وفراب حجم السفد لحساموحيق و دق حموللسفن تين لة كلية حموللة صافية وحمو وكليةحمولة الل تطبقا ل المب رسوم تحسارية. لذلك بددالرسوم ا يناء و أيم السفينة تغيير تصمن فيصمموا السف مك السفن عنح اكبرلميق رببضاعة لتحقلت السفينة المخصصة لغادة فرام وزيا تخفيض الرسوكلية بغرض الحمولة اليلتقل ل تناقمنطلقر. فمن هذا اللبحالى انة في أعا اتزان السفيي تؤثر عليء السفن التلهامة فى بنات المكونا طريق اختزال بعض ا ش الورقة البحثية ا هذةر فيبة عن هذا التغييرتر المت ثايم السف تصملسفن و خاصمة واتزان ا ن علي س ةن الكبيرة فى الحجم السفت النفط ناقلحاويات و سفن مثل سفن ا. Abstract Shipping industry is running from port to port all around the world. So ships have to pay charges such as: port fee, administrative charges and other dues, so the maritime community decided to have one scale to collect these charges upon the tonnage measurement. Finally, in 1959 the IMO started to discuss adopting international standards for tonnage measurement system to have an accurate measurement for the volume of the ship and its size. As a result, the International Convention on Tonnage Measurement of Ships was adopted by IMO in London in 1969. According to this convention, any ship must have gross and net tonnage, which the ship has to pay the port dues depending on the gross tonnage and the bigger the gross, the higher the port fees. Therefore, the navel architects changed in the design of the ships to maximise the profit and minimise the gross tonnage for the benefit of the ship-owners. For such changes, this paper will discuss the effect of tonnage measurement regulation on ship design and safety, as well as the effect on the longitudinal strength, stability of the ship, freeboard, reserve displacement and free ports.
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1
The Effect of Tonnage Measurement Regulation
on Ship Design and Safety
Capt.Ahmed Hamdy
Collage of Maritime Transport and Technology
مستخلص
اتفق المجتمع البحري ان يكون هناك معيار موحد لتحصيل لذلك ابععالم و تالتجارة عبر البحار تنقل من ميناء الى الاخر حول ال
رسوم الميناء والرسوم الادارية من السفن طبقا لحمولة السفينة. ففي القرن التاسع عشر اقرت المنظمة البحرية الدولية نظام
حمولة كلية تين للسفنحمول دقيق وموحد لحساب حجم السفن وفراغاتها ونتج عن ذلك المعاهدة الدولية للحمولة والتي اقرت
مصمموا السفن في تغيير تصميم السفينة أيناء والرسوم الادارية. لذلك بدتحسب رسوم المتطبقا للحمولة الكلية وحمولة صافية و
لتقليل الحمولة الكلية بغرض تخفيض الرسوم وزيادة فراغات السفينة المخصصة للبضاعة لتحقيق ربح اكبرلملاك السفن عن
ش طريق اختزال بعض المكونات الهامة فى بناء السفن التي تؤثر علي اتزان السفينة في أعالى البحار. فمن هذا المنطلق تناق
السفن الكبيرة فى الحجم ةن علي سلامة واتزان السفن و خاصتصميم السفثار المترتبة عن هذا التغيير في هذة الورقة البحثية الأ
.مثل سفن الحاويات و سفن ناقلات النفط
Abstract
Shipping industry is running from port to port all around the world. So ships have to pay
charges such as: port fee, administrative charges and other dues, so the maritime community
decided to have one scale to collect these charges upon the tonnage measurement. Finally, in
1959 the IMO started to discuss adopting international standards for tonnage measurement
system to have an accurate measurement for the volume of the ship and its size. As a result, the
International Convention on Tonnage Measurement of Ships was adopted by IMO in London in
1969.
According to this convention, any ship must have gross and net tonnage, which the ship
has to pay the port dues depending on the gross tonnage and the bigger the gross, the higher the
port fees. Therefore, the navel architects changed in the design of the ships to maximise the
profit and minimise the gross tonnage for the benefit of the ship-owners. For such changes, this
paper will discuss the effect of tonnage measurement regulation on ship design and safety, as
well as the effect on the longitudinal strength, stability of the ship, freeboard, reserve
displacement and free ports.
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1. Introduction
IMO has expressed concern about the adverse effect of gross tonnage (GT) reduction
that enables ship designers to minimize the volume of enclosed spaces above the
waterline such as freeboard, superstructures, deckhouses, sheer, hatch coamings and
hatch covers (IMO, 2007a) and crew accommodation (IMO, 2003b). Moreover, open
top container (IMO, 2007b) and smaller depth design (Grey, 2002) are possible ways to
reduce GT. Consequently, they will influence the design and ship safety which cause
loss of life and property. This paper will discuss the impact of the above methods to
reduce GT and how to lessen their negative effects.
2. The design and ship safety parameters
2.1 Longitudinal strength and ship safety parameters There are at least two factors that influence longitudinal strength: Length/Depth ratio
(L/D) and superstructures. L/D ratio contributes to longitudinal strength (Dokkum, 2008),
when a ship experiences hogging, sagging forces regularly and cargo weight. Depth has significant
effect on ship’s stress. Stress distribution in a beam can be calculated as follows (Smith, 1981).
P = M x y P = Stress at distance y from neutral axis, N/m2
I
M= Bending moment, N.m
I = Second moment of area, m4
Figure 1 illustrates the relationship of the transverse bending stress among the depth of the ship.
As a result any increase in number of stress along the ship will increase deflection and lessen
longitudinal strength which may damage the propeller shafts, pipes, ceilings and other structures
may collapse. Accordingly, the largest L/D ratio will increase deflection and decrease
the longitudinal strength.
3
D
Figure 1. Relationship among D, y and h
to calculate stress
Source: (Rawson & Tupper, 2001)
y1
y2
The adverse effect of lower depth can be minimized by strengthening flanges to
withstand stress especially at amidships such as sheer strake, bilge, bottom and shell
plates which suffer maximum bending moment than other parts. It will maintain the
section modulus which resists bending moment and enables proper transmission of the
shear forces (Schenekluth & Bertram, 1998).
Non-effective superstructures, for example reduced
superstructures, will not support longitudinal strength
because they are not only inadequate in length, but also
they have smaller scantlings than main hull and use
light materials to decrease LWT.
However, superstructures extending at least 0.15L
within 0.4L amidships considered to contribute to
the longitudinal strength (Bureau Veritas, 2006).
Consequently, they must have continuous structures
from main hull with equal scantling and strength
(Figure 2). Figure 2.Good and bad superstructures arrangement.
Source :( Chalmers, D.W.1993)
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2.2 Stability and ship safety parameters
Hatch coverless container is designed to reduce GT because cargo holds are not
enclosed spaces, therefore they exempt from TM 1969 regulation. Ship carries
containers with several layers on deck may arise two problems at least: centre of gravity will rise
and the influence of wind on the ship stability. When the ship is in rolling motion, sea water
will reach cargo hold easier because of coverless. The possibility of hatch coverless container
experience free surface higher than hatch cover container.
Ship carries heavy containers at top layers will rise G position which makes ship unstable. The
arrangement of containers is essential to lower G position, therefore metacentric height (GM)
will reach optimum position. GM affect on GZ (righting lever length) which will
produce stability moment to return ship at upward right position after rolling. Lower GM,
which is caused by rising G position, will decrease stability moment, therefore ship
capsizes at small heel angle. GM should large enough to minimize the possibility of a
serious list under pressure from strong beam winds (Goldberg, 1988). Indeed,
combination between strong wind force which pressures containers above decks and
the lack of securing arrangement causes container loss overboard and influence ship
stability. Consequently IMO (2002) recommended initial GM for all ships should not be
less than 0.15 and the maximum GZ should be at least 0.042 cm for container ship
with L > 100 m.
2.3 Reserve Displacement and ship safety parameters
Reserve displacement or reserve buoyancy is “the volume of watertight hull above the
from a new technology. Maritime Policy & Management. 22 (2), 103-114
2. Bureau Veritas. (2006). Common Structural Rules for Bulk Carriers. Paris: Author.
Chalmers, D.W. (1993). Design of ship’s structures. London: HMSO
3. Clark, I. C. (200) The management of merchant ship stability, trim and strength. London:
The Nautical institute
4. Cleary, W.A., & Ritola, A.P. (1980). Load lines. In Robert Taggart (Ed), Ship design and
construction (pp-173-194). New York: The Society of Naval Architects and Marine Engineers
5. Dokkum, V.K. (2008).Ship knowledge ship design, construction and operation. Enkhuizen, The
Netherland: DOKMAR
6. Goldberg, L. (1988). Intact stability. In E.V. Lewis (Ed), Principles of Naval Architecture
(pp.63-138). Jersey City: The Society of Naval Architects and Marine Engineers.
7. Gray, M. (2002). Time to kill off gross tonnage. The Sea, (159), p.5.
8. Hoogenboom, R. (1994). The ultimate feeder? The technical feasibility of hatch
coverless feeder. SWZ maritime magazine, (1), 20-23. Retrieved February 24, 2008 from world wide web www.knvts.nl/S&W%20archief/Hatch%20coverless%20container%20feeder.pdf
9. International Maritime Organization. (2002).Code on Intact Stability for all types of ships covered by
IMO instruments . London: Author.
10. International Maritime Organization. (2003a, June 5). Adoption of amendments to the
protocol of 1988 relating to the international convention on load lines, 1966 (MSC77/26/Add.1). London: Author.
11. International Maritime Organization. (2003b, July 18). Open-top containerships
International Convention on Tonnage Measurement of Ships, 1969: submitted by The Netherlands (SLF 46/15/2). London: Author.
13. International Maritime Organization. (2005, July 8). Revision of the technical regulations
of the 1966 LL convention a methodology for the revision of the freeboard tables and corrections:
submitted by Japan (SLF 48/9/1). London: Author.
14. International Maritime Organization. (2007a, February 16). Development of options to
improve effect on ship design and safety of the 1969 tonnage measurement convention: submitted by Australia (SLF 50/6/1). London: Author.
15. International Maritime Organization. (2007b, February 22). Development of options to
improve effect on ship design and safety of the 1969 tonnage measurement convention: submitted by ICFTU (SLF 50/6/2). London: Author.
16. International Maritime Organization. (2008). Sub-Committee on Stability and Load Lines
and on Fishing Vessels' Safety (SLF). Retrieved February 23, 2008 from world wide web http://www.imo.org/About/mainframe.asp?topic_id=246&doc_id=1759
Lon
17. J ِ onsson, J.A. (2008). Load line survey. Unpublished lecture handout, World Maritime
University, Malmoِ, Sweden
18. Maritime New Zeeland. (2007). Freeeing ports cover on fishing vessel. Maritime New
Zeeland Guidelines. (7). Retrieved February 24, 2008 from world wide web www.msa.govt.nz/publications/safety_bulletins/issue7-mnz-safety-bulletin-february-