air pollution and energy efficiency

E MARINE ENVIRONMENT PROTECTION COMMITTEE 71st session Agenda item 5

МЕРС 71/INF.29 28 April 2017 ENGLISH ONLY

AIR POLLUTION AND ENERGY EFFICIENCY Supplementary information on the draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions Submitted by Denmark, Germany, Japan and Spain SUMMARY Executive summary:

This document provides supplementary information on the draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions

Strategic direction:

7.3

High-level action:

7.3.2

Output:

7.3.2.4

Action to be taken:

Paragraph 3

Related documents:

MEPC 64/4/42, MEPC 64/23; MEPC 67/4/16, MEPC 67/4/25, MEPC 67/INF.14, MEPC 67/INF.22, MEPC 67/WP.12, MEPC 67/20; MEPC 68/3/7, MEPC 68/3/11, MEPC 68/INF.32; MEPC 69/INF.23; MEPC 70/5/20, MEPC 70/INF.30, MEPC 70/INF.33, MEPC 70/INF.35; MEPC 71/5/13, MEPC 71/INF.28; MSC 93/21/5, MSC 93/INF.13; resolutions MEPC.232(65), MEPC.255(67) and MEPC.262(68)

Introduction 1 The research project Energy Efficient Safe Ship Operation (SHOPERA, www.shopera.org) and the Japan's research project (hereinafter referred as "the Projects") have been working together for revising the Guidelines through technical and practical consideration and evaluation with a view to submitting the outcome and draft revised Guidelines to MEPC 71. The draft revised Guidelines are introduced in document MEPC 71/INF.28. 2 This document provides technical backgrounds of the draft revised Guidelines in the annex. I:\MEPC\71\MEPC 71-INF-29.docxI:\MEPC\71\MEPC 71-INF-29.docx

MEPC 71/INF.29 Page 2 Action requested of the Committee 3

The Committee is invited to note the information provided.

***

I:\MEPC\71\MEPC 71-INF-29.docxI:\MEPC\71\MEPC 71-INF-29.docx

MEPC 71/INF.29 Annex, page 1 ANNEX TECHNICAL BACKGROUND OF THE DRAFT REVISED GUIDELINES FOR DETERMINING MINIMUM PROPULSION POWER TO MAINTAIN THE MANOEUVRABILITY OF SHIPS IN ADVERSE CONDITIONS 1

Purpose

1.1 The purpose of annex is to provide technical background of the draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions. 2

Loading condition

2.1 In order to determine loading condition that should be applied in the draft revised Guidelines from a practical point of view, the Projects carried out case studies using some ships. Figures 1 (a) and (b) compare the ratio of the required brake power to the available brake power between the full load and the heavy ballast conditions in seaways corresponding to Beaufort number 7 and 8 specified by Beaufort scale of wind as examples. The horizontal axis represents the encountered wave and wind angles; zero means head sea. And the vertical req axis represents a ratio of the required brake power PB to the available brake power PBav at the actual rotation speed of the engine in seaway, based on the engine power limit specified by req the engine manufacturer. Note that cases where the ratio PB /PBav is greater than 1.0, the installed engine is not sufficient to exceed the engine power limit. The results show that the full load condition is more severe than the heavy ballast condition with respect to the required brake power for both example ships.

(a) 82,000 DWT bulk carrier

(b) VLCC

Figure 1: Comparison of ratio of required brake power to available brake power between full load and heavy ballast conditions in sea conditions corresponding to BF7 and BF8

I:\MEPC\71\MEPC 71-INF-29.docx

MEPC 71/INF.29 Annex, page 2 2.2 Based on the above case studies, the Projects are of the view that heavy ballast condition is typically less demanding with respect to the required brake power than full load condition. The Projects are also of the view that normal ballast condition is not a relevant situation under the adverse weather conditions, because ship masters should normally change from the normal ballast condition to heavy ballast condition in advance, when informed by the weather forecast. Therefore, the Projects have reached the conclusion that only the maximum summer load condition corresponding to the EEDI condition should be evaluated for tankers, bulk carriers and combination carriers as most severe among the various loading conditions regarding the required power in the adverse conditions. 3

Scenarios for ship's handling in adverse conditions

3.1 The Projects are of the view that the draft revised Guidelines should reflect actual ship's handling in the adverse conditions and be based on realistic scenarios and corresponding environmental conditions and manoeuvrability criteria. 3.2 In order to determine the realistic scenarios for ship's handling in the adverse conditions, the Projects conducted a series of interviews with shipowners, ship masters and chief engineers. As a result, the following facts were identified: .1

the ship masters normally avoid adverse seas corresponding to Beaufort number 7 or more in advance as far as possible for the safety, according to weather forecasts;

.2

in severe seas, the ship masters generally keep out of beam and following seas in order to avoid the resonance of rolling motion and the propeller racing for safety as captain's common sense; and

.3

the situation of "Heave to" such as weathervaning is a very severe situation, which is rare for ship crews, because the ship masters normally avoid beforehand such situations for safety reasons, unless something very unusual happens.

3.3 Finally, the Projects developed three realistic scenarios for ship's handling in the adverse conditions based on the interviews, accident analysis and weather statistics, as well as the analysis of the seakeeping performance of ships in waves: Scenario 1 "Avoidance of adverse seas under gale warning", Scenario 2 "Escape from coastal areas under gale condition" and Scenario 3 "Weathervaning in coastal areas under strong gale condition". 3.4

Scenario 1: "Avoidance of adverse seas under gale warning"

3.5 The first scenario, "Avoidance of adverse seas under gale warning", considers situations when ships avoid beforehand adverse seas corresponding to BF8 or more when they are in coastal areas, because such adverse seas have the potential to cause grounding, contact or collision, as well as damage to hull and cargo. The ships remain fully functional regarding their propulsion and steering abilities and can carry out the usual operation in a complex navigational situation in a developing storm under near gale conditions (BF7). The requirements for this scenario are as follows:


MEPC 71/INF.29 Annex, page 3 Area Weather conditions

Coastal areas BF6 (strong breeze) for Lpp250 m, linear over Lpp between 200 m and 250 m

Encountered wave All headings including head, beam and following seas and wind angle Propulsion ability Speed through water at least 8 knots Steering ability Ability to perform any manoeuvre in seaway from any heading Note: Ships will normally avoid beforehand adverse seas corresponding to BF8 or more, regardless of their position in the open sea or coastal areas; the decision for avoidance will be based on weather forecasts and ship's size in relation to the developing sea conditions to prevent unnecessary troubles. 3.6

Scenario 2: "Escape from coastal areas under gale condition"

3.7 The second scenario, "Escape from coastal areas under gale condition", considers situations when ships are, for some reason, caught in adverse seas corresponding to gale conditions (BF8) when they are in coastal areas. The ships should be able to safely search for safe shelter or escape from the dangerous coastal area to the open sea in a complex navigational situation to prevent grounding, contact or collision, as well as damage to hull and cargo, while having a sufficient speed through water (at least 6 knots) and remaining fully functional regarding their manoeuvrability in a complex navigational situation. The requirements for this scenario are as follows: Area Weather conditions

Coastal areas BF7 (near gale) for Lpp250 m, linear over Lpp between 200 m and 250 m

Encountered wave All headings including head, beam and following seas and wind angle Propulsion ability Speed through water at least 6 knots Steering ability Ability to perform any manoeuvre in seaway from any heading 3.8

Scenario 3: "Weathervaning in coastal areas under strong gale condition"

3.9 The third scenario, "Weathervaning in coastal areas under strong gale condition", considers situations when ships cannot escape from the coastal area under gale condition (BF8) for some reason. In such situations, ships should be able to safely stay in coastal areas under strong gale condition (BF9), remaining able to weather-vane to prevent grounding, with a speed through water of at least 2 knots considering possible tidal current. The requirements for this scenario are as follows: Area Weather conditions

Coastal areas BF8 (gale) for Lpp250 m, linear over Lpp between 200 m and 250 m

Encountered wave Head seas to 30 degrees off-bow for a situation of weathervaning and wind angle Propulsion ability Speed through water at least 2 knots Steering ability Ability to keep heading into head seas to 30 degrees off-bow Notes: Contact and collision accidents are very unlikely to occur under these weather conditions, because almost all ships should have safely escaped from the coastal area according to scenario 2. Moreover, the worst adverse conditions usually occur when the waves and wind come from offshore to onshore.


MEPC 71/INF.29 Annex, page 4 3.10

Significant wave height corresponding to Beaufort number (wind speed) in coastal areas

3.11 Beaufort scale of wind provided by World Meteorological Organization basically specifies wind force, as shown in the appendix. Wave height described in Beaufort scale of wind is only a probable wave height, corresponding to wind speed, in the open sea remote from land and not in coastal areas, as shown in the appendix. All the scenarios considered for the assessment of sufficient manoeuvrability in adverse conditions assume situations when ships encounter adverse seas in coastal areas. Therefore, the Projects need to define wave height corresponding to Beaufort number (wind speed) in coastal areas for minimum propulsion power assessment. 3.12 The waves consist of wind waves and swells induced by local wind and remote wind, respectively. Especially swells damp with the increasing propagation distance. According to the equation for damping of swells developed in Sverdrup and Munk (1947), where swells of 6 m height propagating 191 nautical miles (354 km) reduce in height by about 20% due to the damping effect. Therefore, the significant wave height of swell in coastal areas is less than that in the open sea due to damping. Furthermore, the relationship between the strength of the blowing wind (Beaufort number or wind speed) and the strength of the resulting sea waves (significant wave height) is strongly dependent on the extent of the blowing wind's fetch and the resulting wave's unobstructed run, next to the sea bottom's topography. For equal wind strength (Beaufort number), open sea waves tend to have larger heights and periods (lengths), whereas waves in coastal areas tend to have smaller heights and periods, but are steeper. Therefore, the significant wave height in coastal areas should be obviously smaller than that in the open sea due to damping (for swell), limited wind's fetch (for wind sea) and local bottom effects, although the wind speed in coastal areas may be almost the same as that in the open sea. 3.13 In order to obtain the wave height corresponding to wind speed in coastal areas, the Projects investigated relationships between wave height and wind speed in coastal areas around Japan along the Pacific Ocean and Great Britain along the North Sea. For the Japanese coastal areas, the measured data of wave height and wind speed were derived from the "Statistical Database of Winds and Waves around Japan" provided by National Maritime Research Institute of Japan for the period of 10 years from February 1994 to January 2004. For the British coastal areas, the measured data were derived from the "Wind and wave frequency distributions for sites around the British Isles of Offshore Technology Report 2001/030" published by the Health and Safety Executive (HSE) of United Kingdom. This report presents wind and wave frequency distributions and roses for forty sites around the British Isles. The data were produced using hindcast wind and wave time series from the NEXT model for the combined periods from January 1977 to December 1979 and from January 1989 to December 1994. 3.14 The Projects selected measurement locations in the coastal areas as shown in figure 2 (a) and (b). The Japanese coastal areas include the locations within 20 nautical miles from the Pacific Coast of Japan. The British coastal areas are located at 20-30 nautical miles from the North Sea coastline of Great Britain.


MEPC 71/INF.29 Annex, page 5

(a) Coastal areas around Japan along the Pacific Ocean Map data ©2017 Google, SK telecom, ZENRIN

(b) Coastal areas around Great Britain along the North Sea Map data ©2017 GeoBasis-DE/BKG (©2009), Google, Inst. Geogr. Nacional

Figure 2: Selected coastal areas 3.15 Figure 3 shows the results of the study concerning the relationship between the Beaufort number (wind speed) and the significant wave height. Figure 3 shows that the results for the Japanese coastal areas are nearly equal to those for the British coastal areas. Moreover, the results show that the significant wave heights measured in both the coastal areas are smaller than the probable wave height in the open sea, which is specified in the usual Beaufort scale of wind. It follows from these results that the significant wave height corresponding to a given Beaufort number may be reduced for coastal areas compared to that specified in Beaufort scale of wind. Therefore, the Projects have reached a conclusion that the significant wave heights specified in table 1 depending on Beaufort number in coastal areas and considering a safety margin should be used for the assessment of the minimum propulsion power. Consequently, manoeuvrability criteria and environmental conditions applied to scenarios 1, 2 and 3 are summarized in table 2.


MEPC 71/INF.29 Annex, page 6 Significant wave height measured in the Jananese coastal areas Significant wave height measured in the British coastal areas Significant wave height corresponding to Beaufort number in coastal areas applied to the scenarios Probable wave height in the open sea, which is specified in Beaufort scale of wind (For reference)

8

Wave height (m)

7 6 5 4 3 2 1 0

BF6

BF7

BF8

BF9

Beaufort number

Figure 3: Relationship between Beaufort number and wave height in the Japanese and British coastal areas Table 1: Significant wave height corresponding to Beaufort number in coastal areas applied to the scenarios 1, 2 and 3 Beaufort number

Significant wave height in coastal areas hs (m)

6

2.55

7

3.40

8

4.50

9

6.00

Table 2: Summary of manoeuvrability criteria and environmental conditions applied to scenario 1, 2 and 3

Area Encountered wave and wind angle Beaufort number Wind speed corresponding to Beaufort number Significant wave height corresponding to Beaufort number in coastal areas hs Ship's speed

Scenario 1

Scenario 2

Scenario 3

Coastal areas

Coastal areas

Coastal areas

0 to 180 degrees (All headings)

0 to 180 degrees (All headings)

Head seas to 30 degrees off-bow

BF6 for Lpp250 m

BF7 for Lpp250 m

BF8 for Lpp250 m

12.3 m/s for Lpp250 m



2.55 m for Lpp250 m

3.4 m for Lpp250 m

4.5 m for Lpp250 m

At least 8 knots

At least 6 knots

At least 2 knots


MEPC 71/INF.29 Annex, page 7 Notes:

4

.1

for coastal areas, the significant wave height hs corresponding to a given Beaufort number BF is less than that for the open sea due to the damping effect of swells, limited wind's fetch and local bottom effects; and

.2

for the ship's length between 200 m and 250 m, the weather conditions are linearly interpolated according to the ship's length.

Manoeuvrability criteria and environmental conditions applied in the draft revised Guidelines

4.1 The Projects validated the manoeuvrability criteria and the environmental conditions for each scenario with the use of the comprehensive assessment which can calculate maximum required brake power by solving multi-dimensional equilibrium equations, considering external forces, ship reactions, required and available propeller thrust, brake power, rudder forces and engine power limits. The calculations were conducted for 36 eco-ships (20 bulk carriers with deadweight from 10,000 to 300,000 t and 16 tankers with deadweight from 6,000 to 320,000 t) as shown in table 3. The selected eco-ships satisfy the requirements of EEDI implementation Phase 2. Table 3: Eco-ships used for validations of the scenarios Bulker

Lpp (m)

B01 B02 B03 B04 B05 B06 B07 B08 B09 B10 B11 B12 B13 B14 B15 B16 B17 B18 B19 B20

100 115 110 140 175 175 175 175 175 185 185 185 225 225 285 285 285 300 325 320

DWT 10,000 13,000 14,000 25,000 33,000 37,000 37,000 37,000 38,000 55,000 56,000 56,000 81,000 82,000 180,000 182,000 182,000 209,000 250,000 297,000

Tanker

Lpp (m)

T01 T02 T03 T04 T05 T06 T07 T08 T09 T10 T11 T12 T13 T14 T15 T16

100 110 115 120 125 140 150 170 175 175 180 180 240 230 265 330

DWT 6,000 9,000 12,000 13,000 16,000 21,000 26,000 33,000 35,000 50,000 51,000 52,000 106,000 106,000 150,000 318,000

4.2 The comprehensive assessment was carried out by using a computer program, based on the following computational procedure: .1

req

calculate the required brake power PB to fulfill the Propulsion Ability requirements and Steering Ability requirements by solving multi-dimensional equilibrium equations, taking into account external forces, ship reactions, required and available propeller thrust, brake power, rudder forces and engine power limits; and


MEPC 71/INF.29 Annex, page 8 .2

req

check where the required brake power PB does not exceed the available brake power PBav according to the engine power limit, specified by the engine manufacturer, at the actual rotation speed. req

4.3 The computed maximum ratio of the required brake power PB to the available brake av power PB was compared for each of scenarios 1, 2 and 3 for the eco-ships with deadweight req exceeding 20,000 t. Figure 4 shows the maximum ratio of the required brake power PB to the av available brake power PB , defined according to the engine power limit at the actual rotation speed, for scenario 3 (vertical axis) as a function of the maximum of the same ratio for req scenario 1 (horizontal axis). Note that in cases where the ratio PB /PBav exceeds 1.0, the installed engine is not sufficient to fulfill the Propulsion Ability or Steering Ability requirements. req From figure 4, it was found that the ratio PB /PBav for scenario 3 always exceeds this ratio for scenario 1 for all ships studied. This means that scenario 3 is the more severe situation than scenario 1 for tankers, bulk carriers and combination carriers. req

4.4 Figures 5 (a) and (b) show the maximum ratio of the required brake power PB to the available brake power PBav , defined according to the engine power limit at the actual rotation speed, for scenario 3 (vertical axis) as a function of the maximum of the same ratio for scenario 2 (horizontal axis) for all considered ships. req

4.5 Figures 5 (a) and (b) show that the ratio PB /PBav for scenario 3 always exceeds this ratio for scenario 2 for all considered ships, even when the rudder area is reduced by 30% compared to the original rudder area. This means Scenario 3, "Weathervaning in coastal areas under strong gale condition", is the most severe situation for tankers, bulk carriers and combination carriers regardless of rudder area. Thus, considering scenario 3 is sufficient to evaluate the minimum propulsion power for these ships. Finally, the Projects have reached a conclusion that only scenario 3 should be applied in the draft revised Guidelines from a practical point of view.

[PBreq / PBav]max at 2kn, 0-30deg, BF: each criteria (Scenario 3 for each ship)

1.2

Lpp