National regulations Germany

National regulations usually follow the above international regulations, but may impose additional requirements. German rules are given here as an example.

SBG regulations

In 1984 the SBG (Seeberufsgenossenschaft = German Mariners' Association) issued new regulations for intact stability which consider ship type and cargo type (SBG, 1984). These recommendations refer to the righting arm curve. Table A.5 gives the minimum required values.

• Ships with L < 100 m and 50° < 00 < 60°: h30° = 0.2 + (60° - 00) ■ 0.01.

• Cargo-carrying pontoons: 00 > 30°; e0,^max > 0.07 m rad.

• Containers as deck cargo: GM > 0.30 m for L < 100 m, GM > 0.40 m for L > 120 m, linear interpolation in between.

• Timber as deck cargo, densely stowed: GM' > 0.15 m; /¡3o > 0.10 m for F'/B < 0.1, h30° > 0.20 m for F'/B > 0.2, linear interpolation in between. F' is an ideal freeboard, the difference between ideal draught and available mean draught.

Table A.5 Stability requirements of the SBG for cargo ships (summary)

h30° [m]

GM' [m]

e0,30° [mrad]

e30,40° [mrad]

e0,40° [mrad]

[deg]

General, L < 100m

0.20

0.15

0.055

0.03

0.09

50-60

General, 100 m < L < 200 m

0.002L

0.15

0.055

0.03

0.09

50-60

General, L > 200 m

0.40

0.15

0.055

0.03

0.09

50-60

Tugs

0.30

0.60

0.055

0.03

0.09

60

h30° Righting lever at 30° heel

GM Metacentric height corrected for free surfaces e0,30° Area under static stability curve to 30°

e30 40° Area under static stability curve between 30° and 40°

e0,40° Area under static stability curve to 40°

Stability range; heeling angle at which righting lever becomes zero again h30° Righting lever at 30° heel

GM Metacentric height corrected for free surfaces e0,30° Area under static stability curve to 30°

e30 40° Area under static stability curve between 30° and 40°

e0,40° Area under static stability curve to 40°

Stability range; heeling angle at which righting lever becomes zero again

• Timber as deck cargo, packaged timber: GM > 0.15 m; > 0.15 m.

• Coke as deck cargo: h30° is to be increased by 0.05 m.

• Passenger ships: Maximum heel angles are:

10° resulting from passengers crowding to one side

12° resulting from passengers crowding to one side and turning

12° resulting from lateral wind pressure.

The minimum residual freeboard to the bulkhead deck or openable windows must be 0.20 m when the ship is heeled by the above moments. Ships of over 12 m width must show that the lower edges of the windows above the bulkhead deck are not submerged under dynamic wind conditions. The heeling moment due to passengers crowding on one side assumes 4 persons/m2 for open spaces, otherwise the 'most realistic' assumptions, and 750 N per person plus 250 N luggage (50 N for day trips), centre of gravity 1 m above the deck at the side at L/2.

The heeling moment due to turning is as given for the IMO code of intact stability above.

• Ships with large wind lateral area, except passenger ships: The heel angle under side wind is to be calculated.

MKr = p-A - ^w + y p = 0.3kN/m2 for coastal operation (Bft 9)

p = 0.6kN/m2 for short-distance operation (Bft 10)

p = 1.0kN/m2 for middle- and long-distance operation (Bft 12)

The heel angle may not exceed 18°. The minimum residual freeboard under heel is 10% of the freeboard for the upright ship.

Further regulations concern tankers, hopper dredgers, ships with self-bailing cockpit or without hatch covers, offshore supply vessels, and heavy cargo-handling.

German Navy stability review

All ships (except submarines) in the German navy are subject to a 'stability review' in which the lever arm curves of righting and heeling moments are compared for smooth water conditions and in heavy seas (Vogt, 1988). The calculation of stability in heavy seas assumes waves of ship's length moving at the same speed and in the same direction as the ship. Seen from the ship, this gives the impression of a standing wave. Different heeling moments and stability requirements—e.g. relating to the inclination achieved—are specified for the following sea conditions:

1. Ship in calm water.

2. Ship on wave crest.

3. Effectiveness of a lever arm curve determined as the mean value from wave crest and wave trough conditions.

Various load conditions form the basis for all three cases. The navy adopted this method of comparing heeling and righting lever arms on the advice of Wendel (1965) who initiated this approach. The stability review can also be used to improve the safety of cargo ships, although it cannot account for dynamic effects. The approach is especially useful for ships with broad, shallow sterns.

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