- Table of Contents
- Construction and Structural Strength
- Freeboard and Freeboard Marking
- Watertight &Watertight Integrity
- Water Freeing Arrangements
- Bilge Systems
- Fluid Systems
- Electrical Systems
- Steering Gear
- Fire Safety
- Life Saving and Emergency Equipment
- Communication Equipment
- Navigation Equipment
- Anchors and Cables
- Miscellaneous Marine Equipment
- Protection of Personnel
- Appendix A: Sample Stability Information Booklet
- Section 1: Operational Information
- Section 2: Technical Data and Loading Conditions
- Section 3: Reference Information
A 3.1 Arrangement of Tanks and Ballast
Figure 4: Tank and Ballast Arrangement
- Fuel tank (port)
- Fuel tank (starboard)
- Fresh water tank
- Fresh water tank
- Sewage tank
- Lead ballast keel (18 tonnes)¹
- Draughts are referred to an extension of the underside of keel²
- All other vertical locations are referred to BASE³
- All longitudinal locations are referred to MIDSHIPS
- Trim is defined as: Draught Aft - Draught Fwd
- Design trim = Rake of keel = 1.10 metres
A 3.2 Sail Plan
|Height of Centroid Above Base
|1. No. 1 lib
|2. No. 2 lib
|6. Storm Jib
Figure 5: Sail Plan
A 3.3 Angles of Deck Edge Immersion and Downflooding
|Area of Opening m²
|Angles of Immersion
|100% Consumables degrees
|10% Consumables degrees
Critical downflooding is deemed to occur when the lower edges of openings having an aggregate area (in m² )greater than
(displacement (in tonnes) / 1500) are immersed
i.e. 65/1500 = 0.04 m²
Thus immersion of the galley vent is not regarded as critical and it is the irnmersion of the forward skylight which defines the critical downflooding angle referred to in this booklet.
The master should note that the presence of the vent and skylights significantly reduce the ability of this vessel to withstand downflooding and with these openings securely closed the safety of the vessel is enhanced considerably.
A 3.4 Notes on Stability for the Guidance of the Master
- Compliance with the stability criteria indicated in the booklet does not ensure immunity against capsizing regardless of the circumstances or absolve the master from his responsibilities. Masters should therefore exercise prudence and good seamanship having regard to the season of the year, experience of the crew, weather forecasts and navigational zone, and should take appropriate action as to the speed, course and sail setting warranted by the prevailing conditions.
- Before a voyage comrnences, care should be taken to ensure that sizeable items of equipment have been properly stowed to minimize the possibility of both longitudinal and transverse shifting under the effect of accelerations caused by pitching and rolling, or in the event of a knockdown to 90 degrees.
- In adverse weather conditions and when there is the possibility of encountering a severe gust, squall or large breaking wave, all exposed doors, hatches, skylights, vents, etc. should be closed and securely fastened to prevent ingress of water. Storm boards etc. should be erected and fitted.
- The amount of sail carried is at the discretion of the Master and his decision will have to take into account many factors. In assessing the risks of downflooding, the Master should be guided by Figures 6 and 7.
- Figure 6 shows the maximum recommended steady heel angle to prevent downflooding in gusts. Operation of the vessel at a greater heel angle would result in downflooding if it were to encounter the strongest possible gust in the prevailing turbulent airstream, which could exert a heeling moment equal to twice that of the mean wind.
- Figure 7 shows the maximum recommended steady heel angle to prevent downflooding in squalls. Operation of the vessel at a greater heel angle would result in downflooding if it were to encounter the heeling effects of a squall arising from a storm cell or frontal system which may result in a heeling moment many times greater than that of the mean wind. For this reason the master should have regard to the maximum steady heel angle curves presented for a range of squall speeds.
- By using the readings from his inclinometer and anemometer a Master is able to detemmine the degree of risk of capsize in gusts or squalls which may occur in the prevailing weather system. He may then decide to shorten sail together with other actions he considers necessary.
- Additional care should be taken when sailing with the wind from astem as, in the event of the vessel broaching or a gust striking the vessel on the beam, the heeling effects of the wind may be increased to a dangerous level when the preceding heel angle was small.
A 3.5 Maximum Steady Heel Angle to Prevent Downflooding in Gusts.
Figure 6: Maximum Heel Angle, Gusts
When sailing in a steady wind the vessel heels to the angle at which the heeling arm curve intersects to GZ curve. When struck by a gust the heel angle will increase to the intersection of the gust heeling arm curve with the GZ curve. The heeling moment increases in proportion to the square of the apparent wind speed.
Operation of the vessel at a mean heel angle not greater than 27 degrees ensures significant downflooding openings would not be immersed if it were to encounter the strongest gust in the prevailing turbulent airstream which could exert a heeling moment equal to twice that of the mean wind ( i.e. mean apparent wind has increased in velocity by 1.4).
A 3.6 Curves of Maximum Steady Heel Angle to Prevent Downflooding in Squalls
Figure 7: Maximum Steady Heel Ange, Squalls
Curves of maximum steady heel angle indicate the range of mean or steady heel angles beyond which the vessel will suffer downflooding in the event of a squall.
Operation of the vessel in cyclonic conditions particularly in the hours of darkness, where severe squalls are imminent requires the recommended maximum steady heel angle to be reduced depending on the mean apparent wind speed in accordance with the curves presented above.
A 3.7 Examples Showing the use of the Maximum Steady Heel Angle Curves
Figure 8: Maximum Steady Heel Angle Curves
The yacht is reaching, with a steady apparent wind speed of 16 knots. The mean heel angle is 15 degrees. Forecasts and visible cumulo-nimbus clouds suggest squalls may be imminent. By plotting the heel angle and wind speed (point A in Figure 8) the indication is that the vessel will be in danger of heeling to the downflooding angle in squalls in 30 knots. In order to increase safety from downflooding, say, to withstand squalls of up to 45 knots, sails should be handed or reefed to reduce the mean heel angle to 7 degrees (point A1 in Figure 3) or less.
The yacht is beating in gusty conditions with a mean apparent wind speed of 30 knots. The mean heel angle is 20 degrees. No squalls are expected. The heel angle is significantly less than 27 degrees, the maximum recommended steady heel angle, and there is therefore a good safety margin against downflooding in a strong gust. Plotting these values of wind speed and heel angle (point B in Figure 8) also indicates that the vessel would not be vulnerable to downflooding in a squall unless it resulted in a wind speed in excess of about 50 knots. There is thus no need to reduce sail area on the ground of stability.
Note: Appropriate examples should be presented for the Master, to enable him to interpret the meaning of these curves and understand their use.
¹ The location of all permanent ballast must be shown, and the weight stated if known
² If a vessel has draught marks, their location should be defined here and draughts quoted throughout the booklet should correspond to those locations. Otherwise, draughts may be quoted at the perpendiculars as shown above. Draughts may be referred to the underside of keel or, in the case of a fin or keel with a curved underside, to DWL .
³ Vertical centres of gravity may be referred to DWL or, preferably, the underside of keel amidships
4 While immersion of small openings may not be considered critical by the regulations, their angles of immersion should be brought to the attention of the master, particularly if they are low