Clasification Society Rulefinder 2020 - Version 9.33 - Fix
Statutory Documents - MCA Publications - LY2 - The Large Commercial Yacht Code - 11 Stability - 11.2 Intact Stability Standards - 11.2.2 Sailing vessels

11.2.2 Sailing vessels

Parent topic: 11.2 Intact Stability Standards

11.2.2.1 Monohulls

  .1 Curves of statical stability (GZ curves) for at least the Loaded Departure with 100% consumables and the Loaded Arrival with 10% consumables should be produced.

  .2 The GZ curves required by .1 should have a positive range of not less than 90°. For vessels of more than 45m, a range of less than 90° may be considered but may be subject to agreed operational criteria.

  .3 In addition to the requirements of .2, the angle of steady heel should be greater than 15 degrees (see figure). The angle of steady heel is obtained from the intersection of a "derived wind heeling lever" curve with the GZ curve required by .1.

 In the figure:-

'dwhl' = the "derived wind heeling lever" at any angle θ°
= 0.5 × WLO × Cos1.3θ
where
WLO =

Figure 2

Noting that:
WLO = is the magnitude of the actual wind heeling lever at 0° which would cause the vessel to heel to the 'down flooding angle' θf or 60° whichever is least.
GZf = is the lever of the vessel's GZ at the down flooding angle (θf) or 60° whichever is least.
θd = is the angle at which the 'derived wind heeling' curve intersects the GZ curve. (If θd is less than 15° the vessel will be considered as having insufficient stability for the purpose of the Code).
θf = the 'down-flooding angle' is the angle of heel causing immersion of the lower edge of openings having an aggregate area, in square metres, greater than:-
where
Δ = vessels displacement in tonnes

 All regularly used openings for access and for ventilation should be considered when determining the downflooding angle. No opening regardless of size which may lead to progressive flooding should be immersed at an angle of heel of less than 40°. Air pipes to tanks can, however, be disregarded.

If, as a result of immersion of openings in a superstructure, a vessel cannot meet the required standard, those superstructure openings may be ignored and the openings in the weather deck used instead to determine θf. In such cases the GZ curve should be derived without the benefit of the buoyancy of the superstructure.

It might be noted that provided the vessel complies with the requirements of 11.2.2.1.1, 11.2.2.1.2 and 11.2.2.1.3 and is sailed with an angle of heel which is no greater than the 'derived angle of heel', it should be capable of withstanding a wind gust equal to 1.4 times the actual wind velocity (i.e. twice the actual wind pressure) without immersing the 'down-flooding openings', or heeling to an angle greater than 60°.

11.2.2.2 Multi-hull

  .1 Curves of statical stability in both roll and pitch shall be prepared for at least the Loaded Arrival with 10% consumables. The VCG shall be obtained by one of the three methods listed below:

  • .1 inclining of complete craft in air on load cells, the VCG being calculated from the moments generated by the measured forces, or

  • .2 separate determination of weights of hull and rig (comprising masts and all running and standing rigging), and subsequent calculation assuming that the hull VCG is 75% of the hull depth above the bottom of the canoe body, and that the VCG of the rig is at half the length of the mast (or a weighted mean of the lengths of more than one mast), or

  • .3 a detailed calculation of the weight and CG position of all components of the vessel, plus a 15% margin of the resulting VCG height above the underside of canoe body.

  .2 If naval architecture software is used to obtain a curve of pitch restoring moments, then the trim angle must be found for a series of longitudinal centre of gravity (LCG) positions forward of that necessary for the design waterline. The curve can then be derived as follows:

where:
CG' = shift of LCG forward of that required for design trim, measured parallel to baseline
TFP = draught at forward perpendicular
TAP = draught at aft perpendicular
LBP = length between perpendiculars

Approximations to maximum roll or pitch moments are not acceptable.

  .3 Data shall be provided to the user showing the maximum advised mean apparent wind speed appropriate to each combination of sails, such wind speeds being calculated as the lesser of the following:

or

where:
v W = maximum advised apparent wind speed (knots)
LMR = maximum restoring moment in roll (N.m)
LMP =
limiting restoring moment in pitch (N.m), defined as the pitch restoring moment at the least angle of the following:
a) angle of maximum pitch restoring moment, or
b) angle at which foredeck is immersed
c) 10° from design trim
A'S = area of sails set including mast and boom (square metres)
h = height of combined centre of effort of sails and spars above the waterline
ΦR = heel angle at maximum roll righting moment (in conjunction with LMR )
ΦP = limiting pitch angle used when calculating LMP (in conjunction with LMP )
AD = plan area of the hulls and deck (square metres)
b = distance from centroid of AD to the centreline of the leeward hull

This data shall be accompanied by the note:

In following winds, the tabulated safe wind speed for each sail combination should be reduced by the boat speed.

  .4 If the maximum safe wind speed under full fore-and-aft sail is less than 27 knots, it shall be demonstrated by calculation using annex D of ISO 12217-2 (2002) that, when inverted and/or fully flooded, the volume of buoyancy, expressed in cubic metres (m3), in the hull, fittings and equipment is greater than:

thus ensuring that it is sufficient to support the mass of the fully loaded vessel by a margin. Allowance for trapped bubbles of air (apart from dedicated air tanks and watertight compartments) shall not be included.

  .5 The maximum safe wind speed with no sails set calculated in accordance with .3 above should exceed 36 knots. For Short Range Yachts this wind speed should exceed 32 knots.

  .6 Trimarans used for unrestricted operations should have sidehulls each having a total buoyant volume of at least 150% of the displacement volume in the fully loaded condition.

  .7 The stability information booklet shall include information and guidance on:

  • .1 the stability hazards to which these craft are vulnerable, including the risk of capsize in roll and/or pitch;

  • .2 the importance of complying with the maximum advised apparent wind speed information supplied;

  • .3 the need to reduce the tabulated safe wind speeds by the vessel speed in following winds;

  • .4 the choice of sails to be set with respect to the prevailing wind strength, relative wind direction, and sea state;

  • .5 the precautions to be taken when altering course from a following to a beam wind.

  .8 In vessels required to demonstrate the ability to float after inversion (according to .3 above), an emergency escape hatch shall be fitted to each main inhabited watertight compartment such that it is above both upright and inverted waterlines.

Copyright 2020 Clasification Society, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasification Society, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasification Society'. Clasification Society Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasification Society entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.