11.9.3 Vessels fitted with external ballast keels
Clasification Society 2024 - Version 9.40
Statutory Documents - MCA Publications - MGN 280 - Small Vessels in Commercial Use for Sport or Pleasure, Workboats and Pilot Boats - Alternative Construction Standards - 11 Intact Stability - 11.9 Sailing Monohull Vessels Complying with Section 11.1.1.3 - 11.9.3 Vessels fitted with external ballast keels

11.9.3 Vessels fitted with external ballast keels

  .1 The stability assessment of a vessel may be made by any one of the following methods:-

  • Method 1 as for vessels without external ballast keels, see 11.9.2 above;

  • Method 2 by the full application verified or performed by a Certifying Authority as required, of ISO12217 Part 2 'Small Craft - Stability and Buoyancy Assessment and Categorisation - Sailing Boats of hull length greater than or equal to 6m' in accordance with 11.9.5. Vessels under 6m' in length may not be considered by this method.

  • Method 3 by the 'STOPS' Numeral developed by the Royal Yachting Association (RYA) and discussed in Section 11.9.4.

Note For vessels fitted with one or more top-weight items, examples of which are given below, the ballast ratio should be modified as follows:-

Moments are to be taken about the vertical centre of gravity (KG) of the vessel, which is assumed to be at the waterline. The heeling moments attributed to the top-weight items are resolved, and the ballast weight is reduced, using the formula below.

Noting that:-
CBW = is the correction to the ballast weight
TW = is the weight of the top-weight items being considered
H = is the height of the vertical centre of gravity above the waterline.
DCB = is the draught of the canoe body, taken by measuring the maximum draught at 1/8 of the full beam from the centreline in way of the transverse section, at greatest beam.
DK = is the depth of the keel, taken as the distance between the draught of the canoe body and the bottom of the keel.

The dimensions above are illustrated in Figure 11.2 below.

Note Examples of top-weight items are given below:-

  • roller furling headsail;
  • in-mast or behind-mast roller furling mainsail;
  • a radar antenna mounted higher than 30% of the length of the vessel above the waterline.
  • Ballast weight reductions are to be conducted to the satisfaction of the Certifying Authority.

Figure 11.2

  .2 Permitted area of operation

The permitted area of operation is dependent upon a vessel's range of stability, STOPS Numeral, or Design Category as indicated in the table in 11.9.5.

Parent topic: 11.9 Sailing Monohull Vessels Complying with Section 11.1.1.3
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