DNV DNVGL-RU-SHIPS PART 3 CHAPTER 11 PDF

General

Introduction

The requirements given in this section apply to equipment and installation for anchoring, mooring and towing.

Towlines and mooring lines are not subject to classification. Lengths, breaking strength and number of mooring lines are, however, given in the equipment tables as guidance.

Documents and certificates to be submitted

The documents and certificates to be submitted are specified in Ch.1 Sec.3.

Assumptions for anchoring equipment

The anchoring equipment required is the minimum considered necessary for temporary mooring of a vessel in moderate sea conditions when the vessel is awaiting berth, tide, etc. The equipment is therefore not designed to hold a vessel off fully exposed coasts in rough weather or for frequent anchoring operations in open sea. In such conditions the loads on the anchoring equipment will increase to such a degree that its components may be damaged or lost owing to the high energy forces generated. The class notation DWA provides additional requirements for ships intended for regular anchoring at deep water, see Pt.6 Ch.5 Sec.17.

Guidance note:

If the intended service of the vessel is such that frequent anchoring in open sea is expected, it is advised that the size of anchors and chains is increased above the rule requirements, taking into account the dynamic forces imposed by the vessel moving in heavy seas. The equipment number (EN) formulae for anchoring equipment are based on an assumed maximum current speed of 2.5 m/s, maximum wind speed of 25 m/s and a minimum scope of chain cable of 6, the scope being the ratio between length of chain paid out and water depth. For vessels with length greater than 135 m, alternatively the required anchoring equipment can be considered applicable to a maximum current speed of 1.54 m/s, a maximum wind speed of 11 m/s and waves with maximum significant height of 2 m.

The anchoring equipment required by the rules is designed to hold a vessel in good holding ground in conditions such as to avoid dragging of the anchor. In poor holding ground the holding power of the anchors is significantly reduced.

It is assumed that under normal circumstances the vessel uses only one bower anchor and chain cable at a time.