RECOMMENDED MOORING SPECIFICATIONS, FOR VESSELS UP TO 45 ft.
All independent component parts for every mooring assembly, must be selected to provide the strength and endurance required to hold the maximum size and tonnage of vessel, for which the mooring is licensed, during the most sever weather and tidal conditions that can be expected in the Exe estuary. LEMA Ltd. will consider licence applications for mooring of vessels over 45ft, trots and other special cases, full details of which must be submitted in writing to the Company Secretary.
The holding power of any anchor varies with design, weight and the river bed. Therefore only anchors designed for permanent moorings and their configuration as recommended by the manufacturer for this purpose should be used. LEMA specify that two single arm mooring anchors are used. The size of anchors to be used for permanent moorings, are given in Mooring Schedules A to E.
A concrete sinker is preferred to a single anchor for a permanent mooring. Only suitably designed sinkers, with no upward projections are to be used. A mix of 4 parts quarried, 10mm aggregate to 1 part cement must be used. This mix must be reinforced with a steel mesh and vibrated during manufacture to avoid any air pockets. A 25mm (1”) steel eye or 25mm (1”) chain embedded in the centre of the sinker. The minimum size of sinkers is shown in Table 1.
Table 1, Minimum sizes for concrete sinkers
A single sinker is only allowed for deep water moorings where:
(a) The licensed length of the mooring is less than 12m (40ft), and/or the displacement of the vessel does not exceed 10 Tonnes
(b) The rate of tidal flow is not likely to exceed 4kts.
(c) The river bed is suitable for the use of sinkers.
(d) There is sufficient room.
LEMA recommend that only marine quality, long link, self coloured chain, manufactured to a DIN Specification, should be used. Smaller sizes should have been tested, and were applicable, larger sizes tested and certificated. The minimum sizes of chain to be used for permanent moorings are given in section Mooring Schedules A to E.
The free or working end of the pick-up chain must be shackled to form a loop.
In some cases the Pick-up chain may be replaced with a rope strop. In these circumstances only rope specified as Anchoring Lines must be used. The properties or these ropes will include strength with durability and stretch with flexibility. Both Nylon and Polyester have these properties. Nylon also has good shock absorption and durability. Polyester gets heavier when immersed in water but will remain soft and pliable. The type, size and strength of ropes suitable for use as a Strop are given in Table 3. If used, a rope strops must be terminated with a metal eye spliced into one end and a soft eye spliced in the other end.
Table 3 Type, size strengths of ropes recommended for Strops
Trade names: Anchorbraid (English Braids) or Multiplait (Marlow Ropes)
5 Shackles and Swivels
Only marine quality shackles and swivels that are compatible with the mooring chain must be used.
Large drop forged, self-coloured screw type or locking type Dee Shackles, to BS 3032, or equivalent, that have been inspected and tested are recommended. All shackles and swivels must be thoroughly inspected after 6 months use.
Sizes and breaking loads for shackles and swivels are shown in Table 3.
Table 3 Sizes and Breaking Loads of Shackles and Swivels.
In the interest safety, every consideration must be given keeping the mooring buoy afloat and visible in the highest and strongest tides especially when the vessel is not riding on the mooring.
All moorings must be marked with either an Inflatable Marker/Mooring Buoy or a Ridged Mooring Buoy. An Inflatable Buoy must have heavy duty eye, the size of which will suit the required shackle and the valve must be sealed off with a course threaded plastic screw. A Ridged Mooring Buoy must be foam filled, and remain afloat after sustaining damage.
The mooring buoy must be attached to the riser via a swivel. It must have sufficient buoyancy to remain afloat and clearly visible, at MHWS. The mooring buoy must be brightly coloured and clearly marked with the correct mooring number.
The pick-up buoy must also be brightly coloured.
Maintenance should be based on regular inspections, the time interval for inspections must take into account: exposure (Drying Moorings), regions of the strongest tides (01 and 07 Areas), and following severe storms.
The degree of wear that is permitted before an item is replaced must not exceed 20%, for a mooring likely to be subjected to shock and/or snatch, i.e. off the dock entrance or near the main channel, this should be reduced to 15%
While it is can be accepted that in most cases it is not feasible to lift moorings for winter storage, alternatives that should be considered include the riser being sunk and marked with a buoy, or the mooring buoy replaced with a winter buoy. In both cases the Winter-buoy must be clearly marked with the Mooring Licence Number.