Mooring Installation
Mooring Installation
Moorings are an extremely important feature of coastal areas. A good mooring may well last for an extremely long time, however the rate of corrosion and decay of the mooring can be increased by several factors - usually materials of poor quality or which are inappropriate for the purpose.
Rope risers, for example, are fine when new, but once marine life has started growing on them their strength becomes questionable. The outside of the rope may appear to be in good condition, but the inside of the rope is invisible and may be in a dangerous condition due to shells and plants growing and grinding against the strands of rope, chafing and damaging them.
Puffin Dive Centre moorings are all made up to a standard that is easily recognisable from a construction point of view, as well as being tried-and-tested on a large number of marine craft.
Moorings will vary - depending on the purpose of the mooring, the size (and weight) of the object the mooring is intended for as well as the individual object's susceptibility to being blown by the wind, as well as the depth and rise and fall of the tide in the mooring's intended location.
Shackles used in a mooring are naturally larger than the chain it is being used on
A typical mooring from PDC will consist of (from the sea-bed to the surface):
Mooring Block
A 2 tonne block whose dead weight will be reduced by 1/3 due to displacement. Made from C30 grade concrete with an average 40mm chain eye buried into the concrete construction with strengthening bar looped through the chain. PDC part #85-00148.
Shackle - Mooring Block Eye to Ground Chain
BS shackle of sufficient size to take the ground chain moused accordingly.
Ground Chain
Ground chain, used 32/28mm X 4m long, stud link chain. (The maximum recommended size of stud link chain would be new 34mm stud link any larger becomes impractical due to excess weight). The length of the round chain is typically no more than4m, but can be longer or shorter as required.
Shackle - Ground Chain to Scrub Chain
BS shackle of sufficient size to take the ground chain and scrub chain moused accordingly.
Scrub Chain
Scrub chain which should be heavier than the riser for the express purposes of taking the wear in the 4m rise and fall of the sea. An allowance of an extra metre either side of the extreme tidal range should be used. Used 26/24mm X 6m long, stud link chain. Around Oban, with a typical maximum tidal range of 4m this equates to a 6m length of Scrub chain
Shackle - Scrub Chain to Riser Chain
BS shackle of sufficient size to take the scrub chain and riser chain moused accordingly.
Riser Chain
Riser chain should be of approximately 18-20mm long link for a boat of less than 10 tonnes. The length required is determined on our mooring calculation sheet, but is to all intents and purposes 1m less than the Lowest Astronomical Tide in the area. PDC 19mm long link chain.
Shackle - Riser Chain to Swivel
BS shackle of sufficient size to take the riser chain and swivel consistent with the weight of the vessel, moused accordingly.
Swivel (optional) but Highly Recommended
A swivel consistent with the weight of the vessel.
Shackle - Swivel to Top Riser Chain
BS shackle of sufficient size to take the riser chain and swivel consistent with the weight of the vessel, moused accordingly.
Shackle - Top Riser selected link to Sacrificial Load bearing underwater buoy if Required
BS shackle of sufficient size to take the riser chain and weight/load bearing buoy, moused accordingly.
Weight/Load Bearing Surface Buoy
A weight/load bearing buoy as a marker if sufficiently large, this is to be attached 1m from the end of the riser chain. Recommend PDC buoy yellow medium.(If a larger buoy is requested or required shackle may require to be of a larger size.)
Shackle - Top Riser Chain to vessel Pick-up buoy
BS shackle of sufficient size to take the riser chain and pick up buoy, moused accordingly.
Pick-Up Buoy
A pick up of an agreed length resulting in a loop spliced at an agreed size for use by the client and a pick up buoy at a suitable point close to the end for convenience. Alternatively a PDC standard pick-up arrangement may be used.
Sacrificial Weight/Load Bearing Buoy
Dependant upon the depth of the mooring (9 metres of riser chain or greater) a weight/load bearing buoy as a weight carrier at approximately 4m depth is required, however this should not be critical to the top buoy should it fail, merely a device to allow the top buoy to float even higher in the water for identification of the mooring by the owner and ease of pick up etc. Recommend PDC buoy orange medium. A BS shackle of sufficient size to take the riser chain and weight/load bearing buoy, moused accordingly will also be required if using a load bearing buoy.
