Mumbles Motor Boat & Fishing Club 
 Good things come to them who bait
Club Members Website

Hooked on Fish - Hooked on Fishing

Tight Lines All Round
It is now possible to join for £15 for membership from 1st July to 31 December plus the £10 joining fee total payable £25, securing adult membership for the rest 2017. We also have family memberships at very attractive rates. There is also, for a short time, a special offer of £50 for adult membership from 1 July  2017 to 31 December 2018.
We are now taking payments of membership fees by Standing Order. So next time you pay any fees setup a standing order for automatic renewal of future membership.
   Home      Tide Information      Swansea Marina & Port Information
Admiralty Charts

At sea, Admiralty Chart Datum (ACD) is used in relation to water height. This is based on the Lowest Astronomical Tide (LAT) and is the level below which the predicted tide will never fall, although in practice wind and high pressure may occasionally force the actual water level below this. Values are given in metres and are used as the basis for sounding on all UK navigation charts. This means that any sounding immediately shows the minimum depth of water available - with any known tide level being a 'plus' which may be added with care.

Port of Swansea. The datum for tidal predictions in ABP South Wales Ports is Admiralty Chart Datum. Previous to 2009 these ports used an obsolete datum, usually based upon the lock entrance cill.
 
The ACD zero is 2.82 metres above the cill gauge zero.  Typical tide readings will be 2.8 metres above the previous Ordnance Datum of Predictions.
Swansea Marina Tidal Curves                  Swansea Bay Dredged Channel To Marina
Swansea Channel Maintenance Level (ML) is 4.2m below ACD. Swansea Ferryport Maintenance Level (ML) is 4.9m below ACD.
 
 
Pilotage Notes:
 
In Swansea Bay tidal streams flow anti-clockwise for 91/2 hrs (Swansea HW–31/2 to +6), with at times a race off Mumbles Head. From HW–6 to–3 the stream reverses, setting N past Mumbles Head towards Swansea. Keep seaward of Mixon Shoal. When N of SW Inner Green Grounds (SWIGG) SCM lt buoy, Q (6) + L Fl 15s keep to W of the dredged channel and clear of commercial ships. Yachts must motor in harbour and approach, maximum speed 4 kn.
 
 
 
Datums
 
Two principal Datums are widely used across the UK.  Ordnance Datum Newlyn (ODN) which is applicable across the whole mainland Great Britain, is a convenient zero values to transfer across the whole country and is used by civil engineers and other land based users. Values are given in metres counting positive upwards from zero.
 
At sea, Admiralty Chart Datum (ACD) is used.  This is a level declared for a port or harbour and its approaches and is based on Lowest Astronomical Tide (LAT).  LAT is the level below which the predicted tide will never fall, although in practice wind and high atmospheric pressure may occasionally force the actual water level below this.  Values are given in metres counting downwards and negative upwards from zero.
 
Admiralty Chart Datum is used as the basis for soundings on all UK navigation charts.  This means that any soundings immediately shows the minimum depth of water available - with any known tide level being a 'plus' which may be added with care.
 
Since 2009 only ACD tide heights have been shown in the ABP tide tables.  All regular South Wales tidal-water sounding charts have been drawn using ACD as the datum for sounding.
 
 
Marina & Tawe Locks
 
Enclosed docks and marinas in South Wales have various datums, some based on lock inner cills, some on constructed steps. In some places the dock is dredged to datum, in others a Maintenance Level above or below the datum is dredged.
 
Note: ACD is also referred to as Chart Datum (CD). This is safe enough if there is only one chart datum about.
 
 
Chart datum & ordnance datum
 
Tide levels are quoted relative to chart datum (approximately the lowest level due to astronomical effects and excluding meteorological effects).  The heights of chart datum relative to ordnance datum in the UK. If example the data value for Mumbles/Swansea of 1m relative to ACD and want to convert it to be relative to OND, then this would be -4m i.e. 1m + (-5.00m ).  See above diagrams.