The UKHO/RYA electronic chart plotter series has been discontinued.
At the moment there seems to be two replacements out there (to the best of my knowledge)
a) Meridian Chartware EasyCharts (these guys originally wrote the software for UKHO/RYA) : one CD covers UK, Ireland and English Channel £69.95 incl VAT – http://www.meridian-chartware.co.uk/Shop/PR106-EasyCharts.aspx – there is a discount available for BSAC members or at least they told me so at the Eurotek show in Birmingham last Nov 2010.
b) Belfield Software Chart Plotter: them of the Belfield Tide Plotter fame: they offer same area coverage in a variety of packages with/without Tideplotter on CD, USB stick etc. – http://www.chartsandtides.co.uk/ChartPlotter
For smartphone users I have the Navionics Marine app which covers UK, Ireland and Channel for €20 – bargain! Search for it in the iTunes store or Android Market.
There is a free web app which gives access to charts: http://www.navionics.com/en/webapp
Useful Links for Dive Trip Planning
The ‘In your footsteps’ website gives a very detailed description of slips and harbours around Ireland, including availability of moorings, info on when the slip can be used, and a rather cool map-based calculator for slack and tidal streams: http://www.inyourfootsteps.com/sailing/harbours/europe/ireland