Seapoint is a flat water sailing location.
Westerly - cross shore, excellent blasting straight across Dublin bay, can be epic. Can be gusty if there is any southerly in wind direction. North westerly - as above without risk of gusty winds, ideal direction. Northerly - Onshore, unusual, freezing, limited sailing. North easterly - Cross onshore, if it's not too cold can be a very nice sailing direction over to Poolbeg, can bring in a bit of a wave, but of little use other than for jumping. Bit of wind shadow from pier so best at mid to low tide in NE.
Sailors of mixed ability.
Shallow water from mid to low tide - good for beginners. Submerged rocks at high tide near the beach area and can result in a tricky launch for beginners.
Grassy rigging area but mind the dog shit. Usually windier out in the bay than it is in the sheltered car park so rig appropriately.
Nearby wind station on East pier is updated every minute - http://www.dlharbour.ie/weather/previous_12_hours.php