Sean, as to sacks, I strongly recommend the Fly High gear. the attachments are very nice and the bags are very durable. Just take some measurements, buy yourself whichever bags you think will work (if you don't know, the V-drive set would be a good place to start), buy the Tsunami pump to fill/drain over the side, and you should be good.
Start with 500-800 lbs or so, and one pump, and go from there.
Don't know if wakeside ships to Ireland, but here's what you should be looking for:
Bags:
http://www.wakeside.com/category/boat/ballast/ballast_bags.do?sortby=bestSellers&filterby1=Brand-Fly%20High&filterby2=&filterby3=&size= Pump:
http://www.wakeside.com/product/boat/ballast/ballast_pumps/fly+high+tsunami+pump.do
Good luck!
(Message edited by phenom_1819 on December 08, 2008)