Lots of people will suggest Frio packs, but as long as you keep your insulin (and meter, strips etc) out of direct sunlight, away from engines etc, it should be fine. There will be a medical room on the ship, so you could ask about keeping insulin in their fridge. Personally, I prefer a small stainless steel vaccuum flask as it offers more physical protection against knocks as well as temperature extremes - it will have to be empty of water for hand luggage if flying, but as the insulin will be straight out of fridge, the flask primed with cool water and then closed, that's no problem. I've never been on a cruise ship - plenty of ferries, a couple of HMSs, lots of canoes & kayaks, but no cruise ships, so no other suggestions I can make.
Make sure you have appropriate travel insurance and a European Health Insurance Card (EHIC) for EEC countries.