These things can represent many different things depending on their context in your dream & the context of your life at that point (e.g. news stories or real world events you heard about or are following as mentioned by CFS; Personal things going on in your life at church / work /relationships; your city / state / govenment / country etc )
Some of the things they can represent-
Blue: in addition to what CFS mentioned: sky, heaven, from God, revelation, clarity, sadness (got the blues)
Sea: many people, international / public realm, iteraction between nations, a 'big picture' of something, what is under the surface is unknown, depending on the condition of the sea (rough - turblance/distress, impacting events; smooth peace). Large waves can also symbolize moves of the Spirit.
Ship: large organisation, economy, trade, denomination, church, company
It's important not to disregard any sense you may have in your spirit (e.g.
These dreams i think are god telling me future?)
To seach out the meaning, what you can do is also look for the words in the bible e.g. using
BibleGateway.com: A searchable online Bible in over 100 versions and 50 languages. An advantage of this is that it helps keep your focus on the Lord & His word.
If you would like to post your dreams here ( a separate thread/post for each dream) people can give you feedback to help you understand what the Lord is saying. A wonderful blessing of this form is that there are many people here with different anointings & different backgrounds. So you can receive a number of different perspectives on your dream. The Lord can be saying a number of different things through a single dream so this helps.