You must identify completely the ship you wish to research.
Find the passenger list that states the year of passage, name of the ship, master or captain and the shipping route, such as Liverpool to New York.
You will need all this information to identify the ship because there might be a number of ships with the same name that were built in different places in different years with different construction (rigs) and different sailing routes.
There is no one single source for all the ships and the information about them. There are a few large Websites and repositories in the United States and Europe. Some of the sources have just United States ships and others will have European ships and some will have both.
You might be able to find in registers the physical description, date built, place built, owner or ship line. In other places you may find the ship's history, photos, paintings, drawings, images and rarely crew's lists.
If you still need more information, you can have several ship museums below do research for you.
I will only be covering the passenger and military ships.
Registers
http://library.mysticseaport.org/initiative/VMSearch2.cfm
http://users.xplornet.com/~shipping/Lloyds.htm
Ship Search
http://www.shipindex.org/
Ship Lines
http://www.theshipslist.com/ships/lines/index.htm
Steamship Lines, Ships and Photos
http://library.mysticseaport.org/immigration/LineDetail.cfm
Ship Images
http://www.photoship.co.uk/Browse%20Ship%20Galleries/ - All types of ships, Unites States and European
http://www.theshipslist.com/pictures/ - Mixture
http://www.norwayheritage.com/query_s.asp - Norway ships
Other Websites with Images
http://www.theshipslist.com/Research/Resource.htm#pictures
Book
Ships of Our Ancestors site #1 and Ships of Our Ancestors site #2
Maritime Dictionary
http://maritimedictionary.org/ASP/MarineDictionary.asp Ship Types and Descriptions
http://www.immigrantships.net/newcompass/ships/ship_files/shiptypes_description.html
US Navy
If you will have the hull number, you should not have a problem finding the correct Navy ship.
http://www.hazegray.org/ - Histories and photos at the Directory of American Naval Fighting Ships
http://www.history.navy.mil/photos/sh-usn/usn-name.htm
http://www.armed-guard.com/ships.html
http://www.hullnumber.com/
http://www.navsource.org/
Ship Research Museums
http://www.maritimemuseums.net/ World - Smith's Master Index to Maritime Museum Websites
http://en.wikipedia.org/wiki/Maritime_museum World Maritime Museums
http://library.mysticseaport.org/
http://www.sshsa.org/
http://www.marinersmuseum.org/collections
Try to download the information and/or images. If you can't download and save the information and/or images, try to print out the information and/or images. Your final option is to use a Free Screen Capture software program that you find at http://www.techsupportalert.com/best-free-screen-capture-utility.htm