An Add-on or Addon pack (also: Expansion pack) is a package which includes new content and/or features for an already existing game, and needs that game to be installed to work.
Ship Simulator patches Edit
Although there is a difference between a patch and an addon, VSTEP did release new ships and new features in some of their patches, hence they can be viewed as small addons in themselves aswell.
Ship Simulator official add-on Edit
The official add-on for Ship Simulator 2006 was launched in February 2007 and contained six new ships for the game, a walkabout ability for all ships and some new missions for the new ships. It is known as the Ship Simulator official add-on or Ship Simulator 2006 add-on
Ship Simulator 2008 add-on1 Edit
Although this was never released as an 'official addon pack', this pack is actually an updated version of the SS2006 addon, made available for SS2008. When the Ship Simulator 2006 add-on was released, VSTEP promised the customers of this addon, that they would get a free update of it for SS2008. This to prevent them to have to pay twice, for the same content that would later also find it's way into Ship Simulator 2008 New Horizons.
Ship Simulator 2008 New Horizons Edit
Ship Simulator 2008 New Horizons Included both Ship Simulator 2008 add-on1 and two new extra ships, the Bugsier 2 and the Herkules Atlas, aswell as one new environment, Padstow, Cornwall. The New Horizons add on also included all the patches available for Ship Simulator 2008