M.V. – This prefix stands for Motor Vessel and other terms which could be used are M.S. that stands for Motor Ship. Sometimes these abbreviations are written with a forward slash separating the alphabets rather than the periods. Hence they can also be written as M/V or M/S respectively. As the name itself suggests, they represent ships which are driven by internal combustion engines or diesel marine engines and most of the modern ships including bulk carriers, containers, OBOs etc come in the category of motor ships.
S.S. - you must be familiar with steam locomotives but even ships used to be driven by steam in the earlier days. Of course I do not mean to say that these ships do not exist today, but the number is certainly waning. These ships are known as steamships and use steam generated in the boilers for propulsion rather than diesel engines.
M.T. - this category is closely related to M.V. since it represents a Motor Tanker ship hence these are those types of Motor Vessels which are tankers.
R.V. – these are Research Vessels about which we have studied in detail in related articles such as hydrographic ships and FLIP ships.
F.V. – this stands for fishing vessels that are used for catching fish from the oceans.
FPSO – we have learnt about Floating Production, Storage and Offloading Vessel in a related article
L.B. – lifeboats are used in emergency situations on board ships either when the ship is about to sink or someone has fallen overboard. Check out these interesting articles.
S.V. – though ships are normally referred to as vessels in common language, hence all ships can be said to be S.V. or sailing vessels, yet technically this currently is used to refer to ships which use sails for powering them instead of engines or steam.
N.S. – this is the latest category of ships and refers to nuclear powered ships.
As I told earlier, these are only a part of the entire abbreviation list, but this should be sufficient enough for a newcomer to the shipping arena to know about the most commonly used ships.