U-boat

U-boat is the German word U-Boot; it’s from an abbreviation of Unterseeboot. The main targets of the U-boat campaigns for both world wars were the merchant convoys bringing merchandise from Canada, United States to Europe. Austrian submarines of World War I also known as "U-boats".

The distinction among U-boat and submarine is common language usage, but, unknown in German, and the term U-Boot refers to any submarine.

Raft

A raft is some flat floating structure for travel over water. It is the most basic of boat design, characterized by the lack of a hull. Instead, rafts are kept afloat using any mixture of buoyant materials such as wood, sealed barrels, or overstated air chambers. Traditional or antique rafts are constructing of wood or reeds. Present rafts may also use pontoons, drums, or extruded polystyrene blocks. Hot-air balloon rafts use durable, multi-layered rubberized fabrics, Depending on it’s utilize and size; it may contain a superstructure, masts, or rudders.
Timber rafting is used by the logging industry for the carrying of logs, by tying them together into rafts, and traveling or pulling them down a river. This method was very common up until the center of the 20th century but is now hardly used.
The type of raft used for spare time rafting is almost completely an inflatable boat, manufactured of flexible materials for use on whitewater.

Pinnace

A pinnace is a light boat, propelled by sails or oars, previously used as a "tender" for guiding merchant and war vessels. In modern parlance, pinnace has come to mean a boat linked with some kind of larger vessel, that doesn't fit under the launch or lifeboat definitions. In all-purpose, the pinnace had sails, and would be used to ferry messages between ships of the line, visit harbors ahead of the fleet with messages of state, pick up mail, etc.