As the propeller turns，voids are formed on the trailing and leading edges of the propeller blades causing a loss of propulsive efficiency，pitting of the blades，and vibration. These voids are known as（）.

An example of a modern anchor which has a stock is a(n)（）.

In the piping systems of a vessel，what type of valve gives the least resistance to fluid flow when fully open?（）.

In ship construction，frame spacing is（）.

Anchors are prevented from running out when secured by the（）.

An integral part of a blowout preventer that serves as the closing element on an open hole，and whose ends do not fit around the drill pipe but seal against each other and shut off the space below completely is the（）.

In ship operations，hoisting and lowering pipe in and out of the drilled hole is the main function of the（）.

The boat is stowed on the davit rather than on a cradle with which type of davit?（）

The connected joints of pipe，usually made of three joints of pipe approximately 90 feet long，racked in the derrick when making a trip are called a（）.

Static electricity may be built up by the（）.