Internal Draft Indicators

Internal draft gauges and indicators are frequently installed in large ships. The ship's draft

Figure 3-16.-Plimsoll mark.

can be read from within the ship by using a remote draft gauge in combination with a profile draft indicator. The remote draft gauge provides information to DCC relative to the draft of the ship at a predetermined point. The instrument is located in DCC or in an adjacent compartment. If the remote draft gauge is located in a compartment other than DCC, communication between the two locations is maintained through the 2JZ circuit.

The profile draft indicator is located in DCC. It is mounted in gimbals, which permits the indicator to swing freely with the rolling and listing of the ship. An indicator card, on which is engraved the ship's outline, moves through an angle five times as great as the actual angle of fore-and-aft trim. The outline of the ship on the card is purposely distorted so that the vertical scale of reduction is one-fifth that of the horizontal scale. Thus small angles of trim may be easily detected and read on the indicator card. Information obtained from the remote draft gauge is used in adjusting the "actual waterline" on the profile draft indicator.

Ship Clinometers

To understand the use of ship clinometers, you need to know the meaning of the following terms that refer to the ship's motion or position:

HEEL is a general term that refers to any athwartships inclination, temporary or permanent. In heeling, the ship rotates about a fore-andaft axis.

ROLL is the alternate heeling from side to side of a ship.

LIST is the term used to describe a permanent angle of heel taken on by a ship. In a seaway, the listing ship will roll about its angle of list. When the ship returns to calm water, it will resume the angle of list. As used here, the term list refers to a permanent angle of inclination. A ship may be caused to heel and to remain inclined for more or less enduring intervals by such influences as strong wind pressures from one side, carrying a constant rudder angle, or by large ragged "fins" turned out from a torpedo hole. The term fist is not intended to refer to such inclinations.

TRIM is the difference between the forward draft and the after draft. When the draft aft is greater than the draft forward, the ship is said

Figure 3-17.-Typical clinometer board trim indicator.

to be trimmed by the stern. When the draft forward is greater than the draft aft, the ship is said to be trimmed by the bow.

PITCH is the fore-and-aft motion of a ship about its athwarthships axis.

A clinometer is a spirit level device consisting of a curved glass tube mounted on a calibrated board, as shown in figures 3-17 and 3-18. The glass tube is hermetically sealed.

The Navy uses four types of clinometer tubes, which are designated type A, type B, type C, and type E. Types A and B are employed as trim indicators only. Type A has a long radius of curvature, and the radius of type B is approximately one-third that of type A. Types C and E are used as heel indicators only.

On surface ships, clinometers are installed at vital stations such as DCC, chart house, pilot house, navigating bridge, and main engine control.

Figure 3-18.-Typical clinometer board heel indicator.

A clinometer is most accurate under static conditions-that is, at fixed angles of heel or list or trim. For usual angles of roll and pitch, the clinometer is accurate enough for most purposes. At large angles of roll, however, a condition of resonance may exist between the ship's motion and the motion of the fluid in the clinometer. In such circumstances, an excessively large angle of roll may be indicated on the clinometer. A clinometer is not accurate enough to measure inclination when conducting the inclining experiment.

An inclining experiment is conducted on several ships of each class. This experiment is designed to determine the vertical height of the ship's center of gravity above the keel. The information obtained will be distributed to each ship within the class. This information is used to help determine the ship's stability during various loading condition.

Figures 3-19, 3-20, and 3-21 show typical clinometer reactions to changes in the ship's attitude.

The sounding and security patrol is one of the most important watches aboard ship. When you stand this watch, you need to stay alert. Personnel standing this watch have prevented serious damage by discovering fires and floods before they were able to get out of control.

SUMMARY

In this chapter, you were introduced to ship compartmentation, material condition of

Figure 3-19.-Trim by bow.

Figure 3-20.-Trim by stem.

readiness, compartment checkoff lists, and the DC closure log, along with the relationship of each to watertight integrity. As a Damage Controlman, you will use the information learned in this chapter in the daily performance of your duties. You need to have a good understanding of each topic that has been discussed. If you did not understand any of these topics, go back and review them now before you move on the next chapter.

Figure 3-21.-Heel to port.