100-Ton Master Exam Prep

Sample 100-Ton Master questions

1. 1. 72 COLREGS apply to vessels upon which waters?

   • A.All vessels on the high seas and connected navigable waters✓
   • B.Only vessels on the high seas beyond 12 nautical miles
   • C.Only vessels in international waters beyond 3 nautical miles
   • D.All vessels on the high seas and in U.S. inland waters

   Why: Rule 1(a) states the rules apply on the high seas and in all waters connected therewith navigable by seagoing vessels. This broad application covers coastal, port, and offshore waters unless a nation has established special inland rules for specific waters.

2. 2. A vessel departs a known position at 0800 on course 090°T at 12 knots. What is the DR position at 1100?

   • A.36 nautical miles east of the departure point✓
   • B.24 nautical miles east of the departure point
   • C.48 nautical miles east of the departure point
   • D.36 nautical miles west of the departure point

   Why: Time elapsed = 1100 - 0800 = 3 hours. Distance = Speed × Time = 12 × 3 = 36 nm. Course 090°T is due east, so the DR position is 36 nm east of departure.

3. 3. Which knot is most suitable for joining two lines of equal diameter?

   • A.Square knot✓
   • B.Sheet bend
   • C.Bowline
   • D.Clove hitch

   Why: The square knot (reef knot) is designed for joining two lines of equal size and is commonly used to tie off reefing points and bundling. It should not be used for critical load-bearing applications or lines of unequal diameter.

4. 4. On a Mercator chart, one nautical mile is measured using the:

   • A.Latitude scale at the side of the chart, at the boat's approximate latitude✓
   • B.Longitude scale at the top or bottom of the chart
   • C.Bar scale only, regardless of latitude
   • D.Distance between meridians at the equator

   Why: One minute of latitude equals one nautical mile, so distance is read from the latitude scale on the sides. Because the Mercator latitude scale expands toward the poles, always measure at the mid-latitude of the leg, never on the longitude scale.

5. 5. Standard atmospheric pressure at sea level is approximately:

   • A.1013 millibars (29.92 inches of mercury)✓
   • B.850 millibars (25.10 inches of mercury)
   • C.1100 millibars (33.00 inches of mercury)
   • D.760 millibars (22.40 inches of mercury)

   Why: Standard sea-level pressure is 1013.25 mb, equal to 29.92 inches of mercury or 14.7 psi. Readings are compared against this value; well below it indicates a low-pressure system.