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USCG Exam Practice · Plot true course and distance between two charted points

A vessel required to carry ARPA under 33 CFR §164.38 is also required to carry a speed and distance device under 33 CFR §164.40. At a speed of 6 knots, what is the maximum allowable error in indicated speed under the regulation?

  1. A0.3 knot, because 5 percent of 6 knots is 0.3 knot
  2. B0.5 knot, because the regulation specifies 5 percent of speed or 0.5 knot, whichever is greater✓ correct
  3. C0.6 knot, because the regulation allows 10 percent at speeds below 10 knots
  4. D1.0 knot, because the regulation doubles the tolerance at speeds below 10 knots

Why B is correct

33 CFR §164.40(b)(2) states that speed errors should not exceed 5 percent of the vessel's speed or 0.5 knot, whichever is greater. At 6 knots, 5 percent equals 0.3 knot, which is less than 0.5 knot; therefore the allowable error is 0.5 knot. The regulation contains no doubled tolerance provision for low speeds.

Cited:33 CFR §164.40

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