33 CFR 164.40: Speed and distance indicating devices
Last reviewed: October 14, 2026
This section covers the speed and distance device required on vessels that must have an ARPA. Such a vessel must have a device indicating its speed and distance, through the water or over the ground. The device must meet display and accuracy specifications.
Applies toEach vessel required to be fitted with an Automatic Radar Plotting Aid (ARPA) under § 164.38 of this part.
What it says
Each vessel required to have an ARPA under § 164.38 of this part must have a device that indicates the vessel's speed and distance, either through the water or over the ground.
33 CFR 164.40(a)“must be fitted with a device to indicate speed and distance of the vessel either through the water or over the ground”
The device's display must be easily readable on the bridge by day or night.
33 CFR 164.40(b)(1)“The display must be easily readable on the bridge by day or night.”
Errors in indicated speed should not exceed 5 percent of the vessel's speed, or 0.5 knot, whichever is greater, when the vessel is free from shallow water effect and from the effects of wind, current, and tide.
33 CFR 164.40(b)(2)“should not exceed 5 percent of the speed of the vessel, or 0.5 knot, whichever is greater.”
Errors in indicated distance run should not exceed 5 percent of the distance run in one hour, or 0.5 nautical mile in each hour, whichever is greater, when the vessel is free from shallow water effect and from the effects of wind, current, and tide.
33 CFR 164.40(b)(3)“should not exceed 5 percent of the distance run of the vessel in one hour or 0.5 nautical mile in each hour, whichever is greater.”
Common questions
Which vessels need a speed and distance indicating device?
Each vessel required to be fitted with an ARPA under § 164.38 of this part must have one.
“Each vessel required to be fitted with an Automatic Radar Plotting Aid (ARPA) under § 164.38 of this part”
Must the speed be measured through the water or over the ground?
Either one is allowed. The device must indicate speed and distance either through the water or over the ground.
“must be fitted with a device to indicate speed and distance of the vessel either through the water or over the ground”
How accurate should the speed indication be?
Speed errors should not exceed 5 percent of the vessel's speed, or 0.5 knot, whichever is greater. This applies when the vessel is free from shallow water effect and from the effects of wind, current, and tide.
“should not exceed 5 percent of the speed of the vessel, or 0.5 knot, whichever is greater.”
The text of 33 CFR 164.40
Electronic Code of Federal Regulations (eCFR), current as of April 16, 2026 · Read it on eCFR
Devices to indicate speed and distance
(a) Each vessel required to be fitted with an Automatic Radar Plotting Aid (ARPA) under § 164.38 of this part must be fitted with a device to indicate speed and distance of the vessel either through the water or over the ground.
(b) The device must meet the following specifications:
(1) The display must be easily readable on the bridge by day or night.
(2) Errors in the indicated speed, when the vessel is operating free from shallow water effect, and from the effects of wind, current, and tide, should not exceed 5 percent of the speed of the vessel, or 0.5 knot, whichever is greater.
(3) Errors in the indicated distance run, when the vessel is operating free from shallow water effect, and from the effects of wind, current, and tide, should not exceed 5 percent of the distance run of the vessel in one hour or 0.5 nautical mile in each hour, whichever is greater.
Sections it refers to
The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of April 16, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.