SERVICE AREA
Boating Glossary
A working vocabulary for boat owners: Defined the way they're used on the water, not the way they appear in a manual.
This glossary collects the terms that come up most often in our work with boat owners — at the dock, on the water, in the engine room, on the radio. Some are technical. Some are operational. A few are conventions that don't appear in any official publication but that every working captain knows.
The definitions are written for owners, not for the Coast Guard exam. Where a term is covered in more depth in one of our articles, we've linked to it.
If a term you're looking for isn't here, let us know and we'll add it.
A
Abeam At right angles to the centerline of the boat. An object abeam to starboard is directly off your right side, neither ahead nor behind. Useful shorthand when the First Mate is calling distances from the bow.
Aft Toward the back of the boat. The opposite of forward. The aft end of a vessel is the stern.
Aids to navigation (ATON) The buoys, daymarks, lights, and ranges maintained by the Coast Guard to mark channels and hazards. Every one of them appears on the chart. If you find one that isn’t on the chart, or don’t find one that is, that’s worth reporting.
AIS (Automatic Identification System) A radio-based identification and tracking system used on commercial vessels and many recreational ones. Broadcasts vessel name, position, speed, and heading on dedicated VHF frequencies. Receivers display nearby AIS-equipped vessels on a chart plotter screen. Particularly useful in commercial traffic.
Amidships The middle of the boat, fore and aft. Also the position of a rudder or drive centered on the keel line.
Anchor bridle A two-legged line attachment that connects the anchor rode to the boat at two points on the bow rather than one. Spreads load, reduces shock-loading, and keeps the boat from yawing back and forth at anchor. On larger cruisers, a bridle is the difference between sleeping well at anchor and getting up at 2 a.m. to check the set.
Anchor light The white light displayed at the highest point of a vessel at anchor between sunset and sunrise. Required by the Navigation Rules. Often forgotten by recreational boaters anchoring overnight in protected anchorages.
Anchorage A body of water with adequate depth and protection where vessels customarily anchor. A good anchorage offers protection from the prevailing weather, holding ground appropriate to the anchor type, and enough swing room for the rode you’ll let out.
Anode See: Sacrificial anode.
Astern Behind the boat. Also the direction of travel with the transmission in reverse.
Autopilot Electronic steering that holds a set heading or follows a route from the chart plotter. On a long delivery run it’s the difference between arriving rested and arriving worn out. It does not stand a watch for you.
B
Backing down Operating the boat in reverse under power. Also the specific act of loading the anchor rode in reverse to confirm the hook has dug in. See: Setting Anchor Without Drifting.
Beam The width of a vessel at its widest point. A boat with a 14-foot beam is fourteen feet wide. Also used to indicate direction — a “beam wind” is one coming from directly off the side of the boat.
Beam sea Waves striking the boat from the side. The least comfortable point of travel on most cruisers, because the boat rolls instead of pitching. Often the reason a day’s run gets rerouted.
Bearing The direction from your boat to an object, in degrees. Distinct from heading, which is the direction the boat is pointed.
Bilge The lowest interior space of the hull, where water collects. A dry bilge tells you more about how a boat has been kept than any listing photo.
Bilge pump The pump that discharges water from the bilge overboard. Test the automatic float switch, not just the manual override. The manual switch working proves nothing about the automatic one.
Blower The engine compartment ventilation fan that clears fuel vapors before starting a gasoline inboard. Run it four minutes before you turn the key. Part of every pre-cruise engine room check.
Bow The front of the boat. The opposite of the stern.
Bow line The dock line that runs from the bow of the boat to the dock. Controls fore-and-aft movement at the front of the vessel.
Bow thruster A transverse propeller in a tunnel near the bow that pushes the bow sideways. Helpful in tight quarters and crosswinds. Not a substitute for understanding that the stern drives the boat.
Bowline A knot forming a fixed loop that won’t slip or jam under load. One of the four knots worth knowing cold.
Bridge tender The person operating a drawbridge. The official with authority over when (and whether) the bridge opens for marine traffic. Treated with respect on the radio and during transits. The Detroit River alone has several. See: VHF Radio Etiquette.
Bridle See: Anchor bridle.
Bulkhead A structural wall inside the hull, dividing the interior into compartments. Structural, not decorative.
Burgee The small flag identifying a yacht club, flown from a bow staff or masthead. Recognized at other clubs, and on the Great Lakes a familiar burgee gets you a conversation in most harbors between Toledo and the Straits. See: Ford Yacht Club.
C
Can buoy A cylindrical green buoy with an odd number, marking one edge of a channel. Paired with a red nun on the other side.
Carbon monoxide Colorless, odorless exhaust gas that kills. Accumulates at swim platforms behind idling engines and generators, and inside cabins with poor ventilation. A marine CO detector is cheap insurance against a problem you cannot smell coming.
Chafe gear Protective material wrapped around a line where it crosses a chock or rail: leather, split hose, or purpose-built sleeves. On an overnight in a rolling slip, chafe gear is what keeps a dock line from parting by morning.
Channel 13 The VHF channel used for bridge-to-bridge ship navigation communication in U.S. waters. Used by commercial freighters and tugs to coordinate passing arrangements with each other and with smaller recreational craft. Monitored constantly in commercial waters like the Detroit River and Lake Huron.
Channel 16 The international VHF calling and distress channel. Monitored 24 hours a day by the U.S. Coast Guard. Used to initiate contact, then to switch to a working channel for actual conversation. Not a chat channel. See: VHF Radio Etiquette.
Chart plotter The electronic display unit that shows your vessel’s position on a digital nautical chart. Most modern recreational boats have one. The good ones integrate GPS, AIS, radar, depth sounder, and route planning into a single display.
Chine The edge where the bottom of the hull meets the side. A hard chine is a sharp angle; a soft chine is rounded. Affects how a boat rides and how it leans in a turn.
Cleat A T-shaped fitting on a dock or a boat used to secure a line. The proper way to tie a line to a cleat is the cleat hitch — a specific knot taught early in any First Mate program. Done wrong, the line slips or jams; done right, it holds firmly and releases easily under load.
Cleat hitch The knot used to secure a dock line to a cleat. Two wraps around the base, a figure-eight pattern across the horns, and a final locking turn under the last wrap. Once you’ve tied a thousand, you don’t think about it anymore. Before that, you think about it every time.
Commercial Towing Assistance Endorsement A USCG credential add-on authorizing the holder to perform commercial towing of disabled vessels — the kind of work TowBoatUS or SeaTow captains do. Required for anyone offering commercial towing services. Captain Tom holds this endorsement on both his 100-ton and 50-ton Master Licenses.
Course over ground (COG) The actual direction the boat is traveling across the earth, measured by GPS. Differs from heading whenever wind or current pushes the boat sideways. On the Detroit River the difference is often significant. See: Boating the Detroit River.
Cradle The steel or wood frame a boat sits in for winter storage ashore, sized to the hull. See: Why Fall Haul-Out Books Up in July.
Crew Anyone aboard the vessel other than the captain. In recreational boating, often used interchangeably with “guests” or “passengers.” On a working vessel, crew specifically means people with assigned operational responsibilities.
Cruiser A type of recreational boat with overnight accommodations — sleeping quarters, a galley, a head — capable of multi-day use. Distinct from a center console (open-deck day boat) or a sportfish (specialized fishing platform). Most owner-assisted deliveries are on cruisers.
D
Daily rate The standard daily compensation paid to a delivery captain for time spent operating the vessel. Distinct from travel days and layover days, which may be billed at the same or a different rate per the delivery contract.
Danger signal Five or more short, rapid blasts of the horn. It means the vessel sounding it doesn’t understand your intentions, or doubts you’re doing enough to avoid collision. If you hear it, something is wrong. See: Right of Way on the Great Lakes.
Daymark A fixed navigation marker on a piling or structure, square green or triangular red, without a light. The daytime equivalent of a lighted aid.
Dead reckoning Estimating position from a known starting point using heading, speed, and elapsed time. Predates GPS by centuries and still worth knowing. Electronics fail.
Deposit A non-refundable payment made by the boat owner to secure the captain’s dates for a delivery. Credited against the final invoice. Standard practice in the delivery captain industry; without it, owners can cancel on short notice and leave the captain without work for the dates blocked.
Depth sounder The instrument that measures water depth using sound. Know whether yours reads depth below the transducer, below the keel, or below the waterline. Those are three different numbers, and only one of them is the one you care about.
Displacement The weight of water a vessel displaces, which equals the weight of the vessel. Dock lines, fenders, and ground tackle are sized to displacement, not to length.
Displacement speed The maximum speed a hull can make without climbing onto plane, roughly proportional to waterline length. On a heavy boat it’s usually the most efficient way to cover distance.
Dock hand The marina staff member who assists vessels with arrival and departure. Catches lines, fends off, provides local knowledge about the slip. Treated with the same professionalism as a tradesperson on your house — they help you when they think you know what you’re doing.
Dock line A line used to secure a vessel to a dock. Modern dock lines are typically three-strand nylon or double-braided nylon, sized to the vessel’s displacement.
Dockage The fee charged for a slip, generally by the foot, per night or per season. Transient dockage is the nightly rate for visiting boats.
Documentation Federal vessel registration — the alternative to state registration for vessels over five net tons. Documented vessels carry a USCG Certificate of Documentation and display their official number internally rather than on the hull. Required for some commercial operations and many marine insurance policies.
Downbound Great Lakes shorthand for a vessel traveling with the system’s outflow, toward Lake Erie and the St. Lawrence. Freighters announce upbound or downbound on Channel 13. Learning which is which makes commercial radio traffic legible.
Draft The depth of water a boat needs to float, measured from the waterline to the lowest point of the hull or running gear. Know yours to the inch. Around the St. Clair Flats it matters more than most owners expect.
DSC (Digital Selective Calling) A function on modern VHF radios that allows the user to call a specific vessel directly using its MMSI number, rather than broadcasting on Channel 16. Most modern radios have it. Most owners never set it up.
E
ECOS (engine cut-off switch) The lanyard or wireless device that shuts down the engine if the operator leaves the helm. Since April 1, 2021, federal law requires operators of recreational vessels under 26 feet to use the ECOS link when running on plane or above displacement speed. Most people still call it a kill switch.
Endorsement An add-on credential to a USCG license — for example, the Commercial Towing Assistance Endorsement. Endorsements expand the scope of operations the licensed captain is authorized to perform.
Engine room check The pre-departure inspection of a vessel’s engine compartment. Strainers, fluid levels, belts, blowers, bilge condition, fuel filters. Performed before every run. The single most important habit any boat owner can develop. See: What a First Mate Actually Does Before Departure.
Ensign The national flag flown by a vessel. On U.S. recreational boats it flies from a stern staff. Traditionally raised at 0800 and lowered at sunset.
EPIRB Emergency Position Indicating Radio Beacon. A registered satellite distress beacon that transmits your identity and position to search and rescue when activated. Uncommon on Great Lakes cruisers, standard offshore. A PLB is the smaller personal version.
F
Fathom Six feet. Great Lakes charts are in feet, so the unit turns up mostly in conversation and older publications.
Fender A cushioned device, typically inflatable or foam, hung between the vessel and the dock to absorb contact. The First Mate’s responsibility to prepare, position, and deploy correctly. Floating docks require different fender placement than fixed-piling docks.
Fetch The distance of open water the wind blows across without obstruction. Long fetch builds bigger waves. It’s why a 15-knot westerly makes Lake Erie unpleasant and barely registers in a protected channel. See: Boating Lake Erie.
First mate The person aboard the vessel responsible for assisting the captain in operations — line and fender handling, lookout, radio operation, and in emergencies, operation of the vessel itself. On recreational boats, often a spouse or family member. On working vessels, a paid crew position. See: First Mate Coaching.
Fix A confirmed position, whether from GPS, from crossed bearings, or from a visual on a charted landmark.
Float plan A document filed with someone reliable on shore before a voyage, stating the vessel’s intended route, expected times, and what to do if the vessel doesn’t check in as scheduled. Simple, free, and one of the highest-leverage safety practices available to recreational boaters. See: The First Mate’s Emergency Playbook.
Flybridge The upper helm station on a cruiser, above the main cabin. Better visibility, worse weather protection, higher center of gravity.
Following sea Waves overtaking the boat from behind. Comfortable until it isn’t. In a steep following sea a boat can be shoved off course or, in the extreme, broach.
Force majeure A contractual term referring to events beyond the parties’ control — storms, government-ordered closures, acts of God — that excuse non-performance of obligations. Standard clause in any delivery contract.
Forward Toward the front of the boat. The opposite of aft. The forward end of a vessel is the bow.
Freeboard The vertical distance from the waterline to the deck. Determines how wet the ride is and how hard it is to get back aboard from the water.
Fuel dock The marina station selling gas or diesel, and on most Great Lakes marinas the location of the pump-out as well. Call ahead on the radio a mile out. The good ones will have someone waiting.
G
Gale warning A National Weather Service marine warning for sustained winds of 34 to 47 knots. Well past the point where a recreational cruiser should be underway.
Galley The kitchen aboard a vessel. From the Latin galea. Still called a galley regardless of how modern the appliances are.
Give-way vessel The vessel required by the Navigation Rules to keep clear in a crossing or overtaking situation. A give-way vessel changes course or speed early and obviously, so the other vessel can see what she’s doing. See: Right of Way on the Great Lakes.
GPS The satellite positioning system feeding your chart plotter, your VHF’s DSC distress function, and your phone. Accurate, reliable, and not a substitute for knowing where you are.
Great Loop A continuous waterway circuit through the eastern United States and Canada — Atlantic Intracoastal Waterway, Hudson River, Erie Canal, Great Lakes, Chicago and Illinois Rivers, and the Tenn-Tom Waterway. Approximately 6,000 miles total. Cruisers who complete the full loop are called Loopers. See: Great Loop guide.
Gross Register Tons (GRT) A measure of a vessel’s total internal volume, not its weight. USCG captain licenses are rated by GRT capacity — a 100-ton license authorizes operation of vessels up to 100 GRT. Captain Tom holds a 100 GRT Master License for the Great Lakes and Inland Waters, and a 50 GRT Master License for Near Coastal.
Ground tackle The whole anchoring system: anchor, rode, shackles, swivel, bridle, and windlass. It appears on the pre-delivery readiness checklist for a reason. See: Preparing Your Boat for Delivery.
Gunwale (pronounced gunnel) The upper edge of the boat’s side, where hull and deck meet. Not a seat, and never a seat underway.
H
Hailing port The home port of a vessel as registered with the USCG. Displayed on documented vessels along with the vessel name. Often (but not always) the marina where the boat is actually kept.
Harbor of refuge A protected harbor specifically built or designated as shelter for vessels seeking safety from weather or mechanical issues. Lake Huron has several along its Michigan shoreline — Harbor Beach being the most prominent. See: Crossing Lake Huron.
Harbormaster The person running a municipal or club harbor. Assigns slips, manages transient dockage, and knows the entrance better than the chart does.
Hard aground Stuck on the bottom with no easy way off. Distinct from a soft touch you can back out of. Hard aground on a rocky bottom is a haul-out and a survey, not a tow.
Haul out The annual removal of a boat from the water for winter storage — done at the end of the cruising season in the Great Lakes, typically October. The opposite of splash or launch in spring.
Head The bathroom aboard a vessel.
Heading The direction the boat is pointed, in degrees. Distinct from course over ground, which is where the boat is actually going.
Helm The steering station. Also the act of steering, and by extension the responsibility for the vessel.
Holding ground The bottom material in an anchorage — sand, mud, clay, rock, or grass. Determines how well an anchor will set and hold. Soft mud holds well; rock and grass hold poorly. A good chart and local knowledge tell you what to expect at any given anchorage.
Hull Identification Number (HIN) The 12-character serial number molded into the transom of every boat built since 1972. The VIN of the marine world. Verify it against the paperwork before money changes hands. See: Questions to Ask Before Buying a Boat.
Hypothermia The loss of core body temperature from immersion or exposure. The reason Great Lakes water is dangerous in May and October even on a warm afternoon. Time in the water matters more than air temperature.
I
Idle speed The lowest forward propulsion speed at which a vessel can be operated under control. Used in no-wake zones, marinas, and close-quarters maneuvering.
Impeller The flexible rubber vane wheel that pumps raw water through the engine’s cooling system. A wear item. When one shreds, the pieces travel downstream into the heat exchanger. Carry a spare on any trip longer than a day.
Inboard An engine mounted inside the hull, driving a propeller through a shaft. Distinct from an outboard or a sterndrive.
Inland Waters USCG-defined waters within or directly adjacent to U.S. land — rivers, lakes, bays, and sounds inside the demarcation lines. A 100-ton Master license for Great Lakes and Inland Waters authorizes operation in these waters but not on the open ocean.
Insurance rider A temporary addendum to a boat owner’s marine insurance policy naming the delivery captain as an approved operator for the dates of a specific voyage. Required by most carriers and by all serious delivery captains. See: Why I Won’t Deliver Without an Insurance Rider.
J
Jetty A structure built out from shore to protect a harbor entrance or control a river mouth. Often the first and last thing you pass on a Great Lakes run. Give the end of one a wide berth. They extend underwater farther than they look.
K
Keel The centerline structure running fore and aft along the bottom of the hull. On most powerboats a shallow keel provides tracking and protects running gear in a grounding.
Kill switch See: ECOS. The Coast Guard’s term is engine cut-off switch. “Kill switch” is what everyone actually says.
Knot (unit of speed) One nautical mile per hour. The standard unit of speed on the water. One knot equals approximately 1.15 statute miles per hour. A vessel running at 8 knots is moving at about 9.2 mph.
Knot (line attachment) A method of securing a line to itself, to a cleat, or to an object. Every captain knows a small number of essential knots — the cleat hitch, bowline, clove hitch, and figure-eight stopper being the most commonly used.
L
Laker A Great Lakes bulk freighter, built to the dimensions of the lock system and rarely leaving the lakes. Distinct from a saltie, an ocean-going ship that came in through the St. Lawrence Seaway. A thousand-footer takes a long time to stop and will not maneuver for you.
Launch The spring return of a boat to the water. Also called splash. The opposite of haul out. See: Spring Launch Checklist.
Layover day A day on a planned delivery during which the vessel is not moved — typically due to weather, mechanical issues, or planned rest. Billed at a daily rate per the delivery contract. Owners sometimes expect layover days to be free; they aren’t.
Lee shore A shoreline that the wind is blowing toward, from the perspective of a vessel on the water. The dangerous side. A vessel disabled offshore of a lee shore is being pushed toward the rocks; the same vessel offshore of a weather shore is being pushed away from them.
Leeway The sideways drift of a boat caused by wind. Add it to current and you have the reason your course over ground rarely matches your heading.
License (Master) A USCG Merchant Mariner Credential authorizing the holder to operate vessels of specified tonnage on specified waters. The Master license is the highest level of recreational/light-commercial USCG credential. Tonnage and water-area endorsements determine the scope.
Line A rope, once it’s on a boat. The terminology distinction matters more to traditional mariners than to most owners, but using “line” rather than “rope” is one of the small marks of someone who has spent time on the water.
Local Notice to Mariners The weekly Coast Guard district publication listing changes to aids to navigation, hazards, bridge schedules, and waterway closures. It’s free, and it’s worth scanning before a passage into unfamiliar water.
Lock A chamber that raises or lowers vessels between water levels. On the Great Lakes system, the Soo Locks at Sault Ste. Marie connect Lake Superior to Lake Huron. Loopers meet dozens more. See: The Great Loop.
Lookout The Navigation Rules requirement to maintain a proper lookout by sight and hearing at all times. The chart plotter is not a lookout. Neither is the autopilot.
Low Water Datum (LWD) The reference level that charted depths on the Great Lakes are measured from. NOAA defines it as a surface so low the water level will seldom fall below it. When lake levels run well above datum, you have more water than the chart shows. When they run near it, the chart is telling you the plain truth and the margin you’ve gotten used to is gone.
M
Man overboard (MOB) The emergency of a person in the water. Also the button on most chart plotters that drops a position marker the instant it’s pressed. Press it first, then begin the recovery. See: The First Mate’s Emergency Playbook.
Mariner Reference Number A unique identifier assigned by the USCG to each licensed mariner. Used on the captain’s credential and provided to insurance carriers when securing a rider. Captain Tom’s Mariner Reference Number is 2913289.
Marlinspike seamanship The traditional skill set of working with rope and line aboard a vessel — knot tying, splicing, whipping, and line maintenance. From the marlinspike, a pointed tool used in rope work. The term covers the broader category of practical rope handling.
Mayday The VHF distress call for grave and imminent danger to life or vessel. Spoken three times on Channel 16, followed by vessel name, position, nature of distress, and souls on board. Used only when that is genuinely the situation. See: VHF Radio Etiquette.
Merchant Mariner Credential (MMC) The physical credential the Coast Guard issues to a licensed mariner, listing every endorsement held. It’s what a captain hands you when you ask to see his license. See: My Credentials.
Meteotsunami A wave generated by a fast-moving pressure disturbance rather than by wind or seismic activity. Documented on the Great Lakes and distinct from a seiche, though the two get confused constantly.
MMSI (Maritime Mobile Service Identity) A unique nine-digit number used to identify a specific vessel for DSC and AIS purposes. Programmed into the radio and tied to the vessel registration. Required for distress alerting via DSC.
Mooring ball A permanent anchor with a float, provided by a harbor or club for vessels to tie to. Common in northern Lake Huron harbors. Cheaper than a slip, and you take a dinghy to shore.
N
Nautical mile 6,076 feet, or about 1.15 statute miles. Great Lakes distances get quoted both ways depending on who’s talking, so confirm which one you’re hearing before planning a day’s run.
Navigation Rules The federal rules governing right of way, lights, and sound signals. The Inland Rules apply on the Great Lakes and inland waters; COLREGS apply internationally. Most of the differences don’t affect a recreational cruiser. The rules themselves absolutely do. See: Right of Way on the Great Lakes.
Near Coastal USCG-defined waters within 200 miles of the U.S. coastline. A Near Coastal license authorizes operation in these waters in addition to (or instead of) Inland Waters, depending on the specific credential. Captain Tom holds a 50-ton Master Near Coastal in addition to his 100-ton Master Inland.
No-wake zone A water area in which vessels must operate at idle speed, producing no wake. Typically marked with regulatory buoys. Common in marinas, harbor approaches, and protected anchorages.
Nun buoy A cone-topped red buoy with an even number, marking one edge of a channel. Paired with a green can on the other side.
O
OUPV Operator of Uninspected Passenger Vessels, commonly called the six-pack license. Authorizes carrying up to six paying passengers on an uninspected vessel. A step below a Master license, which covers inspected vessels and larger passenger counts.
Outdrive The steerable drive unit hanging off the transom of a sterndrive boat, combining propeller, gearcase, and steering. Also called a sterndrive or an I/O. Steering the drive is what turns the boat, which is why a sterndrive loses steering the moment the throttles come to neutral.
Overtaking Passing another vessel from behind. The overtaking vessel is always the give-way vessel and stays clear until well past. That doesn’t change based on who has more horsepower.
Owner-assisted delivery A delivery model in which the boat owner rides along with the hired captain, learning the vessel through hands-on operation under the captain’s coaching during the trip. Combines a standard over-water delivery with on-water coaching. See: Owner-Assisted Boat Delivery.
P
Pan-Pan (pronounced pahn-pahn) The VHF urgency call for a serious situation that isn’t immediately life-threatening. A dead engine in a shipping channel is a Pan-Pan. Taking on water is a Mayday. See: VHF Radio Etiquette.
PFD (Personal Flotation Device) A life jacket or other flotation garment. USCG requires one wearable PFD aboard for every person on the vessel, plus a throwable Type IV on boats 16 feet and longer. Wearing one is the First Mate’s leadership responsibility — they go on first, so everyone follows.
Piling A vertical post driven into the bottom, used for docks, slips, and channel markers. Fixed docks are built on pilings, which is why fender placement there has to account for changing water levels.
Pitch The fore-and-aft rocking of a boat, bow up and bow down. Also the theoretical distance a propeller advances in one revolution.
Pivot point The point a boat rotates around when it turns. On most single-screw powerboats it sits forward of amidships. Knowing where yours is turns close-quarters maneuvering from guesswork into geometry. See: How to Dock Your Boat Confidently.
Planing Running fast enough that the hull rides on top of the water instead of pushing through it. The transition is the hump. Past it, fuel burn per mile usually improves before it gets worse again. See: Great Lakes Boat Fuel Cost Calculator.
Port (direction) The left side of the boat, looking forward from the helm. Marked with a red navigation light at night. The opposite of starboard.
Port (place) A harbor, marina, or destination where a vessel calls.
Pre-departure walkthrough The structured pre-trip inspection of the vessel performed by the captain and first mate together. Covers engine room, safety gear, lines and fenders, radio check, and trip plan review. The single highest-leverage activity in any voyage. See: What a First Mate Actually Does Before Departure.
Prop walk The lateral movement of a single-screw boat’s stern when reverse is applied. Caused by asymmetric thrust from the propeller. Predictable for a given boat, and useful in close-quarters maneuvering once a captain learns to read it.
Pump-out The marina station for emptying a holding tank. Discharging untreated sewage into the Great Lakes is illegal. Any marina of size has one.
Q
Quarter The section of the boat between the beam and the stern. A vessel on your starboard quarter is behind you and to the right.
Quartering sea Waves striking the boat at an angle off the bow or the stern rather than head-on or abeam. A following quartering sea is the one that tries to steer the boat for you, and the reason an autopilot earns its keep in some conditions and gets switched off in others.
R
Radar The ranging instrument that displays returns from vessels, shorelines, and heavy rain. The one piece of electronics that sees through fog. Learn it before you need it, not during.
Range A pair of markers or lights, one behind and above the other, that line up vertically when you’re on the centerline of a channel. Line them up and hold them there. Ranges guide vessels into several Great Lakes harbor entrances.
Red right returning The mnemonic for the U.S. lateral buoyage system: keep red markers to starboard when returning from open water or heading upstream. The catch is deciding which direction counts as returning. On the Great Lakes and the connecting rivers, read the chart rather than guessing.
Restricted visibility Fog, heavy rain, snow, or anything else limiting sight. Triggers specific obligations under the Navigation Rules: reduced speed, sound signals, and a heightened lookout.
Rode The line, chain, or combination connecting the anchor to the boat. The scope (length of rode relative to water depth) determines how well the anchor sets and holds.
Roll The side-to-side motion of a boat. The motion guests notice most, and the one that trim tabs and a change of course usually fix.
Rub rail The protective molding around the hull at deck level. It takes the contact your fenders miss. Replacing one costs real money.
Rudder The steerable underwater plate that turns an inboard boat. It only works with water flowing across it, which is why an inboard has no steering at idle in neutral.
Running lights Navigation lights displayed by a vessel underway between sunset and sunrise. Red on port, green on starboard, white on stern (for vessels under 50 meters). Required by the Navigation Rules.
S
Sacrificial anode A block of zinc, aluminum, or magnesium bolted to underwater metal, which corrodes in place of the running gear. Everyone calls them zincs regardless of what they’re actually made of. Freshwater boats generally run magnesium or aluminum. Check them at haul-out. See: What a Marine Survey Covers.
Safe speed The Navigation Rules requirement to proceed at a speed appropriate to visibility, traffic, maneuverability, and conditions. There’s no posted number. The standard is what a prudent mariner would do.
Salon The main cabin of a cruiser. One L, not two. Not a saloon, though after a long day it may serve as one.
Scope The ratio of anchor rode let out to water depth at the anchor location, including height of bow above water. A 5:1 scope means five feet of rode for every foot of depth. Higher scopes hold better; lower scopes are sometimes necessary in crowded anchorages. Most captains run 5:1 to 7:1 in normal conditions.
Sea strainer The filter between the through-hull and the raw water pump, catching weeds and debris before they reach the engine. Checked and cleared as part of every pre-cruise engine room check. On Lake St. Clair in August, that isn’t optional.
Sea trial The on-water test of a boat under consideration for purchase, run at operating temperature through the full range of conditions. Distinct from the survey, though the two are usually scheduled together. See: What to Check on a Sea Trial.
Seacock The valve on a through-hull fitting that shuts off water flow. It should turn freely. A seized seacock is a common survey finding and a real problem on the day you need one.
Securité (pronounced say-cure-ee-tay) A VHF safety message used to broadcast a navigation hazard or non-emergency safety information to other vessels. Less urgent than Pan-Pan, dramatically less urgent than Mayday. See: VHF Radio Etiquette.
Seiche (pronounced saysh) A standing wave oscillating across a lake, driven by strong wind and rapid pressure change. Water piles up at one end, and when the wind lets up it sloshes back and forth for hours or even days. NOAA notes Lake Erie is known for them, particularly with strong southwest winds. Frequently mistaken for tide.
Set (the anchor) The process of confirming that the anchor has dug into the bottom and is holding. After paying out scope, the captain typically puts the engine in reverse and gently loads the rode to verify the set.
Shakedown cruise The first real run of a season, or on a new-to-you boat, taken close to home specifically so that whatever fails, fails somewhere convenient. See: The First 50 Miles on a New-to-You Boat.
Shore power Dockside AC electricity delivered to the boat through a cord and inlet. Managed with the same care as any other electrical system. Check the cord ends for heat and corrosion, and know which breaker comes first.
Shrink wrap The heat-sealed plastic cover applied over a boat for winter storage. It needs vents. Trapped moisture over a Michigan winter does more damage than the cover prevents.
Slip A docking space in a marina, typically with a wooden or floating finger pier on one or both sides.
Small craft advisory A National Weather Service marine advisory, typically for sustained winds around 20 to 33 knots or hazardous seas. It’s an advisory rather than a prohibition, which is exactly why it gets ignored by the people who shouldn’t ignore it.
Souls on board (SOB) The total number of people aboard a vessel. Used in float plans, distress calls, and Coast Guard communications.
Sound signal A horn blast communicating maneuvering intentions or presence. One short blast for a port-to-port pass, two for starboard-to-starboard, five or more for danger.
Speed over ground (SOG) Actual speed across the earth, from GPS. Differs from speed through the water whenever there’s current. On the Detroit River, upbound and downbound runs at the same throttle setting produce noticeably different numbers.
Spring line A dock line that runs diagonally between the boat and the dock, controlling fore-and-aft movement. The most important line on the boat in any docking other than a perfect calm-water approach. Used by the captain to spring the bow or stern off the dock during departure. Often misunderstood by new boaters and underused.
Stand-on vessel The vessel required by the Navigation Rules to hold course and speed while the give-way vessel maneuvers. Holding course is the obligation. It stops being the obligation the moment a collision becomes likely.
Starboard The right side of the boat, looking forward from the helm. Marked with a green navigation light at night. The opposite of port.
Stateroom A sleeping cabin on a cruiser.
Station keeping Holding a position on the water against wind and current using engines and steering. What you do while waiting on a bridge, a lock, or a fuel dock.
Stern The back of the boat. The opposite of the bow.
Stern line The dock line that runs from the stern of the boat to the dock. Controls fore-and-aft movement at the back of the vessel.
Stuffing box The seal where the propeller shaft exits the hull. Traditional packing drips slowly by design when underway. A dry one running hot is a problem. So is one that streams.
Swim platform The deck extending aft of the transom. Where boarding happens, where the ladder lives, and where carbon monoxide collects behind a running engine.
T
Through-hull Any fitting penetrating the hull at or below the waterline. Each one should have a seacock, and each one belongs on the list you check before departure.
Throwable PFD A Type IV personal flotation device — typically a cushion or ring — designed to be thrown to a person in the water rather than worn. USCG-required on vessels 16 feet and longer.
TowBoatUS The on-water assistance network operated through BoatUS. Membership turns most tows from a four-figure bill into a phone call. It’s one of the short-term solutions worth having in place well before the day you need it.
Transient slip A dock space rented by the night to visiting boats. Reserve one for a summer weekend in the North Channel or you’ll be anchoring. See: Planning a Multi-Day Great Lakes Trip.
Transom The flat surface across the back of the hull. Where the HIN is molded, where the outdrive mounts, and where the name goes.
Travel lift The wheeled hoist that straddles a boat, picks it up in slings, and carries it between the water and the yard. What hauling out actually looks like.
Trim tabs Adjustable plates on the transom of a powerboat that change the boat’s running attitude in the water. Used to compensate for load distribution, wind, and sea state. Most owners use them too little; a few use them too much.
Trip plan The intended route and schedule of a voyage — including departure time, waypoints, expected port arrivals, and contingency anchorages. Distinct from a float plan, which is the document filed with someone on shore.
TWIC Transportation Worker Identification Credential. The federal security credential and background check required as part of a Coast Guard captain’s license application.
U
Underway Not made fast to a dock, not anchored, and not aground. A boat drifting with the engines shut down is still underway. The distinction matters for lights and for the Navigation Rules.
Upbound Great Lakes shorthand for traveling against the system’s outflow, toward Lake Superior. Freighters state upbound or downbound in their Channel 13 calls, and knowing which is which tells you where a thousand-footer will be in ten minutes.
V
V-berth The sleeping berth in the bow, shaped by the hull. Comfortable at the dock. Less so at anchor in a chop.
Variation The local difference between true north and magnetic north, printed on the compass rose of every chart. GPS reads true; your compass reads magnetic. Know which one your plotter is set to display.
Vessel delivery The professional service of transporting a boat over water from one location to another, performed by a USCG-licensed captain. Distinct from boat transport (trucking) and from charter (passenger service). See: Vessel Delivery.
Vessel Safety Check The free, voluntary inspection offered by the Coast Guard Auxiliary and the U.S. Power Squadrons. No citation results from it. Worth doing before a first long trip.
VHF (Very High Frequency) The radio frequency band used for marine communications. Most marine VHF radios operate between 156 and 174 MHz. Limited to roughly line-of-sight range — typically 10 to 20 miles depending on antenna height. See: VHF Radio Etiquette.
W
Wake The disturbed water trailing behind a moving vessel. Vessels are legally responsible for their wake — meaning damage caused by a wake to other vessels, docks, or shoreline property is the responsibility of the vessel that produced it.
Waypoint A stored position on a chart plotter, used on its own or strung into a route. A route of waypoints is not a trip plan. It’s a line on a screen that knows nothing about the shoal you didn’t look at.
Weather shore A shoreline that the wind is blowing away from, from the perspective of a vessel on the water. The protected side. The opposite of a lee shore.
Whistle (signal) A standardized sound signal used between vessels to indicate passing intentions in restricted visibility or close-quarters maneuvering. “One whistle” indicates a port-to-port passing; “two whistles” indicates starboard-to-starboard. Used today on Channel 13 voice radio calls more often than as actual horn signals.
Windlass The powered winch that raises and lowers the anchor. Meant for lifting rode, not for breaking a set anchor out of the bottom. Use the boat for that.
Winterize The fall process of protecting a boat’s systems from freezing: engines, water systems, holding tanks, and everything else that holds liquid. The one job where being a week late can cost an engine block. See: Why Fall Haul-Out Books Up in July.
Working channel A VHF channel used for actual conversation after making contact on 16. Recreational vessels commonly use 68, 69, 71, and 72. See: VHF Radio Etiquette.
Y
Yard A boatyard — the facility where vessels are hauled, stored, repaired, and serviced. The term carries the same connotation as a “shop” in automotive terminology.
Yaw The side-to-side swing of the bow around a vertical axis. At anchor, yawing is what a bridle reduces. Underway in a following sea, it’s what steering corrects.
Z
Zinc See: Sacrificial anode.
Closing
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