Glossary
Marine electronics and rigging glossary
Quick answer
This glossary defines 33 marine electronics and rigging terms in one plain sentence each, from CHIRP sonar and side imaging through the Peukert effect and ABYC E-11, and states plainly which figures are published standards, which are boating convention, and which exist only on the reader's own boat.
Marine electronics borrow vocabulary from sonar engineering, battery chemistry, electrical code and old seamanship all at once, and the same page rarely defines all four cleanly. This glossary states each term in one plain sentence, grouped by topic, and marks which definitions rest on a published standard, which are boating convention with no standards body behind them, and which describe a figure that exists only on the reader's own boat, motor or transducer.
A transducer such as the one built into Garmin Striker 4 and a network component such as Lowrance NMEA 2000 network starter kit appear here as concrete examples where a real product makes a definition easier to picture, not as an endorsement folded into the definition itself.
On this page
Sonar and imaging terms
CHIRP sweeps continuously across a range of frequencies rather than pulsing at one, which is the published technology behind sharper fish arches on modern sonar.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Term | Definition | Basis |
|---|---|---|
| CHIRP | A sonar signal that sweeps continuously across a range of frequencies rather than pulsing at a single frequency, producing sharper fish arches and better target separation than single frequency sonar. | Published technology |
| Traditional sonar | A single cone of sonar aimed straight down from the transducer, showing depth, bottom hardness and anything suspended directly beneath the boat. | Published technology |
| Down imaging | Sonar run at a higher frequency than traditional sonar to render a photographic style picture of what sits directly beneath the boat, at the cost of a narrower beam. | Published technology |
| Side imaging | Sonar aimed out to each side of the boat rather than straight down, covering a wide strip of bottom in a single pass instead of only the water under the hull. | Published technology |
| Live sonar | Real time sonar, shown live rather than scrolling, that displays a moving picture of fish and a falling lure as they happen rather than a history of what already passed under the boat. | Published technology |
| Cone angle | The width of the sonar beam a transducer sends out, stated in degrees; a narrower cone covers less water at a given depth but returns a sharper, more detailed picture. | Vessel figure, read off your own transducer's specification |
| Transducer | The sensor that sends a sonar signal into the water and receives its echo, converting between electrical signal and sound. | Published technology |
Mounting and hull terms
Where the transducer physically sits changes what it can see, and the vocabulary here describes real installation choices rather than a sonar mode.
A thru-hull mount is the only style that reads accurately at speed on a deep vee hull, where a transom mount can ventilate.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Term | Definition | Basis |
|---|---|---|
| Transom mount | A transducer mount bolted to the flat back of the hull, the simplest and most common install on a planing boat with an unobstructed transom. | Published mounting style |
| Thru-hull | A transducer mounted through a hole cut below the waterline, which reads accurately at speed on a deep vee hull where a transom mount can ventilate. | Published mounting style |
| In-hull | A transducer glued inside a solid fiberglass hull, shooting sonar through the hull itself with no hole cut at all, at some cost to sensitivity. | Published mounting style |
| Deadrise | The angle of the hull's bottom at the transom, measured from horizontal, which decides which transducer mount style will sit correctly and read cleanly. | Vessel figure, specific to your own hull at the transom |
Navigation and anchoring terms
NMEA 2000 is the standardized network that lets a GPS antenna such as Garmin GPS 24xd antenna and receiver, NMEA 2000 share one backbone cable with sonar, an engine and an autopilot from different makers.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Term | Definition | Basis |
|---|---|---|
| NMEA 2000 | A standardized marine data network that lets a GPS antenna, sonar, engine and autopilot from different makers share one backbone cable and speak the same data language. | Published standard |
| GPS antenna | A dedicated position receiver mounted outside the console, such as Garmin GPS 24xd antenna and receiver, NMEA 2000, which gets a faster and steadier fix than a GPS chip buried inside a chartplotter housing. | Published technology |
| Heading sensor | A sensor that reports which way the bow is pointing even when the boat is stationary, which is what keeps a chart oriented correctly at slow speed or at anchor. | Published technology |
| Chartplotter | A display that combines GPS position with electronic charts, so a boat's position is shown directly on a map rather than as coordinates alone. | Published technology |
| Spot-Lock | A GPS-based hold feature on an electric trolling motor that repositions the motor automatically to keep the boat over one spot, without an anchor going down at all. | Published feature name |
| Shallow water anchor | A pole driven into the bottom by a bow-mounted unit to hold a boat in skinny water, doing an anchor's job without a rode or a swing radius. | Published product category |
| Blowback | The angle a downrigger cable trails behind vertical while the boat is moving, meaning the ball is running shallower than the length of cable let out would suggest. | Published trigonometry |
| Scope | The ratio of anchor rode paid out to the vertical distance from the bow roller down to the bottom, not to water depth alone. | Convention, old seamanship |
| Rode | The anchor line itself, whether rope, chain or a combination of both, connecting the anchor to the boat. | Published term |
Battery and electrical terms
The Peukert effect is published battery engineering describing how a battery delivers less of its rated capacity the faster it is drawn down.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Term | Definition | Basis |
|---|---|---|
| Peukert effect | The published battery engineering principle that a battery delivers less of its rated capacity the faster it is discharged, described by an exponent that differs by chemistry. | Published engineering |
| Depth of discharge | How much of a battery's capacity gets used before recharging; 50 percent is the lead acid convention that protects cycle life, while LiFePO4 makers publish a higher usable depth directly. | Convention for lead acid, published for lithium |
| LiFePO4 | Lithium iron phosphate, a lithium battery chemistry with a Peukert exponent close to 1.0, meaning it delivers close to its full rated capacity even under a high current draw. | Published chemistry |
| AGM | Absorbed glass mat, a sealed lead acid battery chemistry that holds its electrolyte in a glass mat separator rather than as free liquid. | Published chemistry |
| Amp hour | A unit of battery capacity: one amp hour is one amp of current delivered for one hour, conventionally measured over a 20 hour discharge rate. | Published unit, convention discharge rate |
| Voltage drop | The voltage lost along a conductor's length under load, calculated from the conductor's gauge, its length and the current running through it. | Published formula |
| Circular mil | The unit used to state a wire conductor's actual cross sectional area, and the basis of the American Wire Gauge standard used in every voltage drop calculation. | Published standard |
| ABYC E-11 | The American Boat and Yacht Council standard covering marine AC and DC electrical systems, including overcurrent protection placement and ampacity by insulation and location. | Published standard |
| Bank | A group of batteries wired together to act as one larger capacity or higher voltage source, such as three 12 volt batteries wired in series for a 36 volt trolling motor. | Published term |
Communication and safety terms
DSC sends a distress call with position data at the push of one button on a radio such as Uniden UM725G fixed mount marine VHF with GPS, rather than a spoken mayday alone.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Term | Definition | Basis |
|---|---|---|
| DSC | Digital Selective Calling, a feature on a marine VHF radio that sends a distress call with position data at the push of one button, rather than a spoken mayday alone. | Published feature |
| MMSI | Maritime Mobile Service Identity, a nine digit number registered to a specific vessel's radio, which is what a DSC distress call transmits to identify which boat is calling. | Published identifier |
| GPH | Gallons per hour, the standard unit a livewell, bilge or aerator pump such as Rule 603STC livewell pump, 800 GPH straight thru-hull states its flow rate in. | Published unit |
| PFD | Personal flotation device, the general term covering every kind of life jacket, from a foam vest such as Onyx general purpose boating life jacket to an inflatable belt pack. | Published term |
Frequently asked questions
What is CHIRP sonar?
CHIRP is a sonar signal that sweeps continuously across a range of frequencies rather than pulsing at one fixed frequency the way traditional sonar does. That sweep produces sharper fish arches and better target separation between a fish and nearby structure, which is why CHIRP has become the standard sonar technology across nearly every fish finder sold today, from entry level units up to full chartplotters.
What is the difference between side imaging and down imaging?
Down imaging aims a high frequency beam straight down, rendering a detailed, photographic style picture of what sits directly beneath the boat. Side imaging aims that same style of beam out to each side instead, covering a wide strip of bottom well beyond the hull in a single pass. Down imaging shows more detail under the boat; side imaging shows more water around it.
Is NMEA 2000 a proprietary Garmin standard?
No. NMEA 2000 is a standardized marine data network published by the National Marine Electronics Association, and it lets equipment from Garmin, Lowrance, Humminbird and other makers share one backbone cable and communicate using the same data format. A NMEA 2000 device from one brand generally works alongside a NMEA 2000 network built around another brand's core equipment.
What is the Peukert effect?
The Peukert effect is published battery engineering describing how a battery delivers less of its rated amp hour capacity the faster it is discharged. The effect is described by an exponent that differs by chemistry: it is pronounced on flooded lead acid batteries and nearly absent on LiFePO4 lithium batteries, which is the single largest practical difference between the two chemistries under a heavy trolling motor draw.
What does ABYC E-11 cover?
ABYC E-11 is the American Boat and Yacht Council's published standard covering AC and DC electrical systems aboard boats, including overcurrent protection placement near the battery, voltage drop limits by circuit type, and ampacity tables based on a conductor's insulation rating, its location and how many conductors are bundled together in the same run.
What is the difference between DSC and MMSI?
DSC, Digital Selective Calling, is the radio feature that sends a distress call with position data at the push of one button. MMSI, Maritime Mobile Service Identity, is the nine digit number registered to a specific vessel's radio that a DSC call transmits to identify which boat is calling. DSC is the function; MMSI is the identifier that function relies on.
Get the complete rigging shopping list
Every item in the beginner, intermediate and expert rigs for both a boat and a kayak, with running totals, in one printable list. No charge.
One list, no sequence of daily emails, and you can leave at any time.
Researched, not professional advice. This page is compiled from published engineering and regulatory figures, manufacturer specifications and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are boating convention rather than published standards, and they are labelled that way wherever they appear. Marine electrical work is not house wiring. Use tinned, finely stranded marine cable, size it for voltage drop and for the ABYC E-11 ampacity table rather than one or the other, and put overcurrent protection within seven inches of the battery positive terminal, because everything between the post and the fuse is unprotected. A lithium battery needs a charger with a lithium profile. Never load a boat past its capacity plate, and remember that canoes and kayaks carry no federal capacity plate at all, so their stated capacity is the manufacturer own figure. Wear the life jacket, and treat early season water as the hazard it is: cold water immersion takes your breath and then your hands long before it takes your core.