Glossary: the technical words in plain English

What this page tells you: what each technical word on this site means, and where it matters.

Words linked with a dotted underline on other pages lead here; hover or tap them for a short definition.

A
Anode: A block of sacrificial metal (often zinc or aluminium) fitted to protect underwater metal from corrosion. See it in: What’s wrong: technical facts, The AC plant, step by step
B
Bonding / hull potential: Bonding links underwater metals so they share one protection system. Hull potential (measured in volts against a reference electrode, Ag/AgCl) shows whether that protection is working. See it in: What’s wrong: technical facts, The AC plant, step by step, Who supplied and services the plant, Evidence held, Evidence pack checklist
C
CAN bus: The data cable the plant controller uses to talk to the three modules. “CAN-BUS MOD 2 KO” means the controller lost contact with module 2. Each end of the cable chain needs a 120 Ω terminating resistor; without it, communication can drop out. See it in: Home, Timeline, What’s wrong: technical facts, The AC plant, step by step
Chain of custody: A record of where each removed part is stored and who has handled it, so it can still be used as evidence. See it in: Home, Lessons for owners, Root cause: done and still open, Evidence held
Chilled-water plant (CWS): The yacht’s central air-conditioning: machines (chillers) cool a loop of water, which is pumped to fan coils in each cabin. CWS is the maker’s name for the range (Climma/Veco CWS MODUL). See it in: Home, Timeline, What’s wrong: technical facts, The AC plant, step by step, Evidence held
Compressor: The pump that drives the refrigerant round each chiller. It has an electric motor sealed inside; C1, C2 and C3 are the compressors of modules 1 to 3. See it in: Home, Timeline, What’s wrong: technical facts, Interactions, The AC plant, step by step
D
Danfoss MCX controller: The plant’s master controller (Danfoss MCX06D). It runs the modules and shows alarms on its screen. See it in: Home, What’s wrong: technical facts, Evidence held
Design temperature rise (ΔT): How much hotter than its surroundings a transformer is designed to run. Insulation class F allows a rise of up to about 100 °C.
DIS-VOLT: A state shown by the inverter when its supply voltage dips too low (under-voltage). See it in: Timeline, What’s wrong: technical facts, The AC plant, step by step
Duty/standby: Two pumps fitted, one running and one spare, chosen by a selector switch. See it in: What’s wrong: technical facts
E
Earth fault: When current can leak from a live part to the metal frame or hull (earth).
F
Fault code / alarm code: A number the controller shows and logs when something goes wrong (for example code 7 = low water flow, code 30 = inverter alarm). See it in: What’s wrong: technical facts, Claims guide, The AC plant, step by step
Flow sensor / flow alarm: The sensor that checks water is moving through a module. If the flow drops, the module stops to protect itself. See it in: Timeline, What’s wrong: technical facts, The AC plant, step by step, Parts replaced, cause still unknown
Fresh water (FW) / sea water (SW): FW is the closed chilled-water loop that goes to the cabins. SW is the seawater pumped in to carry heat overboard. See it in: Timeline, What’s wrong: technical facts
G
Galvanic corrosion: Corrosion that happens when two different metals are connected in seawater, like a weak battery. Anodes are fitted to corrode first instead. See it in: What’s wrong: technical facts
Glycol: An additive in the chilled-water loop that protects the loop’s metal parts and prevents freezing. See it in: Home, What’s wrong: technical facts, The AC plant, step by step, Evidence held, Evidence pack checklist
Gulf spec: The manufacturer’s configuration for hot climates and warm seawater. See it in: Home
H
Harmonics: Distortion of the supply waveform, often caused by electronic loads such as inverters. See it in: What’s wrong: technical facts, The AC plant, step by step
I
IGBT: The high-power switching transistor inside each inverter drive. See it in: Timeline, What’s wrong: technical facts
Insulation resistance (to earth): How well a motor’s windings are electrically separated from its metal body. High values (millions of ohms, MΩ) are healthy; a few ohms (Ω) means the insulation has broken down. See it in: Home, Timeline, What’s wrong: technical facts, Interactions, Lessons for owners
Inverter drive: An electronic box that controls the compressor motor’s speed by converting the incoming power. One per compressor. See it in: Home, Timeline, What’s wrong: technical facts, Interactions, The AC plant, step by step
Isolation transformer (on board): A transformer on the yacht that separates the boat’s electrics from the marina supply. It helps prevent stray current flowing between the boat and the shore. On this yacht it is always in circuit on shore power. See it in: Home, Timeline, What’s wrong: technical facts, The AC plant, step by step, Evidence pack checklist
L
Lay-up / laid up: The yacht is kept out of use (not cruising, affected equipment switched off) for insurance purposes until repaired. See it in: Timeline, Interactions, Claims guide, Time without cooling
Leakage current: Small current escaping to earth. Measured in milliamps (mA). See it in: What’s wrong: technical facts, Evidence held
Line reactor: A coil fitted between the power supply and each inverter to smooth the current. It is not a transformer. See it in: Home, Timeline, What’s wrong: technical facts, Interactions, The AC plant, step by step
M
Megger test: An insulation-resistance test using a special meter (named after a common brand).
Module / unit: One of the three identical chillers in the plant. Each module has its own compressor, inverter drive and line reactor. “Unit 2” means module 2.
Motor protection switch: A breaker with an adjustable overload setting that trips a pump motor drawing too much current. See it in: What’s wrong: technical facts
P
Phase sequence: The order of the three supply phases. Some equipment needs them in the correct order. See it in: What’s wrong: technical facts, The AC plant, step by step, Evidence pack checklist
R
Root cause: The first thing that went wrong and set off the other failures. Replacing parts without finding it risks the same failure happening again. See it in: Home, Timeline, Interactions, Lessons for owners, The AC plant, step by step
S
Shore power: Electricity supplied from the marina while the yacht is alongside. See it in: Home, Timeline, What’s wrong: technical facts, Claims guide, The AC plant, step by step
Stray current: Electric current leaking through water or metal where it should not flow. It can corrode metal parts quickly.
T
Thermal imaging (IR): Using an infrared camera to see surface temperatures, for example to spot hot electrical joints. See it in: Evidence pack checklist
W
Winding resistance (line to line): The resistance of the motor’s copper coils measured between phases. Balanced values mean the coils themselves look intact.
Witnessed teardown: Opening a failed part in a controlled way, with all interested parties present or invited, so the findings are accepted by everyone. See it in: Home, Root cause: done and still open