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Marine engineering knowledge base
Every article below is written by us and referenced by the free YMH Engineer AI. Search for your engine, system, or standard, or ask the engineer directly.
Engines & propulsion
Engines & propulsion
Volvo Penta D6 service intervals
The Volvo Penta D6 (D6-300 through D6-480) follows a fixed calendar-or-hours schedule, whichever comes first. Oil and oil filter change: eve…
Engines & propulsion
MAN V8-1200 marine diesel service intervals
The MAN V8-1200 (also V8-1300) marine engine uses a 250-hour or annual service interval, whichever comes first. Engine oil and filter: every…
Engines & propulsion
Onan marine genset (MDKD/MDKG series) service intervals
Onan MDKD/MDKG marine gensets follow an hours-based schedule with an annual minimum. Oil and oil filter: every 150 hours or annually. Fuel f…
Engines & propulsion
Yanmar 4JH series service intervals
The Yanmar 4JH series (4JH4, 4JH5, 4JH80, 4JH110) is a common inboard sailboat diesel. Oil and oil filter: every 250 hours or annually, use …
Engines & propulsion
Cummins QSB series service intervals
The Cummins QSB (5.9L and 6.7L marine variants) is common in trawlers and midsize motoryachts. Oil and oil filter: every 250 hours or 6 mont…
Engines & propulsion
Caterpillar C7 and C9 marine service intervals
The Cat C7 and C9 marine engines (7.2L and 8.8L) are common in workboats and larger motoryachts. Oil and oil filter: every 250 hours, use Ca…
Engines & propulsion
Diesel injector failure symptoms and rules of thumb
Diesel injector failures cluster around three symptom sets. (1) Hard start, poor low-RPM performance, blue-white smoke on startup: dribbling…
Engines & propulsion
Marine coolant types: OAT vs conventional (IAT)
Never mix coolant types. Two chemistries dominate: (1) IAT (Inorganic Acid Technology, conventional green): traditional silicate/phosphate i…
Engines & propulsion
Kohler marine genset service intervals
Kohler marine gensets (5EFOZ, 8EFOZ, 20EFOZ, 32EFOZD series) follow a 100 or 250-hour cycle depending on model. Oil and oil filter: every 10…
Engines & propulsion
Northern Lights marine genset service intervals
Northern Lights (M643, M773, M844, M99 series) is the workboat-tough option, heavier iron and longer intervals. Oil and oil filter: every 25…
Engines & propulsion
Diesel genset wet stacking, load banking, and shutdown symptoms
Wet stacking is what happens when a diesel genset runs long periods at low load (below 30 percent of rating). Unburned fuel and moisture acc…
Engines & propulsion
Marine outboard 4-stroke maintenance (Yamaha, Mercury, Suzuki)
Modern 4-stroke outboards (Yamaha F-series, Mercury Verado, Suzuki DF-series) dominate the tender and center-console market. Service interva…
Engines & propulsion
Marine 2-stroke outboard maintenance and troubleshooting
2-stroke outboards (Yamaha Enduro, Mercury Sport 2S, Tohatsu MFS) are common on smaller tenders (5-25 hp) and workboats because they're ligh…
Fuel systems
Fuel systems
Racor primary fuel filter vacuum diagnostics
A Racor primary filter vacuum gauge reading tells you where fuel restriction is happening. Normal reading at idle: 0-2 inHg. Under cruise lo…
Fuel systems
Diesel bug (fuel contamination) diagnostics and treatment
Diesel bug is microbial contamination (bacteria and fungi like Cladosporium resinae) that lives at the fuel-water interface in a diesel tank…
Fuel systems
Marine fuel polishing systems and DIY approaches
A fuel polishing system pumps diesel from the tank through a fine filter and back to the tank in a continuous or scheduled loop, keeping fue…
Electrical
Electrical
Diagnosing battery parasitic drain
A house bank losing charge overnight with no obvious load usually has parasitic draw. Shut off all breakers, then measure current in the neg…
Electrical
Galvanic isolator vs isolation transformer
Both devices break the shore-side ground path that causes galvanic corrosion between boats on the same dock. A galvanic isolator uses back-t…
Electrical
AGM to LiFePO4 conversion gotchas
Swapping AGM for lithium (LiFePO4) is not drop-in despite marketing. Real gotchas: (1) Alternator regulation. AGM tolerates a stock alternat…
Electrical
Alternator sizing and external regulator basics
Stock marine alternators (60-120A) are sized for engine start and running loads, not for house-bank charging. If you want to actually rechar…
Electrical
Inverter/charger sizing and split-phase basics
An inverter/charger (Victron Multiplus, Magnum, Xantrex Freedom) does three things: inverts DC to AC when off shore power, charges the house…
Electrical
MPPT vs PWM solar charge controllers
A solar controller regulates panel output to properly charge a battery. Two technologies. (1) PWM (Pulse Width Modulation): cheap, simple, w…
Electrical
Marine battery chemistries: flooded, AGM, gel, lithium
Four chemistries dominate marine service, each with a different sweet spot. FLOODED lead-acid (Trojan T-105, Rolls, Deka): cheapest per Ah, …
Electrical
Marine battery chargers: sizing, chemistry, split banks
Marine shore-power battery chargers (Victron Skylla, Sterling ProNautic, ProMariner ProNauticP, Charles Marine) come in single-bank and mult…
HVAC & refrigeration
HVAC & refrigeration
Marine chilled-water AC system architecture
Chilled-water AC (Cruisair, Dometic, MarineAire) is two loops. The refrigerant loop (compressor + condenser + expansion valve + evaporator) …
HVAC & refrigeration
12/24V marine refrigeration diagnostics
Marine DC fridges (Isotherm, Vitrifrigo, Nova Kool, Waeco) use small hermetic compressors (Danfoss/Secop BD35 or BD50) driving R134a or R600…
HVAC & refrigeration
Marine refrigerant charging basics (R134a, R410A)
Marine AC and refrigeration use R134a (older systems, being phased out globally), R410A (current mainstream), or increasingly R32 (new-build…
HVAC & refrigeration
Self-contained marine AC unit diagnostics
Self-contained AC units (Cruisair SMX/SMXV, Dometic Turbo, MarineAire) are one-piece assemblies mounted under a berth or in a locker: refrig…
Plumbing & water
Plumbing & water
Marine reverse osmosis watermaker fundamentals
Reverse osmosis (RO) watermakers push seawater through a semipermeable membrane at 800-1000 psi to produce fresh water. Core components: raw…
Plumbing & water
Marine freshwater pressure pump diagnostics
Marine freshwater pressure pumps (Jabsco Par-Max, SHURflo Aqua King, Groco) are 12/24V diaphragm pumps with a built-in pressure switch. Norm…
Plumbing & water
Marine sanitation devices (MSD): Type I, II, and III explained
US law under CFR Title 33 Part 159 recognizes three MSD types for treating or storing sewage on vessels over 19.7 ft with installed toilets.…
Plumbing & water
Watermaker membrane storage and biocide fresh water flush
Reverse osmosis watermaker membranes ($400-1500 each) live or die based on storage protocol. A dry or bacteria-fouled membrane is dead. Rule…
Electronics & navigation
Electronics & navigation
NMEA 2000 backbone architecture rules
NMEA 2000 (aka N2K, SeaTalkNG on Raymarine, SimNet on Simrad) is a single backbone with drop cables to devices. Key rules: (1) Terminators r…
Electronics & navigation
Raymarine EV series autopilot diagnostics
Raymarine EV autopilots (Evolution series) rely on the EV-1 or EV-2 core computer (a 9-axis motion sensor + processor). Setup: the EV core m…
Electronics & navigation
Furuno TZT and radar architecture
Furuno's NavNet TZ Touch series (TZT2, TZT3, TZT9F/12F/16F/22F) is the sportfishing and commercial workhorse. Backbone: NMEA 2000 for sensor…
Electronics & navigation
Marine VHF, DSC, and MMSI basics
Every marine VHF sold since 1999 has DSC (Digital Selective Calling) capability, but many boats never enable it. To use DSC you need an MMSI…
Electronics & navigation
AIS Class A vs Class B: which and why
AIS (Automatic Identification System) transponders broadcast MMSI, position, course, speed, and vessel info to other AIS-equipped vessels an…
Electronics & navigation
Marine VHF, GPS, and satellite antenna basics
Marine antenna selection drives radio performance more than radio choice. VHF antennas rated by dB gain: 3 dB (short 3 ft or emergency), 6 d…
Electronics & navigation
Marine audio system architecture (Fusion, JL Audio, marine speakers)
Modern marine audio breaks into three parts: source (head unit or streaming device), amplifier (usually external Class-D for real power), an…
Electronics & navigation
Starlink Maritime and marine VSAT basics
Starlink Maritime replaced legacy marine VSAT for most recreational and midsize commercial yachts starting 2022-2023. Hardware: two Starlink…
Hull & running gear
Hull & running gear
Cutlass bearing wear signs
Cutlass bearings (also called cutless) are the rubber-lined bronze sleeves that support the propeller shaft where it exits the strut. Wear s…
Hull & running gear
Seakeeper gyro stabilizer basics
Seakeeper gyros need routine service to keep the flywheel spinning safely. Cooling: closed seawater loop, requires clean strainer and functi…
Hull & running gear
Marine anode selection: zinc, aluminum, or magnesium
Sacrificial anodes protect submerged metals from galvanic corrosion. Choose by the water you sit in. (1) SALT WATER: zinc anodes work but ar…
Hull & running gear
PSS dripless vs packed shaft seal comparison
Two shaft seal designs dominate marine inboards. (1) TRADITIONAL PACKED STUFFING BOX: graphite-impregnated flax packing rings squeezed aroun…
Hull & running gear
Sleipner, Vetus, and Side-Power bow thruster diagnostics
Marine bow thrusters come in three power classes: DC electric (up to about 25 hp, most common on 30-60 ft), hydraulic (25-100 hp, larger yac…
Hull & running gear
Antifouling paint types: hard, ablative, epoxy, silicone
Antifouling choice depends on how the boat is used: how many hours underway, how often you haul out, saltwater or fresh, and how many boats-…
Hull & running gear
Tender davit and crane systems: hydraulic vs electric
Tender launching on cruising motoryachts uses either a davit (single arm, pivots overboard) or a full crane (rotating jib, greater reach). T…
Hull & running gear
PWC (jet ski) onboard storage and maintenance
Personal watercraft (Sea-Doo, Yamaha WaveRunner, Kawasaki Jet Ski) on yachts are typically stored on a hydraulic swim platform, on chocks la…
Hull & running gear
Rigid inflatable boat (RIB) tube care and fabric types
RIB tenders (Zodiac, AB, Highfield, Novurania, Williams Jet Tenders) use one of three tube fabrics, each with different maintenance profiles…
Hull & running gear
Water toys onboard storage: kayaks, paddleboards, e-foils
Water toys on a yacht need dedicated storage and handling that most builders don't design for. Options: (1) FLYBRIDGE OR HARDTOP RACKS: alum…
Safety & compliance
Safety & compliance
EPIRB and PLB registration and battery service
EPIRBs (406 MHz beacons for vessels) and PLBs (personal, for individuals) must be registered with NOAA in the US (or the equivalent national…
Safety & compliance
Life raft service intervals and standards
Coastal and offshore life rafts require annual or biennial service at a manufacturer-authorized station, depending on raft type and jurisdic…
Safety & compliance
Bilge alarm and float switch fundamentals
Every boat needs at least two independent bilge pump circuits per bilge compartment: an auto-cycle pump (float switch triggers) and a high-w…
Safety & compliance
Marine engine room fire suppression (Fireboy, Sea-Fire)
Fixed engine-room fire suppression is required by ABYC A-4 for enclosed engine compartments over a certain size and is universal on cruising…