Question 1

What is the stern gland and how do you know when it needs adjustment?

Accepted Answer

The stern gland (stuffing box or lip seal) seals the propeller shaft where it exits the hull. Traditional stuffing box: should drip 1-2 drops per minute when running (slight lubrication is correct — completely dry = overheating of the seal). Maintenance: tighten the gland nut by 1/4 turn if excessive dripping; repack with greased flax every few seasons. Dripless shaft seals (lip seals): require correct alignment and periodic bellows inspection Traditional stuffing box maintenance is one of the most misunderstood boat maintenance items. A completely dry stuffing box overheats the packing material, causes carbon deposits on the shaft, and damages the shaft surface. The accepted standard: 1-2 drops per minute at rest, more (steady drip) when motoring — this is correct and expected. An excessive flow (steady stream) requires tightening. Check the bilge is clear and the bilge pump is functional for any stuffing box vessel. Dripless seals (PSS, Lasdrop) eliminate the drip but require correct alignment and annual bellows inspection.

Question 2

What is the fundamental operating principle of a diesel engine that distinguishes it from a petrol engine?

Accepted Answer

Compression ignition: diesel fuel is ignited by the heat of highly compressed air (compression ratio ~22:1) — no spark plugs are used. Fuel is injected into the compressed air at the moment of ignition Diesel (compression ignition): air is compressed to ~22:1 ratio, reaching ~500-700°C. Diesel fuel (which ignites at ~250°C) is injected directly into this hot compressed air and spontaneously ignites. Petrol engines use ~8:1 compression and require a spark to ignite. The high compression ratio makes diesel engines more thermally efficient (~40% vs ~25% for petrol) and safer (diesel is much less volatile than petrol).

Question 3

Describe the four strokes of a diesel engine cycle in the correct order

Accepted Answer

Induction (air in): piston down, air drawn into cylinder. Compression: piston up, air compressed to high temperature. Power (ignition): fuel injected, combustion drives piston down. Exhaust: piston up, exhaust gases expelled The four-stroke diesel cycle (suck, squeeze, bang, blow): 1) Induction — intake valve open, piston moves down drawing in air only (no fuel). 2) Compression — both valves closed, piston moves up, air compressed to ~22:1. 3) Power — injector fires, combustion, piston driven down. 4) Exhaust — exhaust valve open, piston moves up expelling gases. Two complete crankshaft revolutions per power stroke per cylinder. Multiple cylinders provide smoother, overlapping power strokes.