Why a daily engine check earns its ten minutes

On a monohull, the engine sits under the companionway steps, and most owners give it a glance on the way past. On a catamaran, things are different. You have two engines, often tucked away under an aft berth or behind a panel in a dedicated engine room, and it is entirely possible to cast off the lines without having looked at either of them. That is exactly how small problems become expensive ones somewhere off a lee shore.

The good news is that a proper daily check takes about ten minutes once you know the routine. Do it before you start the engines, while everything is cold, because half the things you need to see are impossible to judge once the bay is full of noise and hot metal. Make it a habit, like checking the weather and the tide, and it will pay you back the first time you spot a drip or a slack belt while you are still alongside.

Oil levels, cold and unhurried

Start with oil, because it is the cheapest check with the most expensive consequences. With the engine cold and level, pull the dipstick, wipe it, push it fully home and pull it again. Read the level on the flat of the stick, not the smear up the side. On a catamaran, remember that the hull may sit slightly bow-down or stern-down depending on how you are loaded, so if a reading looks marginal, check the other engine for comparison and consult your manual for the correct attitude.

• Level: between the marks, never above the top one. Overfilling causes aeration and blown seals.
• Colour: honey-brown is healthy; opaque black or milky grey deserves investigation.
• Saildrive legs: if you have them, check the leg oil through its own dipstick or level plug, and note any emulsion.
• Twins: compare the two engines. If one has used oil and the other has not, that is a message, not a coincidence.

Coolant, strainers and the raw water side

Next, coolant. With the engine cold, the level in the plastic expansion tank should sit between the minimum and maximum marks. Top up with the correct pre-mixed coolant, not neat antifreeze and not tap water if you can avoid it. Never open a pressurised cap on a hot engine; scalding coolant is a genuinely nasty injury and it always happens in a hurry.

Then work along the raw water path. Lift the lid of the sea strainer and check the glass for weed, sand, plastic bag fragments and the small fish that somehow find their way in. Clean it, refit the lid squarely and check the seal. Confirm the seacock is fully open and the lever is where you expect it. If you have a water trap or filter bowl downstream, empty it. This is also your best moment to check the raw water pump for tell-tale drips from the weep hole, which usually means a seal is on its way out.

Belts, hoses and the small things that strand boats

Press the alternator belt with your thumb midway along its longest run. You want roughly ten millimetres of deflection, and no more. Look for glazing, cracks, fraying edges and a shiny underside. A belt that squeals on start-up is not merely embarrassing; it is slipping, and your batteries are paying for it. Carry spares and know how to fit them.

Hoses deserve a slow look rather than a quick one. Squeeze them, look for perishing, bulges, chafe where they pass through bulkheads, and staining at the ends. Check every hose clip by hand, especially those below the waterline, where a double clip is good practice. On a catamaran, the long run between the engine and the saildrive or shaft log gives you more places for a leak to start, so trace the whole path rather than stopping at the engine box.

Filters and fuel: the water you cannot see

Diesel is not the clean, golden liquid we like to imagine. It carries water, sediment and, in warm weather, microbial growth that turns into a dark sludge. Your water-separating pre-filter is the first line of defence, so drain a little from the bottom into a clean glass jar before every passage. Let it settle and look closely: clear diesel is fine, a distinct layer of water or a swirl of dark matter means it is time to change elements and think about your tank.

• Check the pre-filter bowl for water and debris, and drain it fully.
• Note the condition and age of both primary and secondary filter elements.
• Confirm the fuel tap for each tank is open, and that you know which tank feeds which engine.
• On twin-tank catamarans, check the balance line and crossover valves so you do not run one engine dry.

Start-up: leaks, smells and unusual noises

Now you can start. Before you do, clean the drip trays and bilges so that anything you find afterwards is new. Then start each engine in turn and simply stand and listen. You are learning what normal sounds like, so that abnormal becomes obvious. Water should appear from the exhaust within fifteen to thirty seconds, and it should be a steady, warm flow rather than a sputter or a trickle.

Watch for blue, black or white smoke, and note anything sweet, hot or dieselly in the smell. Give it a few minutes at a fast idle, then go back down and look again with a torch: under the water pump, around the fuel filter housing, at the sump plug, along hose joints and under the gearbox. Feel for heat where there should be none. Only when both engines have run clean and quiet for ten minutes should you slip the lines, and even then, glance down once more before you settle onto the helm. That small ritual is what turns a hopeful departure into a confident one.