Understanding WOBBLE and building a departure routine.
WOBBLE is one of the best-known memory aids for boat pre-departure checks. Traditionally the letters stand for Water, Oil, Belts, Bilges (or Batteries), Levels and Exhaust (or Electrics), although you’ll often come across slightly different versions.
None of those versions is wrong. They all remind you to check the boat before leaving.
In this guide we’ve included both Bilges and Batteries, and both Exhaust and Electrics. We’ve also divided the checks into those that are best carried out before starting the engine and those that can only be confirmed once it’s running. That gives you the opportunity to deal with any simple problems first, then confirm they’ve been dealt with before you cast off.
Found Something During Your WOBBLE?
If you’ve already found something that doesn’t look quite right, jump straight to the section that’s most relevant to you.
Water
The raw-water strainer is blocked or dirty.
Oil
The oil level has dropped or you’ve found oil in the bilge.
Belts
A belt is squealing, cracked or feels loose.
Bilges
You’ve found water, oil or coolant in the bilge, or something else doesn’t look quite right.
Batteries
The batteries don’t look secure, the terminals are corroded or they don’t seem to have enough charge for today’s trip.
Levels
The coolant level has changed or doesn’t look right.
Exhaust
There’s no cooling water from the exhaust, the engine is smoking more than usual, or it sounds or smells different from normal.
Electrics
The batteries don’t seem to be charging, a warning light hasn’t gone out, or one of the engine gauges or instruments doesn’t look right.
Some checks can only be carried out once the engine is running. If you’ve cleaned, adjusted or topped something up, continue to the Start the Engine section before deciding whether today’s trip should go ahead.
When you have time, come back and read the rest of the guide. WOBBLE isn’t just a checklist. It helps you recognise how your own boat behaves, making small changes easier to spot before they become bigger problems.
If you’re new to boat systems, our Understand Your Boat hub explains the main systems and components you’ll find on a typical boat in plain English.
Why Bother?
If you’ve carried out a WOBBLE check a few times and never found anything wrong, it’s easy to wonder whether it’s worth doing.
It is.
Most days you’ll lift the engine hatch, spend a few minutes looking around, then close it again without touching a thing.
That’s a good result.
The purpose of WOBBLE isn’t to find something wrong every time you go boating.
It’s to spot small problems while they’re still easy to deal with.
A blocked raw-water strainer might only need cleaning.
A loose hose clip might only need tightening.
A lower-than-expected battery reading may only need a little more charging before you leave.
Those jobs are far easier to deal with while you’re still alongside than halfway through today’s trip.
That’s why it’s worth arriving a little earlier than you think you need to.
The checks themselves may only take ten minutes, but they sometimes uncover a small job followed by a few minutes with the engine running to confirm the repair has worked.
If you’re trying to catch a tide, a lock or a lifting bridge, leaving those checks until the last minute can put you under pressure to make the wrong decision.
Most days, you’ll find nothing has changed.
That’s what you’re hoping to find.
Every time you confirm that nothing has changed, you’re building a picture of what’s normal for your own boat. That becomes your reference point. When something eventually does change, you’re much more likely to recognise it while it’s still a small problem instead of discovering it halfway through today’s trip.
The letters help you remember the checks.
The value comes from recognising when your boat starts behaving differently.
We’ve arranged the guide in the order we believe works best. The first part covers the checks that are easiest with the engine stopped. The second covers the checks that can only be confirmed once it’s running.
Use whatever order works for your boat. Carrying out the checks consistently matters far more than following any particular sequence.
W – Water
The W in WOBBLE usually stands for Water, although what you’re checking is the raw-water strainer.
Most conventional marine diesel engines use raw water somewhere in their cooling system. On an indirectly cooled engine, the raw water passes through a heat exchanger rather than through the engine itself. The water is drawn in through an inlet in the hull, passes through the heat exchanger and is then discharged overboard, usually through the exhaust.
Because this water comes directly from the canal, river, lake or sea, it’s known as raw water.
For the engine to stay cool, that water has to keep flowing.
The two most common places for that flow to become restricted are the raw-water strainer and the hull inlet itself. The strainer catches weed and other debris before it reaches the cooling system. The hull inlet can occasionally become blocked by weed, silt or floating debris before the water even reaches the strainer.
There are exceptions. Many narrowboats and other inland craft use keel or skin-tank cooling instead, where coolant is circulated through a tank or cooling surface fitted to the hull rather than drawing cooling water in from outside. These boats don’t have a raw-water intake or strainer. If your boat uses one of these systems, follow the equivalent cooling-system checks for your installation.
When people talk about checking the W in WOBBLE, they’re usually referring to the raw-water strainer because it’s one of the easiest checks to carry out before starting the engine.
Checking the Raw-Water Strainer
Before opening the strainer, close the raw-water seacock. This valve stops water entering the boat while you work on the cooling system.
If you’re not sure where it is, follow the hose from the bottom of the strainer towards the hull. On most installations you’ll find the seacock where the hose joins the hull inlet.
Once the seacock is closed, remove the lid and lift out the basket.
On most trips you’ll find very little. A few strands of weed or the odd leaf are perfectly normal. If the basket is becoming clogged, clean it before replacing it.
While the basket is out, have a quick look inside the bowl. Make sure the sealing ring is sitting correctly before refitting the lid securely.
What’s Normal?
A little weed or debris in the basket is nothing unusual.
You’re checking that nothing is restricting the flow of cooling water through the system.
Before Starting the Engine
Before moving on, make sure the strainer lid is secure and, most importantly, that you’ve reopened the raw-water seacock.
Once the engine is running, the Exhaust and Electrics checks provide another opportunity to confirm that the cooling system is working normally.
I’ve Found Something. What Now?
“I’ve opened the strainer and it’s nearly full of weed. Can I still go?”
Yes, provided you’ve cleaned the basket, refitted the lid securely and reopened the raw-water seacock before starting the engine.
Once the engine is running, check that cooling water is flowing normally from the exhaust. This shows that water is getting through the system again, although you’ll still want to complete the other engine-running checks.
If there’s still little or no cooling water from the exhaust, the next thing to check is the hull inlet.
“I’ve cleared the strainer but I think there’s a plastic bag over the hull inlet. Can I still go?”
Not until you’ve removed the obstruction.
If the hull inlet is blocked by a plastic bag, weed or other floating debris, you’ll need to clear it before relying on the engine’s cooling system.
If you’re alongside a pontoon, it may be possible to remove the obstruction with a boat hook or similar tool. On many boats the hull inlet is only a short distance below the surface.
If the only practical option is entering the water, stop and think first. At anchor or on a quiet mooring, clearing a shallow obstruction may be possible, but make sure the boat can’t move unexpectedly and that conditions are suitable. Even a small amount of swell or wash can cause you to strike your head against the hull. If you can’t clear it safely, wait until you can.
Once you’ve cleared the blockage, complete the engine-running checks before casting off. If you’re travelling through heavy weed or floating debris, keep an eye on the cooling-water discharge because the inlet may become blocked again.
If the strainer is clean, the hull inlet is clear, the seacock is open and there’s still little or no cooling water from the exhaust, postpone today’s trip and investigate further. The restriction is likely to be somewhere else in the cooling system and is unlikely to be a five-minute fix.
Ownership Tips
Apply a light smear of silicone grease to the strainer seal or O-ring before refitting the lid. It helps prevent the seal sticking and usually makes the lid easier to remove the next time you clean the basket.
Waterways vary enormously. Some stay almost weed-free all season, while others can clog a strainer several times in a day. After a while you’ll know which applies to the places where you boat most often.
O – Oil
The O in WOBBLE stands for Oil, but there are usually two different oils worth checking before you leave: the engine oil and, on many boats, the gearbox oil.
Engine oil keeps moving parts separated by a thin film of oil, helps carry heat away from some of the hardest-working parts of the engine and keeps tiny particles suspended until the next oil change.
Gearbox oil has a different job. It lubricates and protects the gears and bearings inside the gearbox, allowing it to transmit the engine’s power smoothly to the propeller. Like the engine, it relies on having the correct amount and type of oil.
Checking the oil isn’t just about the level.
It’s also about understanding why that level might have changed.
An engine may be using a little oil as part of normal operation, or it may be losing oil through a leak. Working out which of those is happening is often the first step towards deciding whether today’s trip can go ahead.
Checking the Oil
If possible, check the oil while the boat is reasonably level. A boat that’s heeled over or sitting at an angle can give a misleading reading.
Never remove the dipstick while the engine is running. If the engine has been running recently, leave it for a few minutes to allow the oil to drain back into the sump.
Pull the dipstick out, wipe it clean, reinsert it fully, then remove it again to take the reading. The first time you withdraw it, oil can be smeared up the dipstick, making the true level difficult to see.
The oil should sit somewhere between the MIN and MAX marks. Exactly where it sits matters less than whether it’s changed since the last time you checked it. Don’t add oil simply to bring it to the MAX mark if it is already within the manufacturer’s operating range.
If the level needs topping up, always use the grade and specification recommended by the engine manufacturer. If you’re unsure, check the engine manual before adding anything.
Don’t forget the gearbox. Many marine gearboxes have their own oil supply and it may not be the same oil used in the engine. If your gearbox has a dipstick or level plug, make it part of the same routine and always use the oil recommended by the gearbox manufacturer.
What’s Normal?
The oil doesn’t have to sit exactly on the MAX mark. Anywhere between MIN and MAX is within the manufacturer’s operating range.
A gradual drop over several trips is very different from finding the level has fallen dramatically since the last time you checked it.
Don’t judge engine oil by its colour alone. Diesel engine oil often turns black quickly, and colour by itself tells you very little about its condition.
If you’ve only owned the boat for a short time, don’t assume today’s reading represents “normal”. You may have inherited a problem from the previous owner.
Before Starting the Engine
Before starting the engine, take a quick look underneath it.
Is there any fresh oil beneath the engine?
If you’ve already noticed the oil level has fallen, this is another clue that the engine may be losing oil rather than burning it.
Once the engine is running, the Exhaust section will give you another clue about what may be happening. Blue smoke can indicate that the engine is burning oil. It’s another piece of evidence alongside what you’ve already found around the engine and in the bilges.
I’ve Found Something. What Now?
“The oil level has dropped. Can I still go?”
That depends on what else you’ve found.
If the level has fallen slightly since your last check but is still between the MIN and MAX marks, and you can’t see any obvious leaks, topping it up if necessary may be all that’s required.
Once the engine is running, complete the engine-running checks before deciding whether today’s trip should go ahead.
“I’ve found oil in the bilge. Can I still go?”
Before assuming it’s coming from the engine, try to work out where it’s coming from.
A thin film of oil floating on a little water can spread quickly across the surface, making the leak appear much worse than it really is. Gearboxes, hydraulic systems, crankcase breather pipes and even a little oil spilled during routine maintenance can all leave traces in the bilge.
Some older engines develop small oil leaks that owners choose to monitor rather than repair immediately. If that’s the case, you’ll already know where the oil normally appears, roughly how much is typical and how often the oil needs topping up. That’s very different from discovering a new leak or finding that an existing one has suddenly become worse.
If you can identify a small, known and unchanged leak, the oil level has remained stable and the engine is otherwise behaving normally, today’s trip can often go ahead.
If you’ve found a new leak, the leak has become noticeably worse, the oil level has fallen unexpectedly or you can’t identify where the oil is coming from, investigate further before deciding to leave.
“The oil looks milky. Can I still go?”
No. Milky or creamy oil can indicate that water or coolant has mixed with the oil, although condensation can sometimes produce a similar appearance, particularly on engines that aren’t run long enough to get properly warm. If the oil itself has become milky or creamy, don’t ignore it or try to solve the problem simply by topping it up. Find out why it has changed before relying on the engine.
Ownership Tips
Get into the habit of checking the oil before starting the engine rather than when you return at the end of the day. The oil has had plenty of time to drain back into the sump, giving you a more consistent reading. More importantly, if the level is low, you’ve still got time to top it up or investigate before today’s trip begins.
Then check it again after you’ve finished for the day, once the engine has cooled and the oil has drained back into the sump.
The first check tells you whether there’s enough oil before you leave. The second tells you whether the engine has used or lost any oil while it was running.
If the level drops during the trip, the engine may be using or losing oil while it’s running. If it’s unchanged when you return but lower the next time you visit the boat, the loss may have happened while the engine was standing.
Knowing when the oil disappears can make it much easier to work out where it’s going.
If you do need to top up the oil, make a quick note of when you did it and roughly how much you added. You don’t need to measure it precisely. If the bottle has a transparent level strip, a note such as “about a quarter of a litre” is usually enough. Over time you’ll build a picture of how much oil your engine normally uses between services. If that suddenly changes, you’ll notice it much sooner.
B – Belts
Drive belts transfer power from the engine to other equipment. If a belt slips, becomes loose or breaks, whatever it’s driving can no longer do its job properly. That might mean your batteries stop charging, your raw-water pump stops circulating cooling water or another important system stops working as it should.
Checking the Belts
Many belts give some warning before they fail.
You’re looking for signs that a belt is wearing or becoming less effective.
Take a few moments to look at each belt in turn.
Look for obvious cracks, frayed edges, missing pieces of rubber or signs that the belt has been rubbing against something it shouldn’t.
Also look for belt dust around the pulleys. A little dust isn’t unusual, particularly while a new V-belt is bedding into the pulleys. You’re looking for more belt dust than you found last time.
Finally, check the belt tension.
If you have your engine manual, use the manufacturer’s recommendation. If not, press firmly on the belt about halfway between the pulleys. On many traditional V-belts, you’re looking for some movement rather than a precise measurement. The correct figure varies by engine, so use the manufacturer’s specification where available. It shouldn’t flap about, but neither should it feel like a guitar string.
Checking it the same way each time is more useful than worrying about a millimetre or two. You’re looking for evidence that something has changed.
What’s Normal?
Belts are wear items and they’ll all need replacing eventually.
A little more belt dust than before, a slight squeal on start-up or needing adjustment more often can all be signs of belt wear, slipping or another problem with the belt or pulley alignment.
If a belt looks, feels and sounds the same as it did last time, there’s usually no reason to think anything has changed.
Before Starting the Engine
Before starting the engine, have one final look at the belts.
Are they sitting correctly in the pulleys?
If a belt looked marginal during your inspection, the engine-running checks will confirm whether the equipment it drives is operating normally.
I’ve Found Something. What Now?
“My belt looks loose. Can I still go?”
That depends on what you’ve found.
If the belt is otherwise in good condition and only needs a slight adjustment, that’s often a straightforward job that can be dealt with before you leave.
“My belt has cracks in it. Can I still go?”
A cracked belt is showing signs of deterioration. The question is how far that deterioration has progressed and whether you can reasonably trust the belt for the trip you’re planning.
Small cracks, missing pieces of rubber, badly frayed edges or deep cracking are all signs that the belt needs attention. If the belt is visibly deteriorating, replacing it before you leave is the better option. It’s usually much easier alongside than after you’ve cast off.
If the belt only has minor surface wear and you’re satisfied that it is still serviceable, think about the trip you’re planning. Do you have the correct spare belt and the tools to fit it? Would you be comfortable replacing it if it failed? Are you crossing open water or cruising a quiet canal? The answers may influence your decision.
If you haven’t already bought spare belts for your engine, make today the day you order them. Bring them down to the boat next time you visit and keep them on board. They’re inexpensive compared with the inconvenience of needing one and not having it aboard.
Remember that not every belt is equally important. Losing an alternator belt may mean managing your electrical power more carefully until you get home. Losing the belt that drives the raw-water pump is different. Without cooling water, you’ll need to stop the engine before it overheats.
If the belt has deteriorated to the point where you wouldn’t trust it to complete today’s trip, replacing it before you leave is likely to leave you with fewer worries than wondering about it all day.
If the belt looked fine during your checks but starts squealing once the engine is running, don’t automatically assume the belt itself is at fault. The engine-running checks will help confirm whether the equipment driven by the belt is operating normally.
Ownership Tips
A quick vacuum around the front of the engine after a trip makes the next WOBBLE check much easier. Belt dust, fresh drips and other small changes are easier to spot on a clean engine than one that’s covered in months of dust and dirt.
Label every spare belt before you put it away. A piece of masking tape and a permanent marker are often all you need. Write what it fits—Alternator, Water Pump or whatever is appropriate. A few years from now you’ll be glad you did.
If you’re replacing a belt as part of routine maintenance rather than because it’s failed, the old belt can make an excellent get-you-home spare, provided it’s still in good condition. Store it separately from the new one and label both clearly so you know which is which.
If you ever replace a drive belt yourself, take plenty of photographs before you start. Don’t just photograph the belt itself. Photograph the adjustment brackets, bolts, spacers and the position of the adjustment mechanism from a couple of different angles. The belt routing is often the easy part. It’s remembering exactly how everything was adjusted and fitted together that catches people out months or years later.
B – Bilges
The second B in WOBBLE is usually taught as Bilges, but we’ve deliberately emphasised the plural throughout this guide.
Many boats have more than one place where water and other liquids collect. Some have a single engine bilge. Others have several separate bilge compartments beneath the cabin sole, around the engine or elsewhere in the hull.
Throughout this guide, when we talk about checking the bilges, we mean all of the places where your boat collects water or other liquids, not just the easiest one to see.
We’ve also included Batteries because they deserve just as much attention before you leave.
The bilges are one of your boat’s best early warning systems.
If water, oil, coolant, diesel or another liquid escapes onboard, it may eventually find its way into a bilge or other collection area. But liquids can also remain trapped in engine trays, lockers, beneath equipment or in other parts of the boat, so a dry bilge doesn’t necessarily mean there hasn’t been a leak.
Checking the Bilges
The first few times you lift the engine hatch, you may not know what’s normal for your boat.
That’s expected.
Rather than trying to identify every drip immediately, ask yourself four questions.
What have I found?
Roughly how much is there?
Where has it collected?
Can I explain why it’s there?
Those four questions usually tell you far more than the liquid alone.
What’s Normal?
Perfectly dry bilges aren’t necessarily normal.
Some boats collect a small amount of water in certain conditions. Others don’t.
The question is whether you can explain why the liquid is there today.
A little rainwater after heavy weather, water left behind after washing the boat or a few drops from a stern gland may all have straightforward explanations.
Liquid that appears without an obvious reason deserves a closer look.
Before Starting the Engine
Before closing the engine hatch, spend a few seconds looking into the places where your boat normally collects water or other liquids.
Don’t just look beneath the engine.
Look where your boat usually reveals small changes first.
If something catches your eye, ask yourself:
“Can I explain why it’s here?”
The bilges rarely tell the whole story on their own.
They’re an early warning system, not a diagnosis.
Whatever you find should prompt you to look for supporting evidence elsewhere. Oil points you towards the engine and gearbox oil checks. Coolant points you towards the coolant level. Water means asking where it came from. A freshwater leak may also explain why the freshwater pump has been running occasionally even though nobody has been using any water. Once any obvious problem has been dealt with, the engine-running checks will help confirm that you’ve found the real cause.
I’ve Found Something. What Now?
“I’ve found water in the bilges. Can I still go?”
Start by working out where it has come from.
Think about what’s happened since you last visited the boat. Has it rained heavily? Did you wash the boat? Has the freshwater pump been running when nobody was using water? Could the freshwater system have developed a small leak?
If there’s no obvious sign that water is entering through the hull, the water may have come from rain, washing the boat or somewhere within the boat itself.
If there’s only a small amount, nothing else has changed and you can account for it, there’s usually no reason to cancel today’s trip. Keep an eye on it while you’re underway and investigate the cause properly when you have time.
If the amount is increasing, you can’t account for it or you have any reason to suspect water is entering through the hull or another important system, find out where it’s coming from before deciding to leave.
“I’ve found oil in the bilges. Can I still go?”
Before assuming the engine has developed a major fault, remember that oil can reach the bilges from several different places. Oil spilled during servicing, a crankcase breather, a gearbox oil seal or another small leak can all eventually find their way there.
If you’re not sure how much oil you’re looking at, pump or mop a little into a clear container and leave it to stand for a few minutes. Oil and water separate naturally. What first looked like a litre of oil may turn out to be a cup of oil floating on top of rainwater or freshwater.
Then check the engine and gearbox oil levels.
If you can identify a small, known and unchanged leak, the oil levels are stable and the engine is otherwise behaving normally, today’s trip may still be reasonable. What matters is whether the leak is stable and whether you know what you’re dealing with.
If one of the oil levels has fallen, the leak is new, the amount has increased or you can’t explain where the oil has come from, investigate before deciding to leave.
“I’ve found coolant in the bilges. Can I still go?”
A few drops may have an innocent explanation, but coolant appearing without an obvious explanation or a falling coolant level should be investigated before deciding whether today’s trip can go ahead.
Check the coolant level and look for the source before making that decision.
“I’ve found diesel in the bilges. Can I still go?”
Diesel has a distinctive smell and shouldn’t normally appear in the bilges.
A loose hose connection, a weeping fuel filter seal or another small fuel leak can all be responsible.
Find the source first and deal with any leak you discover before deciding whether you’re happy to continue. If you can’t find the source, don’t assume the amount you’ve found is all there is.
Ownership Tips
One of the best times to tidy the engine bay is when you return from a trip. A quick vacuum to remove belt dust and a few minutes cleaning or drying the bilges resets your boat’s early warning system. The next time you lift the engine hatch, fresh belt dust, new drips or unexpected water are much easier to spot.
Some owners use absorbent pads, bilge socks or other products to catch small drips before they spread around the bilges. Others simply place a sheet of kitchen roll beneath the engine. Whatever method you choose, you’re trying to make fresh leaks easier to spot. If you’d like to know more about the different options, we’ve covered them in our Bilge Maintenance Guide.
If you’re spending several days aboard, make checking the bilges part of your morning routine, whether you’re planning to move the boat or not. It only takes a few seconds and can often identify a small problem before it becomes a much larger one.
If you remove oily water from the bilges, don’t pump it overboard. Keep it in a suitable container until you can dispose of it responsibly. Many marinas provide facilities for waste oil and oily water, but check what facilities are available where you’re moored.
B – Batteries
The B in WOBBLE also stands for Batteries, although not every version includes them.
We’ve included them because healthy batteries are essential for starting the engine and powering the rest of the boat.
Your batteries store the electrical energy needed to start the engine and power everything from lights and water pumps to refrigerators, navigation equipment and autopilots.
Before leaving, you’re checking three things:
- Are the batteries securely mounted and in good condition?
- Are the electrical connections clean and secure?
- Is there enough stored electrical power for today’s trip?
Many boats have a separate starter battery for the engine and one or more domestic (or leisure) batteries for everything else on board.
If you’re not yet familiar with what’s around your batteries, our Understand Your Battery Compartment guide explains what the different cables, switches and components are doing and how they fit together.
Checking the Batteries
Start with the batteries themselves.
Are they securely mounted or strapped down?
Can you see any cracks, bulging sides or other signs of damage?
A battery shouldn’t be able to move as the boat heels or bounces in rough water. If it does, it can damage cables, break electrical connections or create a short circuit.
Now look at the electrical connections.
Are the terminals clean?
Do the cable connections feel secure?
Can you see significant corrosion, damaged cables or signs that a connection has been getting hot?
Engine vibration can loosen electrical connections over time, so it’s worth checking that everything still feels secure before you leave.
What’s Normal?
Battery compartments are working parts of the boat.
Dust, older labels and a little surface corrosion on an older installation aren’t unusual.
A battery that has moved, a swollen or cracked case, badly corroded terminals, loose cables or signs of overheating deserve investigation before today’s trip.
It’s also worth becoming familiar with your normal battery readings.
Some boats have a simple voltmeter. Others display battery voltage, estimated state of charge or charging current.
Whether your display shows voltage, battery percentage or amp-hours matters less than recognising when one of the readings differs from what you normally see.
Before Starting the Engine
Think about how you’ve been using the boat since the batteries were last fully charged.
Has it been connected to shore power?
Have the solar panels had a chance to recharge the batteries?
Or has the boat been sitting on its mooring while the batteries have gradually been supplying small electrical loads?
If you’ve just disconnected the shore power, allow the batteries a few minutes to settle before judging the reading. Battery chargers temporarily raise the voltage, so the first reading may give an overly optimistic picture of the batteries’ state of charge.
A lower-than-expected reading doesn’t tell you whether the batteries need charging or whether they’re no longer holding their charge as well as they once did.
The engine-running checks later in the routine will help answer that question by confirming that the alternator is charging correctly.
I’ve Found Something. What Now?
“One of my batteries has moved. Can I still go?”
No.
Secure it before leaving.
A loose battery can damage cables, break electrical connections or short against nearby metalwork.
“One of my batteries is cracked, swollen or damaged. Can I still go?”
Probably not.
Damage to the battery case or signs that electrolyte has leaked out suggest the battery has developed a fault. Investigate before deciding whether today’s trip should go ahead.
“One of my batteries is hissing, getting very hot or smells of rotten eggs. Can I still go?”
No.
Those can be signs of a serious battery or charging problem. A rotten-egg smell can indicate hydrogen sulphide gas, which is highly toxic and highly flammable. A faulty or overcharging battery can also produce hydrogen, which is highly flammable.
Don’t start the engine or operate electrical equipment near the battery if doing so could create a spark.
Stop the sources charging the battery. If you’re connected to shore power, switch off the shore-power supply at the marina or pontoon if you can do so without approaching the affected area. If solar is charging the battery, switch off the solar charging system using its normal controls, provided you can do so without entering the battery compartment.
If you can ventilate the battery compartment without putting yourself into the space, do so. Don’t lean into the compartment or start working on the battery itself if it is hot, swollen, leaking, smoking or making violent or unusual noises.
Today’s departure is on hold until you’ve dealt with the battery or charging problem.
“The terminals or cables don’t look right. Can I still go?”
Loose terminals, damaged cables, heavy corrosion or signs of overheating should all be dealt with before leaving.
Poor electrical connections can cause unreliable starting, charging problems and faults that are difficult to trace later.
“One of the battery readings is lower than usual. Can I still go?”
Think about whether the reading makes sense.
If the batteries have had little opportunity to recharge since your last trip, a lower reading may be exactly what you’d expect.
If they should already be fully charged, the reading deserves further investigation.
Complete the engine-running checks before deciding whether today’s trip should go ahead. They’ll confirm whether the alternator is replacing the electricity you’ve used and help you decide whether you’re looking at a charging problem or a battery that’s no longer storing energy as well as it should.
Ownership Tips
Know how to isolate your batteries before you ever need to.
If your boat has battery isolator switches, make sure you know where they are, which batteries they control and how to use them.
Although your batteries are only 12 or 24 volts, they can produce extremely high currents. A spanner, screwdriver, watch strap or other metal object placed across the terminals can create a short circuit capable of producing intense heat and damaging equipment.
Think about when your charging sources are producing enough power to meet your boat’s electrical demand without drawing significantly from the batteries.
After a sunny afternoon or several hours under engine, the batteries may already be well charged and your charging sources may be producing enough power to run additional equipment without significantly discharging the batteries. That’s a good time to charge laptops, cordless tools and other devices or run equipment that draws a lot of power.
When the batteries aren’t being replenished, think about what really needs to be switched on. Many owners naturally develop routines that suit the way they use their own boat. If you want to understand how the different parts of the system fit together, our 12V Marine Electrical Systems Explained guide takes a broader look at batteries, charging and power use onboard.
The goal isn’t to use less electricity.
It’s to understand when your boat is generating it, when it’s storing it and when it’s drawing on what was stored earlier.
L – Levels (Coolant)
The L in WOBBLE usually stands for Levels. Some versions also include gearbox oil under this heading, but we’ve already covered engine and gearbox oils earlier in the guide. Here we’re concentrating on the engine coolant where the engine has a separate closed cooling system.
Earlier we looked at the raw-water cooling system. On an engine with a closed freshwater cooling system, coolant circulates around the engine and carries heat away before that heat is transferred to raw water through a heat exchanger.
The coolant is different from the raw water.
It normally remains inside the engine’s closed cooling circuit and circulates around the system every time you run it.
Some engines use different cooling arrangements, so the important thing is to understand which system your own engine has and check the level in the way specified by the manufacturer.
Checking the Coolant
Always check the coolant with the engine completely cold.
Many boats have an expansion or header tank with MIN and MAX marks, making the level easy to see.
Others don’t.
On those engines, the manufacturer’s instructions may require you to check the level through a filler neck or another part of the cooling system. If the system has a pressure cap, only remove it when the engine is completely cold.
You don’t need to measure the level precisely. Most owners use the same reference point every time. It might be the level between the MIN and MAX marks, an internal baffle or another fixed reference point specified for the system.
Check it the same way each time. That makes small changes much easier to recognise.
Never remove the pressure cap while the engine is hot. The cooling system may be under pressure and removing the cap can release scalding coolant and steam. If the engine has overheated, allow it to cool completely before investigating or topping up the coolant.
What’s Normal?
Unlike engine oil, coolant shouldn’t normally disappear during everyday use.
Once you’ve learned where the level normally sits, it should change very little.
If you find yourself topping it up regularly, the question isn’t how much you’ve added.
It’s why you’re adding it.
Before Starting the Engine
A quick glance is often enough.
Is the coolant level where you’d expect it to be?
Has anything changed since the last time you looked?
If everything looks normal, refit or tighten the cap securely if you’ve removed it and move on to the next check.
Once the engine is running, the engine-running checks provide another opportunity to confirm that the cooling system is behaving normally.
I’ve Found Something. What Now?
“The coolant level is lower than usual. Can I still go?”
A lower coolant level doesn’t always mean there’s a serious problem.
Think about what’s happened since you last used the boat.
Has the engine overheated recently?
Did you clear a blocked raw-water strainer or remove a plastic bag from the hull inlet?
If the raw-water system became blocked, the engine may have run hotter than normal. On some engines, an overheating event can cause coolant to be pushed out through the expansion or overflow system. Depending on the installation, that coolant may eventually find its way into the bilges.
If you know why the engine overheated, you’ve dealt with the original cause and the engine is now running normally, topping the coolant back up once the engine has cooled completely may be all that’s needed. If the engine overheated significantly or you’re not sure why it happened, investigate further before relying on it.
When topping up, always use the type of coolant recommended for your engine. Coolants aren’t all compatible with one another, and some are supplied ready to use while others are concentrates that must be mixed with de-ionised water. Always read the instructions before topping up the system.
If the coolant level continues to fall or you can’t explain why it’s changing, investigate before deciding whether today’s trip should go ahead.
“I’ve found coolant in the bilges. What does it mean?”
Treat the coolant level and the coolant in the bilges as two parts of the same story.
Has the coolant level dropped?
Did the engine overheat recently?
Can you see any signs of coolant around a hose, hose clip, heat exchanger or expansion tank?
Coolant doesn’t always appear in the bilges straight away. A small leak may take hours, overnight or even a trip in choppy water before it reaches the place where you normally look.
If the coolant level hasn’t changed, you understand why the coolant is there and nothing else has changed, you’ve probably learned something useful rather than discovered a new problem.
If the coolant level continues to fall, or coolant keeps appearing in the bilges without an obvious explanation, investigate before deciding whether today’s trip should go ahead.
Ownership Tips
Carry the correct type of coolant for your engine.
If your engine uses concentrated coolant, many owners find it useful to keep three clearly labelled bottles on board:
- de-ionised water;
- concentrated coolant; and
- coolant already mixed to the correct strength.
Mixing a full bottle accurately at home is easier than trying to make up a small quantity in the engine compartment.
An old coolant bottle makes an ideal container for the ready-mixed coolant. Write “PRE-MIXED” on it with a permanent marker. Label the concentrate and de-ionised water as well. It only takes a few seconds and removes any doubt when you come back to the boat months later.
If you top up the coolant, record it.
It doesn’t need to be precise. Write the date and roughly how much you’ve added in your maintenance log or directly on the coolant bottle with a permanent marker.
One top-up after an overheating incident may have a perfectly sensible explanation.
Finding yourself topping it up repeatedly without a clear explanation is much more useful information than the amount you added. Record each top-up and you’ll spot a developing problem much sooner.
Start the Engine
You’ve now completed the first part of your WOBBLE routine.
Any problems you’ve found have been investigated and, where possible, dealt with while the boat is still safely alongside.
The remaining checks can only be confirmed with the engine running.
The safest time to do that is while the boat is still safely secured. If something still doesn’t look right, you’re in the best position to investigate it.
When you’re ready, start the engine and follow the manufacturer’s instructions for warming it up. Some engines are happy to run briefly at idle while you complete the checks; others should not be left idling for longer than necessary and are intended to reach operating temperature under light load.
The remaining checks fall into two stages.
The first happens almost as soon as the engine starts.
First, confirm that the engine is being cooled properly. If it isn’t, stop the engine before it has a chance to overheat or suffer damage.
Once you’ve confirmed that cooling water is flowing normally, allow the engine to continue warming up as recommended for your particular engine.
Continue with the remaining engine-running checks.
Up to this point you’ve been inspecting the boat with the engine stopped. The next few checks confirm that those earlier inspections were correct.
A clean raw-water strainer is only useful if cooling water reaches the exhaust. A belt that looks in good condition still has to drive the equipment connected to it. A battery with enough charge to start the engine also needs charging once the engine is running.
Over the next few minutes you’ll confirm that the cooling system is working, the charging system is operating normally and the engine instruments are behaving as you’d expect.
Use that time to prepare the boat for departure.
While the engine warms up, disconnect the shore power, prepare the boat for departure and brief everyone on board. Make sure they understand how you’re planning to leave, what you’d like them to do, when they should do it and what to do if something doesn’t go according to plan.
Cast off once the remaining WOBBLE checks are complete. If something unexpected still needs investigating, deal with it while the boat is still securely alongside.
E – Exhaust
The E in WOBBLE is often taught as Exhaust.
Earlier in the guide, you checked the raw-water strainer while the engine was switched off. That told you the cooling system looked ready to do its job.
Now it’s time to confirm that it is.
On most marine diesel engines with a wet exhaust, the exhaust does two jobs. It carries the engine’s exhaust gases overboard and, after the raw cooling water has passed through the cooling system or heat exchanger, it carries that water overboard as well. The two are mixed together before leaving the boat through the exhaust outlet.
Some boats use a dry exhaust or discharge cooling water through a separate outlet. If yours does, check the cooling-water discharge specified for your particular installation rather than looking for water at the exhaust outlet.
Just as the bilges provide clues about what’s happening elsewhere on the boat, the exhaust provides clues about what’s happening inside the engine.
Checking the Exhaust
The first check begins as soon as the engine starts.
Go and look at the exhaust outlet.
If your boat has a wet exhaust, can you see cooling water being discharged?
Every boat is different. Some produce a continuous stream, while others discharge in more noticeable pulses. Don’t compare the flow with the one on the next pontoon. Compare it with what your own boat normally produces.
Don’t just glance once and walk away. Watch it for a few moments. There will be some water left in the exhaust system from the last time the engine ran, so a single splash doesn’t necessarily tell you that the cooling system is working properly. What you’re looking for is the familiar pattern of cooling-water discharge that your own boat normally produces.
If your boat has a separate cooling-water outlet, check that instead.
If there’s little or no cooling-water discharge where you would normally expect to see it, stop the engine before doing anything else.
There’s no point carrying on with the rest of your departure checks until you understand why the engine isn’t being cooled properly.
Once you’ve confirmed that cooling water is flowing normally, leave the engine running and allow it to continue warming up as recommended for your particular engine.
As the engine warms up, keep using your senses.
Listen to the engine.
Most diesel engines sound slightly different once they’ve warmed up. The idle often becomes smoother, the exhaust note may change slightly and the engine gradually settles into its normal rhythm.
You’re listening for anything that sounds different from the last time you ran the engine.
Keep an eye on the exhaust as well.
Has the cooling-water flow remained normal?
Can you see any unusual smoke?
Finally, use your sense of smell.
Do you notice diesel, burning rubber, hot coolant, burning oil or anything else that seems unusual?
Most of the time, the answer will be “No.”
What’s Normal?
Don’t compare your boat with the one on the next pontoon.
Compare it with the way your own boat behaved the last few times you used it.
A little water vapour on a cold morning can be normal.
Many older diesel engines can also produce a brief puff of black smoke or a few specks of soot when they’re first started or when the engine speed is increased after a period of idling. A brief puff isn’t necessarily a sign of a developing fault, particularly on an older mechanical-injection engine. What matters is whether the smoke is brief and familiar or whether it is persistent or noticeably worse than normal.
Persistent blue, black or white smoke all deserve further investigation, although the causes can be very different.
The same applies to changes in the cooling-water flow, unusual noises or unfamiliar smells.
Together with the earlier WOBBLE checks, those observations usually point you towards where to begin investigating.
I’ve Found Something. What Now?
“There’s no cooling water coming from the exhaust. What should I do?”
Stop the engine.
The cooling system isn’t doing what it should, and continuing to run the engine risks serious damage.
Earlier you checked the raw-water system.
Is the raw-water seacock definitely open?
Is the strainer clean?
If your strainer has a transparent bowl or lid, can you see water flowing through it? On many installations you should be able to see water entering the strainer from the hull and leaving again towards the engine. If you can’t see any movement at all, or the strainer isn’t filling as you’d expect, that’s another clue that the problem may be before the engine rather than inside it.
Could the hull inlet still be blocked?
If those all look correct and there’s still no cooling water, the problem is likely to be elsewhere in the raw-water system and will need further investigation.
If your boat has a separate cooling-water outlet, carry out the equivalent checks for that system rather than looking for water at the exhaust outlet.
Before running the engine again, you’ll need to understand why the cooling system isn’t doing its job.
“The exhaust looks, sounds or smells different.”
Ask yourself one question.
What’s changed?
Is the cooling-water flow different?
Is the smoke different?
Has the engine developed a new noise?
Can you smell something that wasn’t there before?
A little vapour on a cold morning or a brief puff of soot from an older diesel may be exactly what you’d expect.
Persistent smoke, a noticeable change in the cooling-water flow, a new noise or an unusual smell all tell you that something has changed since the last time you ran the engine.
Work out what has changed before deciding whether today’s trip should go ahead.
Ownership Tips
One of the most useful things you can do is learn what your engine normally looks, sounds and smells like once it’s warmed up.
There’s no need to measure the cooling-water flow or memorise figures from the engine manual. Once you’ve seen your own engine running a few times, a quick glance is usually all it takes to recognise whether everything looks normal.
When you wash the boat, give the area around the exhaust outlet a quick clean. Fresh soot, staining or other deposits are much easier to spot on a clean hull than one that’s already dirty.
Include your sense of smell.
Wind direction makes a huge difference. At anchor or underway you may not smell the exhaust at all, but while you’re still alongside it’s often only a few moments before you notice whether anything smells different from normal.
Over time you’ll notice the difference before you’ve consciously worked out what it is. A slightly different exhaust note, less cooling water than usual or an unfamiliar smell are often enough to tell you that today’s engine isn’t behaving quite like yesterday’s.
E – Electrics
The E in WOBBLE is also commonly taught as Electrics.
By now the engine has been running for a few minutes and you’ve already confirmed that it’s cooling properly and behaving as you’d expect.
Now it’s time to confirm that the rest of the boat is ready for today’s trip.
Starting the engine doesn’t just bring the engine to life.
It also brings much of the rest of the boat into operation.
The alternator begins charging the battery bank connected to it, the instruments come alive and the equipment you’ll be relying on during today’s trip begins doing its job.
This section confirms that those systems are working as they should.
Checking the Electrics
Start with the engine instruments.
Have the warning lights that should go out gone out?
Are there any warning lights still showing?
Have any alarms sounded?
Now check that the batteries are charging normally.
If your boat has a battery monitor, voltmeter or charging display, compare today’s readings with what you normally see. Some boats begin charging immediately, while others need a few more engine revs before the alternator reaches its normal output.
Earlier we looked at the difference between creating electricity and storing it.
This is where you confirm that the boat is creating electricity.
If the alternator is charging normally, you know the charging system is replacing the power used to start the engine.
Now turn your attention to the equipment you’ll be relying on today.
If you’re using a chartplotter, has it started normally and acquired a GPS position?
If you’re using a VHF radio, autopilot, depth sounder, wind instruments or other navigation equipment, switch them on and make sure they’re behaving as you’d expect.
If today’s trip could involve reduced visibility or returning after dark, check your navigation lights before leaving rather than assuming they’ll work later.
There’s no need to switch on every electrical item on board.
Make sure the equipment you’ll be depending on today is ready when you need it.
What’s Normal?
Some alternators begin charging almost immediately, while others need a few more engine revs before reaching their normal output.
Some battery monitors display voltage, while others show battery capacity, charging current or both.
Some navigation equipment starts almost instantly, while other systems take a little longer to acquire a GPS position or complete their own start-up checks.
The engine instruments also change as the engine warms up.
Oil pressure is often highest immediately after a cold start because the oil is still thick. As the engine warms up, it’s normal for the oil pressure to fall slightly before settling into its usual operating range.
The temperature gauge behaves differently. On most boats it’s showing the temperature of the engine coolant, so it usually starts low before rising as the engine reaches its normal operating temperature.
You’re comparing today’s readings with what you normally see on your own boat rather than trying to memorise numbers.
I’ve Found Something. What Now?
“The oil pressure warning light hasn’t gone out.”
Stop the engine.
The oil pressure warning light should normally go out within a few seconds of the engine starting. Don’t assume it’s a faulty switch or sender. Investigate the cause before running the engine any longer.
“The charging warning light is still on.”
Earlier you checked the alternator belt.
Does the alternator belt still look correctly tensioned?
Does the battery monitor show that the batteries are charging?
Charging systems differ, but a charging warning light that stays on deserves investigation before you leave.
“The batteries seemed lower than I expected before I started the engine.”
Has the engine started normally?
Is the alternator now charging as you’d expect?
If so, you’ve confirmed that the boat is creating electricity.
Whether the batteries are storing that electricity properly is a separate question. If they continue to seem weaker than usual after charging, investigate the batteries before relying on them for longer trips.
“One of the gauges doesn’t look right.”
Don’t expect every gauge to behave in the same way.
Oil pressure often starts high before falling as the engine warms up.
Coolant temperature usually starts low before rising.
If one gauge behaves very differently from normal, or doesn’t behave as you’d expect at all, investigate before casting off.
“One of my instruments isn’t working.”
The answer depends on both the equipment and the trip you’re planning.
If the equipment isn’t essential for today’s trip, you may decide it’s something to investigate when you return.
If you’ll be relying on it for navigation or safety, it’s usually better to understand the problem before leaving than hope it sorts itself out later.
Ownership Tips
Every skipper eventually develops a departure routine that suits both their boat and the way they use it.
If you normally use a chartplotter, decide when you switch it on and when you load your route.
If you keep an electronic logbook, make starting it part of the same routine.
If you regularly rely on an autopilot, switch it on and confirm it’s working before leaving rather than discovering there’s a problem when you need it later.
Some equipment takes time to start up, acquire a GPS position or complete its internal checks. Switching it on while you’re still preparing the boat often means everything is ready when you are.
Think about when your boat has electricity to spare.
Early in the morning, particularly after a night at anchor or on a mooring, electricity may be something you’re trying to conserve. Later in the day, with the engine running or the solar panels producing plenty of power, your charging sources may be producing enough power to meet the boat’s electrical demand without drawing significantly from the batteries.
That’s often the best time to charge laptops, cordless tools and other devices, run an inverter or tackle jobs that aren’t time-critical. Some owners even turn the fridge or freezer down a little during the afternoon, making use of that available charging capacity rather than drawing as heavily on the batteries overnight.
Final Engine Check
By now the engine has been running for several minutes.
The cooling system has had time to circulate properly, the alternator is charging and the engine is approaching its normal operating temperature.
Before casting off, lift the engine hatch one last time.
This isn’t a new inspection.
You’re confirming that the systems you’ve already checked are still behaving as expected now the engine has been running for a few minutes.
Have a look around the engine compartment.
Can you see any fresh oil, coolant or water?
Has anything started dripping?
Can you hear a belt squealing or see one running out of line?
Do you notice any new smells?
Has anything changed since the engine started?
Most of the time the answer will be “No.”
If everything still looks as you’d expect, your WOBBLE checks are complete and you’re ready to cast off.
Ownership Tips
This quick look is useful whenever the engine has been running for a while.
Any time the engine has been running for a while—after a long passage, after working hard in rough weather or when you’ve stopped for fuel—lifting the engine hatch can tell you whether anything has changed while the engine was working.
Fresh drips, a loose hose clip or the first signs of a leak are often much easier to spot before they become something that demands your attention later.
Cast Off
By this point you’ve inspected the boat with the engine stopped.
You’ve confirmed those checks with the engine running.
You’ve also given yourself the chance to deal with small problems before getting underway, when investigating them is usually easier than doing the same job once you’re moving.
Now it’s time to cast off.
Before long you’ll probably stop thinking about the letters in WOBBLE.
The checks remain the same, but the mnemonic gradually fades into the background.
Instead, you’ll find yourself noticing when something doesn’t look, sound or behave as it did last time.
That’s the real purpose of WOBBLE.
Not remembering six letters.
Learning how your own boat behaves.
Have a great day on the water.
Peter Robinson has more than 20 years of hands-on boating experience across narrowboats, motorboats and sailing boats. He writes about onboard systems, maintenance and equipment based on practical long-term ownership and real-world use in the UK and Mediterranean. Learn more on the About page.