Burning issue

Mark Robinson | VOLUME 25, ISSUE 2
"A wall of fire shot down the length of the craft.."
A recent rash of ski boat fires has prompted Club Marine to issue a call for owners of inboard petrol-fuelled craft to be more careful when using their boats.

Case Study1: With the sun warm on his back, the young boy sat cross-legged on the engine cover of the family ski boat, looking forward to a day on the river. Then his dad hit the starter button and the resultant explosion lifted the engine cover with such force it blew the boy into the river some distance from the boat. Although shocked, he was, luckily, relatively unharmed.

Case Study 2: Just after midday, a ski boat owner pushed his boat out from the bank. Aboard were a number of family members, including his wife, and children. The craft refused to start and, detecting the smell of petrol, he raised the engine box cover and waited for the fumes to dissipate. There were no apparent leaks and once the fumes had cleared, he closed the cover and hit the starter button again. A loud ‘popping’ sound ensued and a wall of fire shot down the length of the craft, which immediately caught fire from stem to stern. His daughter swiftly threw the smaller children overboard and everyone else alighted promptly. His wife was airlifted to hospital with severe burns, while he, with less severe injuries, was transported by ambulance.

Case Study 3: Shortly after refuelling, two young men began meandering upstream to give their ski boat, which had a newly-installed engine, a bit of a run. Bystanders observed that it was blowing thick black smoke from the moment it started and then they heard a ‘pop’, followed by a ‘bang’ as the craft burst into flames. The pair quickly bailed out and the boat burnt to the waterline, as it drifted slowly into shore at the very spot a houseboat had just vacated.

In recent times, Club Marine has seen a marked increase in the number of incidents of fires on petrol-fuelled craft, most notably in board powered ski boats. The fires generally begin in or around the engine and are almost universally caused by leaking fuel and the resultant build-up of explosive petrol vapours. Overwhelmingly, the incidents are linked to older craft, typically boats that have ageing automotive engines that may have been modified or otherwise tinkered with by the owners or non-authorised technicians over the years. The cumulative effect of their efforts can have disastrous outcomes, as we’ve recently seen. Petrol-fuelled boat engines have very specific requirements when it comes to fuel systems and safety procedures and need to be regularly maintained and inspected by experienced marine technicians, who know where the trouble spots are and how to deal with them.


“Boats with car engines that have been converted, or marinised, are certainly over-represented when it comes to fires and explosions, and older boats are more prone to problems,” said Club Marine’s National Claims Manager, Phil Johnson. “Some conversions may not have been performed as professionally as owners might think and fuel leaks and electrical problems, such as non-sparkarrested starter motors or alternators, can turn some of these craft into floating time bombs.”

Of particular concern to Club Marine are craft that are used primarily on a seasonal basis and that spend long periods of time inactive or in storage. Minor fuel leaks, and subsequent vapour pockets in bilges and other hard-to-detect areas, can result in catastrophic fires, damage and serious injury to occupants.

“That’s why we have a special Inboard and Performance Ski-Boat assessment report that we require to be filled out in certain circumstances before providing insurance coverage for these craft,” said Johnson.

“Many boat owners don’t realise that fuel vapour can build up undetected on their boats over time.”

“Something as simple as a minor fuel spill when refuelling can produce a pocket of vapour in a boat. Then, all it takes is a spark or naked flame and in a split second the boat is engulfed in flames.

“In our experience, boats with dedicated inboard marine engines tend to have less claims for fire-related damage than those with converted car engines,” said Johnson.


The reason that petrol is so potentially dangerous is because it is highly volatile, with the fumes capable of ignition up to almost 4m away from a pooled source. This inherent danger is further multiplied by its explosive potential. Petrol vapour is highly explosive and may ignite as a fireball, with searing temperatures of up to 8300°C. And because petrol vapour is heavier than air, it will settle in the lowest areas of a boat, usually the bilges. At concentrations as little as one part in 70 to air, it can form a lethal mixture that will explode violently when ignited. In fact, a litre of vaporised gasoline has about the same explosive power as a stick of dynamite.

As serious as the aforementioned case studies were, and given the explosive power of petrol vapour, it was only sheer luck that there were no fatalities. But these cases, along with several other incidents of ski boats bursting into flames in recent months, have created justifiable concern among boat owners, police and insurance companies alike.

Along with Club Marine’s South Australian State Manager, Mike Sinclair, I visited a number of boating companies to try and shed some light on this disturbing trend. What we discovered shocked us greatly and made us realise just how many vessels out there are virtual time bombs, with potentially lethal consequences for their occupants.

Over the course of the day, we visited Elite Ski Boats, Twister Ski Shop and Matrix Marine, and at every stop we were shown examples of fires waiting to erupt. Fitment of incorrect fuel lines or lines in poor condition, poor placement of fuel lines, badly mounted fuel tanks and incorrect carburettors and inappropriate components predominated.


At Elite Ski Boats, Stuart Myles showed us over his premises and impressed us by pointing out the many and various safety features on the boats he sells. However, among the many horrors revealed was a monument to colossal human stupidity that would be hilarious if it wasn’t so potentially lethal. Some mechanical genius had decided to strap a fuel line to, of all things, an exhaust pipe! Definitely an accident just about certain to happen …

At Twister Ski Shop, Michael Bishop rocked us back on our heels by showing us a host of existing problems, along with others just waiting to happen in various ski boats booked in for repairs and servicing in his workshop. Perished and split fuel lines were far too common. Fuel hoses have ratings and for boating use should be of the highest rating available. The cheaper, inferior stuff should be avoided, as it can become brittle and split or break or it may deteriorate when exposed to petrol.

Matrix Marine’s Neil Boyd outlined many precautions and measures his company takes in manufacturing its craft, particularly with regard to fuel system and tank design.

So exactly what did we learn from these experts? Let’s start with an all-too-typical horror story, an outstanding example of which was a ski boat we inspected that had caught fire shortly after refuelling. The clamp that held the hose connecting the transom-mounted fuel filler to the fuel tank had worked loose, allowing fuel to spill straight into the bilge as it was being poured into the tank.

That was bad enough, but as Mike Bishop was showing us some other typical trouble spots, he discovered that the fuel line from the tank to the carburettor on this same boat was cracked in several places and fuel poured out as he held it up.


The routing of the fuel line was also a potential source of leaks due to chafing and, to top it off, the carburettor on this particular boat was off a car rather than a dedicated marine unit. This is a common practice with inboard petrol-engined craft, but many people don’t realise that there is a distinct and important difference between auto and marine-dedicated carburettors. Carburettors designed for marine use will, when flooded, allow excess fuel to overflow down into the inlet manifold, which, at worst, will cause difficult starting. By contrast, motor vehicle carburettors flood externally – generally all over the outside of the carburettor. The result is that the fuel either pools in the top of the engine, or runs down into the bilge, causing a vapour build-up just waiting for a spark to ruin the owner’s day.

Many modern craft, and particularly those with dedicated marine engines, now come equipped with electronic fuel injection, which prevents the risk of flooding and is generally less prone to fuel leakage issues.

Fuel tank mounting is another area where problems can occur. We saw one instance in which a tank that was poorly fastened using welded tabs affixed by flimsy sheet metal screws came loose in the hold. In this instance, the tank broke free, moving around enough to crack fuel lines and loosen the filler inlet connection; both potentially dangerous situations.

The proper procedure for mounting an aluminium fuel tank is to use purpose-built tank mounting rubbers between the metal straps that hold it in place. All too often, according to the observations of our panel of experts, this tried and true method is not employed.

Another problem that arises is with older tanks, which have the fuel pick-ups fitted to the bottom of the tank. If the feed hose develops a leak, fuel ends up in the bilge just waiting for a spark or naked flame to set it off. Accepted modern practice employs the pick-up entry point in the top of the tank, so that any damage or wear and tear can be easily seen and dealt with. Likewise, fuel level sender units are a potential source of leakage and need to be checked from time to time.

Hose clamps are another area of potential risk. They should be checked to make sure they are of the right size, with quality stainless steel clamps being the best choice to avoid the risk of corrosion. Also, double clamps should be used on all fuel fittings for added security. These days this is a legal, as well as a moral requirement, although it seems that not every tank manufacturer or boat builder knows about it. A quick visual check will confirm whether your boat complies.


There is some difference of opinion among boat builders as to whether the plastic rotomolded fuel tanks or aluminium tanks are the best choice. Over time, aluminium can corrode and this needs to be monitored carefully, especially in older boats. However, plastic rotomolded fuel tanks need to be made of a high quality plastic and, like many products, there are well-made and not-so-well-made units out there.

Nevertheless, regardless of quality, all plastic tanks swell and shrink due to the expansion of fuel vapours, with the higher quality ones able to resist this process somewhat due to internal cross-bracing. However, even the more expensive units develop somewhere between seven to 15 per cent expansion, which can impose stresses on the mounting points and filler neck fittings. The best bet is to conduct regular checks on the tank mountings and filler connections as part of ongoing maintenance.

There is also a seemingly unrelated problem that can occur mostly on older craft that rely on external cooling systems and don’t have watercooled exhaust manifolds. The coolant inlets generally employ weed traps that, if they are cheaper items with smaller diameter tubes and filters, can clog easily. According to one of our expert panel, this can lead to engines becoming so hot that the exhaust manifolds glow red, presenting an obvious flash point if fuel vapour is present. The extreme heat can also singe or melt nearby electrical wiring, causing yet another potential flash point.


Which brings us to electrical components, such as starter motors, alternators and distributors. All of these components, without exception, need to be marine-dedicated units fitted with flame arrestors to prevent errant sparks from igniting a fire. Any one is capable of generating sparks and are common sources of ignition in boat fires. If in doubt, have them checked by an expert.

“We’d encourage all owners of in board powered craft to conduct regular inspections of their boats and all fuel and electrical systems,” advised Johnson. “And we’d particularly urge that they have their boats regularly serviced by recognised professional service centres to ensure the safety of themselves and their occupants.”

Onboard safety equipment, especially fire extinguishers, should be in good working condition, and Club Marine suggests owners of inboard petrol-powered craft consider installing quality vapour detectors, ventilation units such as bilge blowers, and warning systems on their craft.

For reference, owners of ski boats and other inboard petrol-powered craft can refer to Club Marine’s Inboard Inspection Report, which can be found in the Forms section of the company’s website at: www.clubmarine.com.au.

For a final word I spoke with Senior Sergeant Bob McDonald, a long-term veteran of the South Australian Police Water Operations Unit, who reiterated the points made above. Sergeant McDonald stressed the need for proper maintenance carried out by properly trained and experienced marine technicians and that boat owners should be aware of the potential trouble spots on their own craft and to keep an eye on them accordingly. He pointed out that a significant number of fires and explosions do not necessarily occur with the first start-up of the day, but rather after the craft has been running for a while. Ventilating the engine compartment before attempting to start the engine is a key factor to keep in mind.

The best approach to take, especially with older carburetted craft, is that you should anticipate the possibility of a fuel leak and take the appropriate precautions, as outlined above. And if you’re considering purchasing an older petrol-fuelled craft, but are unsure about its mechanical or electrical status, be sure to consult a local expert.

If in doubt, don’t hesitate to call Club Marine on 1300 00 CLUB (2582) and we’ll put you in touch with an appropriate boat shop or dealer.

How to-Safety