INVESTIGATION

CASE 25
Petrol Fumes Plus Bow Thruster Equals Explosion
Narrative
A 17m sailing yacht was being manoeuvred in
an anchorage in the Mediterranean when the
owner, who was at the helm, activated the bow
thruster to keep the yacht head to wind. There
was an immediate explosion in the forward sail
locker that blew many of the hatches out of
the deck and badly damaged several bulkheads
and other parts of the interior. Two crew
members, who were on the foredeck preparing
to anchor, were unhurt and the hull remained
watertight. The owner was also unharmed.
On the previous day, with the professional
skipper having left the yacht for a holiday,
leaving the remaining crew member on board
alone, a local fuel supplier had asked whether
he could sell her any fuel. The 20 litre plastic
fuel can that was used for storing petrol for
the yacht’s tender’s outboard motor needed
topping up so the transaction took place. The
fuel tank was usually stored on deck but on
this occasion the crew member stowed the can
in the sail locker, which was located forward
of the main accommodation areas of the yacht
just aft of the anchor locker. The bow thruster
was located in a compartment within the sail
locker.
Yacht bow thrusters use powerful electric
motors that may generate sparks as part of
their normal operation. The full petrol can
had released vapour, possibly due to a change
in temperature or through having not been
properly sealed, and this was ignited on the
first operation of the bow thruster. Thankfully
for all concerned the fuel can did not rupture
in the explosion and there was no resultant
fire. The yacht was transported to a boatyard
for extensive repairs.
Figure 1: Typical bow thruster installation showing electric motor and dedicated batteries
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MAIB Safety Digest 1/2017