The accident, which took place on 5 May, 2013, occurred when all six occupants of the 8m rigid inflatable boat Milly were ejected from the boat into the water as it was making a turn in the Camel Estuary. The engine cut-out kill cord mechanism was not activated as it had not been attached to the driver. Consequently, the boat continued to circle with no one at the helm, at full power, striking some of those in the water, fatally injuring two and seriously injuring two others.
"It is considered poor practice to drive a craft at speed with passengers loose at the forward end of the craft. Not only are the motions in that area more violent than those at the helm position but the centre of gravity of the craft is moved forward which can be detrimental to directional stability."
As part of the investigation, MAIB undertook water trials to better understand the accident scenario and how the boat acted during high-speed turns. Reporting on those turns, a naval architect, commissioned to make a detailed examination of the vessel, noted that: “When executing the turns, the craft initially would take up a high-heel angle. It would proceed to turn, but if the speed was slightly higher than a particular threshold and the turn tighter than a certain degree, the heel angle would increase during the turn, and the aft end would lose grip and slide – thus initiating a ‘partial spin’ or ‘hook’ since the bow did not slide by the same amount. This rapidly took the craft to a position which was appreciably diverted from its original course. The craft would execute a sideways slide and grip suddenly when it landed. Thus the hull’s sideways motion was suddenly stopped.”
"The highest transverse forces were experienced when the boat ‘hooked’ and then returned violently to the upright from heel angles of 40 degrees," the naval architect further added. "It was found on one turn that the boat had role 30 degrees in less than half a second. The nature of the seating in the forward part of the RIB did not provide adequate security against sudden, violent motion. Further, the conservation of momentum experienced by the occupants during such a manoeuvre would have meant that the children would have been unlikely to have been able to keep of the grab ropes on top of the tubes in the forward seating area, even if a warning had been given that the boat was about to be turned."
The naval architect’s analysis also stated that: “It is considered poor practice to drive a craft at speed with passengers loose at the forward end of the craft. Not only are the motions in that area more violent than those at the helm position but the centre of gravity of the craft is moved forward which can be detrimental to directional stability.” This is a particularly pertinent lesson for superyacht crew involved in tender operations who often drive families that may be unaware of the above safety concerns.
As a result of the investigation, MAIB has addressed a number of safety issues. “The evidence of this and previous accidents would indicate that kill cord use is still sporadic, and that much more needs to be done to make attaching a kill cord second-nature when taking over the helm of a powerboat," concludes the report. "Furthermore, Mr and Mrs Milligan were unaware of the hazards associated with allowing their children to sit and stand in front of their RIB while it was travelling and turning at high speed."
The full report on the incident can be read here. To participate in our debate about incident reporting in the superyacht industry, please click here.