Complex sentence: The 12.9 metre vessel built of aluminum alloy is self-righting even when damaged, is powered by two turbocharged diesel engines that allow it to achieve 12 knots in calm seas.
Split into simpler sentences: The 12.9 metre vessel is built of aluminum alloy and is self-righting even when damaged. It is powered by two turbocharged diesel engines that allow it to achieve 12 knots in calm seas.