The PK is built to ram suspect boats, and this is for a purpose.
There are no feasible weapons mounted on the PK to effectively fire
at the boat's engines, let alone doing it at high speed out at sea
at 9pm. The chances of gunfire hitting the passengers are high.
Ramming the engines is likely to be far less dangerous than firing
a HK-MP5 at the boat, although of couse this is from the
perspective of the escaping crewmen, while the officers themselves
are in greater risk. But the police, in typical fashion, would much
rather explain an incident affecting its own men than one where the
public would consider as exessive use of force.