Here's an example of Greenpeace blocking a russian liquid natural gas tanker from reaching port in Finland from September of last year, and here's an example of Greenpeace activists boarding a container ship containing paper to protest deforestation from November of last year, here's another example of the same group boarding a heavy lift vessel to protest offshore oil drilling from January of this year, and here's an example of some scamps vandalizing a wal-mart heiress's yacht from earlier this month.
You're absolutely right, that activists boarding ships or otherwise vandalizing them gets way less press and markedly less discussion than this protest has. Why do you think that is?
I wish this form of protest would catch on elsewhere as well. Every day I'm struck by the number of huge gas-guzzling pick up trucks parked around the city, and seemingly every bed completely empty. Letting out the air to their tires would certainly be slower and more work than the old method of puncturing their tires, but has the dual benefit of not necessitating replacement (which has a carbon cost of its own) and not enabling the vehicle owner to file an insurance claim.