I'm sorry, but I strongly disagree! First off, pirates might be desperate, but they aren't stupid! They know their weapons and they know that they aren't going to do any damage with an RPG. I know RPGs seem like a scary deal, but the chances of actually hitting anything vital are virtually zero! These are dumb bombs with no particular charge made to cut through a stationary battle tank full of fuel and munitions. The worst thing they could do to a large ship with an RPG would be to take out a few navigational instruments (which have full redundancy anyway) or pierce a tank. And even if they were lucky enough to score a direct hit to a fuel tank, you'd get a leak but no explosion. This is not an explosive weapon, it is a cutting weapon. It works by instantly superheating and directing a jet of copper through metal. It is basically a flash in the pan! So you might need to do a bit of painting and mend a small hole in the tank, but nothing major! Even if they shot an RPG at a VLCC you'd probably not see any major damage. Definitely no explosion! To much fuel and no air. You'd need something like what they did to the Limberg in 2002! And anyway, what is a burning ship worth to the pirates?
If I encountered pirates pointing RPGs at me, the last thing I would do would be to slow down! I would point my ship straight at them and hopefully ram them - it is them or me! I know that the masters I have sailed with has the same attitude as we discuss it each time we transit the area (been through there 4 times from March to may). It is even in their standing orders that if we encounter pirates, we are to raise the general alarm and start evasive manouvers and if the pirates are so close that they'll actually be able to get onboard, we are to try and force them away (read: hit them). The last thing you would ever want on a container ship would be to be hijacked as the cargo is worth way more than they could ever hope to receive in ransom, so why would they need us once they have the ship in their possession?
This works on container vessels because they are big and fast. A tanker vessel however has another set of problems! They are basically sitting ducks! They can't manouver and because of the nature of their hull, the wash is dispersed outwards, so if you come up from behind they'll have relatively easy access to the ship despite them travelling at 15 kn. Tankers and small coasters are by far the most exposed vessels!
A cruise ship is ofcause a different matter, but again, you have to look at the alternative! What will happen if the pirates are successfull at hijacking a ship with 3-4000 people onboard. And then again, how many pirates do you think it would take to actually take control of such a massive vessel with so many wannabe-heroes? 4000 people with anything they can get their hands on against maybe 20 pirates with old soviet guns... Once again, they are pirates, not stupid!