If I was armed, I'd think it was the end of Ramadan and plunder the entire convoy! By the time anybody had responded to a 'mayday call' I'd be inside somebody's territorial waters and 'home free'.
There have been a couple of more thoughtful studies done on this. Statistically (based on actual rather than possible he said/she said attacks). Most attacks occur at the local weekend and seem to be carried out by 'people smugglers' who go for targets of opportunity en route with illegal migrants from Africa to Arabia. There was an article reproduced in The Andaman Sea Pilot which talks about piracy around Indonesia. It would appear that the problem there is also largely an 'urban myth'.
Obviously, one has to take some precautions and not be naieve about this but I think the problem is exaggerated.