“A Liberian-flagged bulk carrier is taking on water and not under the command of its crew after being hit by a Houthi drone boat…The Liberian bulk carrier Tutor was struck by a Houthi uncrewed surface vessel (USV) while transiting the Red Sea, the first such successful strike since the Yemen-based rebel group began attacking shipping in the region…”
The Houthi ballistic missiles and Unmanned Air Systems (UAS) have gotten a lot of press, but if you really want to hurt a ship, nothing works as well as placing large amounts of explosive next to the hull at or below the waterline.
Not impossible we will see something like this used in a terrorist attack.
Chuck Hill's CG Blog 
Getting to the point can be made with hobbyist parts available on line – and you can buy I think 3 foot long RC boats online – range is limited and not damage a tanker – but do other damage
Easy enough to make almost any motorboat or personal watercraft remote controlled.
and very hard to know where the controller is. Remote control signals of hobby gear can be jammed if you are ready to do that but also easy to have it guided by GPS waypoints to any known position.
A few years ago much concern about packing a recreational boat with explosives and remote control – several stories aimed at recreational boat owners to call law enforcement if we saw someone turning their boat into a bomb
If you want to scare someone just tie a boat under a bridge and leave it
yes RC can be jammed but someone needs to be expecting an attack and be ready for it