1. It falls into the category of surface trailer objects.

Article 2 (Interpretation) of the Speedboat Laws from 1992 to 2001 - Law 56 (I) / 1992):
"trailer object" means any object that does not have its own independent mechanical power but it is hauled by a high-speed vessel, and for the purposes of this Law it also refers to any person who is hauled by the vessel.
2. Any person who is towed by the trailer must wear a life jacket or have a kind of buoyancy aid device.
Article 2 (Interpretation) of the Cruiser Laws from 1992 to 2001 - Law 56 (I) / 1992):
"Lifejacket" means a type of personal clothing that can be easily worn and securely fastened to the body of an adult person or a child, has buoyancy of at least fifteen (15) kilograms, without having to be filled with air, carries a whistle , has a distinct color and finally it is capable of holding the head of a user who does not keep his senses out of the water.
'buoyancy device' means a type of individual attachment which can be easily and securely worn and secured to the body of an adult person or a child, its buoyancy has to be equal to at least 10% of the weight of the person who wears it, without having to be filled with air and finally it has a distinct color.
Section 5 (1) (Speedboat Operator Obligations) of the High Speed Boats Laws from 1992 to 2001; L. 56 (I) / 1992):
The boat operator, must ensure that any person who is carried or towed by a vessel must wear a lifejacket or has or a buoyancy aid device.
Provisions for the safe use and operation of the surface trailer objects.
3. Regulation 27 (Surface Trailers) of the Speed Boats Regulations 1999 - CP 121/1999:
27. (1) Α surface trailer is any trailer towed on the sea surface.
(2) It is prohibited the use of towing rope and any machinery and articles that are used in order to tow a trailing surface object violating the manufacturer's specifications or, in the absence thereof the practice gained by the marine experience. 
(3) Rope fastening points which should not exceed 50 meters in length, or any other towing means to the high-speed boat and to the surface trailer, and all the mechanisms and materials must be in excellent condition and must be controlled by the owner and the boat’s operator too.
 (4) Whenever a towed surface object is used, the owner and the operator of the high-speed boat must ensure that a second person is on board the boat who supervises the towing procedure, given the fact that the boat's construction  requires so.
 (5) The owner and the operator of a high-speed boat must never tow a towed trailer object in a surface less than 200 meters from the nearest shore, and less than 100 meters away from the signaled area of the bathing area adjacent to the shore.
6) The owner and the boat operator must ensure that any person who is towed by a seawater towing boat, wears a life-jacket or has a buoyancy device and complies with the provisions of these Regulations.
(7) The towing of a towed trailer surface vessel by the owner and the operator of a high-speed boat is prohibited if violating the 16 knot wind speed limit for safe use or when the sea conditions are wavy, as well as before sunrise and after sunset.
4. The maximum rental rates for surface trailers (including VAT) are set out in KPD 135/2015.