Method of installing an underwater riser

A method of installing a subsea riser for carrying hydrocarbons between a sea bed and a surface, said method comprising:

• installing a seabed installation anchored to said sea bed;
• connecting a pipe connecting end to said seabed installation and providing an opposite end of said connecting pipe with a submersible float;
• permitting water to enter said float submerging said float and said connecting pipe while holding said float and said pipe by a suspension line from a surface vessel, wherein said suspension line bears tensile forces corresponding to the weight of said float and of said pipe;
• installing a pulling cable and a return device on said seabed installation and connecting said pulling cable to said connecting end of said pipe, driving said cable on said return device and driving said connecting end toward said seabed installation;
• attaching a submerged pulling buoy to said pulling cable applying additional tensile forces to said suspension line;
• then supplying a gaseous fluid in said float to compensate for tensile forces corresponding to the weight of said float and of said pipe and for at least some of the additional tensile forces;
• and
• anchoring said pulling buoy to said seabed installation, and gradually releasing said suspension line from said seabed installation so that said seabed installation takes up said additional tensile forces applied by said pulling buoy, whereas said float applies a remainder of said additional tensile forces to said pipe in order to hold it vertically.