Connection system for connecting a line to a marine device, which system comprises: a connection hole in the marine device, which establishes a communication pathway between an inside of the marine device and a zone outside of the marine device; a connector appliance associated to the line and configured to be coupled to the marine device in correspondence with said connection hole, said connector appliance comprising a first cover configured to cover a terminal of the line in a watertight manner, said first cover being configured so that it can be opened from the inside of the marine device when the connector appliance is coupled to the marine device in correspondence with said connection hole, in order to allow access to said terminal from the inside of the marine device; securing means for securing the connector appliance to the marine device, said securing means being disposed in such a way that they can be actuated from the inside of the marine device, so as to selectively secure the connector appliance to the marine device or release the connector appliance from the marine device; a second cover situated in the marine device and configured to cover the connection hole in a watertight manner, said second cover being configured to be able to be opened from the inside of the marine device, to allow access, from the inside of the marine device, to said first cover and to the terminal of the line; wherein said securing means comprise means for mechanical interconnection between the connector appliance and the marine device, characterised in that the securing means are disposed so that said means for mechanical interconnection can be actuated from the inside of the marine device when the second cover is not open. a connection hole in the marine device, which establishes a communication pathway between an inside of the marine device and a zone outside of the marine device; a connector appliance associated to the line and configured to be coupled to the marine device in correspondence with said connection hole, said connector appliance comprising a first cover configured to cover a terminal of the line in a watertight manner, said first cover being configured so that it can be opened from the inside of the marine device when the connector appliance is coupled to the marine device in correspondence with said connection hole, in order to allow access to said terminal from the inside of the marine device; securing means for securing the connector appliance to the marine device, said securing means being disposed in such a way that they can be actuated from the inside of the marine device, so as to selectively secure the connector appliance to the marine device or release the connector appliance from the marine device; a second cover situated in the marine device and configured to cover the connection hole in a watertight manner, said second cover being configured to be able to be opened from the inside of the marine device, to allow access, from the inside of the marine device, to said first cover and to the terminal of the line; wherein said securing means comprise means for mechanical interconnection between the connector appliance and the marine device, characterised in that the securing means are disposed so that said means for mechanical interconnection can be actuated from the inside of the marine device when the second cover is not open.