A device for holding a boat speedometer log transmitter in a boat hull has a sleeve body fixed in a perforation in the hull with a longitudinal center opening for removably inserting and retaining the log transmitter in a watertight manner. A head part is coupled to the longitudinal opening for jointly receiving the log transmitter in a watertight manner. An axially displaceable sliding ring is located in a coaxial recess in the head part. A plane ring body supporting a sealing ring is located below the sliding ring. The sliding ring and sealing ring define a plane for guiding a transversely movable blocking slide which blocks and opens the openings for removal and insertion of the log transmitter.