According to the 1983 amendment to the SOLAS regulations 1974 in Chapter III Regulation 6, at least 3 two-way radiotelephones shall be provided on every cargo ship of 500 gross tons or more. The two-way radiotelephone enables communication between the survival craft, the ship, and the rescue boat Precautions shall be taken to prevent the inadvertent selection of VHF channel 16 on equipment capable of being operated on that frequency. A watertight model is required for satisfying GMDSS requirements (1988 amendment).