This paper presents a study of sea-water monopole antenna at very high frequency (VHF) band for maritime wireless communications. The sea-water monopole antenna consists of a feeding probe and a sea-water cylinder held by a clear acrylic tube. The feeding probe is loaded with a disk on the top to improve the excitation of TM mode. A theoretical study of the sea-water monopole antenna based on the three-term theory is presented, which has not appeared in literature. Commercial software packages ANSYS HFSS and FEKO are used to simulate this antenna. Experimental results of a fabricated sea-water monopole antenna with a radius of 50 mm show reasonably good agreement with theoretical predictions. Measurement shows that the proposed sea-water antenna has high radiation efficiency. Meanwhile, due to the transparency and liquidity of sea water, the proposed antenna is almost optically transparent and can be easily reconfigurable. The center frequency of the antenna is tunable by lengthening or shortening the water cylinder, while the bandwidth of the antenna can be adjusted by widening or narrowing the water cylinder.