To ensure safe navigation, navigators collect various types of navigational information, such as geographical conditions, movements of other ships, and weather and sea state during voyages. In recent years, services providing navigational information via the Internet have been developed. These services are especially useful for small ships with limited costs because they do not require specialized equipment such as Automatic Identification System (AIS). However, these services are inadequate for actual navigation because they cannot obtain information on non-AIS ships. In this research, we propose a ship navigational information system that utilizes smartphone sensor data. By using smartphones equipped with location services, gyroscopes, and acceleration sensors, even non-AIS ships can share their navigational information with surrounding ships. Furthermore, small ships that cannot be equipped with so many nautical instruments can obtain the geographical conditions, the movements of other ships, and the impact of weather and sea state on their own ships via a TCP/IP network. A prototype web application was developed and tested on a real ship to verify that it can provide users with navigational information.