"Sea card" is a relatively uncommon term, and finding synonyms for it can be a bit of a challenge. However, a few potential alternatives can be considered. One option could be "nautical chart" which refers to a detailed map showcasing marine navigation information. "Seafaring map" can also be used, indicating a map specifically designed for seafarers or sailors. Another possibility is "marine atlas", which captures the essence of a collection of maps and navigational information dedicated to the sea. While these terms may have slight variations in meaning, they all relate to maps or charts used for navigating the sea, and can serve as synonyms for the somewhat elusive term "sea card."