Start with the ships. A meal, ride or lake walk is a separate stop, so check it independently before extending the visit.
What the park contains
Dangjin describes Hamsang Park as a naval-history site with two decommissioned ships. One was refitted as an exhibition space; the other is displayed in its original state. The city gives the address as 79 Sapgyocheon 3-gil, Sinpyeong-myeon, Dangjin. Check the city's Hamsang Park page for current ticketing and visitor details before setting the route.
Plan around the café, not as a separate free stop
The Hamsan Café is inside the park and is limited to visitors who have bought a Hamsang Park admission ticket. Dangjin lists its hours as 09:00–18:00 in spring and summer, and 09:00–17:30 in autumn and winter. The café overlooks the West Sea and Seohaedaegyo Bridge.
Use the ships as the fixed visit, then add one waterfront or food stop if the actual opening and return fit. The nearby amusement park, marine experience centre and lake promenade are separate venues, so the city overview does not establish a shared ticket or schedule for them.