As an archipelago, inter-island travel using watercraft is often necessary. Boats have always been important to societies in the Philippines. Most boats are double-outrigger vessels, which can reach up to  in length, known as ''banca''/''bangka'', ''parao'', prahu, or ''balanghay''. A variety of boat types are used throughout the islands, such as dugouts (''baloto'') and house-boats like the ''lepa-lepa''. Terms such as ''bangka'' and ''baroto'' are also used as general names for a variety of boat types. Modern ships use plywood in place of logs and motor engines in place of sails. These ships are used both for fishing and for inter-island travel. The principal seaports of Manila, Batangas, Subic Bay, Cebu, Iloilo, Davao, Cagayan de Oro, General Santos, and Zamboanga form part of the ASEAN Transport Network. The Pasig River Ferry serves the cities of Manila, Makati, Mandaluyong, Pasig and Marikina in Metro Manila.