( CNN ) -- The South Korean ferry that sank dramatically on Wednesday with hundreds of passengers on board had been modified after coming to the country from Japan over a year ago , according to reports on CNN affiliate YTN . The Sewol -- operated by Chonghaejin Marine Corporation -- regularly plied the Incheon to Jeju route , a journey that usually takes 13-and-a-half hours , according to information from the company 's website . Jeju is a popular destination in South Korea -- known as the `` Hawaii of South Korea . '' The Sewol is listed at 146 meters long and with a gross tonnage of almost 7,000 tons . It boasts five cargo and accommodation decks . It is listed as having a capacity of 921 passengers , but was only carrying a reported 429 when it unexpectedly started taking on water early on Wednesday . Within hours , all that was above the water surface was the bow of the boat . The ferry was built in a Japanese shipyard 20 years ago and previously operated in that country 's waters . It was refitted upon arrival in South Korea in February 2013 , YTN reported . The ship 's sleeping cabins were reconstructed after its arrival in South Korea , the network said . Korea Diving Industry Institute president Jung Yong-hyun , a former general in the Korean Navy and former commander of the Ship Salvage Unit ( SSU ) told YTN that the refit may have affected the weight of the boat and could be a reason for the accident . According to Jung , the reconstruction added around 239 tons of weight to the boat from its original form . Investigators probing the incident will likely look at various aspects of the boat , including this reconstruction . `` As the center of the weight of the boat becomes higher , it becomes more difficult for the boat to balance , '' the expert told YTN . There have been serious ferry accidents in South Korea before . The most recent maritime accident occurred in 1993 . This was attributed to overcrowding . The Sewol , however , was nowhere near capacity on the night of the 15th , when it left Incheon several hours late -- delayed because of heavy fog . Tough conditions . With difficult circumstances hampering rescue dives -- including tidal currents , choppy , frigid conditions , wind , rain and seabound fog -- more radical engineering solutions are being explored . At around noon on Thursday local time , workers began trying to pump air into the boat , hoping air pockets might be expanded within the structure , helping to lift the ferry . These efforts have proved unsuccessful so far . Authorities say that they will try again when the tide turns . Analyst Jung Yong-hyun told YTN this method has been used previously , on the Costa Concordia and Cheonhanham warship wrecks , as example . Three 3,600-ton `` sea cranes '' are due to arrive Friday to assist with efforts . `` The cranes are being moved as fast as possible , the focus is getting them there early , '' said Choi Myeong-beom , a Ministries of Oceans and Fisheries representative . `` What will be done with them will be determined by the Coast Guard on site . `` If the boat has not been stuck into the seabed then we will raise ( it to ) the surface with cranes and move them to a place where it will be easier to work on them . ''
Difficult conditions are hampering search efforts . She was abandoned upon arrival in Korea in February last year . Rescue workers have been attempting to pump water into the vessel . Three giant ` ` ' cranes '' dispatched to the scene .