November net income declined 67 per cent to 11.3 billion won (S$17.6 million) from 34.2 billion won a year earlier, the Seoul- based company said in a regulatory filing yesterday.
Sales climbed 33 per cent to 723.4 billion won.
The won dropped 2.4 per cent against the US dollar from a year earlier in November, reducing the value of assets abroad when converted into the local currency.
The weaker won also cut gains from hedging contracts Daewoo Shipbuilding owns. The local currency gained 1.5 per cent in November last year.
Operating profit, or sales minus the cost of goods sold and administrative expenses, surged to 42.6 billion won last month, from three billion won a year earlier as the company built more vessels at higher prices.
Shipyards in South Korea, the world's biggest shipbuilding nation, may post their highest annual earnings as demand for vessels rises to a record for a fifth year.
Daewoo Shipbuilding is increasing production to meet an order backlog that stretches to more than three years.
Daewoo Shipbuilding delivered two container vessels and one liquefied petroleum carrier in November, it said.
The shipbuilder had received US$16.35 billion of new contracts at the end of November, increasing its backlog to US$34.48 billion. In the first 11 months, net income surged almost eightfold to 336.8 billion won, from 42.8 billion won a year earlier, Daewoo Shipbuilding said. It had an operating profit of 275 billion won, compared with a loss of 178.1 billion won. Sales climbed 30 per cent to 6.32 trillion won.
Daewoo Shipbuilding gained 0.2 per cent to close at 43,400 won ahead of the announcement. The stock has climbed 49 per cent this year, compared with a 28 per cent advance in South Korea's Kospi index.