(Updates with details, quote from Boskalis CEO)

AMSTERDAM, March 10 (Reuters) - Dutch investor HAL Holding NV on Thursday said it would launch an offer to buy dredging and marine services firm Boskalis in a deal that would value the Dutch company at 4.2 billion euros ($4.7 billion).

Boskalis's Smit Salvage division is well known for its rescue operations, notably playing an important role in the re-floating of the Ever Given ship in the Suez Canal last year.

HAL, which already owns 46.2% of Boskalis, said it would offer 32.50 euros per share, a premium of 28% to Boskalis' closing price of 25.30 euros on Wednesday.

Shares opened more than 30% higher at the start of trade and were at 32.92 by 0824 GMT in Amsterdam.

Boskalis confirmed it had received the unsolicited offer from HAL and said it would carefully consider it.

"I have absolutely no opinion yet about the bid, whether I think it's high or low or opportunistic," CEO Peter Berdowski on a call with reporters.

He said the company would take on external advisers to weigh the bid, and consider interests of other minority shareholders and the company's 10,000 employees before responding.

The offer comes as Boskalis's outlook is bright, with an order book of 5.41 billion euros at year end, thanks in part to contracts servicing offshore wind farms and dredging projects in Southeast Asia.

The company reported a 2021 net profit of 151 million euros, reversing a loss of 97 million euros in 2020. Revenues were up 17% to 2.96 billion euros.

Curacao-based HAL, whose name derives from the Holland America Line, is stock market listed but majority owned by the wealthy Dutch Van der Vorm family.

HAL said if its cash offer is successful it intends to keep Boskalis's current management in place and would not change the company's strategic direction.

HAL has one seat on Boskalis's board, but that board member will not participate in the takeover deliberations.

When asked about the Ukraine crisis, Berdowski said it was too early to assess the impact of the war and Russian sanctions on its earnings. The company had a small office in St. Petersburg but has halted Russian operations and returned staff to the Netherlands.

Among Smit Salvage's many well-known operations is its role in the raising of the Kursk nuclear submarine from the floor of the Barents Sea in 2001.

($1 = 0.9038 euros) (Reporting by Bart Meijer; Editing by Tom Hogue, Stephen Coates and Jane Merriman)