"Boskalis has concluded that the intended offer price per share communicated by HAL is not unreasonable, but in its opinion not sufficiently convincing to recommend this price to its shareholders," the company said in a statement.

Discussions it had entered into with the bidder in the past few weeks to convince it to increase the offered price had not been successful, it added.

HAL, also Dutch, already owns more than 50% of Boskalis. In March, it said it intended to offer 32.50 euros per share in the marine services company in a deal that would value the target at 4.2 billion euros ($4.52 billion).

Boskalis decided to present the offer with a neutral view on the price, giving its shareholders "the optionality to tender the shares under the intended offer (if and when launched) if they wish to do so," it said on Friday.

The bid comes at a bright time for Boskalis, as it has recently raised its full-year core profit forecast, pointing to a well-filled order book and favourable market outlook in the short and medium terms.

Boskalis's order book stood at 5.5 billion euros at the end of March.

In a separate statement, HAL said it expected to launch the offer in the second half of June, with closure targeted for the third quarter of this year.

The companies also reached an agreement on non-financial covenants, including strategy, governance, organization, financing and employees, which Boskalis will positively recommend to its shareholders.

($1 = 0.9301 euros)

(Reporting by Piotr Lipinski in Gdansk; editing by Jason Neely and Bradley Perrett)