Wartsila said on Tuesday it saw significant synergies on costs and combined sales opportunities.
We see Hamworthy as an accelerated short cut to strengthen our market position in the offshore, marine and environmental products, Chief Executive Bjorn Rosengren told reporters.
Analysts said the deal was a strategic fit as Wartsila would be able to reinforce its technology portfolio while creating synergies by linking its service network with Hamworthy's offering.
Wartsila, which had announced talks with Hamworthy last week, said the 825 pence per share offer, backed by the Hamworthy board, valued the British company at about 383 million pounds, net of share options in the target company.
This is the right strategic move for them. Offshore and gas are the sectors which will grow, said analyst Markus Liimatainen at Helsinki-based brokerage FIM.
The price is not too cheap when looking at the multiples, but it seems somebody else has been interested in them too. However, Wartsila can easily afford these type of takeovers with their balance.
The bid is pitched at a 14.3 times multiple on the basis of Hamworthy's enterprise value against core earnings in the last fiscal year.
I think it would be adding to our earnings already in 2012. We will integrate Hamworthy directly after closing of the deal, CEO Rosengren told Reuters.
Wartsila said the takeover was expected to close in the first quarter in 2012. The acquisition is subject to regulatory approvals in Germany and Norway.
Analyst Keith Morris from Evolution Securities said he did not see counter bids likely.
Whilst we believe Wartsila sees Hamworthy as a 'must have', others who might be interested see Hamworthy as a 'nice to have' and are therefore unlikely to get embroiled in a bidding war, he wrote in a note for investors.
Gordon Page, Hamworthy's non-executive chairman, said the board considered the offer attractive for shareholders.
Wartsila had sales last year of 4.5 billion euros (3.8 billion pounds), while Hamworthy achieved revenue of 182 million pounds in its most recent financial year ended in March.
In October, Wartsila reported a bigger-than-expected fall in third-quarter profit and sales as some deliveries were delayed to the current quarter.
Wartsila shares were flat at 20.74 euros by 1030 GMT on the Helsinki bourse while Hamworthy rose 1.9 percent to 825p in London.
Hamworthy was advised on the deal by Hawkpoint and Wartsila by UBS.
(Additional reporting by Juhi Arora and Terhi Kinnunen; Editing by Jon Loades-Carter and Erica Billingham)