Here's something I posted in another thread:
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http://www.m-i-link.com sometimes displays jobs for the marine industry. Alternatively,
http://www.jobstreet.com has quite a bit of shipping / logistics stuff. Click on 'Singapore' and search under 'shipping'. You can also try to contact shipping companies directly. Doa google for 'Riverchelles', they specialise in Marine / Logistics job placements.>>
Further,
http://www.singaporemaritimeportal.com has an extensive list of Shipping, Salvage, Tug/Barge companies (try clicking on their member's list, if I remember correctly).
By the way, what sort of container experience do you have? Handling? Operations? Empties? Stowage planning? 3PL?
Most maritime-related jobs are not listed, so call the companies directly. As for PSA, you have to download and print out their application form and post it to them. Another port you may want to try is Jurong Port
http://www.jp.com.sg or Port of Tanjung Pelepas, which is half owned by Maersk and located just across the causeway in Johor Baruh (Malaysia)
http://www.ptp.com.my
Happy searching!!