The raiders had bladed weapons, according to security consultancy Ambrey.
The Singapore Navy is reported to have acted swiftly when the vessel entered its waters, prompting the perpetrators to depart.
A search of the vessel was conducted and no items were reported missing.
The bulker had last called in Singapore and was en route to Lianyungang in China.
On Friday, the 33,500-dwt general cargoship Vantage Wave (built 2011) was boarded by three robbers while underway in the eastbound lane.
Nothing taken
The cargoship had also called in Singapore and was heading for Caofeidian, China.
The Vantage Wave is operated by Vantage Shipping of Greece.
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