The Lonely Planet’s Thorn Tree travel forum has a discussion thread about whether it is possible to go from Borneo to Singapore by boat.
The answer is yes, you can go to Singapore from Borneo by boat according to one participant, but not directly as there is no boat service connecting the two islands.
So the key is to find Batam in Indonesia from Borneo. Once there, it’s just a matter of a short one hour of comfortable boat ride to Singapore’s Harbour Front ferry terminal.
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