SINGAPORE - A serial molester groped a woman on a Batam to Singapore ferry three times in front of her husband and two children because he thought she had a "good figure", a court heard.

Jobless Tan Yew Song, 53 - who has a string of molestation convictions dating back to 1983 - was jailed for eight months on Thursday after he pleaded guilty to three charges of molesting the 38-year-old, less than four months since he was released from jail.

The ferry was in Singapore waters when Tan first touched her buttock as he walked past her while she handed her children some noodles.

She thought it was an accident and even though he did it a second time, she decided not to pursue the matter.

But when he molested her a third time as she got up to disembark, she and her husband confronted Tan as he tried to walk away.

He apologised but the husband sought help from immigration officers, and Tan was detained.

Tan admitted that he deliberately touched her three times as he thought she had a "good figure".

Tan was jailed for four months on each count, with two of his sentences ordered to run consecutively. The jail term was backdated to the date of his remand on Jan 5.

Tan has seven previous convictions for outrage of modesty and two previous convictions for insulting the modesty of a woman. In 2001, he was sentenced to seven years' preventive detention with seven strokes of the cane.

The maximum penalty for using criminal force to outrage the modesty of a person is two years' jail, a fine, and caning. Those above 50 cannot be caned.