Maldives president Abdulla Yameen has described his deputy as a threat to national security, after his arrest over an alleged assassination attempt last month.
Mr Yameen claimed bomb-making materials had been found during raids on Ahmed Adeeb's associates.
The president was unhurt in the blast on his speedboat, which left his wife and two others slightly injured.
In recent years, the Maldives has been rocked by political infighting.
"The vice-president is being detained for the safety and security of the entire nation," Mr Yameen said in a televised address.
He said the investigation pointed to links between Mr Adeeb and two soldiers who were arrested for tampering with evidence on the boat soon after the blast.
President Yameen and his wife were travelling to the capital Male from the island where the airport is located when the device went off under a seat normally - but not in this instance - occupied by Mr Yameen.
Soon after the blast, speculation began to grow that Mr Adeeb was involved, reports said. Under the Maldivian constitution, the vice-president succeeds the president if he dies, is incapacitated or resigns.
Mr Adeeb, who is among seven people being held for questioning, has denied any links to the explosion.
A court ordered his detention for 15 days to give police more time to investigate.
Earlier, the government said Mr Adeeb would be charged with "high treason".
But the president said he would not fire Mr Adeeb until his case had been decided by a court.
Mr Adeeb became vice president in July at the age of 33. Mr Yameen was instrumental in his rise, sacking the previous vice-president, also on charges of treason, and lowering the minimum age for the president and vice-president from 35 to 30.
The Maldives became a multiparty democracy in 2008 and is a popular upmarket tourist destination, but its image has suffered in recent years due to prolonged political unrest.
Who's who in the Maldives
- Abdulla Yameen - became president after 2013 elections that were plagued with problems. He is the half-brother of former President Maumoon Abdul Gayoom
- Mohamed Nasheed - the country's first democratically elected president, he was forced to step down in 2012 in what he described as a coup. Now serving a 13-year sentence under anti-terror laws
- Ahmed Adeeb - vice-president charged with treason in October 2015 in connection with an alleged plot to assassinate President Yameen
- Maumoon Abdul Gayoom - was Asia's longest serving leader until his 30 years of autocratic rule came to an end in 2008
- Mohammed Waheed Hassan - president from February 2012 to November 2013 - he came to power following the disputed resignation of Mohamed Nasheed
- Mohamed Jameel Ahmed - the fourth vice president of the Maldives from 2013 to 2015. Removed from office after he was impeached