Craig Allen Dodd, 30, from Guernsey, and Oliver Butler, 35, from Jersey, were both given six years for smuggling 7.5kg of cannabis resin by sea.
Dodd was also given a consecutive seven-year jail term for importing 250g of heroin, worth about £150,000.
Guernsey's Royal Court heard both had previous convictions for drug-related offences.
Judge Russell Finch said: "These were not small scale offences, but determined attempts to bring large quantities of drugs into the island."
The pair were arrested in September 2013 during a police and customs operation investigating suspected importation at Bec du Nez, a secluded spot on the island's east coast.
The cannabis, worth £190,000, was found in a rucksack hidden under some wood near an old fishing boat.
In February of the same year, Dodd was arrested after arriving by jet-ski at the QEII marina, in St Peter Port, where customs officers later found a bag containing the heroin lodged between a pontoon floorboard and the walkway.
Phone messages, including one saying "leave stuff in the bunker, and I'll leave the money when I get there", and analysis of Dodd's phone showed he had been in France that day.
Two Channel Islanders have been jailed for a total of 19 years after trying to import drugs worth more than £300,000.