Engineer Doug Oakervee said he was encouraged by the visit
London's mayor visited an area off the Kent coast where he believes an island airport could be built.
Boris Johnson was accompanied on his Thames estuary trip by engineer Doug Oakervee, who helped mastermind Hong Kong's island airport.
Mr Johnson believes an island solution is an alternative to government plans to build a third runway at Heathrow.
Kent County Council leader Paul Carter said his plan was "environmentally and ecologically" a very bad idea.
Heathrow handles more than 500,000 take-offs and landings a year.
Transport Secretary Geoff Hoon gave the go-ahead for a third runway at Heathrow on 15 January, saying the airport was "our most important international gateway".
Mr Johnson, who spoke about the possibility of a new airport during the mayoral elections, said: "[The] trip has reaffirmed in my mind that a new airport in the Thames estuary has got to be factored in as an option for London's long-term aviation needs."
Also on board the 400ft dredger in the Thames estuary was Nick Raynsford MP, chairman of a cross-party parliamentary group that is looking at the plans for the island airport.
But Kent County Council leader Paul Carter said he would fight any proposals to build an airport off the Kent coast.
He said: "Environmentally and ecologically it's a very bad idea to build an airport off one of the most beautiful coastlines in the South East. To say it will be an eyesore is the understatement of the year. It would be totally horrendous."