from Positano to Naples
 

How will it be, if I take ferry from Positano to Naples, than take a cap to the airport. Will it be convinient? How long will it take?

Hydrofoil from Positano to Naples Mergellina takes 45 minutes. From there to the airport by cab takes 20-30 minutes.

Depending on where your hotel is in Positano and the weight of your luggage, the trek to the hydrofoil dock could be long an arduous, especially in the heat.

get the train to naples from positano - approx one hour and far cheaper

The train from Naples only as far as Sorrento or Salerno. From there, you need to proceed by SITA bus or by boat. It's faster to take the hydrofoil from Naples Mergellina direct to Positano. Before arriving in Positano, you may need to make arrangements with the hotel for assistance with luggage (if the hotel is far from the dock).