Ferry In, Fly Out

You can really combine the methods of travel. It is only the itinerary that matters and it has to have the immediate points before and after your mainland Chinese visit in two different countries or eligible territories (eligible territories are Hong Kong, Taiwan and Macau). As you can see, your itinerary is definitely eligible for 240 hour visa free transit. As far as the taking of the ferry from Hong Kong is concerned, I would like to inform you that only two ports in Guangdong province are eligible for entry while using 240 hour visa free transit and they are Shekou in Shenzhen and Nansha in Guangzhou. Please, do not use any other port in Guangzhou beside Nansha since Nansha is the only eligible in Guangzhou city area and not a single one beside it. Fortunately, there are direct ferries from Hong Kong to Nansha, so you can use it for your travel plan. Have a nice visit to China.