There are multiple hydrofoils going back and forth every day because it's only a short distance from the ferry port in Kowloon. I think it's about 50 or 60 miles. A 60mph ferry won't be a very long ride, even dodging the sea traffic and going around the airport.

As far as I know, with a US passport no visa is required for Macau, just like HK, so it's a politically easy trip as well.

However, a jaunt into the PRC requires a visa which needs your picture and a long time to process, as well as a bunch of bucks.

The former colonies of Hong Kong (British) and Macau (Portugal) are now special administrative districts of the Peoples Republic of China, which mean the fences keep out Chinese and allow foreigners in. Mainland Chinese need visas to enter either, but the PRC uses both a source for hard currency, so they maintain gambling in Macau (illegal in the PRC) and manufacturing and trade in Hong Kong and make entry and exit relatively easy with a US Passport.

Hong Kong is a great town for a good time. Either on the cheap or on the American Express Card. Great food, adventure, and insight. The English bent in Hong Kong, Kowloon, or the New Territories takes a bit of the edge off the culture shock. Hope your friend has a great time.

Advise your friend to choose 1st class for comfort and 2nd class for a true Chinese adventure. I always went 1st class on the hydrofoils because it is more comfortable and orderly - but my trips were upwards of 3 hours up the Pearl River to Guangzhou (Canton). We got fed and had a movie and bar and my company foot the bill.