I have family members cruising around the world on their boat and they plan to spend some time in Phuket...There is a port of entry there where people on foreign boats go through Immigration but I wonder whether they would get 15 days or 30 days. Does anyone know ? Obviously a tourist visa is an option, especially if standard entry will be only 15 days.

It depends on the nationality of your friends.

www.mfa.go.th/web/2482.php?id=2490

It depends on the nationality of your friends.

www.mfa.go.th/web/2482.php?id=2490

If the persons concerned are one of the nationalites per Maestro's link, they will be given 30 days, if arrving by vessel, certainly in the case of Songkla and Sattahip ports

Best port of entry is probably Chalong Bay at Phuket. They have the one-stop checkin at the end of the pier, all about as simple as can be. Check-in hours 0900-1600, 12-13 lunch break. If arrive on weekend just check in on Monday. Sail into Chalong Bay, anchor among the other private boat, not with the diveboats. Go ashore in Dinghy for checkin. Not overly rigid about arrival, just check in reasonably soon thereafter. No officials go to boats, all very on the up-and-up. Shopping just as you get off the end of the pier. Avoid the tuk-tuks/taxis who are notorious for ripoffs and bad behavior anywhere on Phuket.