Have you ever dived on the Phinisi liveaboard to the South Andaman as that's who I'm currently looking at for later this year?
Never done Losin but have read good reports. Did you recommend any other operators for this trip than the one you mentioned?
Never been on the Phinisi. It's a relatively new boat, isn't it?
I first did Losin about a decade ago when one of the only boats going there was the Scuba Explorer which was operated in the Gulf by Samui Dive Service. Most of those trips were long hauls between Songkhla and Koh Tao (direction depending on the season). A few years back we went on Scuba Net and had a great time. (Whale Shark!). It's a rather uncommon trip, so you might just pick a boat that meets your schedule. I'd avoid boats that throw in Lopi and/or visit the artificial reefs which consist mostly of old railroad coaches, garbage trucks and ancient battle tanks.
@Centrals - Don't know what to tell you about Tapana. They've always been responsive, but we usually book through an agent. Sainamtalay PADI Dive Center