I had been staying in Phuket before my stay at the Santhiya so I took a taxi to the Marina and had arranged to take the speedboat as required. However, I was not given any information on where to meet the speedboat or if I was supposed to check in with any hotel staff somewhere. I was able to find the speedboat thanks to helpful people around the marina, but the staff at the boat kept asking me if I had checked in. They were not able to tell me where, and after some walkie-talkie and telephone discussions by staff, someone was able to find my name on their list and I was able to board the boat. I do not know if the Sanythiya has a procedure for checking in guests who have not taken the airport shuttle, or if I missed a desk/office at the Marina which belonged to the Santhiya but no one was able to direct me elsewhere.
Keep in mind that Check-In at the Santhiya is 3pm, and if you arrive before that time your room will likely not be available yet! The hotel staff take your luggage when you arrive off the speedboat so while I enjoyed an hour or so at a restaurant getting lunch and waiting for my room, I would have enjoyed my time more if I had grabbed my swimsuit first. I wish the Santhiya had encouraged me to book a later speedboat so I would arrive when my room was ready.
The facilities are fabulous and the buffet breakfast was always a very welcome sight. I can't rave about things more than everyone else already has so just trust me that you will have a fabulous time here.