Nuclear families form the primary residential boat unit. Five to ten boats form a community and travel together. Communities come together annually, forming flotillas of up to thirty or forty boats. During the southwest monsoon, boat flotillas form in protected bays to wait out the bad weather. Most Moken communities rarely wander more than about 50 kilometers in any direction from their home-base island. For most of the year, maritime Moken reside on 6to 8-meter-long dugouts constructed with a deck and sailing mast made from palm sheets. The sides of the boat are built up with stems of a palm placed one on top of the other, caulked with tree resin, and lashed together. Amidship, Moken build a hearth with earth on the deck to avoid fire. A sheltered living area, built on deck toward the boat's stern, is constructed of split bamboo arch supports covered with a removable palmleaf roof, which can be rolled up and stowed away or used as a shelter on shore. When Moken anchor near shore they either build small temporary beach huts or, more typically, continue to reside on boats. Sedentarized Moken construct single-room houses on stilts on the strand or out in the water.