Ko Wa Yai. No idea what the name means, but it's the largest island in the bay leading to Yacht Haven Marina. We anchored around HERE in about 3m of water (at low tide). With the tide we were able to get here in about 1.5 hours motoring from Yacht Haven (no wind, no sailing).
The island is visited by a small number of speed boats and long tails carrying tourists during the daytime. Around 4pm these all depart, leaving the island mostly deserted.
The island has a hiking trail, bar, and restaurant. There's a bathroom that might be one of the smelliest and dirtiest in Thailand (at least in my experience). And there's an outdoor shower setup which wasn't working (no water) when we were visiting. There are also some bungalows and areas for camping. The beach and surrounding area are kept very tidy.
The west side of the island features a nice sandy beach with very shallow water extending far into the surrounding water. This is the side we anchored on for the night.
The sunset from this anchorage was nice, setting over the distant hills of the Thai mainland to the west. Ko Pay Yu is 1.3nm west-northwest of Wa Yai. Had the wind or swell come up, we could have tucked into the eastern side of Pay Yu, but the forecast during our stay called for very light winds all night.
Ko Wa Yai is the largest island you'll pass (and the last big one) on the way out of the bay from Yacht Haven Marina. Just east of Wa Yai is Wa Noi - forming a gate to the channel with Ko Than An to the south.