I flung out an arm toward the surface of the lake, I hiked out hard, feet pressed into the hull, body horizontal. I flew and I danced my fingers in the waves as the boat jumped across the lake, and then, the water was all around me. It was syrupy, heavy and dense. Like gelatin. The shrouds lay sliver in the water, then drifted down, enveloped by the liquid, dulling to greenish grey, then, gone. I curled around the side of the boat, trying to pull myself over the capsized hull but my fingers scrabbled against slimy smoothness. I fell back into the wet, head held above water by the tension of my arms against the hull. I cursed myself for not getting the mast sealed; 20 feet of water-filled aluminum promised no chance of righting the boat. I kicked and my legs became entangled,

I flew and I danced my fingers in the waves as the boat jumped across the lake, and then, the water was all around me I wondered how he was flying, I don't know enough about the story/genre/MC yet to know if you mean this literally or not...I'd obviously guess that you mean he feels like he's flying, but I don't really think this works, especially as later in the sentence you mention the boat jumping across the lake. Also,not sure that fingers dancing in the waves works--maybe "across the waves"? Not sure you need the comma after "then". Also, having him fall into the water at the end of a longish sentence like that doesn't really work for me, a major event needs its own sentence, I think. To be honest, as I speed read it the first time I wasn't sure he had fallen in until the mention of the capsized hull later on.

The shrouds lay sliver in the water, then drifted down, enveloped by the liquid, dulling to greenish grey, then, gone I have no idea what this means. A sailing term, maybe?

I don't really feel a hook at the moment. Somebody has fallen out of his boat, I know nothing about who he is, where he is, why he's out there so I don't feel compelled to read on.

Good luck with it!

Thanks
leslie

I held on.
My fingers were cramping in the cold water. It clung to me, heavy and dense like gelatin. The sun was directly above me searing the crisp, sunburned part in my hair. I willed the heat down to the cold place where my feet were. I shivered.
I drifted away from the city, it grew blurry and small in the distance. I cursed the impulse that had propelled me out of the house that morning for an early sail. My plan to take advantage of the brisk wind and scoot around the lake for a few minutes before work seemed ill considered. I laid my head against the overturned hull. The waves slapped softly, pushing a cushion of water up between my chest and the hull, each pulse a shock of cold against the warmth from the sun-heated fibreglass.

First, the fact that it's a lake vastly diminishes the fear factor. True, there are lakes the size of small seas, but for most people a lake is place where you can't get swept away because sooner or later you're going to hit shore. An ocean on the other hand...now that's really scary.