Kind of depends on your budget, Laurie. The Arc'teryx Firee Hoody soft shell designed is really nice, and is designed for cold/damp conditions. It uses Polartec Powershield, which I think qualifies the best high-end soft shell material out there; it's tough, highly water- and wind-resistant, and offers good warmth. The Firee has a longish cut and full hood, so it provides a lot of coverage. Alas, at $400 it's kind of steep, price-wise. You might also try Mountain Hardwear's Barisian Jacket ($175), which uses a good proprietary material with some stretch, along with good breathability and wind resistance.
Or, just go for a regular rain shell. Outdoor Research's Aspire Jacket ($200) is made from light Gore PacLite material, for a waterproof and breathable piece.
But really, I'm not sure a soft shell or even a regular outdoor jacket is a good choice for you. In an open boat? In 20- to 40-degree weather? I'd go with something much more…well…nautical. Something like Helly Hansen's Coastal Jacket III ($150), which has a waterproof/breathable (but mainly waterproof) outer shell with a full hood. You'd need to layer up under it, but it's really designed for the use you have I mind in a way that most soft shells are not. Or wear what commercial fishers wear: the Helly Hansen PVC Rain Jacket ($85). Totally bombproof heavyweight 0.45mm PVC, extremely durable, resistant to salt spray, chemicals, you name it. On a cold day, with water splashing over the bow of the Zodiac, you'll thank me.