There are a handful of davit builders out there and each has a variety of designs to fit different installation applications. You might want to go to a boat show so you can talk to a few of them to gain some information. A local company to me, but national in sales, is St. Croix Davits or Marine Products out of MN. He does a good job. You have to make sure that your stern pulpit can handle the extra weight if you buy something that attaches to it. Some pulpits are not as hefty as one would like when it comes to this. Catalina might have an opinion on that question. I have installed them on different boats and each is a different approach. You have to get creative. Sorry I cannot give you specific info about your 309, but this starts the thread. Maybe someone else will pipe in.