If you have a 37' Morgan which weighs 1800 lbs you have the only one known to man! I'm sure you meant "18,000 lbs".
I'd go with 5/16" HT (G4 or G40...they're the same) chain. When you get your windless next year, be sure to get one with a gypsy to fit this chain.
How much chain? As much as you can afford/fit. I carry 200' of 3/8" HT chain with my CQR 45 as the primary anchor when outside the Chesapeake Bay, and find it's adequate. I much prefer all-chain rodes for my primary anchor. Also carry a couple of other anchors with nylon rodes attached to 30' of chain.