Boat to be kept in Long Island Sound (generally 6 ft Tide) - if that is a consideration ..
Thanks - Eric
Eric,
It might depend on how protected the anchorage is.
Your harbormaster likely has a chart with requirements on his website.
Ward Woodruff
N33 #8 Margery
Niantic Bay, CT
My NS 30 was on a 300 pound mooring for years on the north shore of Long Island until Superstorm Sandy. After that storm I found BIANKA a 1000 feet across the harbor still attached to the mooring and luckily undamaged. BIANKA is now on a 500 pound mooring. 
Thanks for the cautionary tale - 500 sounds about right…
Eric,
My choice would the the largest(within reason) mooring that your Harbormaster/Marina makes available. Why skimp? My experience is the Nonsuch tends to “skate” on its mooring which is emphasized in a blow. Annual haul/inspection of chain is equally important. Chaff gear & extra painter for a storm.
The Maine coast tends to use granite blocks. The Boothbay Harbor Yacht Club(BHYC) uses three sizes; 750, 1500 & 3000 lbs, with each larger size $100 extra. I use a 3000 lb.
Good luck.
Eric Hakanson
NS 30U #484 “Carpe Diem”
Boothbay Harbor Yacht Club
Boothbay, Maine
Eric C. Hakanson
207.350.5235 (m)
Boothbay, ME
I have attached the Town of Bourne Mooring Requirements. Upper Buzzards Bay, MA can be as nasty as anywhere. I do agree that the Nonsuch will skate. My 26C is moored in the Pocasset River with Bow and Stern moorings. Bow is a 500 mushroom and the stern is a 350 mushroom. Regards, Bob Horne, 1989 N26C, #249. Pocasset, River, MA
I’ve kept a Nonsuch 30C on the Hudson River at Nyack Boat Club for about 20 years. Tidal range about 6 feet, and ebbing current 1.5-2.0 kts. Club members acquire and maintain their own mooring tackle with some guidelines set by the Club. I’ve been on a 400 lb. mushroom which has never dragged. During Superstorm Sandy, however, my boat (NS 30 Shalom, along with about 25 more sailboats out of 100 moored) snapped its pendants and was lost, since replaced with NS 30 Sheba.
The main conclusion from Sandy was that boats that broke loose needed more catenary – no chain wraps, heavier chain, and frequent evaluation of top chain condition, and more attention to the quality of chain, swivels, rings, etc.. Revised mooring standards included (for new moorings) – recommend no mushrooms (only Dor-Mor/pyramid anchors), heavier chain and pendants, and new top chain every 3 or 4 years.
I didn’t change anchors, so in the Hudson with a depth of 12 feet, we have a 400 lb mushroom, with 30 feet of of 3/4" bottom chain, 20 feet of 5/8" top chain, and 20 foot 3/4" mooring pendants - swivels between bottom and top chain, and another swivel between top chain and pendant ring. Mooring (anchor and chain) stays in all season, but with winter stick from November to April.
How to Build a Mooring | Nyack Boat Club
For NS30 our standards would prescribe 500 lb anchor, 30 feet 3/4" bottom chain, 15-20 feet 5/8" top chain and about 20 foot 3/4" polydyne pendants.
– Tony Martin NS30C Sheba, Nyack Boat Club, Nyack, NY