CYA Member David Ellis has researched Shain and reports:

Morris (Mike) Shain designed and built fine yachts and speed boats and was instrumental in the development of motorboat racing as well as sturdy, beautiful cruisers. All of Mike Shain's yachts carried his trade name moniker: Trimmership, Trimmer Ship or even Trimmer-ship. Mike Shain spelled it different ways, and the term is one he adopted from his first job as a trimmer in the upholstery business. He had a shop on Westlake Avenue in Seattle until late 1949 when he moved to massive new facility on West Commodore Way. Many folks are under the mistaken impression that Ed Monk Sr. designed many of the Shains. This is an understandable error as the two shared ideas and worked together often. Monk even is listed as the carpenter on several Shains as he ran the yard for Mike Shain in the late thirties leading up to the entry on the US into WWII. 

Shain developed several models of Trimmer Ships over the years. His "Commodore Model Trimmership" introduced in 1939 became the basis for some 50 patrol boats that were to be built by several builders in yards throughout the local Seattle area. His 63' 1935 ZIMMIE was his first "Airflow Trimmership" of which several variations were to follow all the way through the mid to late 1950s. One of the finest examples of a smaller Airflow Trimmership is the LITTLE SHEPARD which recently has come under new ownership.

From the CYA newsletter "Classic Yachting", of December 2011, historian and CYA Life Member Steve Wilen provided this:

The Shain Manufacturing Company had two locations, first on Westlake Avenue a short distance south of the Aurora Bridge, relocating in 1949 to Commodore Way on Salmon Bay, where for many years MARCO Marine was located. Founded by Morris "Mike" Shain, the company is remembered largely for its unique streamline Trimmer Ships with their reverse "ducktail" or "turtleback" transoms, arced canoe prow and teardrop port lights. (The yard did turn out some power boats with more traditional lines.) Shain was known as "the man who built his boats upside down" and, according to Norm Blanchard, was the only competitor with whom N. J. Blanchard had a cordial relationship. Possibly because of the yard's proximity to the Grandy yard, Shain was another early champion of Ed Monk, Sr.

ForevermoreSeveral versions exist concerning the origin of the name Trimmer Ship: Norm recalled that it evolved from Shain’s previous employment as an auto upholsterer, or "trimmer"; Dave Ellis states its origin lies with Shain's prior employment as a trimmer in a Yakima upholstery shop. Be that as it may, Shain eventually also had dealerships in both Portland and San Diego. In 1956, he sold his business to MARCO, although for a time he continued to supervise construction of some of his designs that were built by MARCO.

The largest of the Trimmer Ships was the 63-foot Zimmie of 1935. Extensively restored in the 1990s and renamed The Red Baron, she was trucked from Seattle to Miami in the 1990s, where she became for several years a member of the USA Fleet. For sale in Florida on the Internet for a time, the listing has been removed, and her current status is unknown. PNW member Forevermore is another winsome example of a large Shain Trimmer Ship.

From Life Magazine, Dec. 27, 1937, Page 66:

49' 1940 Shain Airflow Trimmership FIESTA was built at Morris G.(Mike) Shain's yard on Lake Union and trucked to Lake Union Drydock & Machine Works to be launched via crane. A. B. Ford of Queen City Yacht Club, the yacht's owner, looks on. Her single 105 HP Chrysler Crown with V-Drive allowed for economical cruising at 10 knots.