I'd like information about the cutter R.C. Manning, which was sailing
on the Eastern Seaboard in 1899. There is a record of her being in
Vineyard Haven, Massachusetts that June.  Her ownership, home port, size,
purpose, history, travels, fate -- any or all of this would be of interest to
me.

I believe the website below has all the information you are looking
for (good thing too...as it was the only one I could find).
Due to copy right laws I can only give you snippets of information but
you can read the article in its entirety by visiting the web site.

This is an excerpt from The Dictionary of American Naval Fighting
Ships which has histories of over 7000 US Navy vessels found at the
Haze Gray & Underway - Naval History and Photography web site
http://www.hazegray.org/

Dictionary of American Naval Fighting Ships, Vol.IV- p223 found at
http://www.hazegray.org/danfs/guard/mannin.htm

“Designed as a cruising cutter, Manning was built by Atlantic Works,
East Boston, Mass., for the Revenue Cutter Service. She commissioned 8
January 1898 and was assigned cruising grounds along the New England
coast. Her lines were those of ancestral clipper-cutters, but with a
plumb bow Instead of the more graceful clipper stem. She and her
sister ships Grcsham, McCullock, Algonquin, and Onondago were the last
cutters ever rigged for sail. They also carried the first electric
generators installed in cutters. As a class, they were suitable for
scouting, for rendering assistance, and for cruising at moderately
long range. So successful was the design that these cutters furnished
the general pattern for cutter construction for the ensuing 20 years.”


It is also mentioned on the same site in a discussion of the cutter
Androscoggin (3rd paragraph from the bottom
http://www.hazegray.org/danfs/guard/androsco.htm
“Subsequently sailing south to Norfolk, Androscoggin relieved USCGC
Manning on 1 July, freeing that cutter to undergo an overhaul, During
the course of that brief stint of replacement duty, Androscoggin
visited Chincoteague Island, searching for the schooners Bertha and
Pocomo, whose owners had allegedly been using them for smuggling
whiskey in violation of Prohibition Laws. When her search proved
unsuccessful, the ship returned to Norfolk on 12 July.
When Manning returned to her regular station, Androscoggin received
her final cruising orders: to proceed to the Coast Guard Depot at
South Baltimore for decommissioning…”


Search terms:

cutter R.C. Manning

An excellent feat of research.  Swifter and more accurate than I dared hope for.