This ship portrait shows the vessel in two positions, port-broadside and port-quarter in the distance. She is called a snow rather than a brig, because her gaff-sail is laced to a little jigger-mast which is stepped aft of the mainmast. With her jack and commissioning pendant she is clearly naval, presumably a transport or supply vessel bought or hired by the Navy, but not a fighting ship. The background appears to be Tilbury Fort, opposite Gravesend in the Thames.
<bdi><a href="https://en.wikipedia.org/wiki/en:Charles_Brooking" class="extiw" title="w:en:Charles Brooking"><span title="British painter (1723-1759)">Charles Brooking</span></a>
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<a rel="nofollow" class="external text" href="http://collections.rmg.co.uk/collections/objects/12513.html">National Maritime Museum, Greenwich, London.</a>