In Lloyds Registry of 1838 I can find only one vessel under the name WHITBY, en most probably she is depict on this stamp, could not find on the net a image of her.
Built in 1837 as a three masted wooden ship by Henry and George Barrick in Whitby for Chapman & Co. at London.
Launched as the WHITBY.
Tonnage 347 ton. Dim 99.5 x 24.6 x 19.6ft.
Ship rigged.
In 1837 was she underway from London to Calcutta. Under command of Captain J. Swinton.
She set sail on 13 January 1838 from Calcutta with on board 249 coolies bound for South America via Cape of Good Hope.
05 May 1838 she arrived at Guyana, she was the first ship who carried Indian coolies to the British West Indies. During the voyage of about four months, five persons died.
1839 Was she used in the convict trade to Australia.
18 February 1893 she sailed from Dublin under command of Captain Thomas Walbank with on board 125 female convicts arriving in Sydney on 23 June. 1839.
02 May 1841 under command of Captain W.M. Lacy she together with the WILL WATCH sailed from Gravesend with on board settlers for New Zealand, the WHITBY arrived at Port Nicholson (now Wellington Port) on18 September 1841.
05 November the WHITBY entered the port with on board 60 settlers and equipment and stores what is now called Nelson, and she and the WILL WATCH and the ARROW where the first vessels to land settlers in Nelson and they were the founding fathers of the town Nelson in the South Island of New Zealand.
1843 Was she sold to Thomas Hawson in Moulman, India.
1844 Was she sold to Phillip Richardson, London.
1848 Was the owner Thomas Radcliff, London, and was she barque rigged.
Between 1851/52 underwent major repairs, received a new deck.
1852 Was she owned by William Wright, Sydney, Australia.
16 March 1853 she arrived at Kaipara, North Island of New Zealand from Sydney under command of Captain Bruce.
24 April 1853 when she left Kaipara Harbour the wind dropped and she was driven on the Tory Shoal after the anchor cables parted and was lost. (Most probably crew saved)
Belize 1982 35c sg673, scott? (The stamp shows us a brig rigged vessel, who can give under which flag she is depict?, while I believe there is not a painting of the vessel except the drawing of the three ships in Nelson Port, and most probably the ship depict is a imagination of the designer)
Sources: Lloyds Register 1838. Various web-sites. The convict ships by Charles Bateson, Log of Logs by Ian Nicholson. White Wings, Immigrant ships to New Zealand by Henry Brett. Australian Shipowners and their fleets in the 1850s by Ronald Parsons. New Zealand Shipwrecks.