Sue – more for you. Digging deeper into my father’s notes I found a photocopy of a genealogy prepared by Paul Bridson, the antiquarian and perhaps the father of Manx genealogy . Among the children of William Bridson (d.1799) and Ann (d.1812) he gives:

John baptised Sept 25 1782
married Catherine Whitnam (?)
of the cou[nty] of Cor[nwa]ll (Launceston)
and had several children
including Ann & Mary
who all died young &
unmarried. He died
at sea on his voyage
from Jamaica & was
consigned to the deep in (margin – Gulf of Mexico)
August 18: 1816 His widow died in 1849
and buried at St Georges in Douglas.

I don’t know what sources Paul Bridson used but this John was his uncle so he should have known. It makes me wonder whether this source is fully used by searchers.
Michael Bridson.