Adrian,

Were you using this 1841 census of Patrick for Thomas Shimmin?
Class: HO107; Piece 1465; Book: 10; Civil Parish: Patrick; County: Isle of Man; Enumeration District: 4; Folio: 7; Page: 9; Line: 21; GSU roll: 464357.
Name: Thos Shimmin
Age: 45
Estimated birth year: abt 1796
Gender: Male
Where born: Isle of Man, Isle of Man
Civil parish: Patrick
County/Island: Isle of Man
Country: Isle of Man
Occupation: Ag Lab

Household
Thos Crellin age 40 Ag Lab
Ann Crellin age 30
Margaret Crellin age 70
Elizabeth Lace age 9
John Radcliffe age 2
Thomas Shimmin age 45

I could not make out the place on the census - appears to be Mullin...?

Tim