This James D Niven had various spellings for his middle name Dalziel, Dalzeill, Dalzel and Dalzell. He is often listed as J. Dalzell Niven. Also his last name is hyphenated James Dalell-Niven.

If this is the correct person: [now proven to be James Dalell Niven as listed on his son’s baptismal records and also being a mariner.]
1. James Dalzel Niven was born on July 3, 1874 in Dunmurry, Antrim Ireland, parents Richard Niven and Sarah Elizabeth McCleery.
2. James Dalziel Niven qualified as a second mate June 10, 1893
3. James Dalziel Niven qualified as a first mate of a foreign going ship on January 27, 1896
4. James Dalziell Niven qualified as a Master of a foreign-going ship on May 23, 1898
5. James Dalzell Niven extra master of a foreign-going ship on July 25, 1898.
6. He married Amy Gertrude Deans Dundas who had divorced Oswald Robert Mounsey in 1901. James and Amy married in 1902 and had no children. Amy left James for Charles Kenneth Preston-Cole, but did not divorce. Amy and Charles lived a luxurious lifestyle. [This from dundasfamily.co.uk]
7. James Dalzell Niven had a relationship with Elizabeth Katherine Deakin. They had a son Richard Dazell Niven in 1913. He would have been named after his grandfather Richard Niven and father J. Dalzell Niven. J. D. Niven and E. K. Deakin did not marry, as they could not, since Niven was still married. However E. K. Deakin started using the name Elizabeth Katherine Niven. Sometime after they went their own ways.
8. James Dalzell Niven was in the merchant navy in WWI.
9. By 1939 J. Dalzell Niven was living at 2 Semley Road, Hassocks, Sussex.
10. James Dalzell Niven of Fairfield 2 Semley Road Hassocks, Sussex died July 10, 1948.

Ireland Select Births and Baptisms
James Dalzel Niven, born July 3, 1874, Dunmurry, Antrim, Ireland, father Richard Niven, mother Sarah Elizabeth Mccleery.

The Belfast Newsletter July 6,1874
Births
Niven - July 3 at Chrome Hill, Lisburn, the wife of Richard Niven, Esquire, of a son.

UK Apprentices Indentured in the Merchant Navy
James D. Niven, age 14, date of indenture July 18, 1888, Glasgow, for 4 years, indenture expires in 1892, bound to Aitkin Lilburn & Co.

New South Wales, Unassisted Immigrant Passenger Lists
Ship Ramore Head of Belfast, Thomas McLement, Master, 2913 tons from the Port of Tehio to Sydney, November 1893
James D. Niven, 4th Mate, age 19, of Londonderry, County Down

James Dalzell Niven listed in the April to June 1902 marriage index, St. Marylebone, London volume 1a page 1201. The females on the page are Elizabeth Dutton and a women listed as Amy G W Dundas, Amy G W Deans-Dundas and Amy G W Mounsey. A family history website indicated a James D. Niven married Amy Gertrude Deans Dundas after her divorce from Oswald Robert Mounsey.

UK Campaign Medals Awarded to Merchant Seamen
James Dalzell Niven, born 1876, Lisburn, Ireland

In British Phone directories is J. Dalzell Niven, 2 Semley Rd Hassocks 476, in the Brighton Area (1939 to 1948).

London Electoral Registers 1935
3 Westbourne Park Road, Paddington, Westminster
James Dalzell Niven
Alice May Penfold
Isabel Hannah Stansfield

1939 England and Wales Register
Fairfield, 2 Semley Road, Hassocks, Cuckfield, Sussex
1. James Dalzell-Niven, born July 3, 1874, married, master mariner Commander retired P & O.
2. Isabel Hannah Dalzell-Niven, born April 19, 1894, married, unpaid domestic duties

National Probate Calendar
James Dalzell Niven of Fairfield 2 Semley-road Hassocks Sussex died 10 July 1948 Probate Winchester 29 October 1948 to Reginald Holthouse Hayward superintendent purser. Effects 1682 pounds