pre_text: GasLog Ltd. and its Subsidiaries Notes to the consolidated financial statements (Continued) For the years ended December 31, 2017, 2018 and 2019 (All amounts expressed in thousands of U.S. Dollars, except share and per share data)    6. Tangible Fixed Assets and Vessels Under Construction The movements in tangible fixed assets and vessels under construction are reported in the following table: Vessels with an aggregate carrying amount of $4,407,156 as of December 31, 2019 (December 31, 2018: $4,304,252) have been pledged as collateral under the terms of the Group’s loan agreements (Note 13). As of December 31, 2019, a number of increasingly strong negative indicators such as the difference between ship broker estimates of the fair market values and the carrying values of the Group’s Steam vessels, the lack of liquidity in the market for term employment for Steam vessels and reduced expectations for the estimated rates at which such term employment could be secured, together with the continued addition of modern, larger and more fuel efficient LNG carriers to the global fleet, prompted the Group to perform an impairment assessment of its vessels in accordance with the
table: Vessels Office property and other tangible assets Total tangible fixed assets Vessels under construction
table: Cost
table: As of January 1, 2018 4,217,866 19,224 4,237,090 166,655
table: Additions 49,036 4,678 53,714 637,046
table: Transfer from vessels under construction 642,776 — 642,776 (642,776)
table: Transfer under ‘‘Other non-current assets’’ — — — (1,650)
table: Fully amortized fixed assets (10,000) (192) (10,192) —
table: As of December 31, 2018 4,899,678 23,710 4,923,388 159,275
table: Additions 26,233 1,454 27,687 450,918
table: Return of capital expenditures (11,224) — (11,224) —
table: Transfer from vessels under construction 406,870 — 406,870 (406,870)
table: Fully amortized fixed assets (7,209) — (7,209) —
table: As of December 31, 2019 5,314,348 25,164 5,339,512 203,323
table: Accumulated depreciation
table: As of January 1, 2018 460,815 3,709 464,524 —
table: Depreciation 144,611 863 145,474 —
table: Fully amortized fixed assets (10,000) (192) (10,192) —
table: As of December 31, 2018 595,426 4,380 599,806 —
table: Depreciation 156,826 875 157,701 —
table: Impairment loss on vessels 162,149 — 162,149 —
table: Fully amortized fixed assets (7,209) — (7,209) —
table: As of December 31, 2019 907,192 5,255 912,447 —
table: Net book value
table: As of December 31, 2018 4,304,252 19,330 4,323,582 159,275
table: As of December 31, 2019 4,407,156 19,909 4,427,065 203,323
question: Analyse this data from a financial earnings document. What was the change in vessel cost from end 2018 to end 2019?