NBER Used A Linear Interpolation To Estimate Quarterly Figures When Data Were Given Semi-Annually. Source: Fairplay: Weekly Shipping Journal, January 14, 1937, P. 92, For 1900 On; 1898-99 Read From Chart In Same Source.
This NBER data series q02140 appears on the NBER website in Chapter 2 at http://www.nber.org/databases/macrohistory/contents/chapter02.html.
NBER Indicator: q02140
Release: NBER Macrohistory Database
National Bureau of Economic Research, Price of A New, Ready 7500 Ton Cargo Steamer for Great Britain [Q02140GBQ590NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q02140GBQ590NNBR/, August 29, 2015.