NZR BB class

{{Short description|Class of New Zealand steam locomotives}} {{Use New Zealand English|date=July 2024}} {{Use dmy dates|date=April 2022}} {{DISPLAYTITLE:NZR B^B class}} {{Infobox locomotive |name = NZR B^B class |powertype = Steam |image = Bb class 4-8-0 steam locomotive, New Zealand Railways number 619 ATLIB 276055.png |caption = B^B class 4-8-0 steam locomotive, [[New Zealand Railways Department|NZR]] number 619, circa 1915. Godber Collection, [[Alexander Turnbull Library]]. |builder = [[A & G Price]], [[Thames, New Zealand]]{{sfn|Palmer|Stewart|1965|p=104}} |serialnumber = 63–92 |builddate = 1915 (12), 1916 (8), 1917 (8), 1918 (2) |whytetype = [[4-8-0]] |uicclass = 2'Dh |gauge={{Track gauge|42in|lk=on}} |driverdiameter = {{convert|42.5|in|m|3|abbr=on}} |length = {{convert|52|ft|7+1/2|in|m|2|abbr=on}} |weightondrivers = {{convert|32.5|LT|t ST}} |locoweight = {{convert|43.5|LT|t ST}} |tenderweight = {{convert|25.5|LT|t ST}} |fueltype = [[Coal]] |fuelcap = {{convert|4|LT|t ST}} |watercap = {{convert|1700|impgal|abbr=on}} |firearea = {{convert|16.8|sqft|m2|abbr=on}} |totalsurface = {{convert|724|sqft|m2|abbr=on}} |superheaterarea = {{convert|208|sqft|m2|abbr=on}} |boilerpressure = {{convert|175|psi|MPa|abbr=on}} |cylindercount = Two, outside |cylindersize = {{convert|17|x|22|in|mm|0|abbr=on}} |maxspeed = {{convert|40|mph|abbr=on}} |tractiveeffort = {{convert|20940|lbf|kN|abbr=on}} |numinclass = 30 |fleetnumbers= 55, 109, 143, 144, 147, 167, 169, 171, 197, 222, 618–637 |preservedunits = 1 (B^B 144) |disposition = One preserved, remainder [[scrap]]ped }}

The '''NZR B^B class''' of [[Locomotive#Steam|steam locomotives]] comprised 30 engines operated by the [[New Zealand Railways Department|New Zealand Railways]] (NZR) in the [[North Island]] of [[New Zealand]]. Ordered to replace smaller locomotives of several classes in the North Island, they were similar in design and appearance to the preceding [[NZR B class (1899)|B]] and [[NZR Ba class|B^A]] classes. The first B^B class locomotive entered service in February 1915, with the last to commence operations doing so on 8 March 1917. All were built by [[A & G Price]] Ltd of [[Thames, New Zealand]], and as their cylinders had a larger diameter than the B and B^A locomotives they were capable of generating more power to haul heavier trains. The most visible difference however was the roundtop firebox in place of the preceding classes Belpaire design. The B^B class could haul up to {{convert|700|LT|t ST}} of freight on a level railway line, though they were limited to a top speed of around {{convert|40|mph|abbr=on}}.

==Service==

The B^B class did not solely haul freight trains. They were also utilised to haul passenger trains, generally, on [[branch line]]s where light track meant trains could not be operated at speeds unattainable for the B^B class. These trains included services for miners working in coal mines along branches in the [[Waikato]] region (e.g. [[Glen Massey Branch]]). However, they arrived at the same time as the A^B class Pacific, and as these proved equally adept at hauling freight trains of similar tonnage they were proliferated while no further B^B types were ordered.

In the latter days of steam, powerful locomotives such as the [[NZR K class (1932)|K class]] were hauling heavy trains that the [[NZR C class (1930)|C class]] and other [[shunter|shunting locomotives]] at yards and depots simply could not handle. Accordingly, ten members of the B^B class were modified to perform shunting duties between 1932 and 1938, and they successfully took on the heaviest of roles.

Most B^B locomotives survived into the 1960s. In later years they were concentrated at the yards in [[Auckland]], [[Frankton, Waikato|Frankton]] and [[Palmerston North]]. In the mid-1960s four were sent to Dunedin and Invercargill. During that decade, the complete withdrawal of the class was undertaken progressively, with the last two, B^B 626 and B^B 633, formally removed from service in August 1968. Another one of the last to be withdrawn was B^B 144 in October 1967. It was purchased by Les Hostick. Today it is leased to Ian Welch and is under restoration at the [[Mainline Steam Heritage Trust]]'s [[Parnell, New Zealand|Parnell]] depot. No other B^B locomotive has been preserved.

==See also== * [[NZR B class (1899)]] * [[NZR BA class|NZR B^A class]] * [[NZR BC class|NZR B^C class]] * [[Locomotives of New Zealand]]

==References== {{reflist}}

=== Bibliography === {{refbegin}} * {{NZR Steam Locomotive}} * {{Palmer & Stewart}} * {{When Steam Was King}} {{refend}}

==External links== *[http://www.trainweb.org/nzsteam/bb_reg.htm New Zealand Railways Steam Locomotives - Class B^B] *[http://www.mainlinesteam.co.nz/ Official website of Mainline Steam, owners of B^B 144]

{{NZR Locomotives}}

[[Category:Steam locomotives of New Zealand|Bb class]] [[Category:4-8-0 locomotives]] [[Category:2′D h2 locomotives]] [[Category:3 ft 6 in gauge locomotives of New Zealand]] [[Category:Railway locomotives introduced in 1915]]