Disclaimer: This is a sample subject to revision and not an indication of final product quality.
Overhead ice bunker cars had been proposed as early as the late 1800s. Experimental cars were built by several railroads, but none were built in quantity.
In 1936-7 that the Canadian National and Canadian Pacific built twelve experimental cars to various designs utilizing overhead ice bunkers. Rather than drawing inspiration from past design concepts in North American railroading, the Canadian engineers instead traveled to South Africa and Hungary to study the overhead bunker reefers used by their railroads.
As with prior experimental cars, it was found that product could be kept at cooler temperatures, with less ice and requiring fewer stops for re-icing enroute. The CN was happy enough with their performance that 100 more cars were built in 1939-1940, and by the late '50s the Canadian National and Canadian Pacific rostered over 6,000 cars.
Although a deemed a success by the Canadian railroads, other North American railroads did not follow suit. The traditional thinking as to why this was the case is in part due to their efficiency. Reefers were primarily owned and operated by private car lines and not the railroads. These lines were paid based on mileage, and not the weight of goods carried. Thus, more efficient reefers that could carry more goods reduced the number of cars needed and the corresponding revenue.
But as documented in Pacific Fruit Express (Thompson, Church, Jones; Signature Press), PFE built two classes of overhead ice bunker cars starting in 1940, relying heavily on the Canadian designs and studies. These reports show that PFE had several main reasons that they did not build more of this design.
The overhead bunker design did not cool loads of produce as quickly as an end bunker design (the Canadian cars were primarily for meat service). Even in Canada, end bunker cars were typically specified for produce. Filling the overhead bunkers took more time, and was more prone to damaging the tanks. This was not a major factor in the Canadian cars since they utilized brine tanks. Potential brine leaks, condensation dripping on the load, a higher center of gravity, and increased maintenance costs were other factors.
A great amount of Canadian perishables, particularly meat, was for export. The overhead bunker cars were more efficient at maintaining a uniform temperature when standing than an end bunker car. Circulating fans were beginning to be used on US roads, but they didn't operate well in the Canadian winters. Fans also didn't operate when the car was standing.
The major spotting feature of the Canadian overhead ice bunker reefers was their eight roof hatches, rather than the standard four. Due to the overhead bunkers, the doors are shorter than on other reefers of the era. The Canadian cars also had charcoal heaters mounted under the floor. In end bunker reefers, a removable heater would be used in the ice bunker when needed. The overhead bunker design necessitated permanently mounted external heaters instead.
Photos have documented these cars in service throughout the US, including southern California, Texas and Florida, and everything in between.
There are minor differences between the designs built by the two roads and, as with all designs built over a number of years, new technologies and features were incorporated.
Canadian National Steel 8-Hatch Reefers
The CN cars were built with a standard 11-panel side configuration, 5 panels to either side of the door.
Over the two decades the cars were built, 6 different ends were utilized:
'Square corner' Dreadnaught 'W-corner' Dreadnaught Riveted Improved Dreadnaught (IDE) Welded IDE 'Banana Taper' IDE with rectangular top rib NSC-3 proprietary ends.
There are a great many variations in details such as the door type (hinged or sliding 'plug), brakewheel, running boards, ladders, etc.
Canadian Pacific Steel 8-Hatch Reefers
Cars built for the CP used an unusual side panel configuration where the two panels immediately to either side of the door were half the width of the rest of the side panels.
The CP used 4 different ends on their cars:
Wood
Dreadnaught
NSC-2 proprietary ends
NSC-3 proprietary ends
Just how detailed are these cars? Look at the 5mm Liquid-o-meter
