Type VIIC Free-Flooding Vent Patterns

"MSW Crew-mate Dougie Martindale (Dougie47) has put together a carefully researched article that shows the major differences between boats: different flood patterns, exhaust ports and more, the information that you need to make an accurate boat that stands out from the rest!"

Introduction...

Revell’s 1/72nd Type VIIC U-boat model kit has become a very popular choice in the modelling community. Many modellers have spent numerous dollars forking out for some of the after-market upgrade kits that increase the accuracy of this kit. While valuable time and money is spent on buying and fitting these upgrade kits, modifying the inaccuracies in the free-flooding vents in the Revell kit is very often overlooked. Some of the vents on the kit are missing, some are too large, while others are rectangular when they should be oval.

The purpose of this article is to provide details of all the free-flooding vents that were present in the hull casing of Type VIIC U-boats so that super-detailers of the Revell kit may modify their kits accordingly. The article may also be useful for modellers building OTW’s 1/32nd Type VIIC, since all of the vents have to be drilled out of the GRP hull when constructing this kit. Details of the vent patterns of VIIBs are also included for modellers building the older Revell 1/125th U 47 or U 99 kits.

Variations in vent patterns

Type VII U-boats had a watertight pressure hull which was visible along the central areas of the hull. Forward and aft of this pressure hull were non-watertight structures built of thinner steel. Known as the hull casing, these structures were flat on top to permit movement by the crew, and suitably shaped along the sides to allow for hydrodynamic streamlining.

To make the hull casing free-flooding, the thin steel was punctured with numerous free-flooding vents (also called drainage holes) that allowed water to drain in and out of the spaces between the pressure hull and the inside of the hull casing. Since the water on the inside of the casing was at the same pressure as the water on the outside of the casing, the thin steel of the casing would not cave in, no matter what depth the boat was at.

The free-flooding vents on the hull casing were not identical in each of the 660 VIIC and VIIC/41 U-boats. Variations in the vents occurred primarily between boats built in different shipyards. There were also differences between boats that originated from different batches within each shipyard. Though much less common, there were even minor differences between boats from the same batch. Differences were also present between early and late boats, particularly with regard to the diesel exhaust outlet. These small but distinctive variations in the free-flooding vents can sometimes help us establish the rough time period in which a photo of a U-boat was taken, and can occasionally identify the shipyard from which the boat originated.

The constant modifications that were being made to VIICs, plus the differences in vent patterns between boats, mean that the modeller who is building a detailed model of a Type VIIC U-boat to a highly accurate standard should select a particular boat at a particular time in its career. To facilitate this accuracy, a number of photos of the chosen U-boat should be sought by the modeller.