ORIGINAL: Nikademus
ORIGINAL: Tiornu
I would appreciate it muchly. very interested in this.
All right, I found the following quotes. They're from Henry Schade, a member of the NTM in Europe. You may want to track down his article that appeared in the Transactions of the Society of Naval Architects and Marine Engineers, Vol 54, 1946--in fact, I'm certain you'll want to see it because it spends several pages covering the entire Type XXI construction process. As a bonus, you'll also find articles on turbine development and ice-breaker design.
"In an effort to meet the unrealistic quotas, the section yards and the fitting yards would move assemblies along to the next yard in an uncompleted status which served only to magnify the troubles and eventually cause delays at the assembly yards waiting for the missing items. Because of difficulties of the inexperienced structural plants in producing sections within tolerance, the assembly yards tried to reshuffle sections to get a better match, and some confusion and inefficiency thereby resulted."
so it would seem that the rush rush part is the primary culprit.
I think the Schade quote hits the nail on the head; the fitted-out sections as delivered to the assembly yards were certainly within specs as such, but remedial work needed to achieve this slowed down the rate of delivery significantly.
Sectional construction as such was a good decision; it especially cut down on time to install the equipment, because the interior of the section was freely accessible, mostly from both ends; with conventionally constructed subs all the equipment had to be brought into the pressure hull through the hatches and torpedo tubes, and space for the workers was decidedly limited. Where the Type XXI building process went seriously wrong was with farming out major structural work to companies from a different engineering branch. These were all companies who normally did steel structural construction, like tanks for water towers, bridges, or steel skeletons for industrial buildings. They were not just inexperienced in shipbuilding, but they actually could not understand technical drawings and specifications intended for shipyards, as the specification methods, drawing styles, and the symbology used in the drawings were different. The documentation actually had to be translated first. There was a significant delay before the parts started to arrive at the section yards, and they weren't always complete even if in tolerance dimensionally.
It also appears that thermal expansion effects were not taken properly into account (this isn't much of a problem when the whole structure is assembled piecemeal in one spot), so even if the subcontractors built to precise dimensions, there's going to be trouble if you try matching a section built at 20 degrees C to one that was built at 5 deg C. When the mismatch was significant, the assembly yards would (in tailoring language) cut tucks into the rim of the pressure hull ring and take it in until the diameters matched. That cannot have benefitted structural strength and integrity. The project management office reckoned from the beginning that the first six boats delivered by each assembly yard would probably not be fully combat worthy, regarding them as pre-series production, whereas the navy wanted to get ships to the front as quickly as possible, a conflict of interests that went unnoticed until production problems surfaced.
In hindsight, it would have been better to let the yards do all the structural work; the first boats could have been delivered maybe five or six months earlier if the yards hadn't had to wait for the subcontractors to get their act together. Rolling the hull plates and cutting the steel parts to size could still have been contracted out.
Some comments to modular construction today:
- I once visited the Meyer shipyards who specialize in cruise liners; the ships are assembled in covered dry docks from modules that reach across the whole width of the ship and weigh between 400 and 800 tons. The guide told us that they have a tolerance of 3-4 mm across a hull width of PANAMAX size (about 32,9 metres / 107 ft). Sizing the plates has to take into account thermal expansion/shrinking caused by welding.
- The Airbus assembly lines in Hamburg and Toulouse have to compensate for deformation of the hangar floor due to tidal effects when mating fuselage sections.
