CONFIDENTIAL REPORT 2G-9C S29
	FORMER GERMAN SUBMARINE TYPE IX C-40
	WEIGHT, STABILITY AND INTEGRITY
	SUMMARY
	This type of vessel has adequate stability, but limited reserve buoyancy.  Buoyancy is apparently more concentrated amidship than might be considered desirable.
	Trim and list control is flexible, but apparently has to be augmented at times by movement of personnel to one end or the other of the vessel.
	Workmanship is in general good, and specified tests are complete and thorough.
	March, 1946
	PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H.
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	9C-S29
	GENERAL
	The vessel was designed with external main ballast tanks, fuel ballast tanks and fuel oil tanks, bow and stern buoyancy tanks, regulating and negative tanks; internal trim tanks, WRT tanks, and fuel oil tanks.
	A compensation curve is not available.  A trim table from U-805 is, however, at hand.
	Damage control was the subject of a considerable volume of text material, but very little information appears to have been provided onboard with regard to drafts, load condition, metacentric heights, and weights.  Further discussion on damage control will be found under S88.
	Draft and trim, free-board, immersion and water-lines were subject of some discussion, but available local information is not in all cases complete.
	Stabilizing devices were not provided.  The ballast keel probably acted to a certain degree as an anti-rolling device, but there is no evidence that the type of construction was employed for that purpose.
	Evidence with regard to rolling and pitching is secondary, but will be discussed in the detail permitted by available material.
	Workmanship was in general good, but additional comment on brazing and welding will be found herein.
	Strength information is incomplete, but will be covered to the extent possible.
	Tightness tests were extensive and appropriate to the type of construction employed.
	No information is locally available on hogging and sagging, although the design is such that these occurrences could have presented problems in shaft and tube alignment.
	Riveting and bolting were both employed where appropriate, with few exceptions, and will be discussed herein.
	Tonnage data is incomplete, and will not be discussed.
	Weight Displacement and Stability
	Specification weights on the vessel are as follows:
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	9C-S29
	Hull Groups Metric Tons Hull proper pressure hull plating 104.00   end bulkheads 4.01   pressure hull frames 20.74   pressure hull bulkheads 16.67   foundations and brackets 14.50   platforms 7.00   interior tanks 15.00   outer hull 37.33   stern, stern frame and struts 6.83   rudders and planes 10.51   outer hull frames and bulkheads 22.00   superstructure 24.50   pressure-tight exterior tanks 29.76   insulation, lagging 1.80   conning tower 10.92   ordnance foundations 1.79   torpedo arrangements .90   hawse pipe .45   communications arrangements .99   arrangements for personnel .34   keel 14.19   arrangements for machinery  systems 4.50   welding     9.64   total hull proper (metric tons) 358.37 Shipfitter Work   bulkhead closures, etc. 6.41   railings .50   ladders .11   cleats and chocks .003   flood and drain arrangements 10.75   rudder and plane arrangements 4.25   arrangements for armament 1.45   anchor arrangements 1.78   torpedo arrangements 5.30   ship control (no weight shown)   ballast tank arrangements 17.00   arrangements for crew .45   safety and rescue arrangements 1.30   miscellaneous     1.50   total shipfitter work 59.093 Joiner & Sheetmetal work   officers' and chiefs' quarters 1.95   petty officers' and crew's " 1.90   miscellaneous   .43   total joiner & sheetmetal work 4.28
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	9C-S29
	Painting & Cementing   Painting 5.35   Cementing   .10   Total painting & cementing 5.45 Summary of hull weights   Hull proper 358.37   Shipfitter 50.903   Joiner & Sheetmetal 4.28   Painting & Cementing       5.45   Total hull 419.003     Machinery Groups     Propulsion     Diesel engines 54.00   Circulating water system 3.50   Lub oil system 4.60   Fuel oil system 5.20   Diesel air and exhaust gas system 12.46   Propeller shafts 17.50   Propellers 1.36   Main motors 25.50   Main electric control 3.70   Electric wiring 5.50   Battery 75.50   Battery ventilation .14   Flats, ladders in machinery compartments      .14   Total main propulsion 209.06 Auxiliaries   Rudder & plane operating gear 1.67   Windlass system .62   Compressed air system 18.30   Exhaust gas blow lines 2.53   Main drain pumps .91   Auxiliary drain & trim pump 1.15   Heating and cooking 2.56   Fresh water distilling plant .60   Compartment ventilation 5.80   Torpedo venting, heating and fire control 1.50   Periscope system 4.74   Ship's lighting .50   Searchlights .04   Ship control 1.34
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	9C-S29
	Auxiliaries (Cont'd)   Command and announcing systems 1.10   Voice tube system .43   Signal systems 5.60   Emergency & rescue arrangements .50   Refrigerating .32   Hydraulic systems 2.60   Auxiliary switching system 1.21   Electric wiring 9.54   Shop equipment     .70   Total auxiliaries 64.26 Tools and Parts   Machinery 4.95   Electric 2.01   Ship's boat power plant   .40   Total tools & parts 7.36 Summary of machinery weights   Propulsion 209.06   Auxiliary systems 64.26   Tools and parts     7.36   Total 280.68 Grand total hull plus machinery   Hull 419.003   Machinery   280.68   Total hull plus machinery 699.683   (all dry weights)
	Ballast, for a vessel with a snorkel, 37 mm guns and other late 1944 alterations, amounted to 91021 kg (200500 lbs.) all of which was carried in the ballast keel.
	Ordnance weights are not available.
	Displacement figures are not complete.  Naval Technical Mission in Europe report No. 312-45 on submarine design gives the following figures, which have been substantiated by the available figures on tank capacities, compartment sizes and volume equivalents for known weights:
	Normal diving trim 999 cu. meters Emergency diving trim 1144 cu. meters Submerged displacement 1257 cu. meters Submerged displacement plus free flooding 1545 cu. meters
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	9C-S29
	The center of submerged displacement, according to available trim table, is 29.60 meters forward of pressure frame "0" and 38.80 meters forward of the stern of the vessel.  This is further identified on the ballast diagram as 200 mm forward of pressure frame 42, which is just aft of the center of the conning tower.
	Information with regard to surface and submerged GM is not locally available for this class of vessel, nor is the vertical position of the center of buoyancy known.  If desired, the vertical positions for surface conditions could be computed from the available body plan, "Bauspantenriss und Plattengänge d. Aussenschiffes", No. S I 11005-5006.  (Note: the number given is the one applying to all body plans, and the applicable vessel hull numbers must also be known in order to select the correct plan).
	Complete data on tank volumes and moments is available on the trim table for U-805, prepared by Deschimag, and in the Machinery & Electric Information Book (M und E Kunde) for this class.
	For trim control, trim tanks and WRT tanks are provided.
	Forward trim tanks have a capacity of 5.160 cu. meters, and have a forward moment of 21.06 meters.  After trim tanks have a capacity of 5.040 cu. meters, and an after moment of 23.25 meters.  They are intended solely for trimming purposes, with a fixed quantity of water which can be pumped or blown as desired from one end of the vessel to the other.  An "all empty" or "all full" condition is not contemplated.
	The two WRT tanks forward have a capacity of 6.600 cu. meters and 6.500 cu meters, total 13.100 cu. meters, forward moment of 18.50 meters.  The two after WRT tanks each have a capacity of 3.080 cu. meters and a after moment of 20.72 meters.  Related thereto, the capacity of each tube is 1.740 cu. meters without piston, and 1.680 cu. meters with piston.  Moment for the four forward tubes of 28.90 meters, and for the two after tubes is 30.44 meters.  The WRT tanks are also designed for use as wash water tanks at the start of the voyage.
	Buoyancy, ballast, fuel and regulating tanks are arranged as follows:
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	9C-S29
	Volume in liters Trimming moment in meters Flooding area in sq. meters Venting area in sq. meters Vent valve operating gear Flood valve operating gear Stern buoyancy 14800 - 33.97 1.20 .026 hand none MBT 1 40900 - 28.09 4.17 .159 single valve, air piston none NFO 1a 20500 - 19.13 Compensating none none FBT3 25800 - 13.83 1.40 .106 double valve, air piston hand NFO 2a 46740 - 8.59 Compensating none none FBT 4 32660 - 4.15 1.40 .106 air piston* common with MBT 5 hand Reg. Bunker 30000  - .55) .03 to either or both (.0015 hand hand            ) (          Reg. Tank 17960 + 2.25) (.0015 hand hand Negative 10800 + 4.00 .24 .030 hand hand MBT 5 35720 + 6.56 1.40 .106 air piston* common with FBT 4 hand FBT 6 34260 + 10.67 1.40 .106) quadruple valve air piston, FBT 6 and 7 in common hand          )      **) FBT 7 32600 +17.63 1.28 .123) hand MBT 8 36900 +28.99 3.55 .159 single valve, air piston none Bow buoyancy 11650 + 33.48 .90 .050 hand none
	*      The port halves of these tanks are vented by one valve, and the starboard halves by another valve.  For the four half-tanks there are only two valves.
	**    Includes auxiliary vent line to forward end of tank.
	All hand operating gear is located in the compartment nearest the tank concerned.  When vent valves are operated in power from the low pressure air system, those for MBT 1 and FBT 3 are controlled by one air valve; those for FBT 4 and MBT 5 by a second air valve; and those for FBT 6 and 7 and MBT 8 by a third.
	High pressure blow lines are fitted to all tanks except the normal fuel oil tanks.
	Low pressure (exhaust gas) blow lines are fitted to the main ballast and fuel ballast tanks.  Separate cut-offs are provided at the blow manifold to prevent blowing fuel ballast tanks when carrying oil therein.
	Gate valves are fitted in the vent lines of the fuel ballast tanks between the vent valves and emergency vent valves.  Those for FBT 4, 6 and 7 can be operated from within the vessel.
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	9C-S29
	In addition to the foregoing tanks, the vessel is fitted with two internal fuel oil bunkers, and with collecting and gravity service tanks, fresh water tanks, battery water tanks, wash water tanks, sanitary tanks, and lub oil tanks, each of which is discussed under its appropriate system.
	The total fuel oil which can be carried, with all suitable tanks filled, is 24,9044 liters.
	The total lub oil which can be carried is 12550 liters.
	Total battery water is 505 liters, drinking water is 4070 liters, and wash water (including use of WRT tanks) is 19320 liters.
	Sanitary tank capacity is 1140 liters.
	No safety tank is provided.
	Service conditions encountered, and used basically by the Germans in all calculations, are condition A (Zustand A), in which fuel ballast tanks carry water, and condition B (Zustand B), in which they are filled with fuel oil.  The latter is the normal condition.
	Further, according to the machinery and electrical information book for this class (M und E Kunde), ballast tanks 1, 5 and 8 are intended to give the vessel the necessary surface buoyancy; ballast tank 5 serves also as receptacle for oily bilge water pumped out of the vessel while submerged; the buoyancy tanks provide additional buoyancy and the bow buoyancy tank is a safeguard against running under in a seaway; the regulating tanks serve to compensate for use of oil, supplies and munitions and for the difference in specific gravity of water, and the regulating bunker can be employed as a fuel oil tank; the trim tanks provide compensation for longitudinal changes in the center of gravity of the vessel; the WRT tanks take the water from the torpedo tubes and compensate for the weight and moment of the torpedoes, and in addition provide a means for compensating for weights and trimming moments which cannot be compensated for by the trim and regulating tanks.
	The negative tanks are, under war conditions, carried half full, are completely flooded to accelerate a dive, and are blown at a depth of 9 to 11 meters, which is qualified by "depending upon sea condition or danger of attack".  They are not, however, to be used when going deep, because of the resulting falling rate, inability to compensate at great depths, need to use compressed air in quantity, and resulting pressure in the boat.
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	9C-S29
	Damage control is discussed at length in the General Information Book (U-Bootskunde).  A book for this type of vessel is not available, and it is therefore necessary to amplify under this heading in corresponding sections of the XB and XXI type reports.  It should be here mentioned that the pressure bulkheads are not designed to carry the designed submergence pressure of the vessel.
	List control is made easier by the twin character of most tanks, and the fact that pipe and pump connections permit ready transverse movement of weight to offset any list encountered.
	Draft and Trim
	Vessel dimensions, and drafts, from NavTechMisEu Report 312-45 in the absence of other figures, and depth from the body plan of the vessel, are as follows:
	L.O.A. 251'-10" Maximum 22'-6" Depth from bottom of keel to top of pressure hull amidships 16'-7" (from plan) Maximum diameter of pressure hull 14'-5" (from plan) Mean draft -       Normal diving trim 14'-2"     Emergency diving trim 15'-4"
	Inclining Experiment
	No inclining experiment has been conducted.  The figures in NavTechMisEu report 302-45 must serve in the absence of later confirmatory information.
	Stabilizing
	No stabilizing devices are provided.
	Rolling and Pitching
	Informal comment by U.S. Naval personnel is inconclusive, and no official report of the sea-keeping qualities of the vessel have been received at the moment of writing.
	A tendency to roll is indicated by the shape of the hull.  The Germans noted the tendency to run under and changed the "0" angle of the planes in an effort to offset this drawback.
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	9C-S29
	Workmanship
	Workmanship was generally good, but is not up to U.S. Navy standards.  Individual elements of design which are in themselves excellent have been rendered valueless by the manner in which they have been worked into the ship, and the lack of appreciation of the thought given by one group of technicians by another group of technicians is evident.  This phase is amplified in the appropriate individual sections.
	Welding was good.  The limitations of German welding practice are given in detail in the Naval Technical Mission Europe report No. 45 on the subject of Welding.
	Strength of Hull
	The hull was designed for a submergence of 100 meters (328 feet) with a factor of safety of about 2.5 on collapse at that depth.  Further information on hull strength is not available.
	Tightness Tests
	Tests were extensive and elaborate.  Individual pressure items were sampled for porosity, before building them into systems, and for strength and tightness after assembly.  An operating test of each system completed the series of tests.
	Ratio of test to working pressure depended upon the unit and on the system.  H.P. air flasks were tested to 255 kg/cm2 (3626 psi) for a working pressure of 205 kg/cm2, or 24% over the working pressure, but it is only at high pressures where one finds the percentage varying from 40 to 50% over the working pressure.
	Test and working pressures are carefully detailed in the systems instruction book and in the Machinery and Electric Information Book.  "Atmospheres" (atü) and kg/cm2 are used interchangeably, which is explained in Klingelnberg's Engineering Manual (Technisches Hilfsbuch-Klingelnberg) ninth edition, page 121, where he quotes from the German Industrial Standards (DIN) 1314 to the effect that one "technical" atmosphere = 1 kilogram per square centimeter = 14.223 pounds per square inch.  This figure has been used in preparation of test memoranda at Portsmouth, and for conversion, regardless of whether the figure converted from is atü or kg/cm2.
	Hogging and Sagging
	No information is available on the working of the vessel.  Considering the shape and structure of the hull, however,
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	9C-S29
	alignment problems should have been comparable to those encountered here.
	Riveting and Bolting
	Riveting was used in the superstructure and fairwater, and not on the pressure hull.  (See section S11).
	Bolting was employed in a normal manner, and care was taken to employ corrosion-resistant materials and to avoid electrolytic action.  To increase the life under shock and variable loads, extensive use was made of bolts with reduced shank area, called in German "Dehnmschrauben".  The locations and service of all such bolts are given in a book of prints, titled as above, found on U-1228.
	One such bolt was sent to the Taylor Model Basin for review.  Fir further reference to this type of bolt design, see Marks, page 882, and Klingelnberg, page 146.
	Comment
	One obtains the picture of a conservatively designed vessel without particularly novel characteristics.  Reserve buoyancy is low by U.S. Naval practice, and sea-keeping qualities are possibly impaired by its limited amount and its distribution.  Certainly the habit of not lifting on the far side of a wave is hardly commendable.
	The grouping of vents has both advantages and disadvantages.  The fact that all vents can be opened or closed by turning three cocks is an advantage, but it does not permit selection to suit conditions under which a dive is being made.  The limited reliance placed on the two buoyancy tanks is evidenced by the fact that neither vent valve can be operated from the control room.
	The lack of direct relationship between tank volume, flooding area and venting area is of interest.
	The exterior tanks are designed to provide air cushions above the surface of the water in the tanks when flooded, in order to reduce the effect of momentary high pressures when starting to blow with high pressure air.  The pneumatic effect of this cushion under depth charging could be objectionable.
	There also appears, in text material, reference to the desirability of trimming forward and then aft (durchpendeln) after submergence to be certain that all air is out of the vent lines.  If this measure is necessary, it should be considered a disadvantage.
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	9C-S29
	The use of gate valves in vent lines of fuel ballast tanks, in lieu of blank flanges, is of interest.
	The limitations in the use of the negative tank are also of interest.  Considering the size of the negative tank, the statement that it is impossible to reestablish a neutral condition with the negative alone indicates the possibility of an unfavorable compression ratio, aggravated by the compression of the air pocket at the top of the ballast tanks.  Detailed warning is given in the Special War Experiences, Machinery Section, Part XVIII, page 81.
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