the hermetically sealed class 206A submarine

Hi friends,

among my papers I have found an article that I had written in 1995 for a German ship modeller Magazine. As it may be of some interest for you I have started to translate it into English (please excuse my poor English) and will post it time by time.
Here is the first item:


The Hermatically Sealed Model Submarine

Story of a model submarine of the German class 206A submarine S195 / U16


Preface

This is the story of an unusual model submarine that I started to build in 1976, rebuilding it in the early 1990ies and that is "in service" since 1994 up to now. As the title claims it is hermetically tight by its design concept - we will see later what this means in details. This model is one of the first submarine models with an electronically commutated ("brushless"), wet running DC motor (if not the very first) and is the precursor of my aluminium model S182 / U32 of the recent class 212A of the German Navy that was described in a guest article in one of the latest issues of the AMS "In Depth" magazine.


How it begun...

The story begun in 1975 when a ship modeller friend showed me a poster of one of the first  class 205 submarines of the German Navy. As I already had had the wish to build a model submarine but did not like the World War II types very much I just made up my mind to build this (at this time still modern) type.
The class 205 was the first submarine type of the young Federal German Navy to be built in greater numbers and it were the first to be built with hulls made of non magnetic (stainless) steel to enable them to operate also in shallow waters where mines meant even more a potential danger. In the cold war in these times the were intended mainly to operate in the Baltic Sea. The were rather small, about 500 tons displacement but carrying 8 torpedo tubes in the bow.
The first batch became a disaster soon - although extended investigations on nonmagnetic steel had been made before building, the steel of the hulls began to corrode internally (as later detected as inter- crystalline stress rupture corrosion). So after a few years the submarines were decommisioned for safety reasons. Some years later in the mid 1970ies, the type 206 was built, now with better and corrosion-resistant steel. This class, modernised at the end of the 1980ies as class 206A, was in service for more than 30 years until they were replaced by the class 212A with air independent propulsion system by fuel cells . The rather small class 206A submarines, about 500 tons displacement, 48 metres in length and with a crew of 22, were the first German submarines that crossed the Atlantic Ocean again to join NATO exercises in the Caribbean Sea and to make goodwill visits to the US.      

Another reason to build a model of the class 205 was that it was well suited to be built with a plastic tube as pressure hull and a technics rack insert for radio control, propulsion system and diving system and the batteries. Bow and stern sections could be made of GRP laminates, the conning tower of polystyrene plastic sheet material. This design offered a splendid access to the interior and provided a good structure stability of the hull as well as good conditions for pressure tightness by only a few O-ring seals.
I had seen submarine models with their hulls covered by hatches with "thousands of screws" and I wanted to avoid this design with its inherent drawbacks under all circumstances.
To get sufficient space inside I planned to use a plastic sewers tube of 160mm outside diameter. To fit into the boot of my car I drove as a student those days (a FIAT 127 , I still have this car preserved as a classic car now) the model should not be longer than 125 centimetres so the proportions would be a little compressed.
I designed the internal technics rack as a framework of three 10mm x 10mm steel rods hard solderer together with ring ribs made of 10mm x 2mm flat steel. This framework should extend from the end of the stern with the propeller tube up to the bow bulkhead where the cylindrical section ends. The conical rear section of the hull should be fixed to the frame and the tube should be shifted over the frame just to the beginning of the conical section. There an O-ring seal should provide tightness. The front end of the tube should be covered with a circular aluminium bulkhead plate also equipped with an O-ring seal. Tube and bulkhead should be screwed to the frame by a screw penetrating the bulkhead in the centre and sealed there and going further into a thread in the frame. The bow should be free flooded and attached to the bulkhead. The rudders were designed to be made of brass sheet material and the diving system should consist of a ballast tank made of brass sheet metal to be filled by a hose pipe roller pump.

....(to be continued)

As the model looks today...

here the Story continues


Starting to build...

Just after the design considerations had settled in my mind I started to build the model. Main source of material were several DIY markets where I got the sewers tube, steel rods, sheet brass and so on. I was a student in those days and my working conditions in my small student's flat in the town of my university away from home were very limited (as well as time). By occasion I got access to a (very old)  lathe and could make several things that needed to be turned (e.g. the case and some other parts of my ballast water pump, the front bulkhead and others). By the time I made progress and eventually the model, although being not ready, was at least able to swim and submerge for the first trials.

The first experience did not really satisfy me - the model did run well, the diving system worked as intended but due to the rudder arrangement like that of the original early class 205 submarines (two steering rudders besides the stern section and not in the propeller thrust) the model had a very bad maneuverability, especially when surfaced. With rudders full in port or starboard direction the model needed a circle of nearly 20 metres to turn (in this case it behaved like the original ones which needed tug assistance in harbour very often). It did not make fun to control it with this bad maneuverability
And - what I disliked most - was the fact that the seals for the propeller shaft and for the rudder shafts were not really water tight. After submerging in depths up to 3 metres for a couple of minutes I found some drops of water having penetrated the seals. Due to my limited workshop abilities bearings and the surface of the shafts had been made not so precisely as they should have been and so the leakage occurred. So I thought about improvements...

But in the following time other themes should keep me away from working on the model - finishing my studies, marriage, entering my profession, building a home and founding a family.

Nevertheless I was thinking how to improve the model from time by time but it would last several years until I became able to do it...


(to be continued)

Picture of my model as class 205 submarine U6, bevor rebuilding as class 206 submarine

Interesting account of the development. Slightly leaky shafts and a poor turning circle are common experiences. Look forward to seeing how you sort them out.

David

Hi David,
the bad experience with leaky shafts made me think about a completel different solution (just like Monty Python: "And now for something completely different..."), just see:



New ideas...

Of course improvements would have been possible to achieve by better material of shaft seals and a less "eccentric" running and furthermore polished stainless steel shaft, also for the rudder shafts and also more precise workmanship than I had been able to do in the time when I had been a student. But an idea arose in my head whether it wouldn't be possible to make a complete different approach and avoid sliding seals at all (to quote Billy Joel: "I don't know why I go to extremes..."). A device not being necessary and not being present couldn't be a source of leakage at all. So it was the challenge to design solutions for propulsion and steering. The previous diving system that worked with the hose pipe roller pump was already well suited as the pump was already a hermetically sealed system by principle without any sliding seals or valves.
At the end of the 1980ees I resumed my work on the model.
For the propulsion system I thought first about a magnetic coupling where an inner rotor driven by a conventional motor and equipped with a number of permanent magnets would couple through the pressure hull wall to an outer complementary rotor with magnets that would be attached to the propeller shaft in the free flooding outer area. This would give a perfect hermetical separation between the interior of the pressure hull and the outside water. Only a little later another idea came into my mind: Why using a conventional motor with magnet rotor to drive the outside rotor? A stator system with coils controlled by switching transistors just depending upon the momentary rotor position would do the job even better! In fact such an arrangement would even be an electronically commutated DC motor with hermetically separated mechanical output, or, as we would also say today, a wet running brushless DC motor! So I started my design by making sketches of the mechanics and the commutation electronics, nowadays called as "motor controller". But this was in 1992 and brushless motors were not so common as today...
As the approach for my wet running brushless motor was a completely different one my design was also different to the designs you will see today, in mechanical design as well as concerning the motor electronics. My motor is a sensor controlled motor with block commutation and the motor electronics incorporates an overlay PWM (pulse width modulation) for speed control as well as reverse rotation function. The motor electronics has a direct connection to the servo output of the RC receiver that is galvanically isolated and it provides also a current limiting so that the motor cannot burn off even when stalled. The motor electronics is mounted to the motor casing so it forms one unit.
Designing and building the motor took more than a year...

(to be continued)

Hermann wrote:Hi David,
the bad experience with leaky shafts made me think about a completel different solution (just like Monty Python: "And now for something completely different..."), just see:



New ideas...

Of course improvements would have been possible to achieve by better material of shaft seals and a less "eccentric" running and furthermore polished stainless steel shaft, also for the rudder shafts and also more precise workmanship than I had been able to do in the time when I had been a student. But an idea arose in my head whether it wouldn't be possible to make a complete different approach and avoid sliding seals at all (to quote Billy Joel: "I don't know why I go to extremes..."). A device not being necessary and not being present couldn't be a source of leakage at all. So it was the challenge to design solutions for propulsion and steering. The previous diving system that worked with the hose pipe roller pump was already well suited as the pump was already a hermetically sealed system by principle without any sliding seals or valves.
At the end of the 1980ees I resumed my work on the model.
For the propulsion system I thought first about a magnetic coupling where an inner rotor driven by a conventional motor and equipped with a number of permanent magnets would couple through the pressure hull wall to an outer complementary rotor with magnets that would be attached to the propeller shaft in the free flooding outer area. This would give a perfect hermetical separation between the interior of the pressure hull and the outside water. Only a little later another idea came into my mind: Why using a conventional motor with magnet rotor to drive the outside rotor? A stator system with coils controlled by switching transistors just depending upon the momentary rotor position would do the job even better! In fact such an arrangement would even be an electronically commutated DC motor with hermetically separated mechanical output, or, as we would also say today, a wet running brushless DC motor! So I started my design by making sketches of the mechanics and the commutation electronics, nowadays called as "motor controller". But this was in 1992 and brushless motors were not so common as today...
As the approach for my wet running brushless motor was a completely different one my design was also different to the designs you will see today, in mechanical design as well as concerning the motor electronics. My motor is a sensor controlled motor with block commutation and the motor electronics incorporates an overlay PWM (pulse width modulation) for speed control as well as reverse rotation function. The motor electronics has a direct connection to the servo output of the RC receiver that is galvanically isolated and it provides also a current limiting so that the motor cannot burn off even when stalled. The motor electronics is mounted to the motor casing so it forms one unit.
Designing and building the motor took more than a year...

(to be continued)

Some ideas that will help you magnetically isolate the internal control surface linkages from the external linkages:



David

I actually like that approach allot!

Hello everyone,

sometimes things last a little longer than expected, especially when your grandson is growing up and keeping his grandfather constantly busy... (but this young boy is an enthusiast for modelling, too and this gives hope that our hobby will not die out)

But now I shall continue this building log as announced long before, starting with some pictures of building that electronically commutated (brusless), wet running Propulsion motor. I must apologize for the bad quality of the photographs; they have been scanned from conventional photographs made many years before in 1993.


Making the disk rotor from Aluminium

disk rotor with magnets and motor housing

preparing the stator core , made from iron tape


Motor housing with studs for hall sensors

First test run with Propeller as motor load

The fully assembled motor


Motor installation within the pressure hull

Rebuilding the model...

Besides the development and construction of the motor I also worked to modify (or better: "rebuild") the model. First I removed the old rudder arrangement at the stern section to replace it by that type of the class 206 submarines that has the side rudder behind the propeller instead of the twin rudder arrangement besides the propeller port and starboard of the old class 205.
The new rudder fin was cut out of an aluminium plate of 20mm thickness. Although using an electrical saw this work was stressful and lasted... The fin was then tapered first using a grinding machine and later using a file with much spirit for lubrication to get a smooth surface. The rudder blades were also made from solid aluminium, the bearings were made from stainless steel to provide sufficient stability.
The old conical stern hull section of glass fibre reinforced plastic was slotted to insert the new rudder fin that was eventually screwed to the steel framework of the technics rack.


The rudder fin section


fin and rudder blade

aft diving planes


Inside the rudder fin block two vertical holes were drilled each with a 3/8" thread inside to install the rocking lever force transmissions for acting the rudders. These rocking levers have ball couplings for pushing rods at both ends; the inner ones are attached to the side and depth control servo respectively and the outer ones are linked to the side rudder and depth control planes. The levers have a bearing in their middle by a ball and the outer section wears a rubber tube that acts like a diaphragm to provide the sealing as a continuous but flexible separation barrier between the exterior and the interior of the pressure hull. These rocking lever transmissions are built up as complete components to be screwed in the rudder fin. In case of maintenance they could be easily screwed out and overhauled (but this was not necessary up to now after more than 25 years).


The parts of the hermetically tight rocking lever transmission

The fully assembled rocking lever transmission device


For acting the bow depth control planes I built a magnetic coupler that provides also a hermetic separation. Magnetic coupling was also used to erect the periscope and the snorkel; a small gear motor inside the hull drives a rotor that is equipped with small permanent magnets. Outside the hull there is another rotor with magnets that is attached to a threaded spindle with a nut. The nut is coupled to the periscope and the snorkel and when turning the spindle the periscope and snorkel are erected or retracted respectively.


Deploy unit inside fin (fin removed) for erecting periscope and snorkel


Deploy unit with outer magnet disk of magnetic force Transmission


Inner drive with inner magnet disk

The diving system is also hermetically sealed and avoids any kind of sliding seals. I made further use of my old self made hose pipe roller pump and the solid ballast tank made of brass sheet metal. When filling the tank the air is retained in flexible plastic bags I got from household wax tubes. By this there is always an undisturbed envelope between the exterior and the interior world and moisture will be kept away from the interior of the components inside the pressure hull. Of course you will need space for these air bags but it is possible to spread up onto several smaller bags that can be arranged more easily. A pressure sensitive switch will stop the pump motor when the tank is filled enough to prevent a burst.
The pump is driven by a self designed motor controller that allows also low speed resulting in extra fine ballast trimming if necessary, "drop by drop".


Parts of the hose pipe roller pump

Interiour of the pump

Complete pump with Motor drive



Furthermore I built an electronic levelling regulator to keep the model level when submerged and running on speed. This regulator uses a self made sensor in kind of a spirit level with optical sensing and analogue regulation circuitry acting on the depth control servo.

Power supply of the model is provided by a battery of 10 Nickel Cadmium cells of 7Ah nominal capacity and 12V nominal voltage. The battery circuit is fused and switching is provided by a power relay that is controlled by reed contacts, one for ON and one for OFF. So it is possible to switch the model supply from outside by means of a permanent magnet. The motor electronic and the controller for the ballast pump are operated by 12V whilst the other consumers, especially the receiver, operate on 5V that are provided by a switchmode step down converter with linear low drop post regulation.
The receiver is of double conversion superheterodyne type and operates in PCM mode together with the transmitter; both are from the manufacturer MULTIPLEX. To improve reception of low level signals a self designed selective low noise preamplifier is connected upstream of the receiver.

As an additional function I installed a small video camera in the bow section. The camera is contained in a metal tube that is inserted in the front bulkhead of the pressure tube. The camera window lays behind the door of the upper starboard torpedo tubes so the door has to be opened for camera operation. Because it is not possible to transmit the camera signal itself through the water it must be transmitted via a cable instead. For this purpose I use a video modulator module that converts the signal to a modulated UHF RF signal that is coupled to a coaxial transmission cable that leads from the submarine to a small monitor attached to the RC transmitter. In opposite direction the transmitter signal for control can travel along the cable and reach the model even in grater depths than normal. So it is possible to control the model in more than 5m depth.

For a case of emergency the model is equipped with an emergency buoy that is linked to a cord of 20m length and wound on a drum. The buoy is arrested normally by an electro magnet. In case of emergency it can be released and when surfaced it will mark the position of the sunken submarine. If the model does not stick too much in the mud at the bottom it could be even lifted by the strong cord.
As this electro magnet is located in the free flooded bow section I took care to prevent corrosion problems. So instead of a common iron core a corrosion proof ferrite pot core was used. The coil former with the windings of copper wire were inserted into the pot core and were sealed completely with epoxy glue. The counterpart attached to the buoy is made from nickel sheet metal and also corrosion resistant.


Front view of the interior of the free flooded bow section

(to be continued)

Stunning …. stunning work, sir!

Hi David,
thank you for your compliment.

By the way, your models are also stunning and fine work and they are looking very authentic and realistic.


Klaus-Dieter (nickname Hermann)

As announced I will continue a little further with some pictures...

The following sketches will try to explain the basic hermetically sealed design with wet running Propulsion Motor, rudder control, diving System with hose pipe roller pump and solid Ballast water tank and flexible bags for retaining the air.



Model surfaces, note the empty tank and empty air bag



Model submerged, note the flooded tank and that now the air Content of the tank has blown up the air bag

In both cases the roller pump blocks the water flow into or out of the tank so the buoyancy of the model will not change.

Meanwhile the model is "in service" since 1994 without interruption and maintenance to the Propulsion Train. It has spent more than 400 hours in operation and has run more than 100 miles, mostly in Ponds in our local region around Bremen but also on numerous events like modeller meetings and model exhibitions


S195/ U16 with opened hull on a model event in Schwelm some years before


Some Pictures taken on an event in a Swimming bath, the model down to the bottom in 5m depth with Video camera link via coaxial cable to a small Monitor attached to the RC transmitter


S195/ U16 running surfaced on the lake Weichelsee at Rotenburg near Bremen, northern Germany


(to be continued)

Kind regards
Klaus-Dieter (Hermann)

Klaus-Dieter,
It is good to see you back. You have been missed.
Your submarine is a work of art! Thank you for sharing and inspiring me to build better. Look forward to your next post.
Peace,
Tom

Hi Tom,

thank you for your kind reply. Well, I have been obviously inactive in the last time but I had watched the activities here in the AMS Forum. Meanwhile I am sixty-four (you know that old song "When I'm sixty-four...") and I am still on the job. It is a common experience that with proceeding age you become slower and so you will need more time for your regular tasks. Since 6 years my wife and me are grandparents and our grandson deserves our attention, so there is not much time left for me for the Hobby. But next year I will retire and hopefully have more leasure time...

Kind regards
Klaus-Dieter

A couple of questions, one, how do you prevent water from going into the air bag? And two, why not pump water directly into the airbag or now water bag and not use a tank?
More photos when you can! I am enjoying the workmanship.

Hi,
so I will try to answer your questions concerning the tank design. I must confess that this desing is a little strange and exotic and in total it needs more space.
Of course it is possible to omit that rigid tank made of brass sheet metal and use the air bag as a water bag. The reason why I did it in that more complex way was that this rigid tank has a fixed form so that the location of the ballast water is relative stable. In a flexible water bag the water could slosh in longitudinal direction resulting in an inclination up or down of the Sub. You can extend the tank cross section nearly to the inner cross section of your pressure hull so you can build your tank rather short in longitudinal Dimension. Then sloshing water inside the tank will not have a significant effect to the trimming.

The air bag is only used for venting the tank and you can put elsewhere, whereever there is sufficient space for it. If there is no large space in one volume you can even split up in several bags that may find space more easily. The air bag provides a flexible diaphragm that separates the dry interiour of the pressure hull from the water.

In parallel to the air bags I have provided a pressure controlled switch that stops the ballast water pump if the air pressure reached a certain limit (the tank will be filled about three quarters). So there is no danger of overfilling and of burst of the air bags.

The air outlet tube stud for the air escape out of the tank is located on top of the tank so in upright position of the sub the water inside the tank will stay beneath the air outlet. As the tube diameter is small and the tube is fillid with a little piece of plastic foam water can hardly escape from the tank in direction of the airbags, even if you tipped the sub over. And even it would happen the water would come out of the bags as they become completely flat when the pump has sucked out the ballast water.

I will post more photos soon.

Kind regards
Klaus-Dieter

Thank you. I understand and your explanation makes a lot of sense. Look forward to the photos when you get to it.
Peace,
Tom

Hi Tom,

here come some more pictures. Selecting and scannung from conventional photographs took a little time...

On the first pictures you can see how the propeller was made in a very conventional way.

Turning the spinner



cutting out the blades by a jigsaw



cutting the grooves for the blades



positioning of the blades before soldering



The finished Propeller after bending the blades




The following pictures show the interiour of the free flooded bow section (bow cladding removed)



and the inner side



And then I found some pictures I took in 1999 on the submarine base of the German Navy at Eckernfoerde when there was an event "Day of the open Naval Base".

Here you can see my model put on the so called "battery hatch" (the hatch where you can take battery cells in and out of the pressure hull) of its big brother (see the red arrow)



A sister boat could also be seen approaching the base. There you can see the very small size of these boats (displacement 500 tons, approx. 50m in length, crew of 22 men)



These pictures are historical now as the class 206a was decommisioned since several years. Most boats of this class have been scrapped after having been in service for nearly fourty years (the stainless steel hull represents a reasonable value for scrap metal) . Two boats have been sold to Columbia where they are still in service for coastal survey and two other boats (including S195/ U16) have been retained as carriers for spareparts. We hope that one of the last boats will be preserved as a museum boat...

Kind regards

Klaus-Dieter

That photo with your model on the deck is fantastic!
I love your engineering in that sub. It is a work of art.
Thank you for sharing!