Scratch Build project SM U-23 Class World war one U-boote. Zero Bubble model design.

[Davidh]

Hello all,

The stern printed parts have required ongoing filling and sanding. The parts are slowly looking smoother and more consistent. I haven't done too much further from last week and have spend a bit of time thinking about how to design the interface for these parts as they connect to the hull. In the meantime I have given some thought to the stern and fore hydroplanes, most notably the forward planes. The drawings show some inconsistency with different plan sections showing slight difference in their position horizontally along the hull. As best i can see it these planes are mounted just behind the forward torpedo tubes. I have therefore decided to take a position mirroring that. The planes feature a guard that sticks out just in front of the plane and extends back until it connects the furthest outer extension of the plane pivot shaft. These guards I assumed are to stop mine cables getting stuck and making the cable ride around the plane and then down the hull.

I could have made these parts with a 3D print file. I have actually modelled these parts but decided to go with a Renshape made component anyway. So I cut a thin strip of Renshape and then finely sanded it to the right profile. I then used it to create a template and marked out the outline to cut another. Once thsi was done I then cut out the second plane and then sanded it to mirror the first.




It is interesting looking at a fore plane design that is 100 years old. I wonder how effective long thin narrow planes are. I realize that the designers probably contended with narrow planes being better at dealing with mine cables. I presume that they had very little data to go on as submarines were so new. I wonder if they did any tank testing for hydrodynamics in 1912.



The next step was to drill a 2 mm hole at the pivot point . Fine sanding and making sure that the pivot holes are in exactly the same position.



So I marked out a position along the length of the hull. Found a vertical position and marked it. Then found a horizontal position and then marked that too. I had to carefully drill a either side of the hull in the same spot so that the brass rod would come out at the exact opposite point on the other side.



I have positioned the planes lower than the torpedo tube doors and further back. I have to also think about where the transition point occurs in the Z cut. So the top and bottom hull will be separated vertically just in front of where the planes will be.



I have increased the rake of the planes and angles the inner edges outwards as they head out either direction from the pivot point. The reason for this is that the hull curves up and without this rake then as the plane moves upwards or downwards it will close the distance between the inner surface and the side of the hull and scraping will occur.



More next week.


Dave h

[Davidh]

Hello all,

Since I created the forward hydroplanes and drilled the wholes in the forward lower section of hull for the brass axis, I haven't spent much time further on the planes and have moved on. I will come back to them soon enough, give them a coat of resin and more sanding and smooth over. For a while now I have looked at adding further detail to the lower side decks. The drawings show that there is not much detail on the lower decks, certainly not as much as the top deck. There is one feature that is re-occurring down the length of the hull and that is the access panels that feature along the length. These panels are rectangular with rounded ends. They are raised above the surface slightly and I assume they are access points to the side saddle ballast tanks.

Firstly I cut out a template out of 1mm thick Styrene and then traced around this template to create further access plates out of the 1mm sheet Styrene. There are about 20 per side. I spent and evening cutting the first twenty five of so and finely sanding them down to get them as consistent as possible. Once cut I then marked out the locations according to the drawings and them with some model cement, glued them to the Renshape side decks.






So far I have only done one side, I will then one day get to the other side.

In the meantime I have decided to move the development of the conning tower along a bit further. I have been looking at HWSNBN's write ups in todays work and other places. I have been reading about how to mold a one piece sail or fin out of polyurethane. David has been doing this for a long time and I think that I will find It much easier to fabricate parts if I follow along. So this will be the first model kit that I have built that will have a one piece urethane cast conning tower. So far i have created the lower base section out of a block of Renshape. I have sanded it generally to size and proportion.

in order to do an effective casting with minimal wastage I will need to hollow out the insides and make the wall thickness as thin as possible to economize of urethane and reduce weight. You don't want a solid conning tower for obvious reasons. The easiest way to do this was to split the conning tower in half down its length. So I drew a line and took a hacksaw and started cutting. Once done I then took the Dremel tool and started curving out the underside of the lower conning tower block.



I have tried really hard to get the cut to be nice and straight. If the line is slightly out it wont be of much importance as I will be gluing it back together anyway.



Time to hollow out all the insides. I have used a small Dremel bit with a constant diameter twist bit with curves teeth. This is effective in tearing out the material. I have been very careful in making sure that I don't plunge too quickly into the material. I don't want to punch a hole in the outer surface and so have had to anticipate where that point is as I have worked my way around. I have also aimed for a wall thickness of about 2mm.





More next week.

Dave

[Davidh]

Hello all,

Having cut the lower section of the conning tower in half, I started the process of hollowing out the two sides. The start of this was shown in the previous pics. As I worked my way along I had to do my best to maintain a 1-2 mm thickness of the walls at any given point. This was tricky around the curves where the raised middle section extends upwards. This is a tighter radius and it is easy to poke through to the outside.

I tried to take the thickness initially down to 2 mm and then planned to sand down to around the 1 mm mark with paper and files. This would take time, wanting to make the inside as smooth as possible and also making sure that there aren't any undercuts that might make it hard to get the part out of the mold. I also had to make sure that there was enough thickness for some of the surface features on the outside of the lower conning tower. This would come in the form of footholds and the navigation light recesses on the side.



As can be seen there was one point just forward of the step where I accidentally punched through. Some filler and then some sanding. I am pretty happy with the thickness and its consistency.



You can see even better this blowout. I placed some sticky tape along the front raised section of the tower to cover the hole. I then pasted in some filler and then sanded back to plug and smooth over the hole. I also sanded the edges to make sure that he edge rims mating up against each other are constant and have a smooth transition.



A couple of months ago I cut out a profile for the base of the conning tower. This raised strip sides right where the tower will sit and creates register points for the tower. It is a little shorter than the tower. I may scribe the outline around the edge that you see just to make it a little clearer for the kit builder.




Once I got the two sides looking symmetrical and consistent, I then decided to glue them together. I pressed them firmly against each other and applied some superglue to the edges. Waited some minute until they were secure. I then spent some time sanding inside where the rims joined. I then spent some time drawing up a drawing of the conning tower. This has been quite tricky. Once again, I have had to rely on pictures and the drawings that I have. I have also references the U9 pics from the Das Werke site and others to get an idea of its conning tower. Once again running up against the question of how similar is U9s tower to the U23? U23 being two classes later. I have several early U-boat conning tower photos but unfortunately don't know which U-boat is being photographed so it is hard to be definitive. The only pics I have of the U23 class boats are from a distance and are quite grainy.

Anybody, Anybody?.........




The drawing has been made to best of my ability. After looking at many drawings I made a note of the parts and features that kept appearing in each photo and tried to work out what features looked contradictory from photo to photo. Even after doing this there were still features that left me scratching my bald head. I don't quite know how I am going to do the frame with the fabric wrap around over over the top section of the forward Conning tower. I don't know why they did this? Why would you have Canvas material wrapping around the frame work? It would have to be taken down whenever the boat dived and eventually it would rot, surely?

Any explanation would be greatly appreciated.

Here the forward hydroplane and present. They've been given a coating of resin. The seam in between halves of the conning tower have had a fillet of filler applied and sanded back.




Next week, extending the conning tower upwards.


David H

[He Who Shall Not Be Named]

The drawing has been made to best of my ability. After looking at many drawings I made a note of the parts and features that kept appearing in each photo and tried to work out what features looked contradictory from photo to photo. Even after doing this there were still features that left me scratching my bald head. I don't quite know how I am going to do the frame with the fabric wrap around over over the top section of the forward Conning tower. I don't know why they did this? Why would you have Canvas material wrapping around the frame work? It would have to be taken down whenever the boat dived and eventually it would rot, surely?

Any explanation would be greatly appreciated.

Having stood many a look-out watch within the tight and low fairwater bridge of Guppy-2A I can assure you that rigging whatever wind/water break around you is well worth the work of setting up, and tearing down! Those four-hour night watches with the cold water in your face is all the incentive you need for protection from the spray and occasional dousing with green water! You're supposed to be watching the horizon and sky, not hiding under the bridge combing. No canvas for us, just that retractable, stupid, clear acrylic quarter dome for protection -- worthless!!!!



David

[JHapprich]

Yes, the canvas bridge had to be taken down before diving. It was oil impregnated sail fabric that was installed with on the frame around the conning helm station. In later wartime service, the canvas would often not be rigged, but to my knowledge the sailors at watch were secured with belts and chains on the static frame, wearing oil clothes and "Südwester" hats

Jörg

[Davidh]

Thanks Jorg, David.

Thanks for responding on the Canvas cover over the conning tower frame. It is going to be an interesting part of the tower to reproduce. It must have been time consuming to rig up and pull down and surely during war time, it would have been a source of concern when needing to dive quickly. I remember reading somewhere it took up to 10 minutes to prepare U1 to dive. So I cut out a section of Renshape to make the extended upper section of the tower. This needed a similar profile to the base section although is shorter in length. On either side is a recessed section that looks as though it houses the navigation lights. I am not sure about this though.




Once again for this section of the boat I am going to have to refer to U9 details. I have some conflicting information regarding the rear section of the raised section. I have information that it converges to a fine point aft of the upper hatch. However if you look at the conning tower of the U9 the rear of the upper section curves around to a bulged section that isn't teardrop in shape. I have several photo's showing different configurations.



The pic below from a Das Werke U9 model shows the rear end aft of the hatch is curved and does not converge to a fine point. This pics shows really well the wooden deck frame that sits on top of the conning tower pressure hull. If anyone has further information in the form of more detailed photographs, that would great.




So I have decided to go with the upper section with a pointed stern section. First I cut out a template that you can flip to check for symmetry and then cutting out the block of Renshape I started sanding it to approximately the right size and shape. I then took to the milling machine and used it to mill out all the material inside.



I use the Milling machine to take out most of the material however the mill wont easily go around curves. (I wish it would) This then needs to be removed with a series of round and half round files, then lots of sanding and smoothing on the inside with some filler. Once again making sure that the internal wall thickness is around 1-2 mm.




I cut a little too close to the outside with the starboard top front section. You can see the light coming through. Some filler in here. The front of these upper sections had a bluff front end. I will need to add filler and flatten somewhat. This is also the area that features a reinforced plate section with extra rivets. I have to be careful when I mill the nav light housings to make sure that I don't punch through to the inside.




I have hollowed through to the top as i intend on creating a separate top section with the wooden decking and the periscope housing sticking up through the floor. I can also create a hatch detail on the lathe to add as a feature. Once the upper section has a smooth inside and a good symmetrical outside, it will be ready to glue to the base tower section.

Once again, does anyone have good pics of the early boats? especially the conning tower!

More next week.

[gantu]

[Davidh]

Thanks Gantu,

No one else seems to have pics. So after gluing the middle section of the conning tower to the base I then sanded down the lower edge of the middle section so that it would meet and align with the base. Then some filler and more sanding. I then took a file and sandpaper and smoothed the inside to try and make the inside wall thickness consistent. I also needed to use some filler here to smooth this out. YOu need to bear in mind that a smooth tapered inner surface will make it easier to do the pull of the part from the mold in future.




Some filler needed to get the widest point of the middle section to align and give consistency to the overall shape. The conning tower should have consistent width except where the canvas covering over the railing is involved. It is much wider. As shown in the drawings the mast supports are mounted centrally.



Gone over the overall shape with extra filler. This was needed to correct a couple of small symmetry issues that cropped up with gluing the two pieces together. Here is the conning tower on the main deck section. I had yet to create the vertical sides between the higher middle and lower saddle decks. I needed some extra filler around the rear of the middle section as I came a bit thin to wall thickness at the back end.



Here you can see the close up of the saddle tank access hatches that run up and down the length of the boat. The next step after this is the creation of the top deck. This, as far as I can tell is a wooden deck structure that sits over the top of the pressure hull. The periscope supports and the hatch that protrude upwards stick out above the deck line. There is no metal cover over the pressure hull conning tower dome that I cam aware of. This wooden deck as far as I can tell is just there to effectively facilitate effective drainage of water when patrolling on the surface during a rough swell. Once gain I cannot find too many good photos bearing this out however from other models, including the U9, I can clearly see a wooden deck.




To do this I once again turned to Renshape and traced a profile for the top of the deck. I then decided to simulate the wooden slats by cutting grooves in the Renshape at fine intervals. I found the smallest milling bit that i could and then leveled the piece of Renshape in the vice of the milling machine. I then ran the mill back and forth across the surface of the piece side to side at about 1mm depth. I did this before cutting out the over all shape. Cutting it whilst square is soo much easier.



I also found the time to mark out and mill the nav light recesses on the side. These are pretty straight forward.







Once the deck grooves were cut I just needed to locate the center position for the mast support structure and then mill out the area to mount that. I did'nt mill the entire length of the deck at the very rear section features the space of the main hatch. This would be a smooth surface where I will turn up a hatch and glue it down later.



Once again If anyone has some extra conning tower details, I would love to see them..

Till next week.

David H

[Davidh]

Hello all,

well I've had more time than expected lately. I've had school holidays and because the Central Coast is considered part of the greater Sydney region, which has had a spike in COVID cases we too have been thrown into lock down. Guess who's had to stay home for the last couple of weeks. As a result the U-23's progress has accelerated somewhat, I've managed to get a little more done that I expected to.

So, the main part of the conning tower has been completed including the deck section that sits at the top. The finishing touch to this needs to be the hatch at the back on the section devoid of wooden deck. In order to create the hatch lid I simply machined up a piece of 15 mm dia brass rod down the the required diameter and create the hatch cover. Then I simply took some Styrene and created the supports that hold the hatch cover to the axel. This was small fiddly work.







After this I decided to tackle the railings that are mounted to the top section attached to the deck. I had been thinking about this section for some time as the techniques for making this section would be outside the normal modelling processes and techniques I would expect to use. I have to simulate the sagging nature of a fabric. Canvas and make it look convincing. This would be tricky. I thought of numerous different ways of doing this and weighing up the pros and cons of each as I had to weigh up the complexity of any given structure that I may come up with and how well it could be copies symmetrically and then reproduced in a series of molds. Initially I thought about cutting out a piece of Renshape and curving it to the required shape. Sculpting in the bulges and sags of the material and cleverly carving in the outline of the steel frame behind it. This would take forever.. And to get it just right and opposite on the other side would be a challenge.

The other main idea I had was to actually use fabric over a frame. I thought about using Calico or something like it. This could be made to sap and form over a frame however I also has to think about the thickness of the material and would it be too thin to create silicon molds with. The concern being that if the material is too thin that any pressure on the sides of the molds could cause the side of the molds to press against each other allowing no urethane material to create the thin fabric surfaces needing to be replicated..

I decided on creating a frame made of light thin brass rod. 1 mm dia. I could easily bend this by hand and form the shapes I needed. I started off with creating either end and the top in one overarching shape. I would then create the horizontal and vertical pieces over this.



I decided to use superglue to start with as this would give me an effective and quick means of securing the frame work together. In key points I would introduce cotton thread to wrap around as needed. I cut the small lengths of brass rod to length and then using just a drop of superglue would glue them at the correct intervals. I had to make sure that the horizontal bar running along the middle section curved outward enough to make sure that the vertical rails didn't need to curve inwards. It was really important that the overall line or profile of the bottom ends of the posts followed a curve that would allow them to align with the outer edge of the curving top deck section.



The material of choice finally revealed itself as .5 mm styrene sheet. This material heats nicely under the heat gun for a a little while and then with careful application over the frame makes a nice medium that will sag just enough to make a convincing go at looking like stretched and tired fabric over a frame. It also glues really well with superglue. I am happy with the results. Also helped by the fact that this is the only section of the boat where the shape of the fabric on either side is not expected to be symmetrical!



I then added the small little triangular piece at the top forward section. This material has glued down really well and make the whole frame totally rigid now and not flimsy at all. Before hand the frame was really fragile and some of the vertical posts had broken off.




Thinking about how this whole section would be created using the usual silicon molds got me thinking about the silicon of the mold being trapped around underneath the frame between the brass tube and the styrene. I would need to make sure that the frame world was clearly joined all the way along to the styrene. To do this i decided to used filler pressed in along underneath the gap between. I then took a dremel and carefully ground any material sticking out.








Till next week.


David H

[JHapprich]

Good work! You could even mimic an actual canvas surface by pressing the warm styrene into a fabric sheet.

Jörg

[JHapprich]

Good work! You could even mimic an actual canvas surface by pressing the warm styrene into a fabric sheet.

Jörg

[Davidh]

Hello all,

Hi Jorg, Thanks however i think that if I were to use fabric to create a texture the weave would be too big. Thinking of Germany right now with all that flooding..


So I now started working on the Stern planes. One of the things I have noticed about the planes on these U-boats is that they are small. I just wonder how effective they would have been. So the stern planes are mostly rectangular. I decided to go with Renshape once again. I could have printed them but they are a pretty simple shape and creating two opposite pieces really isn't a big deal. So I took apart of the flat strip of Renshape that I had cut for the deck. About 3 mm thick it is an ideal thickness to start off with .

As I have found throughout the build process, the drawings that I have, lack consistent detail. Photo's have also hindered this section of the boat. The drawings show what look like two individual sizes of stern planes and the side view and section show little information about the height of the stern planes up along the side of the hull. I do know that they are above the stern glands where the shafts exit the boat but how far above?




So I traced out the shape of the profile and marked it out on the piece of Renshape. I then cut around with a knife and repeated the process. I then spent a bit of time sanding and smoothing the overall shape and then repeating the process again with the other side, constantly checking the symmetry with each other. The thickest point of the stern planes will be where the pivot occurs.



The inner forward edge of the plane is angled inwards. I believe this is because the pivoting moment of the plane will mean that if there is not an angled surface then it will hit against the angled surface of the hull and restrict the upward movement of the plane. I will be mounting the planes slightly outwards on the shaft to clear the hull anyway.




I then marked out the pivot point and where the hole would go. So I then set up the drill press and drilled a 1.5 mm hole along the thickness of the piece.




I then took the time to mark out and drill the shaft holes in either side of the hull. I marked down the side of the hull and made sure that the holes were the same distance back either side of the
stern of the boat. This was the last major drilling operation that needed to be done before I could close up the hull with the three deck sections.



The rear inner surface is slightly angled for the same reasons as the inner surface forward of the pivot.





More next week.

david h

[JHapprich]

Hey Dave!

I believe the wider outline of the presumed 2 diveplanes being a protective panel installed on top of the actual plane, somewhere half-way between plane and deck. Take a look at the "Das Werk" U-9. Edit WRONG,see below

Planes look nice, but how much downward angle do they offer.they must have had a cutoff to the inner stern.

Cylinder has arrived, however i need to fetch it from the parcel bureau as i am in holidays right now.

+++ correction after some research +++

There was a frame of steel tubing around the plane.some srof net/mine protection. The plane pivot was located halfways between deck and keel level.

Jörg

[Davidh]

Hi all,

Thanks for the feedback, Jorg. On earlier boats there was the upper framework directly above the planes and even a second plane directly above. I can only think that the frame work was designed to give the crew some idea of where the planes were underneath when docking at a port to make sure that the wharf or pylons didn't bump up and damage the planes that weren't visible. On this class (U-23 class) I am pretty sure that they didn't have an extra set of planes at the front at least unlike the U-9 class. I don't think the planes need a huge amount of travel either way..

The frame work in front of both the forward and stern planes I am confident was to guide mine cables around the outside of the planes and then off the back off the boat so that nothing got snared on a bracket of part of the planes. I could easily see a cable getting wedges in between the plane and the hull at where the shaft exits.

So many times i have laid the outer lower decks in place. The top deck being glued down a while back. Before I glue down the sides I need to check the relative distance either side of the upper deck and make sure they are symmetrical. If one side featured distances that were too far out then I would need to sand back, or if only a small distance I could easily fill but reducing is always easier than adding. So after checking up and down the length of the hull either side it soon became apparent that one side, port was wider than the starboard side around the amidships. This was also confirmed by the side decks. They are mirror image of each other and one overhung the port side more than the starboard. The middle region amidship up to nearly 10 mm variation. this would mean sanding back about the edge and bringing down this measurement so that there simply wasn't greater beam on one side than another.



It became clear pretty soon that I would have to do some aggressive sanding back on the port side and that i could easily sand through to the thin sheet balsa and blow a nice large gap Titanic style. As a result I sprayed some expandable polyurethane foam like I did on the stern end. This wold reinforce the balsa and create a supporting layer if I did need to exceed the sides and i wold be able to resin and glass over the top of it. So i would go hard with the sander and then measure to check as I cams slowly closer to having both sides, even.




I really had to grind down to the frame and into the polyurethane filler foam. This was bought the deviation down to less than a mm. I have also had to make sure that I managed to keep the curve of the hull going. I also ran the sanding block over the top of the frames as I also needed to make sure that they were also level.



Using a thin layer of weave allows to cross the gap between areas where there are voids under the frame and where there are gaps in the foam. Then lots and lots of sanding then filling in low points and then once again, sanding, sanding. In the meantime I have started working on the side vertical strip that join the lower hull deck on the side to the raised upper middle deck. This will eliminate seeing the framework the last visible parts of the inside of the hull.



I need to work on the side strips and mark out and cut the drainage holes and vents on the side. These vents are a distinctive feature of World war One U-boats.



Side next week.


David H

[rwtdiver]

David,

Your submarine is a masterpiece! Your scratch building capabilities is to be admired! Your attention to detail certainly shows in your craftmanship, and your unlimited patience!

Following your build certainly does inspire me to do better! My wife (Retired 32 years teaching school) always tells me, patience will enhance the final results! Thank you very much for sharing this project with our group David!

Rob
"Firemen can stand the heat"