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

[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

[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

[gantu]

[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.

[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

[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

[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

[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,

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,

Thanks David, Jorg.

The stern hull will get more checking and sanding, checking, sanding, checking ....

Months before I started to work on the small stern pieces, mainly the props, the shaft struct bracket, (the bracket that holds the prop on the end of the shaft ) and the shaft mount that interfaces the shaft and the hull. I use a fantastic 3D modelling program that no one else seems to use, Blender. I have been teaching this program to high school students for over ten years and it just does so much. It's animation engine is fantastic. I started working on the screws. Then worked on the brackets. Saving them as an stl. I could then send them to a printer. The printer software that I use makes it a little hard to identify exactly the right size of the part being printed. It doesn't bother me, I am quite happy to print off several different sizes of the one part. It also gives me an opportunity to arrange the part at a different angle and see how the scaffolding breaks off.




Here is the first set of parts, the smaller the parts the more the scaffold can overwhelm it and it becomes harder and harder to pull the part away from the scaffold. The larger the part the less the scaffold is a problem. On these props the fine blades broke away simply too easily. I then scaled up the parts and blades to give them a little more strength.



I printed out about 2 or 3 of each part to test fit and how they looked on the side of the boat and how they interacted together.



It takes a lot of sanding to eliminate the layers in 3D printing. This is one thing about the technique that is unavoidable. Here you can clearly see the layers underneath the primer layers. I have also used spray primer to smooth over and level all the layers however they still tend to show from underneath. They take a lot of sanding to get right. I have designed the parts around a 2 mm shaft. The prop will screw onto a thread on the end. I have thought about molding a brass insert into the strut bracket to support the shaft and reduce wear on the bracket but decided against it.



Here you see the shaft assembly. The bracket angles need a little bit of work to get them at just the right angle to have them flush and seating nicely against the side of the hull. The shaft 'Blister' at the hull end will be seated with a raised section of marked outline for the kit.





Tape is good for checking positioning. The props need to clear but also make the shaft as horizontal as possible. I have had to measure all the parts to make sure that they are all the same distance apart horizontally and vertically from the nominated center point down the middle of the keel.

More detail next week.


Dave h

[JHapprich]

Nice mill, nice boat, nice work! That keel will give plenty of space for trimming ballast. Does it turn a bit to the right bow in the last picture? Also the outline of the stb aft hull looks a bit more courved than port.

;-)


Really jealous for your workshop's window!

Found the missing nitrotube and can move on with pinch valve installation,btw!

Long weekend coming!

Jörg

[He Who Shall Not Be Named]

Your work gets better and better, sir.

David

[Davidh]

Hello all,

Thanks Rob, really appreciate the encouragement. it's just nice to get comments.


So as mentioned last week, I started work on the box keel. This is a long rectangular structure that the boat effectively sits on . I have made mine out of Renshape and cut it to size just using the school circular saw. That allowed me to get a precise flat surface very where however I ended up putting a slight taper along the sides so that the top edge is wider than the bottom. Good for creating draft angle for the hard shell fiber glass molds and eventually a great place to put the keel ballast.




Because of the slight curve of the lower hull I had to give a corresponding curve along the upper surface of the box keel. This would allow the keel to have a snug and smooth mating to the underside of the hull. this would reduce gaps either side that would need filler. So I placed the strip in my whiz bang you beaut milling machine. (I love my mill). I then milled out a lower section in the middle that I would then carve around the create the profile. I then shaved off the sides of upper surface and reduced the material till it met with the flat surface of the mill. Straight forward really.




Then it was simply a case of marking out where I wished to glue down the keel. This is towards the back of the flat section of lower hull. Take the center line and evenly place the keel either side of the line then glue down. I used a modeler's cement.



Rough up the surface before gluing down. This helps the Renshape key to the lower hull surface.




Lots of sanding from last weeks stern section hull correction and re-alignment. I had to sand back after giving a coat of resin to smooth over and reseal the balsa and wood after aggressive sanding had exposed down 'to the bone' so to speak. Had to sand either side of the keel to make sure it was consistent thickness along it's short length.




Then some filler at either ends and some down the sides. then lots of sanding and filling and sanding and..........

More next week....


David h

[rwtdiver]

Hello all,


So after getting the alignment right and with the laser line going straight down the middle of the keel, I marked a spot along one of the section lines forward of where the narrowing of the keel starts. I then took a tenon saw and started cutting either side of the keel as I don't want to snap the keep just bend it slightly. I continued cutting until I reached the sides where the lower decks will be. A cut like this allows me to push the rear hull either way whilst still having the keel intact. It also allows for a limited twist (rotating motion) of the hull to allow for the slight warp that I spoke of earlier.




The circled black market pen section is where the side of the keel is bulging a little to much and some material needs to be taken off. The whitish area is the cut. As mentioned I didn't cut through the keel just allowed it to twist by making sure that the material further away from the keel is wider to allow for a closing of the gap at the gunwales to create a pinch on one side and more of a gap on the other. I needed to pull the hull to the port.




Line it back up on the board, set it up straight and then check that the laser line that it runs right down the length of the keel. The yellow tape helps hold the stern section at the right pinch point to check for correction. After this is done I carefully make checks into the twist.






I then put a very slight twist in the hull to level out the stern and make sure that the two lower decks were level with each other. Once the bend and twist were correct and checked I then took some superglue and glued a couple of points. Sanding back the strip of hull earlier either side of the cut line has allowed me to have a smooth area for the glue and a small amount of resin and light weave. I also put some glue around the inside of the hull area amongst all the foam filler.

I then used some good old filler to fill in the pinch and gap on other side , then sanded back. The alignment is now looking much better. After this sanding, filling, sanding and lots of sanding.

The next major bit of work to be done was the addition of the box keel.This submarine as far as I can see has a box keel and I decided the best way to make with would be with Renshape. The box keel runs for most of the keel that is level. It should be reasonably easy to mold but will have some tight radius for the fiber glass. That could be fun. What i like about the box keel is that it will provide a very nice little compartment for ballast lead. Nice and low.

I took my big block of Renshape to school and after classes ran it though the circular table saw. I ran a strip about 15 mm wide with a rake to allow undercut for the mould even though this boat will be a two part split mold.



All I had to do now was check the level nature of the underside of the hull, check that this piece was all square, which it was and work out where to stick it. That's next week.


David H

David,

I really like how you are using the old building craftsmanship techniques along with the latest technology (laser) to construct your SM U-23! Your craftsmanship is superb! Really neat stuff going on here!

Rob
"firemen can stand the heat"

[Davidh]

Hello all,


So after getting the alignment right and with the laser line going straight down the middle of the keel, I marked a spot along one of the section lines forward of where the narrowing of the keel starts. I then took a tenon saw and started cutting either side of the keel as I don't want to snap the keep just bend it slightly. I continued cutting until I reached the sides where the lower decks will be. A cut like this allows me to push the rear hull either way whilst still having the keel intact. It also allows for a limited twist (rotating motion) of the hull to allow for the slight warp that I spoke of earlier.




The circled black market pen section is where the side of the keel is bulging a little to much and some material needs to be taken off. The whitish area is the cut. As mentioned I didn't cut through the keel just allowed it to twist by making sure that the material further away from the keel is wider to allow for a closing of the gap at the gunwales to create a pinch on one side and more of a gap on the other. I needed to pull the hull to the port.




Line it back up on the board, set it up straight and then check that the laser line that it runs right down the length of the keel. The yellow tape helps hold the stern section at the right pinch point to check for correction. After this is done I carefully make checks into the twist.






I then put a very slight twist in the hull to level out the stern and make sure that the two lower decks were level with each other. Once the bend and twist were correct and checked I then took some superglue and glued a couple of points. Sanding back the strip of hull earlier either side of the cut line has allowed me to have a smooth area for the glue and a small amount of resin and light weave. I also put some glue around the inside of the hull area amongst all the foam filler.

I then used some good old filler to fill in the pinch and gap on other side , then sanded back. The alignment is now looking much better. After this sanding, filling, sanding and lots of sanding.

The next major bit of work to be done was the addition of the box keel.This submarine as far as I can see has a box keel and I decided the best way to make with would be with Renshape. The box keel runs for most of the keel that is level. It should be reasonably easy to mold but will have some tight radius for the fiber glass. That could be fun. What i like about the box keel is that it will provide a very nice little compartment for ballast lead. Nice and low.

I took my big block of Renshape to school and after classes ran it though the circular table saw. I ran a strip about 15 mm wide with a rake to allow undercut for the mould even though this boat will be a two part split mold.



All I had to do now was check the level nature of the underside of the hull, check that this piece was all square, which it was and work out where to stick it. That's next week.


David H