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

[Davidh]

Hello all,

After completing the Anchor hawse area I then decided I needed to do some consolidation and also some symmetry checking. I find that after a couple of weeks of progress on something, I usually find that there is some aspect of the design that needs re-calibration of sorts. I need to go and check and maybe correct something. On my mind for a while has been the back end overall and checking for symmetry. I have been aware that the stern section has been subtly off center. Every so often I place the boat upside down on the alignment board and check something over the length of the boat. This time I chocked underneath to accommodate the rise of the bow section and them made sure that the axis line from the top center to the bottom middle of the keel had the boat perfectly vertical.




I then clamped down my section template and checked its position with my equivalent of "Jo blocks". I then drew my sectional lines once more. These lines help you look down the length of the hull and see any discrepancies in the hull sections, all the lines should be consistent with gradual change as the sections evolve along the length of the hull. I then set up my Laser marker that is mounted in the ceiling rafters and points down at an angle. I use this to cast a straight line along the keel center line of the underside of the hull.



I aligned up the bow, with the laser running vertically up the bow line and then roughly center along the hull. I then made sure that it was hitting the center of the extreme stern. As I did so I could see where the stern section was deviating. Roll down the rear Garage door and you could see the laser even better. The original pencil line along the keel was out. The laser can be re positioned however I found that it was better to simply move the boat on the stocks. The laser in this photo the hits the extreme tip middle of the stern. As can be seen the laser falls off the left side of the transom. Here I will cut the transom and make a break before repositioning it slightly to the left to comply with the laser.




After lots of eye balling and checking the general arrangement of the back end, I realized that there may also be a slight twist in the stern section as the two side decks do not look like they side level with each other. So I thought about cutting the hull and angling it one way them slightly rolling the hull one way as well. This could get tricky..



You can see that alongside the transom not quite being right the stern tube for the rudder that butts up against the stern post is also off. Laser levelers are awesome. I thoroughly recommend having one.
I decided to make a cut well back before the transom starts. I would use a tenon saw as although it has a wide kerf it has a flat wide depth that will keep the cut from meandering.



More on this next week. In the meantime I have also been working on the 3D model. These 3D models are awesome for working out geometries and overall layout. They also make really nice illustrations for the instruction manual. Here are some scenes. The stern, like the real one are a work in progress, however unlike the real thing this is a nice symmetrical build as Blender has a nice mirror modifier.




The faces around the back end are still a bit rough but with some work it will be smooth and look a lot nicer. Stay tuned...



I placed the bare bones of the ZB-2 twin drive cylinder next to the basic hull to check fit and so forth. Also made inroads with the conning tower.

More next week.

david h

[Davidh]

Hello all,

I haven't glued the stern torpedo section on yet as there is still some alignment work to do on the back end. However I decided that I needed to get back to a pressing issue at the front end.
I have a series of pics showing that these boats had at least one anchor on the front end. Illustrations have suggested both sides but as far as I can see from the odd photo, only on one side and the Starboard side at that. This below pic is the main reference.



This pic shows U-23 and 25 in Kiel before the war. This clearly shows an anchor housing on the starboard side of the bow. forward of the emergence of the lower saddle deck and almost half way up from the waterline to the top front deck. As far as i can see there is a molded or shaped section of hull that I am guessing was a piece of casting that acts as the Hawse pipe for want of a better term. I have a vague Idea about the overall shape of the anchor even though there is only so much zooming in on the pic. The Hawse and entire anchor assembly looks like it has been set at about a 20 degree angle.

So I started as I always do when there is some detail involved with a piece. I start sketching what I think I'm going to do. In order to get the hawse shape right, ( the recess that the anchor pulls into, I think) then I needed to get an idea of the Anchor first. I thought that typing I ' World war one U-boat anchors' into Gary Google would bring an avalanche of results ..not. Si i had to find images of anchors that looked similar. "Old anchors" would have to do.




I took a piece of Renshape and cut it to the right size. I then started carving and sculpting. The lower section of the anchor is wider and thicker so I had to create a deeper recess at the bottom of the Hawse.
A bit of Dremel action.




Ultimately I am guessing, the best pic I have is the one at the top of this post unless anyone has anything closer. I haven't had many submissions although Gantu has been giving me some gems.
After a fair bit of Dremelling (is that a word), I then used some smooth sandpaper to give a little subtlety to the overall impression. I intend to create an anchor that will cover over the details inside the hawse anyway so you wont see much of the detail.



I then had to mark out the place where the hawse would be located. This would require me to cut out a square hole at an angle to the hull soe I had to clear out some reinforcing from the inside to get to the spot where I would eventually cut out the spot. This square hole would be slightly smaller in area to the block. I would then simply press and glue the block in shape and fill and sand back the slight thickness of the balsa and resin laminate outer hull.







Till next week.

David H

[Davidh]

Hello all,

This is where the rear torpedo tube assembly comes together and looks something like what that photo shows. So I took a small piece of Renshape and placed it in the lathe to turn up the tubes. Firstly I measured the diameter of the scoops at the front in the bow to make sure that the tubes i came up with would be consistent. I had to make the diameter slightly greater than the diameter of the scoop at the front. I then turned down a smooth dome feature on the front and then a slight line running at the transition point to the dome.



I then marked the center axis down the middle of the piece. Once this was done I then looked at marking out the area that I would mill out to make the recess that would hold the two tubes.
The recessed section will have a flat section that is positioned just where the curved dome section starts. As can be seen from the photo it looks like the top of the curved section along the top rim of the domed section stops at the partition line and from there the curve of the lower tube extends rearward. The joint between the curve of the tube and the general shape of the hull is met by what looks like a plate line or flange that runs down at an angle and curves even lower just beyond the lowest point of the numbers.

I will be creating the diminishing tube curve on the Renshape recreation. I placed the Renshape end pointing upward on some metal squares in the vice of the Milling machine to mill the recesses. Below is what the recessed section looks like. Just need to repeat on the other side.




In order to make the tubes fit I need to take a pretty drastic cut out of the tubes. This will create a roughly elliptical curved section that will then allow the tube to gradually curve up to the full domed door section at the very end. This makes the tube recess look really really small.



First side done with the tube in place. The gaps between the tube and the recessed section it fits into will be filled in with filler and sanded back.



I have noticed that the dividing line that curves up from keel to center top section shows a pronounced bulge outwards. I decided to create a spine of thin Renshape to simulate this and will build up filler either side then sand back to just right.



Here I have placed the half completed section in the area that It will eventually go. The roughed out section was too high and in the interests of thinning quickly I get aggressive and bring out the
rasp.. This will be followed by a lot of further eye balling and finer sanding.

David H

[Davidh]

Hello all,

After working out the precise location of the stern shaft exits, I sanded back the filler that I placed inside the holes so marked so that they created a curved "scoop" like shape similar to the front of the torpedo tubes. This should mold well when it comes to producing the hard shell molds in a couple of months time when the hull is ready to be used as the pattern for the labyrinth of molds that I will need to make to get all the detail. It will most likely be a combination of hard shell molds and silicon soft molds with a glove hard back.

The bow section looks reasonable and so i will eave alone for a while, the stern looks like a bit of a dogs breakfast and so I decided to tackle the next bit of detail that would need tackling and that would be the stern torpedo tube arrangement just above the shafts and rudder. I do have one really good photo taken in 1914 (the month that WW1 started) that shows the rear end of U-39 on the slip at Germaniwerft, Kiel. She was a very similar in design to the U-23 class. As I have no more pics of U-23 in drydock to this detail then I will simply have to go with this. This is actually a really clear photo.



So I started out by marking out a section of the very rear of the hull to cut out and did so. Then I took some paper and made a profile of the shape of the stern from a top view to get the curve right for the piece of Renshape that I would be cutting out to make the section that would compose the twin stern tubes. As can be seen by this photo the stern tube doors are a bulges almost spherical shape and I have spent a lot of time trying to work out the geometry as to how this all works. Still trying to work it out...



I used a paper template to mark out both the horizontal and vertical profiles of the shape. You can see i went short of cutting off the entire back end.I left the section immediately beneath the deck. This would give me a good idea for the template. I would also need to grind down this area later on when getting the stern to behave.



The paper templates put to good work in making sure that the Renshape will be of the right profile when it goes on the back of the boat. Now i just got a coping saw and reduced the piece until the general shape appeared and then it was just a matter of sandpaper.







Fine adjustments with sandpaper and then ready to check fit. The back end itself will still need work so the shape isn't final however it is close.



After this I decided to look at the tube doors. I decided that he best way to create these would be through the use of more Renshape that was machined on the lathe to a cylinder with a domed end. I could turn these two up pretty quick, just had to make sure that the diameter was just right. Once they were done I simply had to put a light crease at the point where the dome starts and the would be on their way to looking pretty good.



Next week, milling the recesses for the tube doors and making everything look like the pic.


David H

[Davidh]

Hello all,

Thanks Scot,

So once the template was glued in place I cut two brass shafts. One that sits, touching the center of the shaft output from the cylinder template and going to an estimated point where I envisage the shaft output location to be. I then cut another short length of brass long enough to go from where I am anticipating the shaft output to be to where I am expecting the shaft to terminate with a propeller on the end. The challenge being to make sure that the two individual shafts meeting end on end are as straight as possible.

I measured the distance that the shaft needs to be from the hull plus a little bit more to allow for blade clearance. I am also thinking about how to make the shaft to be as level as possible. The drawings show the shafts to extend out of the hull almost horizontal. I don't know if I can quite get this as it would mean that the shaft would be quite high. The next major step was making a mock up of the shaft bracket. This would hold the shaft in place and give me the precise positioning of the end of the propeller and I could them work out clearance.

I cut out some small lengths of 3mm brass tube to act as the shaft bracket. I then cut some 1 mm thick styrene sheet to act as the bracket and super glued them on at an angle similar to the drawing section of the U-23 at the stern. As can be seen the lower bracket is almost horizontal and the vertical is nearly, vertical.



Mock up bracket. The styrene can be cut off shorter if needed.




I slid the bracket onto the shaft and after looking at the drawings I worked out where the bracket should be positioned. This would give me an idea of clearance. In order to hold the bracket in place I have cut out some small strips of tape and stuck down the two bracket arms in various spot to check for clearance and positioning of the shaft output.







Here you can see the anticipated exit point of the shaft. I marked the position and repeated the exercise on the other side with another opposite bracket and market the location making sure that they were exactly reciprocal. I checked the position inside and found it was almost exactly where I expected it to be. I then dremelled a hole at an angle into the hull through the resin and balsa layers.



Below you can see the tape holding the shaft in the right exit position.






I cheated here. I've used a spare prop from the Papa class SSGN to get a feel for the size of the prop. Similar clearance, just three blades. I have also put on a basic mock up of the rudder. I may print off one and use that as the template, or I may just do one out of Renshape. You can see that I have cut the exit shaft position.



The last pic, below shows the shaft running through from the center point of the shaft output to the exit point and then onto the stern shaft bracket and ending with a propeller, hopefully. After this I will then push some filler into the hole and use a brass shaft rotated inside the hole to create a curves recess section signifying in the mold the position of the output.






David H

[Scott T]

Make you a marking jig from a pair of calipers or something similar.
Add a tube and drill to mark the location from the motor shafts to the point of the propeller.

[Davidh]

Hello all,

I have been putting off this next stage for a couple of weeks now as I have just been thinking of how to attack it from various angles and methods to think through and work out which angle might be best. I am determined that the location for the shaft outputs needs to be marked on the mold. Not just for me but to make it easier for any customer to not guess where these outputs lie. I needed to come up with a precise point as to where the shafts exit the hull at a tangent to the general curve of the hull at that point. The shaft needs to intercept a propeller shaft bracket just in front of the screw but also needs to align up with the twin shaft outputs of the ZB-2 and or ZB-1/2. It would be great if the rear section of hull was transparent and completely see through. That would make things so much easier.

I decided to make a template or jig based on the positioning of the output shafts of the twin ZB's. This involved cutting two small pieces of 6mm stainless shaft. Then I marked a round disc to represent the end cap diameter. I cut that out and marked out the precise placing of the two shafts and glued them on.




Here I have placed the MDF sheet disc that simulates the end cap of the ZB. I have needed to go in with a file and the Dremel to clear excess expanded polyurethane foam that was sprayed down earlier in order to allow me to sand beyond the limits of the Balsa sheet. Where the disc is, is the furthest point rearward that the ZB can fit.



Template showing precise distance between the ZB shafts. The cut out sections along the bottom allow the discs to fit down snugly into the space where it will reside. The cutouts are to accommodate the balsa stringers that run alongside the bulkheads. Below, glued down with superglue.



Once this template was complete the I could insert it into the back of the bulkhead that it buts up against and then need to clear the area and guess where the shafts will output. I needed to align the template to make sure that it was dead level and in the center of the hull. I also needed to ensure that the top of the end cap doesn't exceed the top of the hull. this could occur in the bottom inner corners where the vertical section between the lower and upper hull sections meet. The end cap clears by about 3mm.




More next week.

David H

[Davidh]

Hi Jorg,

Its coming up now. I do have a Sjormen class , (Sjohasten) but the mould you see in the background is the lower hull half mold for the Gotland class. They are great little boats.

Dave.

[JHapprich]

Hello, David! I am seeing your recent post beeing doubled, that might be the problem. Can see all the pictures in post no.1. Well done! What is the square recess just forward of the tubedoors good for? Ps whats that black hull mould in the background? Sjörmen?
Jörg

[Davidh]

Hello,

I have just posted up my latest build update. It is coming up green with ‘unapproved’ and I guess not showing for everyone else. Could this be fixed please?

David H

[Davidh]

Hello all,

At this point both tubes are in. They have both had a layer of filler applied around the edges of the Renshape tube forward of the tube doors. Once sanded back and another layer added, more sanding. Then a paint brush with some resin around the scoop area. I will need to carefully add some more filler around the gar between the doors and then scoop. ( This is the space for the doors to open inwards). I will have to get into the square corners and smoothly sand back..

[ATTACH=CONFIG]n148723[/ATTACH]

The hull has also had a light sanding back to get out some of the high points and undulations caused by the thicker coat of resin and weave. It is pretty smooth. Once the bumps have been taken out with something thicker I will move through 600, 800, 1000 grit. The formers have received all sorts of spray coats, splatter of resin and splashes of water and as a result look a bit aged.


[ATTACH=CONFIG]n148724[/ATTACH]

Primer grey on the other side and repeat the process.

[ATTACH=CONFIG]n148725[/ATTACH]

Looking from the front back towards the door show small areas where the filler hasn't quite covered over the gaps. Once tube door is slightly forward of the other, so I will need to address that. I also need to define further and make sharp the bow line. I will still need to add more filler along the edge of the scoop line to get the transition between scoop and hull sides just smooth and consistent.

For some time I have been working on interpreting the the middle deck section hull detail. Having never built a U-boat before and certain not one that is over 100 years old meant that I was unfamiliar with the layout and parts that would be found on the center deck. Certainly will not find any red and white hatches like I have always worked with on my soviet boats. My inspiration for working out the deck arrangement has come from the main drawings that I have and the images of the U-9 kit that I have had to rely on when the 2-dimensional-ness of the drawings doesn't quite give me enough. The U-9 model has been good for getting the low down on raised items on the main deck. I am going on the theory that from Class to Class there are only incremental changes and wouldn't be a huge change between the U-9 class and U-23 deck arrangements.

So I have aligned up the middle section of deck that is made of a 4 mm sheet of Renshape and started marking out the placement of hatches and access panels. Once marked out in pencil I could then start on scribing. I have taken a small fine file and have ground it down to a tiny round point. Renshape is fantastic for scribing into. Scribing on a flat surface is definitely easier than trying to with the Renshape strip already attached to the hull.


[ATTACH=CONFIG]n148726[/ATTACH]

I have used an array of circle and square templates to attain some consistency. On this boat many of the features seen up front are also duplicated towards the stern.

[ATTACH=CONFIG]n148727[/ATTACH]

I now have to work through which parts have raised components and which don't. Any more pics that people have of the front deck space would be greatly appreciated.

[ATTACH=CONFIG]n148728[/ATTACH]



David H

[Davidh]

Hello all,

At this point both tubes are in. They have both had a layer of filler applied around the edges of the Renshape tube forward of the tube doors. Once sanded back and another layer added, more sanding. Then a paint brush with some resin around the scoop area. I will need to carefully add some more filler around the gar between the doors and then scoop. ( This is the space for the doors to open inwards). I will have to get into the square corners and smoothly sand back..



The hull has also had a light sanding back to get out some of the high points and undulations caused by the thicker coat of resin and weave. It is pretty smooth. Once the bumps have been taken out with something thicker I will move through 600, 800, 1000 grit. The formers have received all sorts of spray coats, splatter of resin and splashes of water and as a result look a bit aged.




Primer grey on the other side and repeat the process.



Looking from the front back towards the door show small areas where the filler hasn't quite covered over the gaps. Once tube door is slightly forward of the other, so I will need to address that. I also need to define further and make sharp the bow line. I will still need to add more filler along the edge of the scoop line to get the transition between scoop and hull sides just smooth and consistent.

For some time I have been working on interpreting the the middle deck section hull detail. Having never built a U-boat before and certain not one that is over 100 years old meant that I was unfamiliar with the layout and parts that would be found on the center deck. Certainly will not find any red and white hatches like I have always worked with on my soviet boats. My inspiration for working out the deck arrangement has come from the main drawings that I have and the images of the U-9 kit that I have had to rely on when the 2-dimensional-ness of the drawings doesn't quite give me enough. The U-9 model has been good for getting the low down on raised items on the main deck. I am going on the theory that from Class to Class there are only incremental changes and wouldn't be a huge change between the U-9 class and U-23 deck arrangements.

So I have aligned up the middle section of deck that is made of a 4 mm sheet of Renshape and started marking out the placement of hatches and access panels. Once marked out in pencil I could then start on scribing. I have taken a small fine file and have ground it down to a tiny round point. Renshape is fantastic for scribing into. Scribing on a flat surface is definitely easier than trying to with the Renshape strip already attached to the hull.




I have used an array of circle and square templates to attain some consistency. On this boat many of the features seen up front are also duplicated towards the stern.



I now have to work through which parts have raised components and which don't. Any more pics that people have of the front deck space would be greatly appreciated.





David H

[Davidh]

Hello all.

Torpedo Time!....


Torpedo Tubes that is...

The space for the torpedo tubes at the moment currently is a big oversized rectangular box that is begging for something more in terms of details. As mentioned over previous logs I had the dilemma of not knowing whether the torpedo tubes had a boxy appearance rather than having a half round curve. Bernhard Wenzel to the rescue with a picture showing an early U-boat in dry dock with a curved front section of the torpedo tube. The picture looks doctored or even a hand drawing but it was the best I have. The earlier boats such as U-9 have a box like forward tube structure.

I decided to start doing some more detail work at the front end of the boat rather than the back end even though I will be going over both. The rear end is especially needing some attention at the moment but I though I would go with the front.

I measured the area around the box frame that would make up the tube area and measured the width or diameter of the tubes on the original drawings that I was working off. I used various sizes of drill bits to get a feel of the side and dia of the torpedoes and the corresponding tubes.




The width of the torpedo tube space as seen here is about 16mm. This varies as it heads towards the bow. I haven't bothered with sanding and getting the width consistent as it will be filled over with the tube details. I then took a couple of drill bits and placed them inside the tube opening to get an idea of the diameter of the torpedo and tried to get it as close to the original size in the drawing.



To make the curved outer surface of the tubes I decided to take a piece of Renshape and then machine it down to the 16mm width of the outlet then took it a little further just for good measure. I made this piece as long as the length of the outlet. I then took the drill bit shown here and placed in the tail stock drilled a hole through the Renshape to create the hole for the Torpedo.




This is the two turned Renshape pieces that will feature in the torpedo areas to be come the front of the tubes or scoops as I'll call them for want of a better term. The second one hasn't been drilled through yet. Back and front denote the back and front end. Once made I then place them inside the recess area for the tube and mark out the line that will see them sliced in half in a gradual curve to follow the profile of the front of the boat and create the scoop. I had to dremel out some of the recess especially at the back of the box section to accommodate the half tube.



I have had to give some though to the geometry of the Torpedo tube doors. On these early subs they seemed to have the door exposed, unlike later and WW2 U-boats there were no outer shutters. As a result it would seem that the doors opened outwards and as far as I can tell they opened inwards with the hinge on the inside of the tube. In order for this to happen then you would need to have space for the door to open which means that you couldn't have the curved section of the tube in the way for this door to open without jamming. As a result I deiced to create a square section immediately in front of the Bow door to give space to the door top open. The torpedo then moves forward sliding past the open door and runs along side the scoop and then on to target.




The buried torpedo tube terminates with a bulged section as the outer corner of the tube exceeds the curved profile of the hull. As a result there is the bulge that terminated at the door. This was created by
cutting a left over piece and shaping it to coincide with the front edge of the tube. I then placed a small Renshape block in place immediately before the tube door outlet and glued into place. This provides the space for the door to swing back. It makes the tube look a bit awkward and not smooth and streamlines but I don't see any other way they could have made this geometry work.



The bulge and block in place. The front section needed to be raised at the back end to make sure that it would be in line with the axis of the tube as it comes out of the hull. This meant putting down a bed of filler and at the right time pushing the back end of the tube into the soft filler and aligning it so that theoretically the torpedo wouldn't glance off the scoop as it was heading out of the tube. Then I cut out two small circles of Balsa sheet to cap off the door area and glued them to the bulge sections that would sit as the back of the recess and signify the front of the tubes. Line them up and glue them in place.



Early filler, lots more needed.


Stay tuned, more torpedo's next week....


David H

[trout]

https://www.cloudtour.tv/u8/overview...k_station5/5_0

Gantu, that is pretty cool link.
David, thank you for explaining.

[Davidh]

Thankyou David.

David H