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

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  • #16
    Hello Roedj,

    The masts had to be dismantled before diving. This large array would I guess been used for the Marconi style radio set. On earlier boats they also had to pull down and stow the large exhaust stack for the Paraffin engines. This all took time and took vital minutes to do if you needed to dive quickly. This class of boat was among the earliest German U boats to have the new Diesel engines installed making the large smoke stacks redundant.

    After spending a lot of time sanding down and getting consistency, length wise and symmetrical across in section I decided to start sheeting. However before starting this I decided to cut out Renshape strip for the top decks. The three top decks, the raised middle one and then two lower slightly smaller side ones will be made of Renshape. This will be glued over the top of the Bulkheads and the stringers as they run the length of the boat. In order to do this I took my ridiculously big chunk of Renshape provided generously by Hardrock to school and the table saw to cut strips. This stuff is heavy. I cut strips of about 5 mm thick that will make up the decks and the sides.


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    I have also in the meantime created with a small block of Renshape the base of the Conning tower. This was placed on a strip of Renshape and placed onto the hull to get some idea of the overall positioning and look.

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    These decks will be scribed before being glued down to the hull. This will simply make inscribing easier. I am sure that HWSNBN will be watching this one, do I hear a whip crack?

    Anyway, back to the sheeting. I bought some sheets of 2mm Balsa. The plan is to wrap this sheeting around the hull and glue down to the frames. The longitudinal separation of the sheets will be determined by the location of the stringers and the sheets will end over the edges of a Bulkhead where needed. The first piece of Balsa sheet will run the length of the starboard side and will run from the top of the hull (Gunwale) down the side to run along the lowest stringer before the keel. This would effectively cover about 70% of the side surface area.

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    Mark out the profile and then cut out. I then marked the location of the bulkheads by line. Because of the nature of the sheeting and hull shape I will be taking a flat sheet of balsa and wrapping it around
    a compound curve. The curve inwards of the hull line along its length and also the curve downwards. So material has to give. In order to make this easier I cut lines from the bottom of the sheet up untill about 80% of the width of the piece. I then sanded to make a slightly tapering gap. When the piece is pinned up and glued the curve will mean that the balso sheet will close at each cut causing the sheet to confrom to the complex compound curve a bit easier.



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    Pins and pegs.

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    Repeat with the other side.

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    David H

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    • #17
      This is interesting. I'm currently designing a CAD-Model of the Type U-23 imperial subs....found some high-quality plans and got them scanned over christmas. Will be nice comparing the CAD to your model.

      Comment


      • #18
        Hello Dr Schmidt,

        Care to share?

        David H.

        Comment


        • #19
          Work in progress....bow needs remodeling, deck structure needs workover, but getting there.

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          Last edited by DrSchmidt; 02-05-2021, 09:55 AM.

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          • #20
            https://de.calameo.com/read/000802552d298b4cae5de
            Regards Gantu

            Comment


            • #21
              Thanks Gantu,

              There is some good info in there.

              Dave H

              Comment


              • #22
                No problem
                Regards Gantu

                Comment


                • #23
                  Hello all,

                  After sheeting the sides of the hull from the gunwale down to the first stringer, I then started sheeting from the lowest stringer down to the keel. This mean't cutting out a thinner narrower strip of the 2 mm Balsa sheet. The compound curve of this sheet is less and as a result I didn't worry about the same cut and sanding technique as I used on the wider sheet that was mounted higher up. This lower sheeting also stopped two bulkheads short of the bow of the boat. This was because I needed to work on the torpedo tube positions and making the recessed sections for these.

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                  The Torpedo tubs sections were created by making gluing down a flat rectangular strip from the bow back and parallel with the axis of the boat. I then cut out two triangular sections to glue down top and bottom to create the side of the tube sections. The torpedo tubes of this class are a real confusing area to have to build. The research is conflicted. Some drawings and photos suggest that the tubes had curves on the inside of the tube, others like the U-9 kit suggest that the tube was very rectangular. There is also evidence that there may have been a curved bulge profile behind the openings of the doors. Any clear photo's would really help,.. Anybody!!!


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                  I then have to simply cut out and glue rectangular sheets top and bottom around the torpedo tubes. I can then add any curved surfaces later. The U-23 class only had four tubes, two bow and two stern.
                  To glue down the lower strips I used the same technique that I had used on the wider upper sections. Pegs, pins and glue. Sometimes where needed a little tape was introduced.

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                  The stern section like the bow would need adding of further smaller pieces to complete the sheeting. The stern in particular would have a series of complex evolving shapes that would require the sheet to twist and turn to conform to the shape leading up to the stern post. Balsa not always wanting to conform to some complex compound curves. The join lines between the two sheets will be filled and sanded back.

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                  Balsa is easy to pin through. However pine is rather hard. So pining into the keel wasn't easy. In some cases tape would make a less than ideal substitute. I used a fair bit of PVA glue to really secure the sheets in place.


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                  The smaller pieces that comprise the stern. Even these short pieces have needed a twist to get them to evolve to the angles of the next Bulkhead. There will be a lot of sanding. Because I my have to sand fairly aggressively in some places, I can see that there will be points where I will probably sand through the sheet. I am considering using some expandable urethane foam behind the Balsa on the inside. This will allow me extra shaping space behind the balsa sheeting already there.

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                  Since the sheeting has been completed i have started filling the seams between the sheets. The next task is to spend a fair amount of time checking once again for symmetry and also the subtle undulations of surfaces that may not be absolutely consistent along the length of the hull. There will be several checking techniques that I will use over the next couple of weeks.

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                  David H

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                  • #24
                    Originally posted by Davidh View Post
                    Hello all,

                    After sheeting the sides of the hull from the gunwale down to the first stringer, I then started sheeting from the lowest stringer down to the keel. This mean't cutting out a thinner narrower strip of the 2 mm Balsa sheet. The compound curve of this sheet is less and as a result I didn't worry about the same cut and sanding technique as I used on the wider sheet that was mounted higher up. This lower sheeting also stopped two bulkheads short of the bow of the boat. This was because I needed to work on the torpedo tube positions and making the recessed sections for these.

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                    The Torpedo tubs sections were created by making gluing down a flat rectangular strip from the bow back and parallel with the axis of the boat. I then cut out two triangular sections to glue down top and bottom to create the side of the tube sections. The torpedo tubes of this class are a real confusing area to have to build. The research is conflicted. Some drawings and photos suggest that the tubes had curves on the inside of the tube, others like the U-9 kit suggest that the tube was very rectangular. There is also evidence that there may have been a curved bulge profile behind the openings of the doors. Any clear photo's would really help,.. Anybody!!!


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                    I then have to simply cut out and glue rectangular sheets top and bottom around the torpedo tubes. I can then add any curved surfaces later. The U-23 class only had four tubes, two bow and two stern.
                    To glue down the lower strips I used the same technique that I had used on the wider upper sections. Pegs, pins and glue. Sometimes where needed a little tape was introduced.

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                    The stern section like the bow would need adding of further smaller pieces to complete the sheeting. The stern in particular would have a series of complex evolving shapes that would require the sheet to twist and turn to conform to the shape leading up to the stern post. Balsa not always wanting to conform to some complex compound curves. The join lines between the two sheets will be filled and sanded back.

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                    Balsa is easy to pin through. However pine is rather hard. So pining into the keel wasn't easy. In some cases tape would make a less than ideal substitute. I used a fair bit of PVA glue to really secure the sheets in place.


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                    The smaller pieces that comprise the stern. Even these short pieces have needed a twist to get them to evolve to the angles of the next Bulkhead. There will be a lot of sanding. Because I my have to sand fairly aggressively in some places, I can see that there will be points where I will probably sand through the sheet. I am considering using some expandable urethane foam behind the Balsa on the inside. This will allow me extra shaping space behind the balsa sheeting already there.

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                    Since the sheeting has been completed i have started filling the seams between the sheets. The next task is to spend a fair amount of time checking once again for symmetry and also the subtle undulations of surfaces that may not be absolutely consistent along the length of the hull. There will be several checking techniques that I will use over the next couple of weeks.

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                    David H
                    David,

                    Ounce again, I am seeing incredible work being done on this forum! The time consuming patience you are showing this beautiful wood build! Fantastic work David!

                    Rob
                    "Firemen can stand the heat"

                    Comment


                    • #25






                      Regards Gantu

                      Comment


                      • #26
                        Thanks Gantu,

                        I've already got these pages, but appreciated anyway. Thank you Rob for the compliments.

                        As mentioned in the previous write up, checking for symmetry and overall consistency becomes something that I need to work on. It is still a fair war off before I get to a point where if symmetry isn't checked then the inaccuracies are irreversible. Along way off from that yet. However this not being my usual PVC pipe with turned ends Nuke boat means I need to take things methodically and carefully to check that everything is balanced.

                        For starters there is lots of sanding, especially along the seams where sheets meet. Once that it done then lots of filling. Being sheeted with only 2 mm thick sheet means that if a high point is higher than 2mm, I will be sanding out the sheet and just create a hole where thicker Balsa would have been great to have. I do have some Sika expandable polyurethane foam in a can that could back up behind the sheet in an area of anticipated aggressive sanding.


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                        The completely sheeted hull with the top sheet of Renshape medium that will give all the top deck detail without much Renshape being needed. I had noticed that the Transom was skewing to one side. This area again like the rest of the hull was only lightly sheeted and so aggressive sanding would just lead to busting holes. As a result I used some of the expanding foam to bulk up this area for sanding and what i anticipate would be a bit of surgery to get it right along the keel axis line. So spray i did.

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                        This stuff really expands a fair bit. You can see it has risen up around the height of the Bulkheads. In this pic i have already cut it back and also sanded the underside of the thin Balsa to reveal the urethane underneath. Forward of the exposed foam you can see that the balsa forms an uneven surface that I am going to have to take to later to smooth and create the gradual transition that I am after.


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                        You can see in this pic how the rear raised keel section leading to the transom isn't in alignment with the datum line running to the bow. (Black line.) It is straight to the bend then it veers off to the left. Later on I would do a series of cuts and push the keel back to the right. The foam helps bulk up the structure and give support. The transom itself will need slight relocation. this picture really shows the rough nature of the sheeting and the need for care full smooth transition checking.

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                        I also aligned up the stern post for where the rudder shaft would protrude upwards and marked this with a small brass tube. Here the stern back block has been glued into place. This is where I intend on cutting a section out and fashioning the stern torpedo tubes. I actually do have a good picture of this. Here i have pasted some P.V.A just to protect close the surface of the foam.


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                        The stern plane arrangement will be different however I intend on doing the torpedo tubes like this. If only i could find a bow photo this good. I have spent some time creating a board to calibrate and check symmetry. I have made a couple of L blocks to push up against and use to measure the height and measure between to check against the axis line. This board is actually my sanding board turned up side down.

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                        I have set up a laser line from the ceiling to shine down and get an absolutely straight axis line down the keel. then carefully take measurements from either side of the axis. Then determine where to sand or fill.
                        The sheeting at the very front above the tubes needs some filling in as it is recessed somewhat. that will come later. Last week I spoke of my dilemma with the bow tube design. Bernhard Wenzel, builder of the U-9 from the Sonar site and inspiration for the Das Werke kit of U-9 sent me a great little pic of the bow of one of these boats clearly showing a curved tube section. Thanks Bernhard!

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                        Once again if anyone has good pics, I would certainly appreciate it.


                        David H

                        Comment


                        • #27
                          Nice job david i keep going for picīs.

                          Gantu
                          Regards Gantu

                          Comment


                          • #28
                            Hello all,

                            True to form Gantu has been going hammer and tongs looking for pics of the U-23 class. Appreciated Gantu. Especially those bits of blueprint from what look like original drawings.

                            At this point some transom re-adjustment was necessary. As mentioned previously it was slightly off to the port and need to be angled over to the center line. To do this I made a cut in the keel about 50 mm forward and effectively broke the keel. I also made a cut in the transom about half way up where the top of the rudder wold be mounted and cut in a little. I then shifted the keel section, lower transom section and a small mass of Balsa and polyurethane foam sideways. I then pasted some PVA glue and pinned it down in its new position. The keel now looks much more aligned. I am certain i will have to do some more subtle work on this later but looking better for now.

                            In the meantime, I have a pic that I am curious about, please if any one can answer what is below that would be great. Don't be shy...


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                            As mentioned previously, there are numerous issues with regards to photos and drawings conflicting. I have one drawing that shows two top views with the forward planes in two different positions.

                            So once the Keel alignment had been sorted it was back to the board to do some general checks for symmetry. I have a laser light mounted on a rafter in the ceiling and its pointing down to create a long straight line that I can use as the datum along the keel. I just have to line up the board and then boat. Rubber bands and hooks and then don't bump it.


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                            The big "L" brackets ate so that i can run a ruler across the top of the deck and accurately measure the distance from the edge to the centre line. Made at school from the scrap bin they are made of "Jarrah" a hard Eucalypt that makes beautiful furniture but will smoke your drill bits! I will be making a piece that straddles the hull and will give an accurate perpendicular reference line along the bottom of the hull when turned up side down. This will effectively give me section lines as you cast your eye down the length of the hull being able to easily see where a profile may be out. But that's a week of so away.

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                            Eventually I will get around the laying out the patterns on the centre deck section and then start the business of scribing. Once I do that I'm very confident a certain HWSNBN will come out of the woodwork so-to-speak and berate me on my progress. I still need to do a little investigate of layout of the deck. I am heavily going off U-9-U-19 data, there doesn't seem to be much shift or evolution in the deck design between these classes but once again I am open to anyone with anything further.. Some ZB's in background.

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                            So after marking out any little undulations and irregularities, I put to work with filler and sandpaper. I will try my best to get as many inconsistencies out before the first layer of resin goes down and seals the hull. So here its lots of filling and lots of sanding. i have to say the boat generally looks really symmetrical, but i know that I check and check and then get to a point where I more on and any changes are not possible and then notice...

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                            Filling, sanding, filling, sanding, repeat....

                            David H

                            Comment


                            • #29
                              Drying out rubber mats that normally go under the feet of the guys standing watch at the battery switch-boards?
                              Resident Luddite

                              Comment


                              • #30
                                Thanks David,

                                No one else has given any suggestions as to the two items hanging over the front deck of a U-boat. What is interesting is how 'Das Werke' in Germany have molded them into their kit of the U-9. Before I saw this photo I though that it was a fixed piece of the hull as shown by the U-9 kit even though I had not seen them on any other photos. I am spending a bit of time looking over all the old photos that I can get and find that although photos are relatively consistent, plans and drawings are sometime contradictory. There is not a lot of detailed information on the U-23 class however there is good detail on the U-9 class and so I am trying to determine apart from obvious overall hull design changes whether there is much deviation with hull details between the two classes. I am thinking of using the U-9 class as the template for much of the detail I need to put into U-23.

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                                So, after the filling and sanding of the hull and checking as much as possible to get the hull consistent, I was finally at the stage where I could give the hull a coating of polyester resin. This would seal the hull and also give just a little more thickness to sand back with high points and so forth. The initial layer would probably use a fair amount of resin as the Balsa acts as a sponge and really sucks it up. Once a good coat had been put down then subsequent layers would require less and this would certainly be the case when it came down to putting the weave on.

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                                Sunning itself by the Pool. The first coat of resin has gone down and the hull is getting a distinct tan like appearance but not from the Rays. The filler doesn't absorb the resin like the balsa so you tend to have excess over these areas. You simply need to redistribute. I left the hull to dry for a couple of hours before giving a light sanding. The resin had done a good job of sealing and I could actually put the hull in the water and it floated quite nicely no leaks. No lead for buoyancy so it would easily have capsized it I weren't holding it.

                                I decided to give the hull a light spray of primer grey. I did this to help give a better show of the overall texture that the resin layer would give. and to see any undulations that may not show up with just lighting alone. The Grey does help you see the surface from different angles and pick up inconsistencies you may not otherwise.

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                                In this state I noticed one thing in particular. This photo makes the hull look as though the keel is not centered. As though it is lopsided to the right. It is'nt, it's just the angle, however what I did notice over time was that the keel as it transitions to the hull and the surface area to either side of it transition to the common shape of the hull too quickly. There needed to be a much more gradual gradient change in this general area. I decided to get aggressive with it from the start and then back down on the abrasives. I started with a Rasp and some serious filing back and forth either side of the keel as it transitions to the consistent hull shape.

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                                I then did more and more as I aimed to take the shape to a much more gradual transition. The filing was taking the profile down to the thinnest areas of Balsa, so much so that the frame work is showing through. This would require internal back up. I further spray of some of the polyurethane filler was required to back this up. I would also combine with filler.

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                                The filler is great for reinforcing the insides when I'm grinding the outer profile to within an inch of its thickness (more like a fraction of a mm) but It will play havoc later on when i need to set up the shafts and work out where the shafts will exit the hull. This will need to be done soon and certainly before I smooth down the hull too much as I need to work out how to represent this on the mold. David, need you help on this one! I think it's going to need a bit of geometric gymnastics...


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                                After going hard with the rasp and gradually beating the rear end into submission and an nice curve, I started the process of sanding down the rest of the hull. sanding back the primer is a good way of seeing the high and low points as the primer high points ware away quick.

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                                As mentioned David, I will need to work out how to best determine where the shafts exit at the back of the hull. Having all that urethane filler in the back ain't helping however I have started clearing it out and will make a mock up of the stern ZB-1/2 twin shaft end cap with the precise locations of the shafts on it. I then intend on slotting it behind the bulkhead that is where it would sit. I then need to run shafts from the two points that simulate the shaft outputs on the stern end cap mock up and find where they will go out and at the same time make sure they hit the brackets. X-ray vision would be really great for this one!..


                                David H

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