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

[rwtdiver]

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.



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!!!








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.



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.



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.




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.



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.




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"

[Davidh]

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.



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!!!








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.



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.



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.




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.



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.




David H

[gantu]

No problem

[Davidh]

Thanks Gantu,

There is some good info in there.

Dave H

[gantu]

https://de.calameo.com/read/000802552d298b4cae5de

[DrSchmidt]

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

[Davidh]

Hello Dr Schmidt,

Care to share?

David H.

[DrSchmidt]

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.

[Davidh]

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.




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.



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.



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.








Pins and pegs.


Repeat with the other side.



David H

[roedj]

Here's are some real newbie questions for you.

Wassup with the radio masts? Did they have to be folded down when they dove? Did the periscope extend up above the masts? How does that work?

Captain Curious

[gantu]

[Davidh]

Hello all,

Thanks David,

So after creating the top middle deck section with a strip of balsa and then checking the width of the top section of the Bulkheads I then turned towards giving the hull a little more definition by creating further channels in each of the bulkheads to take another stringer along the side of the hull on both sides. This would increase the rigidity further and allow further points of contact with the sheeting when it came time to lay down on the side of the hull when closing up. So i marked a line along the length of the hull about half way up the height of the bulkheads and made sure that they were all level. I then took with my Dremel cut off disc and started cutting the grooves needed to place the stringers, also made of balsa down in place and flush with the outer edges of the bulkheads.




You can clearly see some of the balsa strips designed to widen the bulkheads and make sure that they are flush through the curve with the stringers. These stringers will give extra points of gluing and adhesion to the balsa sheet that will be laid down to cover the hull. They also help to give a more full perception of the overall hull shape.



All this Balsa is taking me back to the days when I would make Sailplanes out of Balsa and Plywood spars. I would then cover the wings with a very fine silk and dope as they were vintage scale models. I still have my Reiher, 'Sperber Junior' and 'Minimoa' in the rafters. Beautiful Gull wing gliders designed in the golden age of soaring... the beautiful thing about Balsa is that it is so easy to work work. You can glue pieces that are a bit rough and not precise and just sand to size. This is the case with the bow. It is a bit rough but after lots of sanding will look the part.



At this point i have also taken the keel of the boat and rubbed it sideways back and forth along my flat sanding board. It didn't need much. It was pretty close to straight.



I then repeated the process by measuring half way between the earlier stringer and then keel I marked out another line. Then taking the Dremel, I then cut another set of notches for another stringer to be set in place. Once all the stringers were in place and dried I then went over the framework and gave a smooth and slow sanding. You have to go slowly so that the paper doesn't catch and pull the bulkheads out of place.



Once again, If anyone has pics, please don't hesitate to get hold of me,


Dave h

[He Who Shall Not Be Named]

It's most refreshing to see a traditional model-builder at work. Most instructive, sir.

David

[Davidh]

Hello all,

Less work this week as I have been back at work for the start of a new teaching year. However I did manage to get a few more structural aspects of the hull cut out and glued into place. I have spent several hours measuring the bulkheads either side of the center axis and making sure that they are the same. I have been looking at the curve of the hull from every bulkhead and making sure that the transition from one to the other is smooth and not too abrupt. I have been eyeballing down the length of the boat and looking to see if any bulkheads stand out. These were sanded down and if needed to gain material I cut strips of Balsa and curved them around the outer shape of the Bulkhead to conform. once glued down they would be sanded to make sure that the transition would be uniform.




I then took my sanding board and sanded down the tops of the bulkheads and the top spine to make sure they were level. I had to be very careful that as I push the top along my long sanding board I don't catch and pull the bulkhead right out out and trash the whole thing. In this pic above you can see the Balsa inserts along the curves to bring the bulkhead into alignment and transition with the rest of the hull.




As you can see in this pic the beam stringer on the port side did'nt extend sideways enough, I had to create an extra strip of Balsa to create a smoother more consistent curve around the stern of the boat.



Overall I am pretty happy with the alignment and consistency of the frame. I took a sheet of 2mm Balsa and cut out a profile that would match the central raised deck on this sub. Early U-boats featured three decks the inner raised deck and two side decks over the saddle tanks lowered about 300 mm lower than the center. So i spent a fair bit of time making sure that the profile was symmetrical and that the centre line aligned with the centre line of the top spine. then that the deviation sideways equally matched the sides of the Bulkhead profiles of this raised middle deck section.






More next week. As mentioned, please, anyone with good photos of this class please get back to me, as yet I haven't been able to find much more.


Dave.

[Davidh]

Hello everyone,

I am at the tail end of the summer holidays and have managed to get a good amount of work done on U-23. As seen in the previous photos I had cut out all 20 bulkheads and managed to get them into position along the keel and a top spine for want of a better term. I had to make sure that the Keel was straight and the top spine also with no sagging possibly caused by the bulkheads leaning one way or the other. Gussets were glued in place along the keel to support the vertical position of the Bulkheads and also make sure there was none of the sideways deviation. After being content with the straightness of the keel and then bulkheads I then glued in the top spine.

You may also notice on the previous pictures that there are notches cut where the sides curve down. This is for the side stringers that will form the widest part of the hull. The beam, effectively. Once the bulkheads ,keel and top spine were glued in, I then cut the balsa strip at about 5mm x 5mm square and then placed that in the side notches. I had to make minor adjustments to the notices to make sure that the stringer was straight on both sides.



The bow features a near vertical bow line. This was joined simply for starters with a piece of balsa connecting the keel with the top spine and getting some reinforcing later. The side stringers that follow the line of the bean did not extend all the way. I have had to add further sections bow and stern. Pins hold them in place until glued. This take me back to the days when I built RC Sailplanes.





Further gussets have been placed to hold and secure the beam stringer to the bulkheads. All the time whilst doing this checking that the bulkheads remained straight and true. I had also started checking that the bulkheads deviated by the same amount each side of the top spine. The beam stringer effectively terminated forward at Bulkhead 19 as the side saddled disappears into the hull forward of this the hull drops vertically to the keel.






I have only so far found only one pic of U-23. The one above which i suspect was taken after launch as the caption below says Krupp Germaniawerft Kiel. (thanks Jorg!) I will be using pics of U-23/26 because that was the class although U-22 was similar.



The basic shape is starting the take form. I intend on putting further stringers around the sides as I will be sheeting the hull initially with 2-3mm thick Balsa sheet. The stringers will help stop sagging or should I call it oil canning?

Please, if anyone has obscure pics of this boat, especially dry dock ones that would be greatly appreciated...


David H