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

[Davidh]

Hello all,

I now had all the parts laid up and just needed to pull them out of the molds. The top mold needed a gel coat layer and then some weave along with strand around the edges and sides of the hull. This would reinforce the curve in the outer top hull where it bends down to meet the lower hull. Once this was set and hardened then I could pull it from the mold. This was pretty straightforward and when it came out of the silicon mold I was very happy that there were no air bubbles, "tripe" or wrinkling. Fantastic. There would be less post processing needed. The Aluminium 'L' reinforce-rs had also created a dead smooth and flat main deck section. No undulations!'



The Blue tape a placed over the edge of the mold to pull the silicon mold outwards in order for the rim of the top mold to meet with the rim of the bottom. I didn't really need to , the fit was really close.



The top mold part pulled from the mold. As mentioned the decks are all dead level and flat. There are virtually no air bubbles and no tripe. (wrinkling of the gel coat.)
Very happy with how its turned out. Probably the best top mold I have pulled on any kit.





After removing the acrylic top flange templates, I could them unscrew the wingnuts from the underside attachment points and then start prying the two main hull molds apart. I then managed to get one half off and this is how the part turned out. Some minor wrinkling in various places but not a lot. The keel and then stern transom have turned out really well. The joint line between the stern torpedo section and the stern of the main hull is barely noticeable.



The main lower hull out of the mold and after a clean up. The stern and bow sections have been cleaned up and are looking really nice. Still will need to get some filler onto the tripe areas.



Stern section and then light reflecting shows a smooth series of decks.



The rim or flange along the top of the lower hull has turned out well. It is thick enough that hen I sand it back level there is enough material underneath not to have any thin sections that create holes.



There was plenty of sanding to get to this picture. The top mold was laid on my sanding board and moved back and forth to get a nice level surface. The same was done with the bottom mold upside down to get a nice level surface along the rim. It was at this point that I noticed a slight lopsided-ness at the amidships with the beam. I didn't notice it before, bummer however, you really have to look at it to really notice it. I think that I will be able to sand it out to extent to create a more gradual curve on the offending side.
The interface between the two pieces however, is really good especially this early on.



The bottom bow section mold is pretty good considering it was my first hybrid Silicon / hard shell mold. There is a discrepancy line around the torpedo tubes where the two mediums interface. This will be sanded and filled out. Here you can see I have already drilled the holes for the forward Hydroplanes that fit towards the back of the bow section. The rearward lip is also visible. The next step will be creating the forward attachment point that will be an aluminium plate with a bolt hole and a hole in the main hull for the attachment.



In the meantime I got busy working on the Conning tower. I had cast the parts for these much earlier and hadn't got around to working on them. I scrubbed back and smoothed any imperfections on the surface. Then some filler and more sanding and a tiny bot of work on the Dremel. I did the same with the conning tower deck casting and then glued this down. The sides of the deck won't be seen as they will be covered by the canvas covered frame pieces. These needed a bit or work of their own.



Helm and Daughter compass? These pieces fit into small holes cast into the deck and the conning tower forward base. I drilled holes in the deck to make sure water could escape.




A light coat of paint to simulate the wooden deck of the conning tower. Starting to look OK. I was really worried about how the molds for the frame and canvas covering were going to turn out but I am going to declare that they are my 'Piece de resistance'. They turned out better than I expected. A light spray of a canvas like shape of beige and faded red of the rescue flotation ring.




More later.

David H

[Davidh]

Hi Joerg,

Thanks,

The whole ballast tank is acrylic. I have made several acrylic ballast tanks over the years. You just have to make sure they aren’t sitting in the sun. Expansion and contraction of different sections. Otherwise they work really well. Blow the ballast briefly in bow down trim and then as the boat comes to the surface and levels off, then blow the rest. About the work on the raised radio masts…

Dave.

[JHapprich]

Getting dizzy just from watching! well done, impressive development and a nice guy sitting by the pool - ah nice video.

Are the Ballast tank endcaps acrylic as well? have you testet shock resistance? what happens should you blow the ballast with bow down?

You could finalize the lateral limberholes with a small rattail file

Very nice model!

Am staying warm ;-)

Jörg

[Davidh]

Thank you.

A dry acrylic surface and cyano, absolutely. It’s effectively welded. Extremely strong.

Dave.

[redboat219]

David,
Great video. I noticed you used CA for sealing the ballast tank, is it strong enough to resist the pressure?

[Davidh]

Merry Christmas !

Enjoy.




Part three...

https://www.youtube.com/watch?v=f18tME33iaw

Thanks for Watching..

David H

[Davidh]

Hi Joerg,

Thats right, a nice thick gel coat and weave.

[JHapprich]

How did you create that flawless stern? Thick gelcoat and weave only?

[Davidh]

Hello all,

After cleaning up the molds I was almost ready for putting down a gel coat and laying up the first parts. I could do any number of the molds. Coat the Hard shell molds in PVA and with the Silicon ones I could just go right ahead. However I decided to add another feature the main hull molds that would make fabrication of the main hull part trickier but would lend to a much better middle hull half. I wanted to put an inner flange along the top of the Middle hull mold. This would give the top hull mold a flat surface to sit on and would also lend some rigidity to the overall frame. To do this I decided to use some acrylic sheet that would bolt down to the top flange of both middle hull halves. I then took a texta and marked out the curve of the rim of the mold and then added an extra overhand rim of about 10 mm. This is where I would cut along the length. I then cut this out and drilled a series of holes along the main flange of the hull molds and after more release agent could bold these long strips of acrylic sheet to the flange. The Gel coat would be next and then would be brushed up underneath with a brush, in the video I bent a brush to get up underneath here. I now gel coat the two halves separately and then lay up some continuous strand before joining the two halves and putting a little more gel coat down the keel and then a conventional layup for the rest of the one part hull mold.







The Acrylic sheet ends before the stern hard shell glove mold. As the first boat out of the molds is mine I didn't mold the stern separately as I had to ship it nowhere. The white masking tape helps to avoid flash down the inside flanges of both halves.



Gel coat down. Nice and thick and 27 degrees.



You can see how the Gel coat has worked up under the rim of the acrylic sheet. I created a similar fitting for the bow. I wanted to mold a register lip into the back end of the forward lower bow section. To do this I created an acrylic boat that goes across the perpendicular flange at the end of the bow molds. This piece follows a profile just a little bit shallow of the overall hull bow profile. This is designed to create a slight 'dam' effect with the gel coat and a raised step with the weave that will when pulled away translate to a slightly inner register lip. That's the plan anyway....



Wrapping the resin and weave around the complex profile of the torpedo tube doors wasn't easy. Some kind of profile that I can press up against the mold might do. The register idea works however there is some dribble along the in side flange between the dam and then flange.




Several layers of 225 weave. Extending to the rear stern torpedo section.



Finally removing the lower bow section. It is a bit rough but nothing that filler and sanding won't fix.



My Horten Ho 229 front end looks like a Troll doll.



More next week.

David H

[Davidh]

Thank you Nick and Rob,

Thats right Rob, I will be putting this kit on the market in January.

Sneak Peek.

[Monahan Steam Models]

David,

Fantastic work! I’ve enjoyed following along and seeing your step by step progress with the build.

Nick

[rwtdiver]

Hi David,

I am really fascinated with your work. Now that the molds are complete, if I do understand this method correctly, you can use the same molds over several times for making hulls?



The old masterful handmade mold method, and the new 3D printing technology method! This hobby has really come a long way! You are a master, David!

Rob
"Firemen can stand the heat"

[Davidh]

Hello all,

As mentioned I'm now on summer holidays and have managed to accelerate the build. So I though that a mid week update would be in order.

Now the moment of truth as pretty much the whole ordeal that is creating all the molds for the hull have been completed. Its taken about two weeks worth of effort. A lot of resin and a truckload of 225 weave. I am fortunate as the 225 was supplied by a friend of mine who is a shipwright and one day he came over with a massive roll of the stuff that he'd had in his garage for years and he'd wanted to get rid of it. There must be about 30-40 meters of the stuff.

Anyway I had completed the hard shell of the top mold and created and glassed down the plywood egg crate box frame onto the top. Everything has cured and its time to split the molds from the masters and see how well two weeks of work has gone. I start tapping with mallets and start prying open with plastic wedges that go in and widen the gap between upper and lower halves. Eventually you get the cracking sound. The use of Gaffer tape strip before laying up the top mold has created a convenient separation between top and bottom mold halves that can be utilized. I start pulling on these.

The top mold, the most recently created came off quite easily. The hard shell separated and left the silicon on the master. I then peeled that off the master and laid it back in its hard shell and surveyed, the silicon had taken with it the surface layer of paint from the master but otherwise than that there were no thin spots in the mold and NO AIR BUBBLES, YAY!!!

The mold was straight and true making it easily the best upper hull silicon mold I have created.



I just need to trim around the edges and clean off the residue paint with some acetone.



You can see the paint peeled off the top middle deck of the master.



First half of the main hull mold separated. So far so good, minor blemishes but nothing big. Then I pulled the second half off the other side of the master and it had some tripeing or wrinkling of the gel coat down the bottom near the keel. Nothing that couldn't be fixed with filler and sanding. Meanwhile I have taken the bow and stern molds off.



Here all the molds are assembled. The two pieces of the bow with the hybrid silicon torpedo tube detail and the stern one piece tube detail. I like the two tone colour arrangement.
These are held in place with 4 mm stainless steel bolts and wingnuts. As you can see there are pockets where the grey primer has come off the master and simply needs to be pried off.




The tiny divits in the stern are the markers for the shaft brackets.



The joints between the different sections are really nice. Then fit really smoothly. It just needs a good scrub up.



Finally the top and bottom halves.



Still more cleaning needed however these molds have turned out really well. They weight a ton!

David H

[Davidh]

Hi Rob,

Thanks for the comments. Yes, it takes years to develop these skills. I try and do something different on each kit as I gradually introduce a new technique for something here or a slightly different use of a material there. This boat has the most appendage parts and the most complex molds and dies of any model that I have built. Most of the consideration behind designing a mold or die a certain way is to make the manufacturing process easier. But often It still feels like its two steps forward and two back..

At this stage I am still adding layers of silicon to the Glove mold. I bought a big 4 Kg tub of the silicon and intend on using it all for this particular part of the mold. I will make it quite thick and with the help of the aluminium stiffener ' L ' brackets should make the flat sections of hull really flat and consistent. This shape is reasonably easy to pour silicon over, I dont have any large vertical surfaces that need a thixotropic hardener to keep it there. There is the rise at the bow and that's about it.



First layer of silicon goes down smooth. Its only about 3-5 mm thick.



These are the Aluminium L brackets that will be embedded in the silicon to help keep the decks flat and rigid. A fair amount of the silicon is used up trying to make sure it makes its way in through all the holes. It also goes along way to roughing up the surface of the silicon to help make sure that the hard shell keys in effectively.



Second last layer. Now I just have to cover and make sure that the silicon completely embeds the Aluminium.



Final layer and then the retaining strips of pine have been cut free to reveal the overall shape of the silicon mold. I have cut small "V" shapes outlines in the sides to act as further Keying grips for the rim of the hard shell. The numbers on the side were put there as indicators of how high the deck at that point was above the flange. This is because I was concerned that I may not be able to tell if the Silicon mold was thick enough. I could measure the height of the silicon at that point and take it from the measurement on the side to get the thickness of layup.




Side view of the bow section showing the torpedo tube cavity on the lower side hybrid mold and the top hull one piece Silicon mold. Now all I have to do is paint some PVA release agent on the flanges and gel coat up over the silicon. You need to make the Gel coat thick as the Silicon does not like it and it will separate. I put some thick gaffa tape around the rim of the flange to help get a good prying point for when I pull the two mold sections apart. In the home straight now.



Gel coat down and then some continuous strand followed by the 225.



Down by the back shed. The irregular lumps and bumps of the silicon lay up mean that the weave has a hard time pulling in the undulations. Hit is with heaps of resin and chop some 225 into small bits and make a paste. A couple more layers to go.




Finally..



Like the underside the top also required some of the "Egg crating" to give it torsional strength. Once again I created the plywood frame that would give it support and make a stable table to work on when laying up. I initially glued the frame up after making sure that it was square and wouldn't rock back and forth. I could then drop it in place and then simply resin it up around the sides .





Finally everything done! Once i pull these two halve off then I can finally make some finished parts and start the creation of the final model.

I'm finally on Summer holidays at the moment so the speed of development should pick up. Fiber glassing has been a bit delayed though, as we are going through a "La Nino" cycle and are having more rain than we would usually get. We haven't had any sweltering 40 degree days yet and the conditions for glassing haven't been ideal.

David H

[rwtdiver]

There really is a lot to understand about all the different processes and different materials that you are using on your build. This sub building method must take a great deal of time to learn and master for sure. I really appreciate you describing and taking photos of your build as you go David. Thank you...

Rob
"Firemen can stand the heat"