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

[Davidh]

Hi Joerg and Rob,

Yes it can be messy, especially when it has been curing for a couple of days and you pull the mold apart and its still guey in some places. That's really annoying.

Anyway, back to the bow molds. So I created a dam for the silicon to be poured into the cavity at the front of each bow mold. This dam was made from a strip of clear plastic from a drink bottle glued in place with some RTV silicon. I sealed around the base of the plastic dam and then drilled a hole through the flange of the bow mold and screwed it to the base board. This would help pull in the mold to the master even further and reduce the riding up of silicon that I talked about in the last write up. I then placed the mold on its side and then mixed up some silicon and poured into the dam area. I would then repeat the process after it had dried to the other side mold.


As mentioned before closing all this up I put a circle of play-Doh around the area to stop the silicon riding up. This pic shows the general arrangement.




Here you can see the Silicon dam has been poured. You can see the clear RTV silicon at the base acting as the seal. Brown stuff is actually some other silicon. The clear plastic is just pulled away after setting.




After completing both bow Silicon cavity molds, then I have completed the entire bottom section of the mold. I can then separate the main board from the master. This will reveal the top half of the mold and make it look like it is sitting at surface trim so to speak with a flat level of Fibre glass flange all round. I just had to carefully separate both halves. The Gelcoat should be fully cured by this stage.



In this pic you can clearly see the rim of left over sealing Play-Doh from around the edges. This will get scraped off. Also you can see the stern Silicon hard shell mold. This turned out really well and I am happy with it. I just needed to get the Dremel and start cutting off the excess glass abound the sides that then sand it back to a smooth consistent rim.




I would use a fine file and then tip of a Stanley knife to pry up the dried up Play-Doh left over in the seal between the hull and splitter board.




Here you can clearly see the transition between what will be the top mold, yet to be produced and the complexity of the bottom mold. I use wingnuts to secure the bow and stern molds to the two main hull molds.



I used some Play-Doh to create some undercut areas that would act to grip the silicon mold and make it less likely to pull out of the hard shell. There is no need for the stern most Silicon mold to need to come out of its hard shell. These grips are seen by the bulges in the rim of the hard shell.




After cleaning up this lower mold, flanges and Play-Doh, I then started on the fabrication of the upper mold. This is an easier mold as it is a one piece mold. This is usually on my previous models the first mold that it made, however I felt that with the complexity of the lower hull mold I really needed to tackle it first. This upper section is completely done with Silicon and has a hard shell. Being a quite flat surface I was quite concerned about the strength and rigidity of the mold could be compromised by it being flat. I certainly didn't want and undulating silicon mold. I would like my previous molds use some stiffening.



The Silicon, like the stern lower hull mold would need to be dammed in. It would just be a much bigger dam. Here I had strips cut and then screwed down to the flanges of the mold.




On my previous molds I was concerned that long flat sections of Silicon mold now matter how well the hard shell had been made may exhibit sections where some undulations may occur. ( A wavy up and down inconsistency). I do not want this on any account. I have in previous years used security door mesh, the really stiff and hard to bend stuff. It is expensive and this time I couldn't get any from my usual free source so I got creative and decided on some Aluminium (Al You min e um) 'L' profile from Bunnings and went through the laborious effort of drilling hundreds of holes for the silicon to weave its way.
This will be embedded about 1-2 layers into the pour and covered over.



Nearly there.



First layer of silicon down. About three to go.

Next week....

[rwtdiver]

David,

I am amazed watching the progress on your build! I totally do not understand the process of how it is done. Truly "Old School" for sure. Please do not think I am being disrespectful! But what a sloppy mess that process is, but yet I have seen the wonderful end results that you and David M. have achieved with this system. Truly amazing!!

Thank you for sharing this build with us!

Rob
"Firemen can stand the heat"

[JHapprich]

Hi david, i found my recent glass layup would not fully cure with PVA insulation of the mold and i made a very thin layup of only 3 sheets and epoxy.

Website pictures look much nicer now!

Jörg

[Davidh]

Still not happy with the weather. Apparently we are in La Nino weather cycle so this years Summer has been cancelled. I am felling very ripped off... Rain most of the week..

Anyway back to the U-23 molds.

Last week I had siliconed up the back end to create the very stern torpedo tube section. This mold straddled both sides of the hull and after pouring the silicon, I could then remove the form work and then Play-Doh and then put down the Gel coat and then layers of 225. I decided to cut a small triangular piece of plywood to act as a reinforcing gusset in the corner of this molded hard shell.



I now turn to the bow section of the boat and then other side mold. After pulling off the main splitter board I could then start with creating the second half. I can then pull away the end Flange board from the front of the second main hull side. this flange will act as the wall for the rear of the other bow mold. I then clean up this surface and pull any register points that are still stuck in this flange. Applying PLay-Doh into the gaps between the splitter board and the sides of the bow. I then like the other side placed some Play-Doh into the recesses of the Torpedo tube scoops in order to create the cavity for the silicon hybrid mold. I then a couple of coats of PVA release agent. I also sanded back the vertical flanges.




I created the Play-Doh section in the torpedo scoops with a slightly roughed surface and undercuts to try to impeed the silicon mold from accidentally coming out. This is unlikely as it will be poured by a series of big holes from the other side .




Pink Gel coat.



Once the Gel coat is down I can then lay up layers of the 225 weave. I have also laid down roving strand in the corners to help with the 90 degree turns in the edges where the bow meets a flange. The next major step is to place the Egg crating feature in place. I designed and worked out the geometry of this before hand and based it on the rough shape that the layers of weave being laid down were producing. Unlike most previous hulls it is split like the hull. I aimed to have the top edge of the plywood sheet to be higher than the center line flange that runs the length of the mold. This would help it act as a stable surface. I drilled a series of hulls in the flange before placing and glassing up the base of the box. These holes will be for the bolts and wing nuts that will hold the whole mold together.




This view shows what is pretty much the finished 5 part mold in all its skeletal / reptilian form. I have already drilled the flange bold holes for the front side bow and along the main flange. The box egg crate reinforcing has been glassed all around and the thing will weigh a metric ton. The next step will be taking the two bow molds off and scraping out the Play-Doh, cleaning them up, drilling holes and creating the small dam for the silicon.




A mixed bag of results with the surface of the first half. There was a little bit of crazing in the surface, I wonder if excessive use of PVA may have caused this. The flange surface of the Gel coat is also a bit under cured. This is a bit annoying as it only had a week to cure. Next step is to scrape out the Play-Doh and then clean up the cavity. The crazing on the main surface will be carefully sanded back and given some light filler then sanded back further. Some of the area around the register points has chipped. As long as the register is good I probably wont touch this.




I think the other side turned out a bit better. There is less crazing on the actual mold surface even if there is some rough areas around the flanges. Nothing that can't be cleaned up.



About the sand back the respective flanges.




After a clean up the two bow mold halves look a lot more respectable. The drill holes in the cavity area will be for the silicon mold from the outside. The mold halves will be pressed once again up against the master. There will be a "ring' of Play-Doh around the rim of the area to be molded to try and stop excess silicon riding up in any cavity area between the mold and the master. This is the single biggest thing that I don't think that I can control as I cannot guarantee that the mold and mast will press absolutely tight against each other.



On the outside of the mold I created a small "Dam" with some plastic from a drink bottle. This is on its side and the whole mold will be tiled on its side and then silicon will be poured into the three holes that you can see. The screw is an attempt to get the mold as close to the master and flange boards as possible.



More next week.

David h.

[Davidh]

Hi Joerg,

It took about two weeks in October. Fortunately I had a week of good weather was in lock down and couldn't really go any where, plus I had a big 4 litre tin of resin to use up. It's tedious sticky work. I've got to say down the back has proven to be a very good place to do glass work.

Dave

[JHapprich]

"I take the trestle table down here because my wife has complained about the smell for a while now and I get it. Fair enough however when our daughter uses the nail polish remover in the lounge room I am diplomatic about not making comparisons..."


Ohhhh, how well i know that

Looks like a nice place to work.

Looks like a Horten's sharp end.

How long all together took it to make all the hull molds?

Well done!again, jealous for your "cold" wheather!

[Davidh]

Hello all,


Another week of busyness and the warmer weather I am expecting is somewhat late in coming. It should by now be a balmy warm 30 degrees around this time of year as we head towards summer and heading into ideal fiber glassing weather. Instead its barely pushing 21.

Anyway, Last week I pulled off the main vertical splitter board that separates the two side hulls of the mold and also the front two molds but stops short of the back one piece mold that will straddle either side of the central board. It had come to the time to remove it so that I could work on creating the second main hull side. This would mean that the read flange board remains in position however readjusted with it now being placed up against the first main hull center line flange. Then the forward flange needs to but up against the main hull center line flange minus the main splitter board. Clear as mud?



Once again some of the register points got stuck inside the mold. A screw and screw driver would usually fix that.I did find a bit of crazing along the Gel coat mix where it had lifter a little from the surface of the splitter board. Arrggh! Really annoying. However nothing that a little filler and sanding back can't fix. In the above photo you can clearly see where the flange support board was mounted against the main splitter board. Now the main flange board from the other side will be butted up against the flange of the original main hull flange. Once the main hull is done then that flange board will be removed and will create the division between the main hull and the space to be created for the other forward bow section and silicon cavity.




The below photo clearly shows the partition between the forward lower bow mold and the main hull mold. The forward flange board is reassigned to just in front of the partition line between the two parts and will allow for the flange of the other main hull part to line up precisely with its mirror opposite. Here I have just finished sanding back the rough weave above the main hull vertical flange. I do big wide flanges...Once again there will be sealing with the Ubiquitous Play-Doh.



In the below photo you can see the step numbers and step 3 is almost ready to roll. The forward flange board has been re positioned just forward of the forward flange split between main hull and bow section. The rear flange board doesn't move yet and won't until this other main hull mold is made and then rear flange then acts as the wall for the stern one piece mold. So now Play-Doh and PVA release agent and some nice late spring weather to glass up.



I have a new fibre glassing area. I have a decent sized backyard and a small shed. I take the trestle table down here because my wife has complained about the smell for a while now and I get it. Fair enough however when our daughter uses the nail polish remover in the lounge room I am diplomatic about not making comparisons... Anyway this gets really good sun all day long, I just have to put up with the noisy mynahs swooping me now and then. They also chase the Kookaburras which is annoying. Reallocated register points forward and stern.




Gel coat down.



225 weave down. I find this tedious and tiring work but know that the outcome will be awesome.



At this point I have created the stern flange that will back up against the stern mold so I can take the rear flange off now. This back end reminds me of two things, a frog sticking its head out, or the front end of the Horten Ho 229 jet fighter. I can't decide. The stern side flanges of the main hulls clearly contrast in colour differences. Clear away the yellow Play-Doh and then ready for a little dam work.




Damn construction work!



Silicon flood!




As can be seen the wood strips act as a dam for the silicon. What is less noticeable is the use of Play-Doh to create a series of gripping points within the mold to stop the silicon mold from coming off the hard shell. These Play-Doh bits will create cavities that will be filled by glass from the hard shell and will hold the silicon mold inside the hard shell.



Cleaned up Daffy duck.



Gel coat Daffy Duck. this thing is going to weigh a ton.




Now it just needs lots of 225 weave, sunny weather and resin. Once hardened it will then be onto the last section of the mold which is the other front bow section and the creation of the Silicon hybrid parts.
The pigment difference is really noticeable here.

David H

[Davidh]

Hello all,

So I have created the first of the main hull side molds. Lots of repetitive laying up of weave and resin, gets tedious but you can see the slow and gradual progression towards the eventual finished product. The next step is to make the first of the bow side molds. Firstly I need to remove the forward flange board that terminates the main hull mold. This is simply done by unscrewing the base of the support flange board and taking the screws out of the main vertical board. Once all the screws are removed then pulling off the flange board is pretty straight forward. Once the flange board is pulled off I check the surface. Usually when I pull these boards away then the register point usually gets stick in the cavity that it produces. I then need to simply pull this out, usually by just wiggling it.



The register point is still embedded in the flange. One of the easiest way of getting it out is to wind a screw into the back of the register point and then pull it out. Once this is done I run some sand paper inside just to smooth it out. The masking tape was placed over the front section so that if there is some slop with the resin whilst doing the main hull section , I didn't get any on the forward section. If I did and I didn't notice it would dry and be major pain to get off.



The register point pulled and two new points added, I then go around the gaps and seal once again with Play-Doh. Smoothing it over with a flat blade and getting it nice and smooth. I also take a sanding block and sand back the rough fiber material around the flange. This will make the two separate pieces easier to get apart and not have weave and resin from both mold ends inter mixing and being impossible to separate.

After all this is done I then need to undertake a part of the mold that I haven't done before. The torpedo tubes present an interesting geometry challenge for the mold. I could have decided to continue with the hard shell mold over the torpedo tube features as It is a split mold and would com apart sideways, this would work however, I have decided to create a small section of the hard shell mold with a small silicon molded section built it so that It becomes a "hybrid / hard shell mold". This has presented a few complications for me in regards to how to go about this. So I chatted with HWSNBN a few times with drawings to detail and communicate my ideas and concerns and to check that I had got the idea right. (these drawings can be seen in "tool time")

In order to do this I would need to create a cavity over the area that I wanted to make the small silicon reservoir or insert into. To do this I would need to cover over the area that would be where the silicon would reside to make what would be a hollow cavity after the outer hard shell was removed. This was done using a chuck of Play-doh shaped over the torpedo tubes. I also create an irregular shape in the play-Doh to help the silicon grip. I made the outer section of the Play-Doh wider that where it touches the master, creating a subtle undercut to help trap the silicon mold, not that It will really come out. The pour for the mold will be done through a series of drilled holes on the outside. and a temporary plastic dam put in place.



The Play-Doh that will create the cavity. Once all this is done, then several layers of PVA release agent.




Once this is done then a Gel coat goes down. Then several layers of the 225 weave.




Several layers of 225 weave and plenty of resin and persuasion around the register points.



After this is cured, I will then pull off the main vertical splitter board and then place the forward flange board at the exact same space but on the other side to create the other middle hull and then the other forward bow section. The difference being that there is no center vertical board to attach this to. Lots of screws underneath then . Getting the vertical board off has taken a little bit of knocking, it has come off in pieces. Its all in the timing and sequence around the splitter boards and then flanges that you create..



More next week.

David H

[Davidh]

Hello all,


Busy setting up the molding boards, making sure that they were square and true. I drilled and screwed in numerous self tappers all over the boards to reinforce and hold them in place. Then once this was done I stated looking at the positioning of the Registration points. The small domed dowels that will register the mold halves correctly to each other. The next major task to do was to seal around the mold gap. I used the jigsaw to cut out both the hull and then vertical longitudinal hull separation using this tool. It ain't perfect and as a result I have to plug the gaps so to speak. The best way to do this is with Play-Doh. Push in, press down with a smooth tool and then screed along to create a flat smooth seal between the master and then splitter board. The smooth tool hopefully means that you don't get a ripple effects caused by the dough pulling up slightly. Don't do this in direct sunlight as the moisture in the clay or Play-Doh can evaporate and then you get cracks in the seal and that ain't good.




This here shows the forward part of the main hull and the Play-Doh substitute. Seal all the way around. One side only at the moment. As you can see one register point down on the front flange. The stern section has one register point, that will register the one piece rear silicon glove hard shell tool for the very stern . I also placed a tiny bit of Play-Doh inside the shaft hole. This should mold nicely.




Four register points along the length of the hull and one point at either end. After all the dough has sealed the gaps then I apply several layers of PVA release agent.



Release agent gives a nice shine.





Once the PVA release agent is down, I ended up putting three coats down , I could then think about the initial layer of the mold. I mixed up some Gel coat. I usually do a bright orange Gelcoat for the molds however this time I didnt have any so I found some red Maroon red ochre coloured pigment to throw in that gives it some colour. After this initial gelcoat layer I started laying down weave. About a year ago a friend of mine who is a shipwright gave me a massive roll of a light chopped strand matt called "225". This stuff is light enough that it will bend around and generally conform to the shape you want (with enough resin) yet thick enough that 203 layers would be sufficient.



I brush out the Gel coat quite wide to make the mold flanges quiet large.




I ended up laying down about 3-4 layers of the 225 weave. This gives a good thickness to the mold and combined with the curve of the hull, the end flanges and longitudinal flanges should make for a very rigid mold.It will still get and egg crate arrangement. The biggest challenge is getting the weave to wrap around the registration points and not stick up or out. If you work with enough resin and dab, dab, dab you will eventually beat the fibers into submission. I also have to press the 225 into the corners. I also used long strand that I have to reinforce the cornered areas.




Ready to pull the front flange boards off and do the bow next week.

David H

[Davidh]

Hello David and Rob,

Thank you. If it helps inspire someone to give it a go and clarifies processes then so be it.
The molds have turned out really well. There will be more about that in next weeks write up…
Dave.

[He Who Shall Not Be Named]

Beautiful video. Looks like you stuck to the plan presented in those great shop sketches.

David

[rwtdiver]

Thank you David,

Next video installment.

https://www.youtube.com/watch?v=J_Dz0GmsFkE&t=513s

David H.!

That YouTube showing your building process was amazing! You and David M. have really mastered the skills required to truly SCRATCH build a submarine! I truly respect what you do!

Thank you for putting up the video of your work! You and David M. are truly masters!!

Rob
"Firemen can stand the heat"

[Davidh]

Thank you David,

Next video installment.

https://www.youtube.com/watch?v=J_Dz0GmsFkE&t=513s

[He Who Shall Not Be Named]

The mold-board with parting planes is coming along as planned. Good work so far.

[Davidh]

Thank you David,


We are slowly working our way through Spring, temperatures going up. Hitting mid 20's and early 30's, nice weather for mold making. However I still need to keep building the main mold board for the hull. So after cutting out the profile of the hull, with the hull turned upside down and the board sitting right on the waterline just below the lower deck edge. Once the hull was level fore and aft I then made sure that the hull wasn't listing. Once that was done, I drilled a couple of holes along the underside and placed some blocks underneath to hold the hull in just the right place.



The next major step was to create the register point. These register points are made from wood dowels that are sanded down to a point. I then cut these off and then put a coating of resin over the top to seal them. A light sanding followed. These register points will be screwed or glued down to the mold flanges in order to create the bulges that create precise register points for the mold. Fiber glassing around them can be a pain in the neck but they are necessary.



These register points will only be on the vertical flanges that separate the lower hull mold pieces. They wont be needed for to hold the bottom to the top. They will never need to be joined. Below shows the register points just before the resin is applied. I have used screws to hold them to clamps whilst drying.



The stern section will be a separate mold that straddles the width of the rear. This will be a silicon hard shell mold.



The next major step is to produce the vertical splitter board / partition between the two sides. This board needs to line up with the center of the keel to make sure that the two side molds are the same width. Marking it out accurately to then cut it accurately was a bit of a challenge. I used my depth gauge to try and outline the profile that I would need to cut. Had to make sure that the pencil lead is at just the right height. After several runs and lots of cross measuring I think that I finally got it right. I then took the jigsaw and made the cut.



Because the stern mold crosses the width of the hull, I will need to cut the vertical board just in from the stern so it does not run the full length and will not get support after the stern. The cross piece will support the vertical board on both sides. Once this was cut I then needed to mark the point where the cut would be made for the stern board. once this was done I needed to create the stern profile in order to make a nice flush surface for the cross board and its interface with the horizontal board.



This profile matching device is a cracker!



The only other flange is the forward bow board that will separate the middle hull section and create the bow section. This will be a two part mold and feature a hybrid silicon and hard shell mold in one. I have never down this before and so it should be interesting. The torpedo tubes are just below the equator split between top and bottom. The hybrid silicon mold will be covering the torpedo tube bulges and forward "scoops" where the torpedo comes out. This silicon area will be covered by Play-Doh in order to create the cavity that will be later filled.



Screwing down the boards from underneath and behind. When this side is complete then this board will be applied to the other side.

More next week.

David h