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

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  • JHapprich
    Captain
    • Oct 2017
    • 713

    #46
    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

    Comment

    • Davidh
      Captain
      • Nov 2010
      • 719

      #47
      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.

      Comment

      • Davidh
        Captain
        • Nov 2010
        • 719

        #48
        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.


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        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.

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        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.

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        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.


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        More next week.

        David H

        Comment

        • Scott T
          Commander
          • May 2009
          • 378

          #49
          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.

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          Comment

          • Davidh
            Captain
            • Nov 2010
            • 719

            #50
            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.

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


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            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.

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            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.


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

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            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.

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            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.


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            David H

            Comment

            • Davidh
              Captain
              • Nov 2010
              • 719

              #51
              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.

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              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...

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              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.

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              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.

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              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.

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              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.

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


              David H

              Comment

              • Davidh
                Captain
                • Nov 2010
                • 719

                #52
                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.

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                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.


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                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.

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                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.

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                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.

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                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

                Comment

                • Davidh
                  Captain
                  • Nov 2010
                  • 719

                  #53
                  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.

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                  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.

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                  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.


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                  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.

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                  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.

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                  Till next week.

                  David H

                  Comment

                  • Davidh
                    Captain
                    • Nov 2010
                    • 719

                    #54
                    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.

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                    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.

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                    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.


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                    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..

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                    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.

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                    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.


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                    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...

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                    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

                    Comment

                    • Davidh
                      Captain
                      • Nov 2010
                      • 719

                      #55
                      Hello all,


                      So after getting the alignment right and with the laser line going straight down the middle of the keel, I marked a spot along one of the section lines forward of where the narrowing of the keel starts. I then took a tenon saw and started cutting either side of the keel as I don't want to snap the keep just bend it slightly. I continued cutting until I reached the sides where the lower decks will be. A cut like this allows me to push the rear hull either way whilst still having the keel intact. It also allows for a limited twist (rotating motion) of the hull to allow for the slight warp that I spoke of earlier.


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                      The circled black market pen section is where the side of the keel is bulging a little to much and some material needs to be taken off. The whitish area is the cut. As mentioned I didn't cut through the keel just allowed it to twist by making sure that the material further away from the keel is wider to allow for a closing of the gap at the gunwales to create a pinch on one side and more of a gap on the other. I needed to pull the hull to the port.


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                      Line it back up on the board, set it up straight and then check that the laser line that it runs right down the length of the keel. The yellow tape helps hold the stern section at the right pinch point to check for correction. After this is done I carefully make checks into the twist.

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                      I then put a very slight twist in the hull to level out the stern and make sure that the two lower decks were level with each other. Once the bend and twist were correct and checked I then took some superglue and glued a couple of points. Sanding back the strip of hull earlier either side of the cut line has allowed me to have a smooth area for the glue and a small amount of resin and light weave. I also put some glue around the inside of the hull area amongst all the foam filler.

                      I then used some good old filler to fill in the pinch and gap on other side , then sanded back. The alignment is now looking much better. After this sanding, filling, sanding and lots of sanding.

                      The next major bit of work to be done was the addition of the box keel.This submarine as far as I can see has a box keel and I decided the best way to make with would be with Renshape. The box keel runs for most of the keel that is level. It should be reasonably easy to mold but will have some tight radius for the fiber glass. That could be fun. What i like about the box keel is that it will provide a very nice little compartment for ballast lead. Nice and low.

                      I took my big block of Renshape to school and after classes ran it though the circular table saw. I ran a strip about 15 mm wide with a rake to allow undercut for the mould even though this boat will be a two part split mold.

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                      All I had to do now was check the level nature of the underside of the hull, check that this piece was all square, which it was and work out where to stick it. That's next week.


                      David H

                      Comment

                      • rwtdiver
                        Vice Admiral
                        • Feb 2019
                        • 1768

                        #56
                        Originally posted by Davidh
                        Hello all,


                        So after getting the alignment right and with the laser line going straight down the middle of the keel, I marked a spot along one of the section lines forward of where the narrowing of the keel starts. I then took a tenon saw and started cutting either side of the keel as I don't want to snap the keep just bend it slightly. I continued cutting until I reached the sides where the lower decks will be. A cut like this allows me to push the rear hull either way whilst still having the keel intact. It also allows for a limited twist (rotating motion) of the hull to allow for the slight warp that I spoke of earlier.


                        Click image for larger version

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ID:	149854

                        The circled black market pen section is where the side of the keel is bulging a little to much and some material needs to be taken off. The whitish area is the cut. As mentioned I didn't cut through the keel just allowed it to twist by making sure that the material further away from the keel is wider to allow for a closing of the gap at the gunwales to create a pinch on one side and more of a gap on the other. I needed to pull the hull to the port.


                        Click image for larger version

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ID:	149855

                        Line it back up on the board, set it up straight and then check that the laser line that it runs right down the length of the keel. The yellow tape helps hold the stern section at the right pinch point to check for correction. After this is done I carefully make checks into the twist.

                        Click image for larger version

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ID:	149856


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ID:	149857

                        I then put a very slight twist in the hull to level out the stern and make sure that the two lower decks were level with each other. Once the bend and twist were correct and checked I then took some superglue and glued a couple of points. Sanding back the strip of hull earlier either side of the cut line has allowed me to have a smooth area for the glue and a small amount of resin and light weave. I also put some glue around the inside of the hull area amongst all the foam filler.

                        I then used some good old filler to fill in the pinch and gap on other side , then sanded back. The alignment is now looking much better. After this sanding, filling, sanding and lots of sanding.

                        The next major bit of work to be done was the addition of the box keel.This submarine as far as I can see has a box keel and I decided the best way to make with would be with Renshape. The box keel runs for most of the keel that is level. It should be reasonably easy to mold but will have some tight radius for the fiber glass. That could be fun. What i like about the box keel is that it will provide a very nice little compartment for ballast lead. Nice and low.

                        I took my big block of Renshape to school and after classes ran it though the circular table saw. I ran a strip about 15 mm wide with a rake to allow undercut for the mould even though this boat will be a two part split mold.

                        Click image for larger version

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ID:	149858

                        All I had to do now was check the level nature of the underside of the hull, check that this piece was all square, which it was and work out where to stick it. That's next week.


                        David H
                        David,

                        I really like how you are using the old building craftsmanship techniques along with the latest technology (laser) to construct your SM U-23! Your craftsmanship is superb! Really neat stuff going on here!

                        Rob
                        "firemen can stand the heat"

                        Comment

                        • Davidh
                          Captain
                          • Nov 2010
                          • 719

                          #57
                          Hello all,

                          Thanks Rob, really appreciate the encouragement. it's just nice to get comments.


                          So as mentioned last week, I started work on the box keel. This is a long rectangular structure that the boat effectively sits on . I have made mine out of Renshape and cut it to size just using the school circular saw. That allowed me to get a precise flat surface very where however I ended up putting a slight taper along the sides so that the top edge is wider than the bottom. Good for creating draft angle for the hard shell fiber glass molds and eventually a great place to put the keel ballast.


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                          Because of the slight curve of the lower hull I had to give a corresponding curve along the upper surface of the box keel. This would allow the keel to have a snug and smooth mating to the underside of the hull. this would reduce gaps either side that would need filler. So I placed the strip in my whiz bang you beaut milling machine. (I love my mill). I then milled out a lower section in the middle that I would then carve around the create the profile. I then shaved off the sides of upper surface and reduced the material till it met with the flat surface of the mill. Straight forward really.


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                          Then it was simply a case of marking out where I wished to glue down the keel. This is towards the back of the flat section of lower hull. Take the center line and evenly place the keel either side of the line then glue down. I used a modeler's cement.

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                          Rough up the surface before gluing down. This helps the Renshape key to the lower hull surface.


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                          Lots of sanding from last weeks stern section hull correction and re-alignment. I had to sand back after giving a coat of resin to smooth over and reseal the balsa and wood after aggressive sanding had exposed down 'to the bone' so to speak. Had to sand either side of the keel to make sure it was consistent thickness along it's short length.


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                          Then some filler at either ends and some down the sides. then lots of sanding and filling and sanding and..........

                          More next week....


                          David h

                          Comment

                          • He Who Shall Not Be Named
                            Moderator
                            • Aug 2008
                            • 12254

                            #58
                            Your work gets better and better, sir.

                            David
                            Who is John Galt?

                            Comment

                            • JHapprich
                              Captain
                              • Oct 2017
                              • 713

                              #59
                              Nice mill, nice boat, nice work! That keel will give plenty of space for trimming ballast. Does it turn a bit to the right bow in the last picture? Also the outline of the stb aft hull looks a bit more courved than port.

                              ;-)


                              Really jealous for your workshop's window!

                              Found the missing nitrotube and can move on with pinch valve installation,btw!

                              Long weekend coming!

                              Jörg

                              Comment

                              • Davidh
                                Captain
                                • Nov 2010
                                • 719

                                #60
                                Hello all,

                                Thanks David, Jorg.

                                The stern hull will get more checking and sanding, checking, sanding, checking ....

                                Months before I started to work on the small stern pieces, mainly the props, the shaft struct bracket, (the bracket that holds the prop on the end of the shaft ) and the shaft mount that interfaces the shaft and the hull. I use a fantastic 3D modelling program that no one else seems to use, Blender. I have been teaching this program to high school students for over ten years and it just does so much. It's animation engine is fantastic. I started working on the screws. Then worked on the brackets. Saving them as an stl. I could then send them to a printer. The printer software that I use makes it a little hard to identify exactly the right size of the part being printed. It doesn't bother me, I am quite happy to print off several different sizes of the one part. It also gives me an opportunity to arrange the part at a different angle and see how the scaffolding breaks off.


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                                Here is the first set of parts, the smaller the parts the more the scaffold can overwhelm it and it becomes harder and harder to pull the part away from the scaffold. The larger the part the less the scaffold is a problem. On these props the fine blades broke away simply too easily. I then scaled up the parts and blades to give them a little more strength.

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                                I printed out about 2 or 3 of each part to test fit and how they looked on the side of the boat and how they interacted together.

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                                It takes a lot of sanding to eliminate the layers in 3D printing. This is one thing about the technique that is unavoidable. Here you can clearly see the layers underneath the primer layers. I have also used spray primer to smooth over and level all the layers however they still tend to show from underneath. They take a lot of sanding to get right. I have designed the parts around a 2 mm shaft. The prop will screw onto a thread on the end. I have thought about molding a brass insert into the strut bracket to support the shaft and reduce wear on the bracket but decided against it.

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                                Here you see the shaft assembly. The bracket angles need a little bit of work to get them at just the right angle to have them flush and seating nicely against the side of the hull. The shaft 'Blister' at the hull end will be seated with a raised section of marked outline for the kit.


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                                Tape is good for checking positioning. The props need to clear but also make the shaft as horizontal as possible. I have had to measure all the parts to make sure that they are all the same distance apart horizontally and vertically from the nominated center point down the middle of the keel.

                                More detail next week.


                                Dave h

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