1/72 688 class

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • a1965l
    Lieutenant Commander
    • Apr 2020
    • 147

    #61
    I did stuff today!

    After a small amount of thinking, I came up with an idea for a test tank. perhaps not the greatest, but it worked. Cinder blocks and plastic sheeting... easy. Only issue is it's only about a foot deep, which should be all I need. I took a guess at what kind of ballast I would need. Judging from the 4 or 5 lbs I had to put in the tugboat to get it to sit at the waterline, I put all the lead I had on hand in the keel, and dropped the boat in the water without the top hatch.

    Sank right to the bottom. Ok then.

    I put a more reasonable amount of weight in and dropped it in. Got this, and if it's not obvious from the picture, there is zero roll stability, as expected:

    Click image for larger version

Name:	20200531_141717-X4.jpg
Views:	319
Size:	72.8 KB
ID:	140083

    That's not a bad waterline, though... but once I put the hatch on, it was a whole new ballgame.. that additional weight didnt' work in my favor, again, as expected. If you look at the bottom of the picture, you can see the weight I've removed. Just for ****s and grins I submerged the boat to see, and not surprisingly it went right to the bottom of the tank and sat there. Hard. I blew ballast, and it came right up, in fact, it didn't take more than a few seconds for it to get positively buoyant and broach. I kept blowing, expecting to see air bubbles, but apparently the escaping air filled the hull and it got really buoyant:

    Click image for larger version

Name:	20200531_142233-X4.jpg
Views:	350
Size:	67.8 KB
ID:	140084

    It also didn't help that the weight slid around, and went aft when it took the up angle. Let's get some roll stability... so I cut some pink foam and worked it around a bit..

    Click image for larger version

Name:	20200531_153933-X4.jpg
Views:	301
Size:	62.4 KB
ID:	140085
    Click image for larger version

Name:	20200531_153920-X4.jpg
Views:	395
Size:	65.7 KB
ID:	140086

    And that's where I am right now with the waterline. it's got the good LA lean going, prop is entirely underwater. Roll stability is very good on the surface, it's a little more tender under the water but that's expected. Submerged it's just barely positively buoyant... it does sit on the bottom of the tank but it's very light there. I wish the tank were a little deeper. it does seem to submerge stern first and rise bow first. I'm going to hold what I have here for now, I'm certain some trimming is in order but I have other things to do and I am going to add another layer of cinder blocks to make the tank deeper. One thing that really surprised me, this is all the ballast I used:

    Click image for larger version

Name:	20200531_154541-X4.jpg
Views:	263
Size:	72.8 KB
ID:	140087

    I thought it would take a lot more.

    "It does not take so many words to speak the truth" Chief Joseph

    Comment

    • a1965l
      Lieutenant Commander
      • Apr 2020
      • 147

      #62
      Forgot to mention. There were a few drops of water in the WTC engine room side.. I did a reverse pressure check in the tank but didn't see any bubbles, so no idea where the water is coming from. I guess I should have exercised the controls while doing it.
      "It does not take so many words to speak the truth" Chief Joseph

      Comment

      • a1965l
        Lieutenant Commander
        • Apr 2020
        • 147

        #63
        I couldn't tell, exactly. I've been tipping the boat towards the stern to drain the water from the hull, additionally the MSD needs to be tilted to remove it from the hull. I did note than when pressurizing the hull, I would get air out of the snort line.
        "It does not take so many words to speak the truth" Chief Joseph

        Comment

        • a1965l
          Lieutenant Commander
          • Apr 2020
          • 147

          #64
          Busy doing other things. My how time flies when you're having fun wrestling with machines. Mechanically, only small details remain until the maiden voyage. I affixed the lead and foam (and not very much of either!) with hot glue, which should allow for repositioning as required. I know, the cool guys use silicone, but I've had good luck with hot glue, and it's easy and fast.

          Click image for larger version

Name:	D7K_6441-X3.jpg
Views:	256
Size:	56.7 KB
ID:	140861

          Click image for larger version

Name:	D7K_6442-X3.jpg
Views:	232
Size:	69.2 KB
ID:	140862

          I had to relieve the foam to clear the locator tabs on the lower hull.. nothing to it. I installed the stern planes and rudders, only thing left to do is to secure the free half of the adjustment sleeve and lock the adjustment in. I was considering using a wheel collar to do that, it will require some thought and some soldering. I'm trying to decide if it's worth it to leave it adjustable, there's no real reason to think that the alignment will change unless bumped. So I'll just keep it simple and secure with some super glue. Simple is good.

          Click image for larger version

Name:	D7K_6438-X3.jpg
Views:	251
Size:	64.3 KB
ID:	140863

          Click image for larger version

Name:	D7K_6439-X3.jpg
Views:	238
Size:	56.7 KB
ID:	140864

          Yes, I did notice the misalignment and corrected it. So the next pictures should be in the nieghbor's pond.
          "It does not take so many words to speak the truth" Chief Joseph

          Comment

          • a1965l
            Lieutenant Commander
            • Apr 2020
            • 147

            #65
            Well, if that didn't look like enough foam and lead, it's because it wasn't. The boat seemed very stable in the test tank, but in the pond on any more than just tick-over throttle it was heeling badly. Plus it needs to sit more level. Ah well, live and learn. Also, It appeared to be slightly positively bouyant in the tank, but in teh pond.. eh, not so much. I did take the precaution of holding on to it while I flooded... much to the amusement of the big 'ole snapping turtle that turned up to spectate. In other news, turning circle is not so good... but I expected that given the size of the rudders and the relative weight of the boat. it's not unmanegable, but it's big... also trimmed way to far down at the stern.. bow came right up out of the water. I'll get it... tomorrow is another day.
            "It does not take so many words to speak the truth" Chief Joseph

            Comment

            • Akula54
              Lieutenant, Junior Grade
              • Jul 2011
              • 29

              #66
              Hello,

              I take advantage of the subject to ask you the question about the propeller.
              I plan to build an 1/72 LA Class, and I already have a 3.75" 7 blade scimitar OTW propeller purchased with an old Upholer hull.
              Do you think it's suitable for this boat or too big ?
              I searched everywhere on the web, I did not find the size of a real LA prop (probably classified).
              Nothing specified on 3D printed kit.

              Your opinion ?

              regards

              Comment

              • HvyCGN9
                Lieutenant Commander
                • Jan 2013
                • 187

                #67
                Here's a pic of a later VLS armed 1/72 LA class from a few years ago up in Sydney...
                .Click image for larger version

Name:	MD060807.jpg
Views:	218
Size:	42.3 KB
ID:	140971

                And with a Collins class RAN boat..
                Click image for larger version

Name:	MD060805.jpg
Views:	246
Size:	48.6 KB
ID:	140972

                Comment

                • a1965l
                  Lieutenant Commander
                  • Apr 2020
                  • 147

                  #68
                  Originally posted by Akula54
                  Hello,

                  I take advantage of the subject to ask you the question about the propeller.
                  I plan to build an 1/72 LA Class, and I already have a 3.75" 7 blade scimitar OTW propeller purchased with an old Upholer hull.
                  Do you think it's suitable for this boat or too big ?
                  I searched everywhere on the web, I did not find the size of a real LA prop (probably classified).
                  Nothing specified on 3D printed kit.

                  Your opinion ?

                  regards


                  I have a propellor on mine that is just at 2.25" in diameter. At what appears to be proper surface trim, to me, the propellor is completly under water, as it is on most U.S. boats. I'd have to suggest that your 3.75" prop is going to be just a little too large. If you have scale plans, you could make an estimate based on where you think the waterline would be, and gauge a prop size from that. I can't say whether or not my prop is too big for the motor I have, it's a little larger in diameter, but not much, and generally subs aren't hot-rodded around anyway.

                  I know I've been slacking... have some other projects that require more immediate attention. Thats life...
                  "It does not take so many words to speak the truth" Chief Joseph

                  Comment

                  • a1965l
                    Lieutenant Commander
                    • Apr 2020
                    • 147

                    #69
                    Back in the water! After a carefull, educated guess about where to put more weight and foam, I did so. No test tank this time.. right into the open... pond. Anyway. Surface trim looks pretty good:

                    Click image for larger version

Name:	20200709_133621-X4.jpg
Views:	196
Size:	55.2 KB
ID:	141521

                    So lets get underway. First thing I note is that stability is much improved. I did some full ahead crash asterns, and while the boat rolled significantly, it came back to vertical very rapidly. So no worries there. I also note that the turning circle is very large... very very large. Even on this giant pond I had to back down and to a couple J-turns. I need to get more rudder throw, and I think the only way to do that is a longer horn on the servo.. more on that later. Other than the gray section, it looks pretty good in the water moving around. 2 clicks of throttle are all it takes.. any more and the prop starts to cavitate. More than enough power, I think. It is apparently very heavy, as backing down takes a fairly scale amount of time, even with full throttle.

                    Click image for larger version

Name:	20200709_133720-X4.jpg
Views:	180
Size:	75.9 KB
ID:	141522

                    Click image for larger version

Name:	20200709_135042-X4.jpg
Views:	184
Size:	51.5 KB
ID:	141523

                    Click image for larger version

Name:	20200709_135058-X4.jpg
Views:	179
Size:	68.2 KB
ID:	141524

                    Now.. the bad news. I did a static dive pierside. Went down stern first. I mean straight up stern first, and wound up with just the bow above water. On a plus note, it seems to have some positive buoyancy, so there's that. I don't think I can redistribute any foam, really, so some lead right in the bow and we'll see what that gets me. I can still put some foam way high, where it will only affect submerged buoyancy. But that's another day. I also note that backing down on the surface it showed a tendency to drive the stern down with some way on. Probablly related to the previous issue. Kind of hairy, really, when it happens.. but the pond is, at worst, chest deep where I'm running so I'm not terribly worried...

                    anyway, time for some scale stuff. I ordered some dry transfer material from Amazon, that can be prnted on with an ink jet printer, I'm going to slack and use that to make markings, etc etc.
                    "It does not take so many words to speak the truth" Chief Joseph

                    Comment

                    • a1965l
                      Lieutenant Commander
                      • Apr 2020
                      • 147

                      #70
                      More fun with ballast today. I moved weight from midships/slightly aft to forward in an attempt to make the boat submerge on an even keel. Too much... trimmed down at the bow and it dove bow first.

                      Ok.

                      Left one chunk of weight fairly far forward, and moved the rest aft. Not as aft as it had been, but back. Surface trim is fairly level. Forward, when she gets a little speed on, the prop comes out of the water. Backing down is even, no tendency of the stern to dig in and dive. Boat submerges on a mostly even keel. It seems that I'm trapping some air here and there, as I can still "burp" some after I've flooded the tank. Before I burp, it's slightly positively buoyant, after burping, definetly negative.

                      I suppose I should add that since it's negative I did not dive while underway, and have not navigated underwater. Only dives I did were pierside with my nervous hand right there.. wish sometimes it worked that way with airplanes!

                      As an experiment, I pushed the boat underwater with the tank unvented (full of air). It seems that to hold it underwater, I have to apply pressure at what appears to me to be fairly close to the geometric center of the boat, which I take as good, meaning the buoyant forces are evenly distributed along the length of the boat. With the tank vented, holding the boat under the keel, I don't feel any tendencies to dive or climb.

                      But that negative buoyancy. Would I be better to remove some weight, or add foam? I have very good stability, I guess a round boat in the water is going to roll to some degree, but it's really very stiff and comes right back to vertical. Removingt weight is going to change the force on the righting arm, obviously. Foam to correct negative buoyance would be added high in the hull, over the regular waterline (well, I don't know if that's possible on this boat), but at least as high as I can.
                      "It does not take so many words to speak the truth" Chief Joseph

                      Comment

                      • Akula54
                        Lieutenant, Junior Grade
                        • Jul 2011
                        • 29

                        #71
                        Originally posted by a1965l

                        I have a propellor on mine that is just at 2.25" in diameter. At what appears to be proper surface trim, to me, the propellor is completly under water, as it is on most U.S. boats. I'd have to suggest that your 3.75" prop is going to be just a little too large. If you have scale plans, you could make an estimate based on where you think the waterline would be, and gauge a prop size from that. I can't say whether or not my prop is too big for the motor I have, it's a little larger in diameter, but not much, and generally subs aren't hot-rodded around anyway.

                        I know I've been slacking... have some other projects that require more immediate attention. Thats life...
                        Many thanks for your advice !
                        I will look in Propshop catalog the best prop that could fit.

                        Comment

                        Working...