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Moebius Skipjack

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  • Ken, can you show where you placed the weight?
    There is no greater enemy than one’s own fears. It takes a brave man to face them.

    Comment


    • Sure. I placed a piece of blue tape on the exhaust housing. That is the center of the boat fore and aft. Since I have weight in the bow due to all the hardware for the torpedo doors, I first added the two 4 once weights to the left in the picture. At this point the boat is balanced on a small piece of wood at the fore & aft center. I then added the two larger weights forward and balanced against those with the 4 weights to the left under the sub driver. The boat is now balanced assembled on the fore and aft center. I left a space between the foremost and aftmost weights for water to drain when it needs to. Nothing to show yet on the flotation. The wire mess you see is for underwater LED's.

      David's The Joys of Trimming out a Wet-Hull type R/C Submarine document
      https://www.rcgroups.com/forums/show...mentid=5362406

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      Last edited by Ken_NJ; 09-16-2021, 10:43 AM.

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      • I think I should have done the submerged trimming first. But I didn't.

        I have about 2 pounds of lead in the boat so that the center of the SD is the balance point. I have foam situated so the boat is floating at the surfaced waterline.

        For submerged trim I rubber banded foam to the aft deck and have the boat level but it's deck awash and waterline at the base of the sail. What should I do to get it lower?

        I'd check in Bob's book but Amazon is screwing me on delivery.

        Comment


        • Originally posted by Ken_NJ View Post
          I think I should have done the submerged trimming first. But I didn't.

          I have about 2 pounds of lead in the boat so that the center of the SD is the balance point. I have foam situated so the boat is floating at the surfaced waterline.

          For submerged trim I rubber banded foam to the aft deck and have the boat level but it's deck awash and waterline at the base of the sail. What should I do to get it lower?

          I'd check in Bob's book but Amazon is screwing me on delivery.
          You ****ed up.

          Submerged trim first -- ballast tank fully flooded. That way you have firmly established the amount of fixed lead weight AND amount of buoyant foam to make the boat neutrally buoyant and statically stable about the roll and pitch axis. After that, to establish the designed waterline, all you have to do is empty the ballast tank and move the foam vertically -- above or below the designed waterline -- till the boat floats at the correct surfaced waterline.

          Just the vertical position (above an/or below the designed waterline) of the foam is changed between the two conditions of trim.

          You people!

          https://youtu.be/TlXHCykk7fU

          David
          Resident Luddite

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          • Cra*p, f***, dam....it

            Anyway. Start over?????

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            • Originally posted by Ken_NJ View Post
              Cra*p, f***, dam....it

              Anyway. Start over?????
              Remember this, always: You are here to be punished!

              David
              Chief Inquisitor
              Resident Luddite

              Comment


              • I'm notorious for not reading directions. Aren't most guys? My girlfriend always chides me for not reading the directions. Maybe I should start.

                In the case of the Marlin, probably didn't do it right from the start, but I got it. The second time with the SJ, didn't do it right, but I'll get there. Hopefully when I get to the XXIII I do it right from the start.

                David is always right! Listen to David! Read and understand the procedures that David wrote! Do not deviate from David's directions! Do not do anything to be punished by David!

                Comment


                • Originally posted by Ken_NJ View Post
                  I'm notorious for not reading directions. Aren't most guys? My girlfriend always chides me for not reading the directions. Maybe I should start.

                  In the case of the Marlin, probably didn't do it right from the start, but I got it. The second time with the SJ, didn't do it right, but I'll get there. Hopefully when I get to the XXIII I do it right from the start.

                  David is always right! Listen to David! Read and understand the procedures that David wrote! Do not deviate from David's directions! Do not do anything to be punished by David!
                  (my work here is done)
                  Resident Luddite

                  Comment


                  • Originally posted by Ken_NJ View Post
                    I'm notorious for not reading directions. Aren't most guys? My girlfriend always chides me for not reading the directions. Maybe I should start.

                    In the case of the Marlin, probably didn't do it right from the start, but I got it. The second time with the SJ, didn't do it right, but I'll get there. Hopefully when I get to the XXIII I do it right from the start.

                    David is always right! Listen to David! Read and understand the procedures that David wrote! Do not deviate from David's directions! Do not do anything to be punished by David!
                    Ken,

                    Don't feel bad! I have been in David's sites many times as well! It's all a learning process for sure, but we have a great teacher to learn from!!

                    Rob
                    "Firemen can stand the heat"

                    Comment


                    •  
                      Make it simple, make strong, make it work!

                      Comment


                      • Boat is submerged with 1" of the sail above the water. And level.

                        If I blow the tank surfacing the boat leaving the foam exactly where it is in the picture, same place as submerged. The boat is slightly down at the bow and slightly up at the stern. What should I do to get both ends at the waterline? I did not move the foam vertically, didn't have to.

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                        Comment


                        • Originally posted by Ken_NJ View Post
                          Boat is submerged with 1" of the sail above the water. And level.

                          If I blow the tank surfacing the boat leaving the foam exactly where it is in the picture, same place as submerged. The boat is slightly down at the bow and slightly up at the stern. What should I do to get both ends at the waterline? I did not move the foam vertically, didn't have to.

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                          Move the after pieces of foam up above the designed waterline and check that the boat assumes the correct waterline with the ballast tank empty. If need be, cut off portions of the next-in-line set of foam blocks and mount them above the designed waterline. Keep doing this till the boat assumes proper trim when on the surface.

                          David
                          Resident Luddite

                          Comment


                          • Did as you said. As the boat submerges it goes down bow heavy then levels out. As it surfaces, it comes up bow heavy then settles with the bow slightly down and aft end slightly high above the WL. You can see the engraved WL in the pictures. Seems like it's unbalanced, the bow needs to rise as much as the stern needs submerge.

                            I played around with different combinations, couldn't get it right.

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                            Comment


                            • Experimenting.

                              I added a very small weight at the aft end and added a small block of foam under the bow. Now the boat submerges and surfaces level. But in this configuration the submerged WL is below the sail planes.

                              Yes i know the weights go low.

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                              Last edited by Ken_NJ; 09-19-2021, 07:28 PM.

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                              • At the center of gravity remove a small hunk of buoyant foam from above the models surfaced waterline. This will not change surfaced trim, but will bring the submerged trim down a bit more than what you have now. Keep removing chunks of foam till you have about an inch of sail sticking into the air in submerged trim.

                                Almost there, Ken!

                                David
                                Task Master extraordinaire
                                Resident Luddite

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