Triple Screw Boat

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Triple Screw Boat

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  • This topic has 40 replies, 10 voices, and was last updated 3 weeks, 6 days ago by Queequeg Quint.
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  • #105712
    ashley needham
    Participant
      @ashleyneedham69188

      That`s really nice Q, really nice, well done…and even better as it is a `head` build.

      . Just the right amount of detail, great colour scheme, very neat.

      A couple of pictures of it at speed would be good.

      Ashley

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      #105713
      Chris Fellows
      Participant
        @chrisfellows72943

        As Ashley says very nice. You certainly had room for triple screws!

        How does it go at speed?

        Chris

        #105725
        Queequeg Quint
        Participant
          @queequegquint38270

          I will get some more action photos next week.

          As for how it handles, with all three motors running, the turn radius is miserable. It makes an extremely wide turn because the thrust of the three propellers nearly overpowers the three rudders. So, we have set it to run the center-motor independently of the two port- and starboard-motors. If I deactivate the center-motor on turns, it turns very nicely.

          More pictures:

          lots of gold thereThe three 5-blade propellers on the Dolphin look like a treasure of gold just beneath the stern!

          Engine RoomEngine room or Torpedo bay!

          #105729
          Chris Fellows
          Participant
            @chrisfellows72943

            You've sorted it anyway, but the rudders do look as though they'd benefit from being a bit longer. As you say nice props!

            Meant to say before, impressive workshop! smiley

            Chris

            #105821
            Queequeg Quint
            Participant
              @queequegquint38270

              #105894
              Queequeg Quint
              Participant
                @queequegquint38270

                Here is a video of my first run of the boat. Boat is very stable. Steering is good, even at full throttle. However, the boat is not as fast as I had hoped. The battery might have needed a better charge, but what i discovered is this: on two motors (port & starboard), the boat runs plenty fast. Activating the center motor adds only a little bit more speed. I was hoping for a significant increase in speed upon activating the third center motor. The bow does lift a bit when you activate the third motor, and the boat makes a lunge forward, but it is not significant. I will try again with a fresh charge of the battery soon.

                I'm using three 5-blade propellers with 55mm diameter, being turned by three MFA Como 800 motors on 12-volts. I wonder if switching to 4-blade will increase my top-speed a bit.

                #105898
                Chris Fellows
                Participant
                  @chrisfellows72943

                  In my view increasing from one prop and motor only has generally a negligible effect on speed. Reason being that the speed is governed by the revs. It might increase slightly as the load on each motor will be reduced and the motors are able to rev higher but it won't be significant.

                  The advantage for more than one motor is acceleration and more power which will increase the speed of a big heavy displacement hull pushing lots of water out of the way, to a point.

                  I think that when some folks, particularly with planing hulls, ask about twin motor set ups they think that the motors only need to be about half the size but that isn't the case. Maybe slightly smaller than a single motor set up but that's about it.

                  So I think when the third motor kicks in it initially takes load off the other two and they accelerate, hence the lunge, but then the top speed is then restricted by the max revs being achieved. And of course the third prop when not running is acting as a big brake which will then contribute to the lunge!

                  Increasing the voltage might help a bit but sounds as they it might be over-propped as well. Any reason why you used 5 bladed props and why you're considering 4 blade? Would have thought that 3 blade and maybe 50mm would be the best bet? I bet there is a fair amount of weight in that boat as well with three motors, prop shafts and rudders etc? What battery are you using?

                  Chris

                  Edited By Chris Fellows on 15/09/2023 13:03:38

                  #105902
                  Queequeg Quint
                  Participant
                    @queequegquint38270
                    Posted by Chris Fellows on 15/09/2023 12:47:13:

                    In my view increasing from one prop and motor only has generally a negligible effect on speed. Reason being that the speed is governed by the revs. It might increase slightly as the load on each motor will be reduced and the motors are able to rev higher but it won't be significant.

                    The advantage for more than one motor is acceleration and more power which will increase the speed of a big heavy displacement hull pushing lots of water out of the way, to a point.

                    I think that when some folks, particularly with planing hulls, ask about twin motor set ups they think that the motors only need to be about half the size but that isn't the case. Maybe slightly smaller than a single motor set up but that's about it.

                    So I think when the third motor kicks in it initially takes load off the other two and they accelerate, hence the lunge, but then the top speed is then restricted by the max revs being achieved. And of course the third prop when not running is acting as a big brake which will then contribute to the lunge!

                    Increasing the voltage might help a bit but sounds as they it might be over-propped as well. Any reason why you used 5 bladed props and why you're considering 4 blade? Would have thought that 3 blade and maybe 50mm would be the best bet? I bet there is a fair amount of weight in that boat as well with three motors, prop shafts and rudders etc? What battery are you using?

                    Chris

                    Edited By Chris Fellows on 15/09/2023 13:03:38

                    Thank you for your insightful comment. Much appreciated. Indeed, this is a heavy boat. Big and heavy. I went with 5-bladed because some of the real triple-screw boats I studied all had 5-blade props. Several years ago, I did an experiment on another boat: 4-blade vs 5-blade, both same diameter. When I switched to 5-blade, the boat gained acceleration, but lost a bit of top-speed. So, I wonder if reducing the number of blades might increase the top-speed of my triple-screw boat. I reckon with three propellers, I already have plenty enough acceleration, so reducing the number of blades might be acceptable.

                    The battery is a 12-volt NiMH, which I had custom manufactured so it can handle a high current-draw.

                    #105903
                    Chris Fellows
                    Participant
                      @chrisfellows72943

                      You've answered my question as regards the battery as it was the current draw I was thinking about, as when operating at full throttle even a slight drop off will affect performance particularly when marginal.

                      Can you get plastic 3 blade props in the size you want. That would be the best for testing purposes before investing in the nice shiny ones, especially when you need 3!

                      I don't know much about brushed motors but looking/listening to the video reinforces my view that it's a lack of revs which is the problem. It could be argued that a coarser pitch could provide more speed but if the revs drop as a consequence no advantage is obtained.

                      Chris

                      #115510
                      foamfoils
                      Participant
                        @foamfoils

                        Hi Chris: My name is Steve from Hamilton Ontario Canada and have been into flying for over 40 years but due to my age now 69 and getting tired of crashing it’s time for me to come down earth or should I say water. I have a 1 meter sail boat and a Billings police boat with 2 screws that works well enough for me to have fun with but I recently purchased a Graupner Weser fire boat kit 43″ long with 3 screws on 3 550 motors. I read your article on your 3 screw 3 rudders and found it very informative, my boat has 2 rudders with the 3 screws , rudders only on the 2 outboard units no rudder for the center screw. I would like to try and do the same thing you did with being able to shut down the 2 outboard motors and run the middle motor only. If it’s not too much trouble to ask could you please draw up a schematic drawing of how you managed to do this, and what ESC’s you used for a boat, I am only familiar with aircraft equipment and have to learn all the equipment for boats. You can post it in the forums or email me direct to [email protected]   I will be using my Spektrum DX6 radio for this as I need all 6 channels to make all the bits work but if the setup requires more channels then I will be shopping for a new radio. Thanks for letting me ramble on and for all the help you can offer.  Steve ( formally from Manchester UK )

                        #115516
                        ashley needham
                        Participant
                          @ashleyneedham69188

                          Q. As a cheap easy try out I would get three x50 props to try. You may have to search for handed ones, but they are inexpensive and although two blade, may actually give more power than the larger 5 blade ones as the motor will rev more.

                          looks good though, and stable for such a large boat. The small speed increase when adding essentially 1/3 more power is undoubtably due to the fact that to go twice as fast you need 8 times more power, not just twice the power due to the resistance of the water and air increasing non linearly to the speed (without looking it up, but I think it’s right), especially  more so with a heavy boat like yours.

                          Ashley

                          #115522
                          Richard Simpson
                          Participant
                            @richardsimpson88330
                            On foamfoils Said:

                            Hi Chris: My name is Steve from Hamilton Ontario Canada and have been into flying for over 40 years but due to my age now 69 and getting tired of crashing it’s time for me to come down earth or should I say water. I have a 1 meter sail boat and a Billings police boat with 2 screws that works well enough for me to have fun with but I recently purchased a Graupner Weser fire boat kit 43″ long with 3 screws on 3 550 motors. I read your article on your 3 screw 3 rudders and found it very informative, my boat has 2 rudders with the 3 screws , rudders only on the 2 outboard units no rudder for the center screw. I would like to try and do the same thing you did with being able to shut down the 2 outboard motors and run the middle motor only. If it’s not too much trouble to ask could you please draw up a schematic drawing of how you managed to do this, and what ESC’s you used for a boat, I am only familiar with aircraft equipment and have to learn all the equipment for boats. You can post it in the forums or email me direct to [email protected]   I will be using my Spektrum DX6 radio for this as I need all 6 channels to make all the bits work but if the setup requires more channels then I will be shopping for a new radio. Thanks for letting me ramble on and for all the help you can offer.  Steve ( formally from Manchester UK )

                             

                            Steve, it is interesting to note that there are actually very few dedicated model boat orientated radio sets available.  In fact the only ones I can think of are the Robbe F-14 and F-16 units.  99% of us use a generic radio, most of which are designed for model aircraft use.  Your Spektrum is a perfect example, with all the functionality required to operate either fixed or rotating wing aircraft.  The plus side for an ex aircraft modeller is that you are probably far more familiar with the mixing and programming capabilities of the radio than most model boaters will ever be!  I have a Dx6i and a Dx6e but still think mixing is something my wife does when she is baking.

                            Formally from Manchester but now in Ontario!  You lucky person.  I used to live in Manchester, Sale to be exact, and spent my early years on cargo ships across the North Atlantic between Manchester and Montreal.  I have always thought one of the best places to live would be Canada.  An absolutely beautiful place.  I bought quite a few christmas tree decorations in those days, real ceramic and wood, so I get a reminder every year when we decorate the tree.

                            #115526
                            Colin Bishop
                            Moderator
                              @colinbishop34627

                              Steve,

                              A lot of us use products from Component Shop who sell the ACTion Electronics range of speed controllers, mixers and many other electronics items.

                              https://www.componentshop.co.uk/

                              Useful examples of wiring applications using their gear can be found on this archived site:

                              http://vp-airsoft.co.uk/ms.html

                              Colin

                              #120867
                              Queequeg Quint
                              Participant
                                @queequegquint38270

                                Here is a video of the triple-screw boat running rather aggressively today. I ran for about 40 minutes with no problems.  Motors and ESCs were only slightly warm.  Hull was very stable. During turns, I lose lots of speed, as you can see in this video. But on a straight line, it speeds up.

                                Dolphin (the yellow boat): Three MFA Como 800 motors, Three 5-blade brass propellers, Three rudders

                                Ambassador (the red boat): One MFA Como 850 motor, with pulley gearing it down 2:1.

                                Both boats: 12-volt NiMh battery.  Mtroniks ESCs.

                                https://www.youtube.com/watch?v=boJ1Z-SZlQo

                                #120871
                                Richard Simpson
                                Participant
                                  @richardsimpson88330
                                  On Queequeg Quint Said:
                                  Posted by Richard Simpson on 15/07/2022 10:56:02:
                                  Mine is just an observation and in no way a critisism but, in real practice the centre shaft would not protrude as much as yours does for very sound engineering reasons. In your model the engineering concerns are not relevant however it does leave you with an arrangement that, to me, just looks a little odd. Extending the keel to come up to the rear of the propeller would be way too much work so it would be interesting to see what it would look like if you simply pushed the centre propeller back a little to reduce the amount of exposed unsupported shaft.You may well then think that it looks odd not having the props in line but, as I said I simply see it from an engineering perspective.

                                  Can you explain the engineering reasons for your suggestion? I’m curious.

                                  My apologies for completely missing this, nearly a year ago!  I was thinking of a vibration and stress reversal perspective.  In full sized vessels you would not have unsupported shaft for any great length to avoid vibration and the weight of the shaft would tend to create a possibly unperceptible sag that would cause stress reversals as the shaft rotated, eventually leading to cracks.

                                  Not a problem in models other that it can just look a little odd if you are not used to seeing a length of unsupported shaft.  Having said that when you get into the realms of performance boats, as it could be argued you are here, vibration in unsupported shafts can be a challenge.

                                  #121074
                                  Queequeg Quint
                                  Participant
                                    @queequegquint38270

                                    A few actions shots today.

                                     

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