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  • #120619
    Alasdair Allan
    Participant
      @alasdairallan37423

      Hi Len – you wanted  longer video, so am happy to oblige! see above link

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      #120620
      Stephen Garrad
      Participant
        @stephengarrad28964

        Brilliant, she looks really good. Well done.

        Stephen

        #120623
        Alasdair Allan
        Participant
          @alasdairallan37423

          Cheers Stephen!

          #120624
          Richard Simpson
          Participant
            @richardsimpson88330

            Just a feeling Alasdair, the model seems to be ballasted perfectly, she sits right and stays at the right level when under way.  She also seems to be stable so I can’t see why any adjustments to ballasting would make any difference to poor astern performance.  I would be concerned that any adjustments might have the effect of spoiling the excellent performance you have going ahead.

            I notice you say that when going astern sometimes she lists to port and sometimes to starboard.  To be honest many model boats perform badly when going astern for a variety of reasons, mostly to do with the way the water flows over the hull and reacts with the rudder.  In your case when going astern the rudder has very poor flow over it and I suspect it may be doing nothing more than pushing the model to one side or the other.  A problem with paddlers is that the hulls tend to be fairly narrow and therefore do not have a great deal of resistance to heeling.  It is obviously more stable going forward with a flow over the hull keeping things a little bit secure.  Go astern though and the flow is poor so you’ve lost that inherent stability from the flow of water over the hull.

            Colin has just finished a paddler so I’m sure it would be interesting to hear how his model performs when going astern and I would try asking more if possible.  There is a paddler specific forum by the name of ‘Paddleducks’, which might be worth joining where there is a wealth of paddler specific experience available to ask questions.

            #120627
            Alasdair Allan
            Participant
              @alasdairallan37423

              Thanks Richard. Yes, I don’t plan to muck about with the ballast I presently have.  If I do make an alternative keel at some point and it doesn’t work, I will go back to using this experimental one, as it screws onto a captive nut epoxied to the bottom of the boat.  I also agree that, for the reasons you give, going astern is just not suited to this hull shape.  Even real paddlers often buffet about a bit when going astern. yes would be very interested to hear about Colin’s paddler.

               

              #120628
              Alasdair Allan
              Participant
                @alasdairallan37423

                On paddle ducks, I had tried them a while back, but wasn’t really getting mucn response to anything i said, compared to this site, but I will try then again!

                 

                #120631
                Richard Simpson
                Participant
                  @richardsimpson88330

                  Paddleducks was never very active but they do have an amazing library of drawings and plans and some very knowledgeable members.  I suspect membership there is dwindling as with everywhere else and not being replaced so I guess you just have to persevere.

                  #120637
                  Colin Bishop
                  Moderator
                    @colinbishop34627

                    Curiously enough, on its one and only outing to date my paddler seemed to be better going astern! I was handicapped by a significant breeze though which tended to push the model over in some courses so the leeward paddle ‘dug in’. I need to try it out in a calm situation but, one way and another due to other commitments and the weather, the opportunity has not yet arisen.

                    I think the deep keel contributes a lot to the stability of your model as it imparts a strong righting moment to offset any  any irregularity caused by differential thrust from the paddles. My paddler is intrinsically stable but I think more prone to wobbling as the external ballast is simply stuck on the bottom of the hull. On its initial trip it was also prone to wobble caused by the mixer slowing down and reversing the inboard wheel on a turn. I have adjusted the mixer to give a much milder effect and am hopeful this will help smooth things out.

                    With regard to going astern, I think Richard is probably right that the waterflow around the hull may be the culprit. People assume that it is the rudder which turns a ship but that is not always the case. The rudder simply introduces an asymmetric effect which effectively makes the hull slightly banana shaped and it is this that causes the vessel to turn.This is why the old sailing ships had such apparently small rudders for their size. The rudder simply needed to ‘unbalance’ the hull. If course, sticking a prop in front of the rudder redirects thrust as well which pushes the stern round to accentuate the turn. A paddler doesn’t have a prop so, as Richard points out, the effect of the rudder can be unpredictable when going astern. It could be diverting waterflow unevenly, especially if it is not at dead centre. On a single screw vessel, the astern thrust will go to one side when the engine is reversed so the ship will inevitably steer (or not steer) more one way than the other! This can often be predicted and taken advantage of in both model and full size form.

                    My Bilsdale is a a full bodied tubby ship so is likely to behave rather differently to the long slim Glen Rosa.

                    There is one other possible influence which Glynn Guest has discovered in that fixed float paddle in particular can cause a sort of ‘hydraulic lock’ by scooping water up into the paddlebox which can affect thrust, that is why there are usually louvres on the side of the box to allow water and air to escape.

                    The Paddleducks site (which appears to be currently inaccessible) has a lot of information but some of it is contradictory which probably goes to prove that building and successfully operating a paddler model is a lot more complex than its propeller driven counterpart!

                    Colin

                    (DTR)IMG_4667IMG_4693 (DTR))IMG_4694 (DTR))

                     

                    #120639
                    Alasdair Allan
                    Participant
                      @alasdairallan37423

                      Thanks Colin – great photos (and some interesting physics!) I should have said also that, mindful of the Princess Alice disaster of 1878, I have avoided independently driven paddle wheels!

                      #120641
                      Colin Bishop
                      Moderator
                        @colinbishop34627

                        Alsadair, I’m not sure that independent paddle wheels had anything to do with the Princess Alice disaster. The ship was run down by the Bywell Castle.

                        However it is certainly the case that independent paddles could potentially affect the stability of the long narrow shallow draught excursion steamer hulls and It was considered advisable to lock the shafts. It also meant that only one engine was needed – much less complicated.

                        Tugs needed independent wheels for maneuverability, they were short and wide and more stable.

                        My Bilsdale was based on a paddle tug design, hence the independent drives. It certainly did complicate things!

                        Colin

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