Delta Foxtrot Posted January 22, 2016 Author Share Posted January 22, 2016 Posted by PatMc on 21/01/2016 22:19:06: DF, have you considered using oars ? No! Not within the rules for this record. Quote Link to comment Share on other sites More sharing options...
Delta Foxtrot Posted January 22, 2016 Author Share Posted January 22, 2016 Posted by Simon Chaddock on 21/01/2016 21:35:07: Delta Foxtrot My concern is not that an air prop won't work in water but with its efficiency when doing so. An air prop is designed to work well in a very low density medium and has relatively thick section high aspect ratio blades. whereas a water prop has very wide low aspect ratio blades that have a very thin section. A water prop is that shape for sound hydrodynamic reasons. With only limited 'human power' available you would be well advised to use the most efficient design of prop for the medium in which operates. Simon, The Reynolds numbers for a prop operating at the same non-dimensional conditions in water are only 1.5 times that in air, so very similar so the boundary layers would likely also behave very similarly. Similar here in this context is used in an aerodynamic sense. Therefore if the prop does not suffer from cavitation, and I now think this most unlikely, the efficiency should be quite similar. As for the comments of prop shapes marine vs aircraft see john and my earlier posts Quote Link to comment Share on other sites More sharing options...
Delta Foxtrot Posted May 25, 2016 Author Share Posted May 25, 2016 Just an update on the progress of this project. The project is proceeding very nicely and there is a website and Facebook page for any one interested. **LINK** I have done aero design work on a bespoke propeller as well as assessing the likely performance of off the shelf props like the APC series. We have done tests on a scale model and just started tests on a full size prototype boat and the initial results look encouraging. The detailed measurements of boat drag vs speed and propeller performance on the full size boat will start in a few weeks, but the initial trial/shakedown shows the boat speeds vs pedalling cadence and perceived level of effort are in the right ball park. The boat cruises in the 4 to 6 mph region and has hit 9.5 mph. I am sure the performance will. Be improved with the development work planned. Edited By Delta Foxtrot on 25/05/2016 20:32:36 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted May 25, 2016 Share Posted May 25, 2016 Just a note on the fluids that are necessarily included in your experiment. Air will compress, but water will not. This accounts for small diameter thin blade screws in water, and thick, large diameter blades in air. Save time and omit air screws in water. Quote Link to comment Share on other sites More sharing options...
onetenor Posted May 26, 2016 Share Posted May 26, 2016 Paddle bladed props running at low speed would seem to be the way to go in this instance Moving maximum mass with each blade The equivalent of a long slow (ish ) push.Blade shape I think would be broad at the tip.Think of the prop shape on Briunel's boats ( Eastern /Britain 6 paddle ended blades to handle the torque and relatively low revs .Recent tests have showed that it was very efficient even for modern times let alone then . I could be miles off track but that is the way I would be looking Quote Link to comment Share on other sites More sharing options...
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