One of the great things about running the blog on www.kingpropulsion.com is that I get to share thoughts, ideas, cool stuff and data that I find. This serves me well. As a wandering academic and a curious engineer (is there another type?) I am always fascinated by the world around me and always wondering how things can be done different, or better. I will confess that the joy of solving, “little puzzles” as someone once put it to me does not resonate in me, my brain simply does not work that way. Rather the ingenuity behind solving the problem, now there we have something.
So to get to the matters at hand for many years I used to lecture at Newcastle University in the UK, mostly during my PhD. I did enjoy it I would say. If you have ever presented papers at a conference, it is kind of like that but the audience are trying to stay awake from partying the night before (also true of conferences); not always thrilled to be there (I know hydrodynamics is not popular with the marine Engineers) and it is also, for the most part, thankless. For a conference you spend hours crafting your presentation, give it your all and receive comments and praise at the end, even if it is only applause from the small audience who showed up. For lecturing the work is done the same, but the students don’t really get what it is they are getting or how much they will use this later in life and seem to want to get the credits and move on. Reading this back that sounds cynical but it really was not the case for me. Once the knowledge that the class filed out faster than academics heading to a free buffet was accepted, I had fun and tried to make my course engaging. So this next segment on Propeller History was one such part of my course. There really wasn’t any one person who did invent the propeller (spoiler alert) it but lots claimed the accolade – as we will see. If It goes well then I will put some more topics out there to help everyone. I do find there is a bit of a gap in all this so maybe it will help. I’d just like to say a note of thanks to Prof. Atlar at Newcastle University who encouraged me to do the lecturing in the first place, and many other beneficial things in my life.
In terms of propulsion I think it is common knowledge that from the earliest times people have been faced with the problem of transport across the surface of the water. From the use of the hand to the use of the paddle little development occurred in ship propulsion until the invention of the steam engine which for Naval Architects was a game changer as ships could sail into the wind rather than with the wind. There is an old English saying, “Any propeller will propel any ship” and it is possibly because of the truth of this statement that there have been so many patents for propulsive devices. For, no matter how revolutionary the design some measure of success was assured. As a consequence of this we have had fish tail propellers, duck-foot shaped propellers, a perpetual sculling machine, multi-turn screws and even a propeller of variable diameter. Most of the novel propulsive devices are now extinct and most of the merchant ships operating on the trade routes of the world are fitted with a fixed pitch screw propeller. New designs and new methods of energy recovery are changing the design of the propulsor as we see podded propellers and energy saving devices like PBCF’s (fancy propeller nuts that help the flow), guide vanes and so on being introduced, but I get ahead of myself.
As you can see from slide 6 there really are all sorts of shapes and sizes to a propeller, these are two very different types. The bronze colored propeller on the left is optimized to be quiet, while the red one on the right is optimized for ice, very different mission profiles. I hope to explain why this is so in the coming posts and to shed light on things like why do aircraft propellers and ships propellers differ? Which is the best propeller for my boat? An so on.
To do that though I need to start somewhere a bit odd, from slide 7 you can see a simple sculling method of propelling a boat. Wiggling the oar behind makes a pattern in the water not to dissimilar to that of a flag in the wind. Those furls in the flag are swirls of air called vortices, that cause a pressure change and hence create lift. A tough concept to grasp without proof, but think of the wind on the pole and how it is able to shake it side to side, even as the wind hits it perpendicular to the pole! In a nut shell that is the basics of propulsion and how the sculling boat is able to move. Except for the scull you use the pole to move the water and not the water to move the pole.
Let me extend this idea further, an aircrafts wing and a propeller blade have so much in common but people don’t generally get it. The aircraft wing generates lift through forward speed, the propeller does this as well, but it is restricted to rotating rather than linear motion. OK so, have you have ever put your hand outside of the window of a moving car? You can feel the effect of lift and drag super easy! Give it a try, at some point your hand will be aligned to the flow (wind) and it will not do anything, we call this the zero lift angle and it is important in propeller design. Then tip your fingertips up and your hand is pulled up, fingers down and it is pulled down. This is known as lift, a phenomenon created by changing the flow over and under a surface, a pressure differential. As your car gets faster you will also feel the arm being pulled back with the wind, this would be the drag. So with simple methods it is easy to show the two key components for a propeller to work, lift and drag.
So that wraps this post up. I will break down all of these concepts again when I cover them in detail. The great thing about Naval Architecture is that it is the concepts that are hard, once you have those nailed you can change the world and take on so many ideas – the above is a pretty big one of those! Next I will move onto describing the two types of vessels I will be considering (displacement and planing craft) and start at one of the most efficient forms of propulsion – the paddlewheel!