I’m making a boat for a physics project and the propulsion system which I originally envisioned for it doesn’t appear to be viable for it. The system involved two horizontal “paddle wheels” spinning in opposite directions as shown in figure 1. At first,I thought this would work, but now I’m thinking that the force of the water pushed forward would counteract the force of water pushed backwards.
Now, I’m thinking about having two verticals wheels like in a traditional paddle ferry such as in figure 2. Would that work better?
If any mod has a problem with this being “schoolwork help,” the point of the project is to have a boat that doesn’t sink when you get into it. The propulsion system is just something extra that I thought up. Would it work?
Those diagrams are awful, but if I understand correctly you have opposite spinning paddle wheels at the corner of the boat. If that’s the case, assuming that the paddle wheels are the same, the boat will just go in circles.
If the wheels are completely submerged in water, I don’t think it would provide any forward thrust. If you had just one wheel in water, it would just spin the boat instead of moving it in any particular direction, right? If you add a second wheel, it would try to spin the boat in the opposite direction. The forces cancel out, and the boat would just sit there, stirring water but not moving.
In your second figure, I assume only the bottom of the wheel is in water? If so then it would work. (Of course you knew that already, since the design is used in real-life steamboats.)
treis, I know they’re bad diagrams. I’m not going to put a considerable amount of effort into a diagram that i won’t be turning in, especially if the point gets accross with mediocre pictures.
scr4, that’s what I thought. When I envisioned it at first, I thought it would work but then when I actually thought about it, I realized that the forces would cancel each other out. I posted here to make sure that I was thinking straight. Thanks for the help.
I think it would move forward (in figure 1) since the dual paddles coming together will help aim the water stream. If you built half-circles that surrounded the outer-half of the paddles underwater, I think that would improve it. But either way, it won’t be as efficient as having a paddle which is only pushing water one way.
You could work on creating folding paddles if you want to get fancy.
Oh I see now. I think it theoretically could work, especially if you get the blades to interlock in the middle. Basically you need the drag to be higher in the middle than on the outside. However, I’m guessing the chances of you building something like this without a large amount of effort and skill is small.
Rather than making the paddles horizontal, how about inclining them so that the forward facing part is just above the water? Doesn’t have to be vertical, say maybe 30 degrees off of horizontal.
I think that Sage Rat is correct in saying that the vertical paddles would be more efficient. We aren’t allowed to test the boats until the due date (because water line prediction is part of the grade) so I need to figure out all aspects of the propulsion system without putting it into the water. I’m thinking that i’ll have a bike chain and gears which connects to rotating handlebars on one side and a gear connected to the “paddle wheel” on the other. What would be a good gear ratio to use?
It’s not because the force from two wheels is canceling each other. You’re not considering that the blades are sending force outward from all around the blades at once. Force is being directed equally in a 360 degree circle all the time from each wheel. You’ve made two impellers for a water pump without a directing housing. You have to house the impellers and direct the output, or move them so at one point they are out of the water like a paddle wheel boat.
I would say that you should do a little bit of testing to work out a gear ratio. For instance, you could figure out how efficient paddle wheels are using models and then figure out how hard you can pedal. Choosing a gear ratio isn’t something we can help you with because we don’t know how big your boat is, how big your paddle wheels are, how big your legs are, or how much effort you’re willing to expend to make the boat go forward.
This isn’t an invitation for you to tell us all of these things (unless you’re also trying to get us to sell you our old pants) because it isn’t, after all, our project. But pictures at the end would be nice. I like pictures of boats.
Sorry to bring this thread back up but we just had our boat race so I have pic! We ended up having so much to do in our other classes that we didn’t have time for gears, so I made the woman do all of the work :p. It turned out fairly well; we won the award for best mechanical boat.
Here is the boat being loaded into the water. I’m on the other side of the boat helping out, but the boat obscures me.
Sorry I had to blank my girlfriend’s face out; she didn’t want scores of lovestruck dopers descending on her. And neither do I, thank you very much :p. I’m quite glad the project is overwith; it took hours and hours to complete and it drained quite a bit of time from other homework and activities that we needed to do. The day of the race was definitely worth it though; everyone had a lot of fun. All in all, it was a good experience.
