propulsion project

For an engineer the drawing is very poor. The wording and the drawing don't correspond. What must be able to move 3cm up and down? If you gave me this as a blueprint to build something I would laugh. A drawing should be selfexplanatory.

 

From the sketch you show, I think I have an idea what the intent is here, but I have had to make some assumptions. It is however, my interpretation: as Gonzo says, the drawing is not good!

I am no naval architect, or an engineer. I am an architect, and I lecture at a university in the subject.

I’m sure there are plenty of people here that are able to give you a complete and detailed proposal for the boat that would work well.

However, in order to learn from the project, which, after all is the intent, I would suggest that you investigate the problem and experiment, perhaps focussing on a number of areas.

Things to think about:

1. Speed: What are the factors that limit the speed of your vessel? How can they be overcome?

2. Stability: consider the width and length of your vessel with regard to stability. What are the payoffs as the vessel gets longer or wider?

3. A straight course. How can you ensure the vessel runs straight? What might cause your vessel not to run straight?

4. Estimating time taken. You have some energy transfers to work out, from the potential energy stored in the tank, to the kinetic energy in the ‘spurt’ (jet), and in the boat. Conservation of momentum. There will be losses in this system, which I suspect will be considerable. Will the jet be able to impart all its energy to the vessel, or might the vessel have moved out of range before it has fully discharged the tank?

5. the moveable device at the back of the boat looks like it is a ‘push plate’ for the jet. I assume it is moveable to ensure it can align with the jet. Could the force which the jet imparts on the vessel tend to move the vessel in any way other than a forward direction?

6. Constructional robustness. You don’t want the vessel to fall apart during the trial!

7. I am sure the more knowledgeable members of the forum will be able to suggest other factors to investigate and experiment with. Perhaps if you can frame some more precise questions, it will stimulate some helpful responses from the forum.

It has been demonstrated time after time with problems like this that successful design comes from intelligent experiment: trying something in a ‘quick and dirty’ build, learning from the experiment, and building ‘quick and dirty’ again and again, rather than trying to build a ‘perfect’ design straight off.

 

Put some time into making a good design. It is the basic skill for engineering or architecture. A picture should be worth a thousand words.

 

thank ytou tiny turn trip!

 

Yes, its a very confusing diagram.

It intrigues me though.

Assumption 1 - the Coke is just to provide a standard weight

Assumption 2 - the vessel has to be propelled by the Kinetic force in the two metre tank.

My first thoughts, which may be wrong once the project is explained are to actually transfer the optimal amount of water from the 2 metre tower into the boat rather than drive a propeller.

I would have a very large outlet tube running from the water storage place, straight out the stern - acting like a water jet.

Or is it easy to just have a jet of water squirt the boat from the bottom of the 2 metre tank across the line ????

 

I read the coke bottle just as payload. I'm with you on the last option: a jet of water out of the tank pushes a passive vessel from the 'shore.' Don't know whether the diameter of the tank outlet is a variable, I suspect not. There is in any case a fairly complex set of variables...

 

the coke bottle is just to make the problem harder to solve. And the problem with the tank is that it is given by the university so we cannot touch it. We have to construct a boat that is adaptable to the jet, but we can´t do anything to the jet. And the teacher hasn´t decide how the jet will be (the diameter, the area through which it comes out, etc)
But i need your help! does anyone know or have the design of a quick boat? we know it has to be thin and long, but we dont know how thin and long! any model serves, we can just scale it.
And another thing. We were thinking it might be a good idea to make the place where the boat recieves the jet concave, so that the energy transfered from the jet can be better used, but we are not sure if our thoughts are true.
Any opinions?
thanks!

 

Perhaps a catamaran with 2 relatively long and thin hulls and a plate to receive the energy burst above surface? Or will the nozzle be located below surface?

 

You want an answer to a question that hasn't yet been formulated. The nozzle, the dimensions of the tank, and the parameters of the test have to be established first. As I told you before, if you need a boat to reach five meters, make at least five meters long. You will have instant contact. The way you posted the question, it is the best answer.

 

I'm with Watsons assumptions here....

The range of the spurt of water will decrease, as the tank delta h decreases, therfore the "kick" from the will probably only be available the first meter or so.. reducing the possibility to reach the other side, or at least increasing the time to reach it. At the start you'll (probably) have more water kicking you forward than you can make use of, due to the inertia (of the bottle/ boat), the rest will only splash out, giving you nothing.

What about a "closed" boat (closed as in enough bouyancy) with a deck that's allowed to fill up with water, during the first kickstart, an small outlet tube aft in the boat, will during draining, as the boat empties give some (a little) forward thrust, also the water will give you added wieght, increasing the inertia of the boat making the boat slide longer....

Just some brainstorming here....

(brain, what's that? I'll look it up...)

Edit:
Come to think of it; I would make a "funnel" in the deck, to make the boat more stable, when deck loads up with water, drain pipe from that centre area, pointing aft..... And the bottle placed as much in center as possible too, but without closing the outlet...

 

Soooo....;

then you'll get the Bernoullis equation from the tank....
(delta h, outlet tube diameter, spurt range.... kinetic energy...)
The inertia of the boat.
Acceleration
The resistance in the moving hull, at a certain speed. at reducing speed (better choose an average speed here... (educated guess, based upon the estimated speed when loosing forward thrust from the main tank)).
speed decreasing.
the time (or position) when you'll not getting any energy from the spurt from the main tank....
Then the draining of the boat, (Bernoullis again..) Time....

To me; schools out

Did you know that Bernoulli did one of his most famous equations on his honeymoon trip? History tells that he was looking into a bed of flowers and got the idea/ solution....

 

we had thopught about that too...but since we still dont know how the jet will come out, we are not sure that it will be a good idea. The thing is, also, that the boat will be really light, so water might be able to impulse it through the 5 metres. And it has to have only one hull so it cant be a catamaran.

 

Light (weight) is reducing the kinetic energy, once moving, i.e. goes to a halt quicker. Mostly the mass from the 1 ltr/ kg bottle then...
Maybe also get out of the "spurt" too early to collect enought kinetic energy to beat the competitors...

Guess I like your teacher...

 

The instructor will have to describe the outlet jet in order for a good design to come forth. That is:
How high is the jet off the surface?
What is its diameter?
What is the angle off horizontal of the jet?

With these facts established, you can calculate the time it takes the tank level to fall and how far the jet will reach after the boat gets moving. These calculations are not trivial and will take some study. The lightest boat will start faster and be able to use the higher kinetic energy when the tank is most full.

The boat must be stable in attitude and direction. This makes a catamaran a good candidate in both regards.

Long ago, my son had to build a sailboat to sail the length of the local swimming pool as a Cub Scout project. We did a foam hulled catamaran with a large rudder off each transom and a square sail well forward. His was the only boat that actually made it across the pool. I would start with the same kind of boat for your project. Doing the background investigations as suggested by others above is where you should start. Even if we could give you a complete design, we should not do so. Having you work out the details yourself is the only purpose in the exercise in the first place. A failed attempt that you work out for yourself will be more beneficial than building the winning boat that you do not understand.

 

Its a great problem. Too light a boat and you run the risk of a fast start and then dying in the water, just out of the range of the still flowing jet. Too heavy and you extract the maximum available energy from the tank, but *maybe* don't accelerate to a fast enough speed to be first over the line.
Back to Gonzo's 5metre long vessel plan.