help please! project

Hi! im making a project and i know nothing about boats! please help me!
we have to built a boat on any material. It has to carry a 1 litre bottle of coke fill up with water, in any part of the boat, but vertically. It has to advance 5 metres in a tank of water 40cm of width, a bit more than 5 metres of lenght. The boat has to be only moved by a jet of water that hits it 10 cm on top of the flotation line, with a deviation of 3 cm (7 to 13). The jet of water comes from a tank filled up with 15 litres of water, and its free surface is at 2 metres from the ground, while the tank that contains the boat has its free surface at 40 cm from the ground. We don't know how the jet is going to be (its force and how much it will last), the teacher is still deciding it.
We need the design of a quick and stable boat, and we were thinking of doing it in plumavit. We know it has to be thin and long, but we dont know how thin and long.
Also, we thought of making the bow/prow (that is where the jet will hit it) concave, because we think less of the energy given by the jet will be wasted, but we are not sure of this either!

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RE: help please! project

I'm not much on design but the quickest way of making and modifying a model boat is with styrofoam insulation. Just glue several layers together with 5 minute epoxy then rough out the shape with a sharp knife and smooth it out with a sanding block. Titebond 2 wood glue would work as well but takes a few hours to dry.


RE: help please! project

Wait, the jet for propulsion is going to hit the BOW of the boat? I thought I was following you all the way up to that point.


Also, Are you limited to one hull? This sounds like a great project for a simple catamaran. 


-- James

RE: help please! project

Becareful putting epoxy on foam it can eat through it, test it first. You can always use foam safe CA found at your local hobby shop. With the accelerator it drys instantly and is eaiser to use than epoxy.



RE: help please! project

If it were me, I'd probably submerge the bottle and just put something at waterline to help with stability.  The bottle being submerge will help prevent any sort of capsizing and will also be easier to move with a smaller "boat" because it's already filled with water and bouyant.

It will make the boat move slower,  but there will be no concern for loss of your "payload". 

Your idea of making the concave bit of the boat is quite a good idea, actually, as it will even out the force of the propellant across a larger area of the boat.


RE: help please! project

A one-boat-builder here, so far from expert but I've seen several references in here and other places for making cardboard boats that are quite floatable.  I believe CLC even has a design on a canoe but that probably won't fit your length spec?  If you Google Cardboard Boats, you should be able to find something.  Good luck.  bob h

RE: help please! project

Sounds like a fun project!!!

1) Hull(s) shape

I would definetly do a multi-hull. Not exactly a catamaran tho perhaps a "tri-hull".

Something like:

vUv (or v-U-v)

The center "U" can provide the bouyancy and be an efficient menas of carry the payload. The "v" sections are for stability and tracking (and only minimally wetted).

2) Tracking

I suspect straightline tracking is going to be a big factor in performance of maintaing a <20cm deviation over 5m.

One idea might be to have the "v" sections be asymetrical so that if the craft heels to one side, the asymetrical nature of that now loaded "v" will correct the track. Unsure here tho since it might also start teetering back and forth and then S down the path)

As you already know ... longer will be better for tracking.

3) Propulsion

I'd give some thought to some sort of "funnel" that takes in the stream of water directed at the boat and then (via tubes)  redirects the force under the displacement.

something like:


/     _____  (this is waterline)



Might also be able to use "vanes" within the "funnel" to correct tracking ...


Like I said, sounds like a fun project!


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