It the segment where you powered a boat with compressed air. I was thinking you had to much drag. The myth might be a little more fun if you used something like a soap box derby car, or a gocart. Just a suggestion. It would be fun to watch you power a cart with air, as well as seeing how you would stop it. Maybe an up hill drive??

When I was a kid we raced CO2 powered model cars. The cars had a socket in the aft end that accepted a CO2 cylinder (about 3/4" in diameter and 3" long). There were 2 small screw eyes on the bottom of the car that hooked over a wire that guided the car along the track. To begin the race you used a small hand-operated device that pierced the cylinder end to allow the CO2 to escape.

The fad did not last long because the cylinders were not cheap, and the races lasted only seconds.

just a though...


but could a normal boat (prop driven) be given increased speed / decreased drag by blowing air though loads of small holes on the underside of the hull, causing an air cushion? like airhockey...

quote:

Originally posted by JimTopbloke:
just a though...


but could a normal boat (prop driven) be given increased speed / decreased drag by blowing air though loads of small holes on the underside of the hull, causing an air cushion? like airhockey...

Hovercraft are excatly that. They are used all over the world as ferries and as military transport and landing craft. The added advantage is that they can move over land as well as over water.

Not quite what I had in mind there Fred...


I am only talking of a relatively small amount of air, like the level of co2 gas in coke for instance, would this reduce the drag on a hull in anyway? or would it actually increase it as the bobbles stuck to the underside?

quote:

Originally posted by JimTopbloke:

I am only talking of a relatively small amount of air, like the level of co2 gas in coke for instance, would this reduce the drag on a hull in anyway? or would it actually increase it as the bobbles stuck to the underside?

In a displacement type boat hull (one which retains the same basic underwater configuration at all speeds - sailboats, ships etc.) the major resistance to movement is wave generation. The boat must move water out of its way as it progresses, and thus expends energy creating waves. The second resistance to speed is skin friction, that is, the friction of water moving over the hull. At relatively low speeds (sailboats and ships) wave generation is by far the greater of the two types of resistance. Even if you could create and maintain a layer of bubbles over the hull (and if that would indeed reduce skin friction) the overall decrease in resistance would be minor.

In high speed planing type boat hulls, wave generation is greatly reduced by the boat moving over the top of the water rather than through the water. Now skin friction (and air resistance, but that is a different issue) becomes more important. However, there is already air under a planing hull and the trick is to keep that air from causing the craft to become airborne (as we have all seen in boat races).

Its about surface area isn't it?

So wouldn't catamaran hull provide more impressive results?

How many hulls you have makes no difference in this issue. The same comments I made earlier apply to single hull, catamarans, or trimaranes.