Another new propulsion system

[DEDave]

Hello all:

We have been doing tank tests on another new propulsion system - one that uses forced air.

The system is very simply in concept:

Use a Roots blower (2-25 psi) to force air out of specially designed nozzles below the water line. Similar to a water jet, but using air instead. The nozzles use a Cornada (similar to a paint sprayer) to add water (mass) to the air stream as it exits the boat. This increases the force (F=M*V).

The test vessels (very small scale right now) exhibit some remarkable results, with hp/static thrust/weight ratios better than mogas. Common valves are used to control thrust and additional nozzles can be plumbed in the bow in order to act as a bow/stern thruster. We can even control the internal water system, davits, pumps, wenches and generate AC power from the air stream/pressure.

I have two questions to the group:

1. Has anyone ever heard of such a thing and why did it not work? We hate reinventing a wheel with a flat tire.
2. Since there is no running gear (other than rudders), what is the decrease in power that we can expect to be required for various hull types? I have heard that on a 2 wheeled planing boat as much as 25% of the resistance is because of the running gear?

Any help/comments would be app'd....

[SailDesign]

Dave - If you've figured out how to control the "wenches" on board, you'll make a mint ;-)
Now, if one could only get the wenches on board in the first place....

Steve <sorry - I love typos>

[DEDave]

Now that would be something! I would guess that is like free energy - just can't be done.....Dave

[ted655]

There is a reason automobiles dom't use air for the medium in brakelines. It compresses. Even a tiny amount has to be bled off.
Might work on a small scale, but in the real world it will be a live bait aretor on steroids. The fish will love it.

[BrettM]

Might be stuffing up your entire thory here but Force= MA, Momentum = MV

[yipster]

DEDave,
did you check the renewed PDX site in the steam engine thread? some steam jet casestudy's on http://www.pursuitdynamics.com/default.asp ok, steam is no blower but it gets close, above a pic.

[tonyvv]

I have done some work on both compressed air, air with water and steam. The only way it would work is to use high pressures @ 2000 psi. After a small explosion I called it quits. Also the energy require was greater than just attaching a prop. Steam boilers are not cheap either or very efficient.

It seems that the air is compressed and then exhaused in a straight line.

Then the air expands in a spherical manner which does work in a lot of directions that are not the best.

[PAR]

What would you gain with this new type of drive system? Jet drives provide shoal draft and no prop to hurt things, but require much greater HP for the same performance of an outboard or shaft setup. The reward for that system is shoal running and proplessness (is that a word?)

Any engine can run a generator or alternator for electrical output of your liking, what is the benefit of using your system?

Outboards provide portability, I/O's can generate much more power then outboards, shafts even more. Maybe air driving a shaft or jet impeller, if you can get more efficiency then current setups.

You need to sell the savings or benefits to make this a marketable project. Would your setup be a simpler operation then hanging an outboard? Why would an owner repower with your system, etc . . . engineer that, then move on to working out the mechanical/electrical/physics issues.

Good Luck,

[Willallison]

Jet drives provide shoal draft and no prop to hurt things, but require much greater HP for the same performance of an outboard or shaft setup.

Not so - you don't think that almost all of the large fast ferries and motoryachts use waterjets because they provide shoal draft?...no - its because they are more efficient at their designed operating speed.

[Nick Sloan]

This may be a fairly offbeat post, but since PAR above was suggesting to DEDave that he would need to come up with some good reasons for preferring compressed air to existing propulsion systems, I thought I'd share some thoughts about a specialised interest in the subject.

My son goes to school about 2 miles away, up a straight river with very variable depth of water and often lots of reed. The reed makes for difficulties with propellors and oars, and since I have a large compressor in the workshop, I was wondering whether it would be practical to store enough air in portable gas bottles to do the trip there and back.

The special circumstances, in summary, are prop-unfriendly water, short predictable range, ready access to air for recharging, the need for a simple, cheap system, and no particular concerns about performance. (I'd be interested to hear more about DEDave's sytem if he'd care to email me.)

[Randytea]

Your idea has merit, it something that has been tried by the military in the former Soviet Union. IT was dropped when they determined that Wing in Ground hulls (essentially an airplane shaped hull with short lifting wings and several jet engines) were even more efficient. This craft skims the sutrface flying as much 10' over the surface.

http://www.bugattiyachts.com/Designe...Ekranoplan.htm

back to your question. We ran tests on a concept similar to your suggestions. Instead of an internal combustion engine a small gas turbine fitted with a vectoring thrust cone was placed in direct contact with the transom-water plane.

The results: extremely fast acceleration and exceptional high speed operation with reasonable fuel consumption. Acceleration was controlled by a combination of turbine speed and thrust cone vector.

The "challenges": steering(a 3d cone (think f-22 raptor) is expensive and causes violent steering action), diverting water from the cone assembly during slowing or stopping manuevers, no reverse gear, slow speed operation.

Basically if you can develop a way of bleeding off the excess thrust you will have solved many of these problems. Expirements can be run using a small turbine built from the casing of an autimotive turbocharger or a surplus tail rotor or APU turbine from a military helicopter (available from many surplus dealers under $2k).

[Keith King]

Dear DEDave,

I see you haven't posted on the boat design forum,for awhile. I was reviewing some earilier post When Finally- I saw you posting. I've been working on a similar "squid type" engine design for about 5 years. We need to talk ! There is another source with much higher air pressure. With a "brain" (a device to control a fuel / air injector, spark plug, and an electric exhaust valve, and vary the speed of the cycle). I could show you how to increase water intake which also increases power. I'm down to NO moving parts in my power plant (When the control system is electronic). Methane hydrate would be my fuel of choice but you could use most. Change comes slow. Good Luck!

Sincerely,

Keith

Originally Posted by DEDave

Hello all:

We have been doing tank tests on another new propulsion system - one that uses forced air.

The system is very simply in concept:

Use a Roots blower (2-25 psi) to force air out of specially designed nozzles below the water line. Similar to a water jet, but using air instead. The nozzles use a Cornada (similar to a paint sprayer) to add water (mass) to the air stream as it exits the boat. This increases the force (F=M*V).

The test vessels (very small scale right now) exhibit some remarkable results, with hp/static thrust/weight ratios better than mogas. Common valves are used to control thrust and additional nozzles can be plumbed in the bow in order to act as a bow/stern thruster. We can even control the internal water system, davits, pumps, wenches and generate AC power from the air stream/pressure.

I have two questions to the group:

1. Has anyone ever heard of such a thing and why did it not work? We hate reinventing a wheel with a flat tire.
2. Since there is no running gear (other than rudders), what is the decrease in power that we can expect to be required for various hull types? I have heard that on a 2 wheeled planing boat as much as 25% of the resistance is because of the running gear?

Any help/comments would be app'd....