Airboat with Horizontal Fan

[tom kane]

The more research I do the more attractive air propulsion looks for a shallow water propulsion.

[Yellowjacket]

Tom,

If you are looking at hover in ground effect you aren't seeing what is happening if you put a bottom on your contraption.

When you are in ground effect, one way of looking at it is that the pressure rises over the ground in a small area and that is what helps improve the lift. When you are pushing down on the top of your hull, that is a reduction in lift.

Bottom line is that your fan (that you think is going to generate lift) is actually going to generate mostly forward thrust and a tiny percentage of lift. The lift will come from the inlet lips and the effect of increasing the velocity of the air across that horizontal surface.

[tom kane]

Thank`s yellow jacket. the last concept and others shows air flowing down the outside and inside of the bottomless craft giving close to normal airflow of a usual design.
I would be quite happy with a helicopter used as a boat then I would not be controlled by air traffic laws and need a pilots license because it could be argued that it is a ground effect vehicle. (Maybe).
Trying to build a vehicle for my needs is not only about the science of flying but getting away from control of officialdom. I don`t want to go fast,efficiently, or high. I do not want a million dollar project. Just to be able to get where I want to go as quiet as possible in very thin water.

[Submarine Tom]

Sounds like a sailboat may be your answer Tom.

-Tom

[Yellowjacket]

Tom,

What you will eventually get to is some kind of variation on the hovercraft theme if you want to do this efficiently.

Here's why...

Power is equal to the mass of air you pump times the pressure that you pump at. If you simply pressurize the area under a given surface and you don't have any flow, it will lift, but it won't cost you any power either. If you are trying to pump a lot of air (like a helicopter actually does) it costs you a lot of power to move the air and that takes fuel.

Another way to look at it is that lifting force is equal to the mass times the acceleration of the air. But the energy it takes to change the momentum of the air is equal to the mass times the velocity squared. Simply put, if you want double the thrust with the same mass flow you have to put in four times the energy to get it. This is why, if you want to lift something efficiently you want to move a lot of air at a lower pressure.

A hovercraft is a very efficient means of floating a weight because you are only supplying air to make up for the leakage at the edges of the skirt.

If you want something that will work in very shallow water think about some type of skirt that you can deploy to increase the planform area and then pressurize it to provide the lift you need. If you aren't trying to go fast you can put the skirt into the water a small amount and your leakge goes do nothing and you end up with a very efficient way to get across shallow water.

[tom kane]

Originally Posted by Submarine Tom

Sounds like a sailboat may be your answer Tom.

-Tom

I have always carried a sail and used it many times in my power boats and it is grand just drifting across the shallows but the wind does not always go in the right direction.

[tom kane]

The boats I have used have floated in about 4 inches of water and at low speed keep that draught. A cushion craft has the same draught as a boat of the same weight things being equal. Skirts get snagged on rocks and snags and all the hovercraft I have seen are very noisy and would not be tolerated and can not go where I go because of steering and necessary speed...What I have used is probably as good as I can get but air propulsion would make forward travel easier on props ect.,

[tom kane]

Some interesting images of air flow through a horizontal fan.

[Yellowjacket]

Originally Posted by tom kane

The boats I have used have floated in about 4 inches of water and at low speed keep that draught. A cushion craft has the same draught as a boat of the same weight things being equal. Skirts get snagged on rocks and snags and all the hovercraft I have seen are very noisy and would not be tolerated and can not go where I go because of steering and necessary speed...What I have used is probably as good as I can get but air propulsion would make forward travel easier on props ect.,

Fan noise is proportional to power loading, and for the amount of lift you are trying to create, the power loading is going to be high unless you use a huge low speed rotor. If noise is a consideration you are going in the wrong direction entirely. And this comes from someone who has been turning taxpayer dollars into noise at a prodigious rate for 30 years.

A low speed air cushion vehicle would be an order of magnitude more quiet than the fan system you are thinking about.

I'm just saying that some type of skirts that expand your planform area would get you up over the shallows with a lot less power draw and noise than any open fan is ever going to do. If there are snags and things then perhaps it isn't going to do much good, but the amount of lift you can create with your fan is going to be close to worthless unless you want to go 100 miles per hour forward....

[tom kane]

If I can have a boat that floats in 4 inches of water and operates in any direction in 8 inches of water as my previous boats did, adding an air propulsion that would push me in the direction I want to go to deeper water where I can use an outboard. That is what I want.
There are a lot of Air Driven Outboards and many people building air fans to push boats around on youtube (not that I have looked at them yet) there must be some successes as they are being used for Bow Fishing and other uses on some big boats and there are plenty of air boats doing big speeds with vertical fans. I think that a horizontal fan can do just as well and be better balanced with gyroscopic balance for safety and be more easily quietened. There are some interesting fans with curved blades giving different air flow. I have spent a lot of time around very big capacity air fans in Industries and some of these fans are demanded to be quiet otherwise many complaints arise. Any lift achieved would simply be a bonus.
I have looked at a skirt for a cushion craft using plastic tubes with positive air pressure to assist lift and contain support air.

[tom kane]

Proposed skirt for cushion craft.