Using what is produced here you can use these equations to find out what CFM rating your leaf blower will need to lift a given sized hovercraft.  In other words if you know what size your hovercraft is and how much it weighs you can solve for the required lifting power you will need! 

Here is the problem and solution:

Given:  An air cushion vehicle is supported by forcing air into the chamber created by a skirt around the periphery of the vehicle as shown.  The air escapes through the clearance between the lower end of the skirt and the ground (or water).  Assume that the hovercraft weighs 300 lb and is essentially rectangular in shape, 7ft by 4ft.   A leaf blower provides lift with a flow rate of Q = 400cfm (this value is given at hardware stores).

Find:  Determine the clearance between the lower end of the skirt and the ground with the given values. 

Assumptions: The volume of the chamber is large enough so that the kinetic energy of the air within the chamber is negligible. 

We start with supporting the load

and

Where:
W = weight of hovercraft in lbs.
A_° = area of craft
w = width of hovercraft in feet
l = length of hovercraft in feet.

The following equation is formed:

Where:

So that

With h = ground clearance it follows that:

So therefore the following formula is created:

Now solve for h:

300 cfm = 5 cubic feet per second (just divide by 60 seconds in a minute). 

Now plugging in the givens we know, we obtain that with this leaf blower will create a clearance between the skirt and the ground of:

h = .0024 ft which is .0287 inches off the ground. 

NOTE: Using what is produced here you can rearrange these equations to find out what CFM rating your leaf blower will need to lift a given sized hovercraft.  In other words if you know what size your hovercraft is and how much it weighs you can solve for the required lifting power you will need!