(Pictures are below the text.)

What is a prop?
A prop is a device that when properly designed will efficiently produce a given amount of thrust at a given rpm.  A poorly designed prop will require large amounts of power to perform the same job as a highly efficient prop.

What features make up a good prop?
Typically a good prop will incorporate many sophicated design features.  Not all of these features are required for a prop to be considered good.  Airfoil design, blade shape, blade twist, blade droop, leading/trailing edge angle, tip shape and the number of blades are just some of the things that need to be considered when determining if a prop is good or not.

Do I have a good prop?
Typically a good prop is an efficient prop.  The higher the thrust output for a given amount of power, the higher the efficiency rating would be for that prop.  An efficient prop for a hovercraft should produce a large amount of thrust at the lowest rpm possible.  This typically means that the prop will have a thick airfoil section, a wide chord that tapers towards the tip, high pitch angle at the root, a lesser pitch angle at the tip and a squared off to a slightly rounded tip.  Leading/trailing edge angles and blade droop can be incorporated in the prop to keep the center of mass along specific axis to provide better blade loading distribution and help minimize vibration problems. 
There are many other features, and many variations of these features, that might be considered when building props.  Typically the least efficient props have long, thin blades that may taper slightly and may have the same blade pitch along the full length of the blade.  These props are usually required to operate in the higher rpm ranges to generate the thrust levels typical for use on hovercraft.  This can make them undesirable as the faster a prop spins the noisier it becomes.  If you go wide, long and slow you should have a powerful and relatively quiet prop.  In other words, it'll probably be a "good prop".

This is my prop.  It was made for me by Earl.  I think he did a fantastic job of designing and building
it for me.

Earl's craftsmanship is outstanding!  I'll just let the pictures speak for themselves.

Look carefully and you will notice some of the features Earl put into the design.  There is a nice blade shape as well as plenty of twist from the root to the nicely shaped tip.

Earl also swept the leading edge back to keep the blade mass through the center of the hub.  Look at the finish he put on it!  He put a lot of time into this prop for me.  Thanks Earl!

Earl gave me a 1" center hole but I had to add the three hub bolt holes.  I drilled holes for a 1/2" OD compression sleeves that would accept 3/8" bolts.

I used a chain sprocket as a hub as well as to drive the prop.  I replaced the standard bushing bolts with extra long threaded rods that would hold everything all together.

After about 10-12 hours of running I found I had broken two of the three prop hub bolts.  I noticed them as I was getting ready to load back up after a day on the water.

You can see the basic installation of the prop, sprocket and chain.  The hub bolts and prop shaft are a little long but I was test running it for awhile to be sure everything was ok.

The prop bolts broke because the bushing tightened itself deeper into the sprocket.  Basically, as it tightened itself, it made the bolts appear to loosen.  With the extra movement in the prop they broke.

You can clearly see here where one of the bolts broke.  With the prop loose it caused the rod to fatigue and break at the arrow.  It sure was an eye opener when I saw two broken bolts out of three!

Here's a picture of the final assembly after I solved the problem causing the bolts to fatigue and break. I used spacers to prevent the bushing from being drawn to far into the sprocket hub.

Another shot showing the sprocket, spacers, bushing, prop and lock nuts on the prop hub bolts.

The spacers are just the right length to allow the bushing to be tightened into the sprocket at the proper depth to provide a good grip on the shaft.  Then I used fender washers, lock washers and double nuts to mount the prop.

Another view from the rear of the final assembly of the prop installation.  The prop shaft still needs to be trimmed to the correct length.

Erosion is something you have to watch for on your props.  These two pictures show the damage on the blades after ten hours of operation.  There is no erosion at this time.

The worst damage are these nicks.  They are only superficial and only just expose the surface of the glass cloth layer.  I think they are nicks from shells kicked up off the beach.