As a former dune buggy owner living on the soft sand of Lake MI, that's cool. Have to agree no one will let that on any beach. I am using the soft wheel Cat Trax on a H-18 and going down to the water is easy. With the water low 200 yards and uphill 50 feet isn't fun. If someone could come up wiith something inespensive I'll bet they could make a lot of money at a few regattas.

How about a gearbox from a commercial walk behind lawnmower attached to a 12 volt motor and some ATV tires. All State Parks and most city parks do not allow motorized anything on the beach.

the solution is easy!! A lighter boat...

Here is an electric aircraft tug on Ebay. It's set up for AC, but could likely be converted, or the idea adapted, relatively easily.

How about a counterweight type setup where the weight (Rolling resistance) of the trailer/dolley is balanced. That way you are only fighting the weight of the boat itself when rolling the boat and trailer up the ramp, which is easy enough, unless it is very steep. Without the boat, the trailer/dolley is pretty neutral (able to be rolled up and down with equal ease)?
Too me, this would be the low maintenance solution
I am imagining a small wheeled dolley with a hitch ball, with a cable to a "derick", say 1/4 times as high as the length of the ramp run plus the flat area where you hitch up. The derrick has a 4:1 travelling block ... and 4+ X weight of trailer/dolley counterweight...
Any takers...

sorry, read 4+ x rolling resistance of Trolley dolley counterweight up hill

How about beach wheels that are a modified version of a Segway? Get the boat balanced on the wheels, turn it on, and when you dip the bows down, it goes forward, dip the sterns down, and it goes backward.

I found a web site that says you can build a Segway-type thing yourself inexpensively.

Or an old set of blocks to give you 2:1 or 3:1 purchase and a lot of 3 strand cheap rope. Tie one end to the boat and the other to a stake in the sand (or something) and start pulling - however, this doesn't really solve your single handing issue. I sometimes have to move my trailer in my backyard using this method.

The aircraft tug looks about like the best idea, similar to what I would design & fabricate in my garage. Just exchange the motor to 12 volt and add a deep cycle battery. Change out the lift portion to accept a tube to connect to any Cat Trax and an adjustable riser to hold up the front main beam of any cat. One of these per catamaran club would be neat.

Just remember when adding an electric motor to anything that will be submerged is going to make it complicated.

Having worked on the Segway develpoment, I can tell you there are no cheap alternatives to a Segway, yet. The components that make it work are still very expensive.

The aircraft tug (if it is one of those small ones designed to fit on the front wheel of a small plane) will definitely not work on sand. They are designed ot work on fairly level paved surfaces. Plus you would have to seal everytign to keep the sand from tearing up the bearings.

After reading all of these posts, it seems the simplest solution would be to mount an ATV winch to a post. Then take the post to the top of the hill, bury the other end of it an inch or two in the ground with it angled "uphill" and have guy wires, two of them, like you would when putting up a cheap dining shelter you can get a Wal-Mart. Use a 12V battery to power the winch and a remote switch to operate it.

This is a totally portable system, the mechanism is kept out of the water, and there are no powered "vehicles" on the beach.

With a little bit of experimentation this could be worked out.