Landsailing

After some time sailing boats, I was sitting at my desk at work when a fellow sailed by the window on a skateboard while holding a small windsurfer sail.  My mind wandered...   Searching the web for ideas I found the design of the Manta landsailer to be practical approach.  My approximation was around $150 for materials. 
Major inspiration came from the fine Colorado landsailing site,  http://www.windisfun.com/  which also features many variations on the landsailer form that might adapt well to your particular tools and materials. Rick Hypes' site has grown to become a major influence in DIY landsailing.

This thing is a blast to sail and goes about 35mph in 15-17 mph wind on asphalt and is controllable in tight turns.  With a heavy wind, the acceleration resembles a small two-stroke motorcycle.  I have yet to sail it where I can fully open it up but 45mph might be the safe limit.  At times the windward rear wheel lifts, adding to the fun.  An Avocet bicycle computer calibrated to my front tire measures speed.  Most areas like parking lots run out of room at maximum speed and at that point you have to turn quickly.  Being able to corner well is one reason to keep the center of gravity low and have tires that grip well.
The front-to-rear weight distribution doesn't seem very critical as long as your weight is just in front of the rear axle.  The center of the sail area should be about above the center of gravity of the landsailer with pilot.  There are more precise explanations involving the center of effort in relation to the center of lateral resistance....... blah blah.  You can figure it out nicely if you crack a sailing book and consider traction variables.
The weight without sail rig is about 70 pounds and carries easily on the roof rack of my Honda CRX.

Don't know how to weld?  The sooner you learn, the better.  Sticking metal together can be elevated to a high art but I haven't had this experience.   My first weld on a VW muffler looked like a cow pie but  has held for six years now and my welding has improved to where once in a while I make a nice looking weld. 
My welding rig is about as cheap as you can get, a 110volt 70amp arc welder made in Italy and sold under the Campbell-Hausfeld name at Home Depot.  It cost less than $100 and uses 1/16" #6013 electrodes.  The electrodes are a bit cheaper at a welding supply store in bulk.  Other suppliers such as Harbor Freight Tools stores have similar low-priced arc welders as well as metal cutting tools.
Drawbacks of this arc welder are:  Burning through thin steel occurs easily if the bead is run too slowly.
Thick steel requires multiple passes.  Arc welding takes much practice and patience.  Your first welds can tick you off!   Weld appearance isn't very pretty. 
Advantages are:  It works.  It stores neatly on a shelf.  It is inexpensive.  It very quickly pays for itself.  It allows you to do many things in the shop that were previously impossible.
Or you can tack your pieces together with an arc welder and have a pro do the final welding.  If you do this be sure the joints fit well or you'll hear about it.
Don't be casual about welding safety, use all the right protection like welding gloves, boots, long pants, eye shield, etc.  Hot spatter goes through nylon sneakers as if you are barefoot!   A MIG welder would be better and easier, and if you can get one so much the better.  They cost around $275 and up and weld thin metal better and have cleaner welds with less spatter.  
One tool I would recommend is a 4" angle grinder.  Mine cost $19 and is worth every cent.  For cutting tubing, a Skil saw with a metal cutting abrasive blade ($3) beats hack sawing.

Square steel tubing was used where possible because it's easy to cut and fit into clean joints, easy to clamp, joints have more contact area for longer weld bead and brackets fit squarely against it.  Round tubing is stronger  but a bit harder to work.  So far no failures using 1 1/4" with a 1/16" wall thickness steel have appeared  but the next heavier tubing was just too heavy. A good metal supply store is worth searching out.  My local store has stamped tabs, brackets, gussets and flanges for cheap prices, saving much cutting, drilling and grinding to make small parts.  Home supply stores are pricey for steel stock but the chain link fence supply area has some bargains in tubing and bracketry.

Bicycle Parts A cheap girls 20"-wheeled bicycle frame provides the steering components.  Be sure the frame is not fancy chrome-moly tubing, since it requires a different type of welding.  The headset bearings should be sound even though most of the weight is carried by the rear wheels. The photo shows my original homemade seat and a too-flimsy wheel. At this point the frame was tested on hills.  The brake lever and bicycle computer are mounted on a steel tube with a rubber grip inside the frame rail to avoid snagging the mainsheet.  A VW bus heater cable provided an outer sleeve for the brake cable.

Steering

Since my wheelbase is long, a rod is used with ball joint ends to connect the fork and tiller.  These joints are available at good auto-parts stores (used for linkages) or from go-kart shops.  Keeping my feet together and away from the front wheel has worked well and the ball joints are tight and strong.  The tiller is a 1" tube on a bicycle stem which is cut off squarely on the bottom to pivot in a steel sleeve with a bolt to retain it.  3M non-skid tape keeps feet on the tiller and a welded tab attaches the control rod.  The rod is a 1/2" tube with bolts welded to each end.  Adjustment is made by turning the ball joint on the threads and locking with a jam-nut.  Head tube angle will affect steering response.  At an angle of 60 degrees handling is good but a slightly greater angle might help traction on the tightest turns.  The front wheel tends to "flop" to either side of center, so in the photos a bungee cord can be seen from a bracket behind the fork crown to a bolt at the bottom of the front down tube.  This isn't really needed but it smooths low-speed steering a bit.  The control rod attachment at the fork is a piece of welded-on angle stock.  Check the angles the rod-ends must turn so they are with the limits of the ball-joints.  Testing with clamped-on brackets will help.

New blocks aren't cheap, so used ones are worth searching for at marine swap meets or even making them from scratch.  The cheaper ones have plain bushings as opposed to Delrin ball-bearings but if they are used where the line has the least movement, toward the rear of the boom, they are fine.  Actually a plastic thimble (the teardrop-shaped liner for a line loop) can serve as a block at the rear.  I like having a least one good quality block where the sheet exits the boom to my hand.  I'm experimenting with a ratcheting block to take some of the strain off my hands during longer sailing sessions.  More purchases (more mechanical advantage) are helpful, but increase the sheet length.  The tail of the sheet sits in your lap or drags on the ground.  The boom doesn't usually swing as far from the center line as it does on a boat, so less line is needed.  This line must move freely, not kink, be easy to grip and not stretch too much. Get good sailing line.

Two smooth-tired wheelbarrow wheels on 5/8" bolts are working fine so far on the rear.  They are also available with knobby treads, and 8" trailer tires can also be fitted, but the smooth ones work for me.  The crude bearings are to be replaced with go-kart bearings to quiet them and decrease rolling resistance.  The front is a road tire on a BMX plastic wheel with a chrome-moly axle and new bearings.  The 20 inch bike wheel on the front chatters slightly in the hardest turns, and a wheelbarrow wheel might have better lateral stiffness and soft-surface traction. A bicycle brake caliper is mounted up front, not to stop, but to park with a rubber band on the brake lever.  When nature calls, you want to find the rig where you parked it!

The importance of the seat was apparent on my first few sailing sessions.  At first I had made an elaborate upholstered seat with layers of backpacker's ground pad and naugahyde.  Now I'm using a fiberglass seat from a demolished bowling alley with no padding.  It sits lower to help my head clear the boom.  After a shiny new paint job, it's so slippery that it now has a seatbelt to keep me aboard.  After a little time in a kite-buggy with a sewn webbing seat, I would use that type next time, and nothing else.  Very comfortable and stable.

With experience sailing any boat, you can landsail with ease.  If not, a beginning sailing book from the library will get you up to speed on theory.  Just disregard the watery parts and study points of sail and how a sail works.  A big practice area and light winds are all you need to learn.  Keep your speed down until you can tack and jibe with certainty, and keep a good lookout at all times.  Remember you essentially have no brakes, and the sheet controls the power.

Gloves and a helmet are a smart idea.  At low speeds they seem silly, but in a 20mph wind with the rig leaning at speed you can feel a bit naked as the ground rushes by.  Sailing gloves can help you grip the sheet and prevent grinding your palms in a fall.  Watch out for the boom as it swings.  It can knock you silly after it shatters your favorite sunglasses.  Really!  Check your equipment regularly for safety, and to prevent small defects from growing into large failures.  Although I use a handbrake on the front wheel, it is only of use to park the rig or hold it at rest.  It is useless for braking at speed.  As on a sailboat, there are no brakes so you must learn to tack and jibe.  It's fun!

When the wind launches you on your way, the power is clean, quiet and best of all, free!