I figured the single fat tire might float over the sand better than the two smaller wheels, however, mounting two fat tires on a trailer would either make for a very wide trailer (overall) or a very narrow cargo space.
The single wheel trailer seemed to be the answer.
My brother used to have a single wheeled trailer called a Bob which he took on a bike trip we made from Pittsburgh, PA to Annapolis, MD. It worked really well and was pretty stable.
Step 1: Hub for Fat Tire
Start by disassembling a steel front bicycle hub. Doesn't have to be anything fancy, just weldable.
I cut the hub body in half using a pipe cutter.
Next I cut a piece of 1 1/4" EMT (galvanized thin wall electrical conduit) to the proper length for the tire width, to act as a spacer for the hub halves.
- IMPORTANT - The galvanizing was ground off the ends of the EMT prior to welding)
A wheel mount disc was fabricated from a 1/4" thick steel plate, cut round, with a 1 1/4" hole drilled in the center and (4) 3/8" bolt holes drilled to match the wheel. Since the 1 1/4" EMT is an inside diameter, I had to file out the hole for a snug fit to the EMT.
Using a piece of threaded rod longer than the finished hub width, with several different sized washers, I clamped the halves of the cut hub onto the EMT spacer. With proper washer sizes, the hub self-aligned for later welding.
Before welding the hub halves to the spacer, however, the wheel mount disc must be welded to the spacer. In my case, the location was offset from center to match my wheel. I aligned the disc on the spacer it using magnetic clamps.
Then the hub halves were clamped to the ends of the spacer with the threaded rod and welded in place.
Step 2: Trailer Frame - Rear
I hacked an old Raleigh women's bike apart for the chainstays. It provided some interesting geometry to work with (triple stays)
Looking down vertically on the stays, they were not straight in order to work with the bicycle geometry.
A few tweaks with a hammer and they were straight.
Step 3: Trailer Frame - Hitch Mount Part 1
This provides a strong, smooth side-to-side action.
I fabricated a mount for my bike from the forks, using a piece of 3/4" EMT to span the width of the bike from fork to fork and provide a mounting location for the fork tube to receive the headset tube. This basically made a really wide fork.
Holes were drilled and bolts installed in the bike frame to allow this new fork hitch assembly to be easily detached from the bike.
I bracketed the fork tube to the trailer hitch pin left from the previous trailer I had been using.
Step 4: Trailer Frame - Hitch Mount Part 2
I realized that the design allowed for plenty of side-to-side movement, but not for up and down movement.
The solution I came up with was to create a hinge using small steel tubing which fit snugly with a steel rod pin, both of which I picked up at the local hardware store.
I welded a small, 3" long piece of the steel tube to the head tube.
I then cut down a piece of steel angle and welded that into a notch cut into the end of the 1 1/4" EMT main support tube.
- Important note again - remove galvanizing from areas of EMT before welding it -
I then welded two short pieces of the same small steel tube material onto the ends of the angle, leaving a gap between then slightly large than the 3" length of tube welded to the head tube.
It should be noted that the main support tube was bent using an EMT bender prior to welding the angle into the notched end.
The steel pin holds the tubes and acts like a door hinge.
I had to grind away areas of the steel angle to make enough clearance for what I deemed as adequate vertical movement. We'll see if it is enough.
Step 5: Trailer Frame - Cargo Hold
I first laid out the general size of the cargo area using the bulkier items I would typically carry for surf fishing (tackle box, cooler, bucket).
EMT was bent with a conduit bender.
I made two almost identical perimeter rail sections, with one being slightly longer overall than the other, since I wanted the upper one to have a slight slope towards the back. It turns out that it was also required due to the main support tube bending outward for the cargo area as it swept towards the head tube. The length was changed simply by locating the rear cross bar further up the side rails on the bottom section.
Step 6: Finishing the Frame
I also added 4 vertical pieces of 1/2" EMT at the corners.
Everything got spray primed and spray painted.
I used gray to match the bike frame and decided to paint the new hub and the fork hitch yellow to match the accents on the bike.
Step 7: Webbing
Before tying the cord onto the frame, I wanted to add something to the frame at the cord connection points to help keep the cord from slipping and rubbing the paint of the frame.
Also at the Depot, I found Gorilla tape. It is like duct tape, but thicker and tougher and about 1" wide.
I laid out the webbing about 3" apart on all frame members.
I had book called The Ultimate Encyclopedia of Knots and Ropework which I bought a number of years ago and never really used, so this seemed to be the perfect opportunity.
I tied the cord to the top side rail of the frame using what was referred to as a Round Turn & Two Half Hitches, then ran the cord down and around the bottom rail, across the bottom of the cargo area and then up the opposite side, tying it to the opposite top rail.
The I did the same thing from the back top rail to the front top rails, wrapping the cord around the horizontal cords at each crossing.
Lastly, I ran a cord at mid-height around the entire cargo area.
Step 8: Rod Holders
The PVC is easily cut with a circular saw.
Holes were drilled in the PVC for securing the clamps (2 per clamp) with #10 x 24 machine screws.
Clamp locations were consistently marked from the bottom of the PVC, but the top clamp locations differed depending on were the rod holder was located on the frame, since the top and bottom rails are not parallel.
A 2 1/2" machine screw (through-bolt) was used at the bottom hole to act as stop for the rods or other items placed into the rod holders.
3/4" machine screws were used for the other (3) holes on each rod holder. A 1/2" hole was drilled on the outer side of the rod holder so that the screw head could fit through and nest on the inside face of the inner side of the rod holder (see pictures). I used one of those screw driver that has a built-in screw head gripper to help feed the screw head through the 1/2" outer hole and through the smaller hole on the other side.
Gorilla tape was used once again to provide a tackier surface for the attachment. The 1/2" EMT clamp was pressed over the frame and screw to the PVC rod holders with the #10 machine screws.
Step 9: Completed Project
Obviously, the wheel is the heaviest single part and probably weighs more than the rest of the trailer, although I do have a light-weight aluminum rim and lightweight slick.
The frame with webbing and (6) PVC rod holders is incredibly light (have not actual weighed it with a scale, will do some day), but it is light!.
Tomorrow I go to the beach for 1 week for the maiden voyage of this trailer.
I am hoping to get better results with the single fat tire than I did with the 2 smaller tractor tires.