the top bars are about 36" total length, and the supports are about 21" center to center. here's a general breakdown of parts (all parts were from Lowes except the wheels):
(1) 3/4" X 36" threaded rod
(4) 3/4" flat washers
(4) 3/4" nuts (I only have 2 - will pick up another pair soon)
(2) 1 1/4" pipe x 5' long
(2) 1 1/4" Crosses
(4) 1 1/4" Tees
(4) 1 1/4" Caps
(8) 1 1/4" 45-degree elbows
(2) 1 1/4" to 3/4" slip and thread fittings
(2) 3/4" slip and thread fittings
(1) 6' piece of pipe foam insulation (supposed to be for 1" pipe - it was the largest I could find, on sale for 31 cents... it doesn't wrap all the way around, but covers enough for me)
(2) foam wheels w/ plastic bushings (from Wheeleez)
a handful of zip-ties, and spray paint (if desired)
I probably got the names wrong on the last 2 PVC fittings - the 1 1/4" fitting slips into the 1 1/4" cross, and the other end is female threaded for a 3/4" fitting. Then the 3/4" male threaded portion is screwed on. The 3/4" axle fits pretty snugly inside of that fitting.
I will probably revisit Lowes to see if I can find a PVC piece to fit inside the 1 1/4" pipe, and then the 3/4" rod inside of that - similar to the style Jim Manta used for his dolly - but I think his axle diameter was smaller, so am not sure if I can get that to work out or not, based on available pipe sizes, anyway.
I like it! Think you could post a picture of the dolly with your 'fish on it? I'm having a hard time visualizing the size. As far as you comment on the wheels and the beach goes, at least for the beaches we have here in South Carolina, I would go with something more balloonish to get through the soft sand.
Tag, the dollie idea is great & if slaveish copying is a sincere form of flattery, consider yourself flattered.
The photo of the twin trailer you use as your avatar... can you post or point to a hi-res version? The lads & I will have our 2nd boat ready for the water this week & we'll need to modify our trailer...
I think for future use, I will make sure to run vertical supports down to the trailer, so I don't smash the lower boat.
Here's a bit more describing the build: I made a frame using (2) 2×6′s and (2) long 2×4′s. the frame is about 4′-3″ wide and 6′-0″ long. the (2) 2×6 boards were roughly shaped, top and bottom, to match the deck curvature for my Sunfish (bottom) and my Super Porpoise (on top). I also threw a couple diagonal 2×4′s in the front corners, which helps keep the frame from racking when I’m lifting it on and off the lower ‘Fish. I used a few pieces of pipe insulation over the edge of the 2×6′s to keep from scratching the decks. the previous owner of my Sunfish had made a nice jig out of wood – shaped like a “Y” sort-of, that slides into the daggerboard trunk, and holds the sails/spars – you can see it sticking out up from the daggerboard trunk on the upper boat. he also had another “Y”-shaped bracket mounted at the front, but to make it work I had to make my own quickly to raise the height of the “Y” to work with the double-stacked Fish. the “Y” I made and the older one are interchangeable, though, so I can switch back to his bracket when I transport just the 1 Fish.
just a quick update - as I was driving down the highway, with the dolly strapped to the top of my Sunfish, the 3/4" nuts vibrated loose - and I lost 2 of them, plus a washer, and almost lost a brand new wheel. I had only driven maybe 10 or 15 miles on the highway, too! I had used (2) nuts each side.
I have since gone back to Lowe's, and bought some 1/8" cotter pins (similar to picture below) - so now I am using only (1) nut per side, but drilled a 9/64" hole in the end of the axle, and stuffed the cotter pins in there to lock everything in place. lesson learned. I debated buying the nylon locknuts, but the cotter pins were quite a bit cheaper.
oh yeah, the dolly worked pretty well for launching my boat at a boat launch that was packed sand. I have still not tested it in dry/soft beach sand, although I will admit, I'm thinking it might not have fat enough wheels. we shall see.