The pros use hefty plywood forms which require a pickup truck to transport, but I wanted something lightweight and compact.

Google "Sand Sculpture" and the results will boggle the mind... but the common thread between the larger sculptures you see out there, is that they all use some kind of form to pack the sand pile before the carving starts.

These forms were made for our second stab at sand sculpture (my team: Me, My 10-year-old, & my 8-year-old), but the forms worked great (plus we won first place in the intermediate division at the Long Beach, Washington Sandsations Competition), so I thought I'd pass them along.

Step 1: 30' Square Worth of Squid...

We were building a giant (colossal?) squid, which was pulling a hapless sunbather into the ocean.

It was entitled "Hazards of Sunbathing II," and it was the sequel to our first sand sculpture (photo below), which won the "comedy" award at the 2007 "Friends of the Dunes" competitionin Eureka, Ca.

Monsters eating people is always funny, right?

No photo available of the completed squid, I'm afraid, but I've posted another photo below that gives an idea of the scale...

We had a 30' x 30' square in which to work, meaning we'd need a pretty big squid, and therefore a pretty big pile of sand. I'd used a flexible plastic (compost bin) form for "H.O.S. 1," and while it did work well enough, I wanted to go bigger.

The problem was, we planned a family road trip around the competition, and we didn't have much room in the Dodge Caravan for luxury items such as shovels and enormous plywood boards. I solved the shovel issue ahead of time by asking the kind folk at our lodging locale for that day if we could borrow a shovel or two, but the forms...

Step 2: Materials

-Two sheets of thin plywood
-Retired climbing rope
-Drill (bit sized to rope)

All I had on hand were a few thin (1/4") plywood sheets, so I ended up going with two different sizes:
"Large" form: Eight pieces, 18" x 2'
"Small" form: Six pieces, 1' x 2'

The exact dimensions (and number of pieces) don't matter much; I stayed small because I didn't want the sand to break the thin plywood. If you have thicker lumber (and are less concerned with portability) you could certainly make your pieces larger.

Slice up your plywood, and drill two holes near each board's edge, as shown. I clamped each stack and did all of the the drilling at once.

Step 3: Rope It Up

Feed your rope through each "stack," tie off the ends, and leave a long length of rope.
In the diagram below, the rope would be about 16' long, or, 2'(length of each board) x6 (approximate circumference), + 4' (tail).
Burn or tie off the cut ends of the rope as needed, then coil the contraption up and head for the beach! Notice, the whole package ends up very compact: just the volume of the stacked boards plus some coiled rope.

Step 4: Set It Up

To use your form, pull the boards out, setting up one side at a time. Keep the rope on the outside.

Place the end of each board just behind it's neighbor's rope holes, as shown.

Pile a little sand at the corners, and soon your form will be upright, and shaped something like the "top view" image below (or the photo of the form in action, on the "intro" slide).

If you pull the rope a little tighter at the top than you do at the bottom (add a bit more sand first), you'll create a slight taper, and a stronger pile.

At first, just hook the tail of the rope into a gap, then once you get a bit of sand in and the form is holding it's shape well, tighten up the ropes and tie them off.

Step 5: Fill, Wet, Pack, Peel, Carve!

Now, fill it up!
Consult the masters for pointers (Here's one), or use google. you can get really involved and sieve out shells and hike miles for the finest sand, or just pile what you've got on hand.
Add water, stomp around on your pile, then add more sand. Once it's full, add another form or two until you get the height you're shooting for.
Peel the top form, carve it, then work down and peel the next one down until you're form-free. Then pull the ropes to stack your forms, and Have fun!

Step 6: Next...

I'd be interested to hear if anyone has any suggestions. I plan to keep working along these lines, playing with materials.
I've made another form out of a plastic trash can that weighs almost nothing and rolls up quite well; that will go on top of my two plywood forms for the next sculpture, whenever that is!
Larry Nelson has a beautiful custom form made from sailcloth, and I've seen roofing materials being used for forms, too. Chime in!