I recently made a 3d spongebob cake. It was 12x18 cut into 4ths. I was worried transporting it because it was a little shaky.

What can I do? How thick does my board have to be?
How do you get the dowel not to go through the boards?

(bad me I've been using skewer sticks for my own projects)

Please help!
Donyell

Whenever you stack cake there should be support every 4" you go up so in this case you stacked the cake 8" high. There should have been (starting from the bottom up) cake, filling, cake; cakeboard, cake, filling, cake. Dowels go in the bottom 4" 'layer' before the cakeboard part is added.
Boy, that's hard to explain!

Then if transporting, the cake should be on a board 4" larger than the cake -- like a 10" cake on a 14" board.......But........... the smaller the bottom of the cake the bigger the board should be. Since your cake was something like 5"x12" it should go on a board 14x8 then place the whole thing on a much larger board just for transporting.
Still using your 5x12 cake as an example, hammer one or 2 dowels in that will go all the way thru the cake and into your boards. (I would use 2 - one at each end - a couple of inches in from each end). Once the cake is where it will be displayed you can remove the extra large board and the long dowels. (Fill in the holds w/some icing or decoration).