I am making a Indiana Jones Fedora cake. I had to scale it up a little to make sure it will feed enough people, so the hat part itself needs to be about 6 inches tall to be in proportion to the brim. I have filled and stacked the first two layers of cake, so I am up to 4 inches in height. I have another layer to add now but am not sure if I need to have it on a cake board. I would rather not as I will have to carve the cake, which means carving through the cardboard.

What do you think? Do I need to dowel and cardboard for another 2 inches of cake? The top of the hat tapers in so the additional layer will be of a smaller diameter.

If it were any bigger than a 6" I'd say definately put on a cake board & dowel but I feel you can safely go that high w/only a center dowel to help hold it together for tansport.
Yes, there is a 'rule of thumb' of doweling anything over 4" but as you said, it's being tapered & as I said a 6"er should be o.k.

Thanks kakeladi. I think I will risk it for the sake of making the cake easier to carve. The additional layer is a 6" sitting on a 10", but it will also be whittled down quite a bit so not much cake is likely to remain of the extra layer.