I can't get my mind around a Bobtail in the horizontal plane. How do you envision that working?
I suppose you could use a 40m Bobtail on 15 if you used current feed. Other than that, I'm trying to think of a solution to the multiband issue with a Bobtail-- can't think of one at the moment. What do you have in mind?
The bobtail performance depends on the ground/soil conditions a lot. the antenna itself is a no radial ground plane, but it still seeks ground. Monoband performer.
Look at an N4GG array.
http://ars.nc4fb.org/antenna-articles/n4gg1.pdf
I played with this on 11 meters, ( great test band as antenna are small size).
I heard DX on the array that I did not hear on the 4 element yagi at 50' or the imax at 70', yet the N4GG array heard the dx and I was able to make the contact. Ends of the array was only 9' from the ground, feed point at 18' or so. Very little high angle receive. Locals could not hear me working the DX, they could not hear the DX station either.
To me the array is just phased verticals 1/2 wl seperated, PRO is no tuner required and can be made multi band as the article states.
CONS, narrow beamwidth pattern, But if you can move one end of the array and say work into EU in the mornings and early afternoons then change the direction and work the JA's and Asia in the evenings it might be a decent wire antenna to have on the farm.
QST this month has an article on a portable beam made of wires and a 40' fiberglass pole for apartment dwellers, It was a cool article, the issue is in my truck or I could tell you who wrote the article, depending on the band it is a three or four element wire vertical yagi, pretty neat.