The shape of the gullet is like so:
This shape works many horses with "average" conformation (if such a term can be applied). Even if you have a really wide "average" horse, a standard tree could work:
The hoop tree is more like an inverted "U", or a gambrel roof (and in some extreme cases, think Quonset hut):
With a hoop tree, the gullet is shaped so:If you have what I refer to as a "table backed" horse, you might need a hoop tree:
Heh. Fun with PhotoShop. I sent it to Edie as a joke, and she thought it was pretty darn amusing, and had our web mistress put it on the web site ...
Here's what I really mean:
The shape isn't quite right. The orange arrows show where there would be areas of concentrated pressure, which would wind up making the horse sore.
Here's the same back with a hoop tree. Note that it follows the shape of the horse's back much better.
Now, let's take it to the other end of the spectrum. Here's a more "roof" shaped back:
If you try to put a hoop tree on this horse, note how low the saddle would sit, and how all the pressure would be concentrated on the ends of the tree points (provided it didn't bang into the wither first):
Same horse, standard gullet shape. The weight is distributed the entire length of the tree points:
Next up: Panel Configuration.