Right, as far as the seat pad part, there is no air space, or "gullet". If you
are not overweight for your horse, can ride balanced, and use a good
blanket/pad, it's not as much a problem as you think. Here's why, and this is
my educated guess and opinion; but you'd best wait for the designers' reply
anyway, because I can't speak for my horse, I just experimented to find her
preference:
I'm not a saddle-maker, so I can't tell you the purpose of a gullet. It's
probably for extra insurance so that the tree doesn't cut off blood circulation
along the spine. If you use your seat bones and upper thighs to support
yourself on your sports saddle, it will be similar to having room for
circulation along the horse's spine, except for your tailbone area, but riders
usually will make sure to prevent any impact there!
A "solid" tree on a conventional saddle is there to provide weight distribution
of the rider and other items of burden, in the exact same purpose as the frame
on a backpack for a human. Being from the UK, I suppose you know what a
rucksack is. It's a regular-size backpack without a frame, not a weeny little
daypack like American schoolchildren use for their books. Some people prefer
them, even for long backpacking trips, to the conventional frame-packs.
Anyway, the purpose of a frame on a conventional backpack is to distribute the
load onto your back from your shoulder straps. The problem the frame causes is
the same problem a saddle tree can cause: sore spots from pressure points, if
the fit is not perfect.
I think there is a place/time to use a rucksack as there is a situation to use
a Sports Saddle. I think people who prefer rucksacks and Sports Saddles like
them because the weight of the load is able to settle across a surface more
evenly. At least there is the opportunity for that. The two men I've talked
to about rucksacks seem to carry as much weight in them as other guys, but they
conditioned with those packs, and carefully arranged their items. I would
guess that rucksack users could carry more weight with a frame, however. I
haven't tried a rucksack on a trip yet. I'm trying switching back and forth
between a treed saddle and my Sports Saddle this year, just to see how my horse
does.
With a treeless saddle, there must be some stiffness to the fabric (the Sports
Saddle uses neoprene between leather layers) for weight distribution to occur.
The shape of the horse and the shape of the rider define the shape of what goes
between, if it's hard. If it isn't, it's easier to fit. In my opinion, a
Sports Saddle may not be the best single choice for a tall heavy rider on a
long-backed out-of-shape horse because it may not be able to distribute the
weight as well as a well-fitting treed saddle. IF the horse can be conditioned
enough it may be all right.
I'd welcome any other philosophical counter-opinions! Sincerely, Bridget
Brickson