And why would I need full stringers?
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Best answer I can muster...
A jet pump, speaking Berkeley type pump (which would include the Dominator, American Turbine, Legend, Bayjet, Jacuzzi etc.) basically only drives the hull by being glued (for lack of better terminology) to the hull at the keel.
All the horsepower generated from the engine gets transferred to the pump (which is rigidly mounted to the hull) via the stringers, this power technically has to be transferred with the engine wanting to torque over while being bolted to wood that is simply glassed to the hull.
With a quarter stringer hull, I like to compare the construction to a car that is a Uni-Body, there is no frame. In stark comparison, the full stringer hull would be compared to a full frame car.
It has to do with structural integrity, safety and performance.
I disagree with the ride quality comment though, if your quarter stringer boat rides worse than a full stringer hull, I would go buy a box of Sawzall blades and make some flower boxes out of it, it definitely should not be used as a boat...

The rail kit has three "major" benefits.
The first is that there are many more areas of contact with a rail kit than compared to a standard four point set up this makes it incredibly strong.
The second is the engine can be removed and installed in a fraction of the time compared to a four point and this allows you to leave all the string bolts in place and not disturbing the wood more than you have to.
The third is, they simply look badass and have endless adjust-ability, but once dialed in, becomes plug and play......

Hope this helps.