It doesn't, but that is not the point. The point is that the spi DOES calm down the boat alot WHICH feels just as if the bows are lifted. Mathematically and physically speaking the feeling is very much correct but the explanation isn't. However, reality only adheres to what truly happens (feels) and not whether our human explanation for the phenomenon is correct or not.

It will be far to complex to get into this in detail and unless you are science junky it would be pointless trying to explain it as well.

Main point still is and will always be that adding a spi will make the boat more controllable downwind and will make the boat feel more resistance to pitchpoling and sure enough with the spi set you do pitchpole alot less often.

The difference, when the spi is handled right, is such than no crew nowadays sails without a set kite on the downwind legs NO MATTER how strong the winds. Personally, I much rather sail SINGLEHANDED downwind in a blow with a set kite than without. That is how much more in control you can feel.

This all has been my experience on both the Prindle 18 that I added a spi to as my new boat the Taipan F16. So my advice to all is to start slowly with the spi and build up skill gratually but also to work consistantly towards a skill level where you can always pull a kite no matter what the conditions are.

Good luck !

Wouter