Outriggers, from my experience, affect mostly paddling performance, rather than sailing - making paddling less comfortable and much slower.
They also reduce sailing performance in light winds - lower speed and wider upwind angle.
They don't reduce neither upwind, nor downwind sailing performance in strong winds, - usually you have to reef anyway, even with outriggers, because you have much more wind than you can handle effectively. I would think that they increase sailing performance in strong winds, as the boat is heeling less (making it more efficient).
They have a lot to do with stability. In gusty winds people capsized in Klepper double with much smaller BSD sail - 24 sf, without outrigger. And they capsize in monohull sailing canoes (no outriggers) from time to time. I would never go to a multiday sailing trip without outriggers, - with the boat full of expensive gear.
Folbot outriggers are.. welll.. let's say this is a last resort. Not because of lower strength. They are bulbous, and when something doesn't look right, it usually doesn't sail right (and sailing a kayak is already a low-performance sailing, so it needs any help that it can get). Still, with Balogh virtually unavailable now, they could be an option - in the worst case they would reduce both sailing and paddling speed by 0.5 knot (compared to BSD floats), and upwind sailing angle - barely perceptibly.
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