After all depowering that can be done through tuning is done, reducing sail area is the safest and most effective next step towards depowering.
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When you talk about depowering, I assume you mean, as far as the main is concerned, maximum downhaul and minimum outhaul. How about mastrotation - fully in? Reducing sail area is on modern F18s not an option since we don't have self-furlings jibs anymore ...