Boom Reef blocks and winches installation design As you remember I made 4 reefs on my new main sail, and 4-th i would likely never use ;) I tried to calculate what could be loads in reef lines on my boat and get really surprised numbers. My sail: Configuration Luff remaining Estimated area Full-sail area Full sail 11.14 m 25.60 m² 100% Reef 1 9.45 m 19.2 m² 75% Reef 2 7.80 m 13.6 m² 53% Reef 3 6.13 m 8.8 m² 34% Reef 4 4.46 m 4.9 m² 19% At fourth reef set, about 4.9 m² of mainsail remains exposed to the wind.  At a worst-case wind speed of 60 knots, that sail area produces approximately 3.7 kN force.  If about 40% reaches the reef clew, the clew must take 1.5 kN. Because the two reef-line legs pull at a shallow angle of about 10°, each leg carries approximately (1.5 ÷ [2 × \sin(10°)] = 4.3) kN. Allowing a 50% increase for gusts, flogging and shock x1.5 =  6.4 kN. so, a reef block i need for about 8 kN working load. The same logic calculation gives us about the same loads o...