Class History The J/24 is an extremely successful one-design keelboat. Attention to the rules and strict international control provides close racing and attracts the world's top sailors. The J/24 is also popular with weekend club sailors because it is fun, responsive in all conditions, and can...
The J24 Vang blocks attached to the boom and the mast have a safe working load around pounds at least 750 pounds, and safety factor of between 3 to 4. So a breaking load of 2500-3000 pounds is in the ball park.
The blocks in the middle of the cascade can be lesser strength, depending on the mechanical advantage of the falls.
see also, Harkens recommendations for the Vang on a J105 (35.5’)
Class History The J/105 is a family racer/cruiser that combines a simple sailplan, clean deck layout and practical interior, with enough get-up-and-go to suit the most avid competitor. With sustained speeds of over 14 knots, this maneuverable keelboat features cockpit control at its best: an...
for a J105, Harken recommends a block with a safe working load and breaking strength about 2500 for the blocks on the bond of the cascades (on the boom and mast)
I Don’t know of any 29 mm blocks with breaking strength over 2000. The Harken 29 mm wire block has a 2000 pounds max anda safe working load load f 500. Harken 29 mm Carbo blocks have a breaking strengthof 1000 pounds.
ps sorry for the bad typing and grammar errors. I’m typing on my iPad with one hand.