Calculating (or at least approximating) the sailing load on the dagger board is done by analyzing the static forces/moments.

The righting moment of the boat can be approximated by estimating the location of the CG of the boat itself and the crew and multiplying the horizontal distance of the CG from the leeward hull....CG of boat = 400LB x 4ft= 1600 lb-ft. CG crew = 350LB x 12ft = 4,200 lb-ft. Total righting moment = 5,800 lb-ft.

To fly a hull, the rig must generate a heeling moment equal to the righting moment. If you estimate the height of the CE for the rig at 15 ft above the hull, then you can calculate the side force of the rig.
Side force = 5,800 lb-ft / 15 ft = 387 LB.

Since the daggerboard must produce lateral resistance to counter the side force of the rig, the board must be capable of supporting this load at it's CE (of course the hull and rudder also contribute to the lateral resistance, but for the purpose of approximation, one can assume the board supports the entire load). If you assume that the CE of the daggerboard is 2.5 ft below the hull, then the board should be capable of supporting 387 lb at a distance of 2.5 ft from the bottom of the hull. At a distance of 1.25 feet from the bottom of the hull, it would support a load of 770 lb and at a distance of 5 feet from the hull, it would support a load of 193 lb.

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