Bretschneider , golfperiode
$$\frac{g \cdot T}{U} = 2 \pi \cdot 1,2 \cdot \tanh \left[ 0,833 \left( \frac{g d}{U^{2}} \right)^{0,375} \right] \cdot \tanh \left[ \frac{0,077 \left( \frac{g F}{U^{2}} \right)^{0,25}}{\tanh \left( 0,833 \left( \frac{g d}{U^{2}} \right)^{0,375} \right)} \right]$$