The kinetic energy of the moving yacht must be absorbed by the ropes. It can be calculated with the following mathematical formula.
E kin = m v ² / 2 = Braking force x Braking distance
E kin … kinetic energy [ Joule ]
m … yacht's inertia [ N ] (Info: 1 Kg = 9,81 N ~ 1 daN )
v … speed [ m / s ]
Braking force … [ N ]
Braking distance … [ m ]
Example 40' yacht:
Area exposed to wind: 15 m²
Weight: 10 tons
The following calculation in based on 'conventional' docking system
with ropes (bow line-mooring, stern lines, 2 diagonal lines)
Stern diagonal lines: length 10 m, 25% max. elongation, 7.200 kg breaking force
Speed | Ballast
Weight | Kinetic
Energy | Braking
Force | Rating | Braking
Distance |
[m/s] | [kg] | [Joule] | [ kg ] | [ m ] |
0,01 | 10.000 | 5 | 38 | harmless | 0,01 |
0,1 | 10.000 | 491 | 380 | 0,13 |
0,2 | 10.000 | 1.962 | 759 | critical | 0,26 |
0,3 | 10.000 | 4.415 | 1.138 | very critical | 0,40 |
0,5 | 10.000 | 12.263 | 1.897 | 0,66 |
1,0 | 10.000 | 49.050 | 3.795 | Danger of
overstress | 1,31 |
1,5 | 10.000 | 110.363 | 5.692 | 1,97 |
2,0 | 10.000 | 196.200 | 7.590 | 2,50 |
A movement of 0,3 metres per second or more results in braking forces which can be crutial for cleats and ropes.
