An apparatus comprises a) a spar comprising: i) a central portion; ii) a first end portion; iii) a second end portion; b) a first resistance device; c) a second resistance device; d) a first tow line connected between: i) the first end portion; and ii) the first resistance device; e) a second tow line connected between: i) the second end portion; and ii) the second resistance device; f) a first shock absorber configured to connect: i) between the first end portion and the central portion; and ii) a first side of a movable structure; and g) a second shock absorber configured to connect: i) between the second end portion and the central portion; and ii) a second side of the movable structure.