All 4 eye hunter boats use a system. They are basically just long very heavy duty marine grade bungee cords that take up the pressure of the heavy pulled from bumps and here's from bigger waves. Allows the boards to run smoother.

Line leave the main spool goes forwards through a high quality pulley, then rearward through another pulley then out to th board. Make sure the line can not slide of pulley and get pinched between the pulley and housing holding the axis the pulley spins on or the line can get cut or damaged. Don't chea out here, good ones are about 50 bucks each.