This is a set of Heavy Duty Dock Springs. 

 

These springs were intended for a one ton service truck and have about 1800 lbs per inch compression strength.  They weigh about 35 pounds each.  FYI, my dock is a steel two slip with composite decking, steel roofing, a big swim deck, two boat lifts, a 24' deck boat, and a 21' fishing boat.  The boats alone weigh 10k lbs.  I estimate the total weight of the loaded dock around 30k lbs.  

 

These springs are the size I have on my dock and they do a great job smoothing out the dock's movements. 

​

If your dock is a double slip heavy dock (like mine) or a two story double slip exposed to large water and the big wind that comes with that, then the Heavy Duty Dock Springs will handle your dock.