Damping forces to stop boat oscillation

I have a boat that check 4 points to see if they are under water at any given time. When they are under water a force equal to the force required to hold the boat up dived by 4 plus an extra force that varies by depth(1/4 of the required boat force is applied at any point).

This works great to hold the boat up however the boat continually bounces between all 4 points very fast, i want this to happen but at a much slower rate to give the effect of boat bobbing/rolling. I would imagine that i need a damping force of some sort, any idea how i would go about it here is the code i have:

  //finding the height above and below the water, downdist
   //  is the height above water, the 4 points are frontl for //front
    // left point frontr for front right point,etc,etc
     float distfl=floatheight-frontl.transform.position.y;
                 float distfr=floatheight-frontr.transform.position.y;
                 float distbr=floatheight-backr.transform.position.y;
                 float distbl=floatheight-backl.transform.position.y;
                 float downdistfl=frontl.transform.position.y-floatheight;
                 float downdistfr=frontr.transform.position.y-floatheight;
                 float downdistbr=backr.transform.position.y-floatheight;
                 float downdistbl=backl.transform.position.y-floatheight;
                 //36.75 is the force required to //hold up the boat dived by 4 from the 4 points //acceleration=force/mass 9.8*15=force,15 is mass, 
     //147=force to hold boat up,147/4=36.75
                 if (frontl.transform.position.y<floatheight){
                     boatr.AddForceAtPosition(Vector3.up*(36.75f+(distfl*36.75f)),frontl.transform.position);
                 }
                 
                 if (frontr.transform.position.y<floatheight){
                     boatr.AddForceAtPosition(Vector3.up*(36.75f+(distfr*36.75f)),frontr.transform.position);
                 }    
                 
                 if (backl.transform.position.y<floatheight){
                     boatr.AddForceAtPosition(Vector3.up*(36.75f+(distbl*36.75f)),backl.transform.position);
                 }
                 
                 if (backr.transform.position.y<floatheight){
                     boatr.AddForceAtPosition(Vector3.up*(36.75f+(distbr*36.75f)),backr.transform.position);
                 }