diff --git a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.C b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.C
index 554e482c21..ed771efa6f 100644
--- a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.C
+++ b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.C
@@ -49,7 +49,8 @@ sixDoFRigidBodyDisplacementPointPatchVectorField
     fixedValuePointPatchField<vector>(p, iF),
     motion_(),
     initialPoints_(p.localPoints()),
-    rhoInf_(1.0)
+    rhoInf_(1.0),
+    rhoName_("rho")
 {}
 
 
@@ -63,8 +64,14 @@ sixDoFRigidBodyDisplacementPointPatchVectorField
 :
     fixedValuePointPatchField<vector>(p, iF, dict),
     motion_(dict),
-    rhoInf_(readScalar(dict.lookup("rhoInf")))
+    rhoInf_(1.0),
+    rhoName_(dict.lookupOrDefault<word>("rhoName", "rho"))
 {
+    if (rhoName_ == "rhoInf")
+    {
+        rhoInf_ = readScalar(dict.lookup("rhoInf"));
+    }
+
     if (!dict.found("value"))
     {
         updateCoeffs();
@@ -93,7 +100,8 @@ sixDoFRigidBodyDisplacementPointPatchVectorField
     fixedValuePointPatchField<vector>(ptf, p, iF, mapper),
     motion_(ptf.motion_),
     initialPoints_(ptf.initialPoints_, mapper),
-    rhoInf_(ptf.rhoInf_)
+    rhoInf_(ptf.rhoInf_),
+    rhoName_(ptf.rhoName_)
 {}
 
 
@@ -107,7 +115,8 @@ sixDoFRigidBodyDisplacementPointPatchVectorField
     fixedValuePointPatchField<vector>(ptf, iF),
     motion_(ptf.motion_),
     initialPoints_(ptf.initialPoints_),
-    rhoInf_(ptf.rhoInf_)
+    rhoInf_(ptf.rhoInf_),
+    rhoName_(ptf.rhoName_)
 {}
 
 
@@ -160,6 +169,7 @@ void sixDoFRigidBodyDisplacementPointPatchVectorField::updateCoeffs()
 
     forcesDict.add("patches", wordList(1, ptPatch.name()));
     forcesDict.add("rhoInf", rhoInf_);
+    forcesDict.add("rhoName", rhoName_);
     forcesDict.add("CofR", motion_.centreOfMass());
 
     forces f("forces", db(), forcesDict);
@@ -200,6 +210,8 @@ void sixDoFRigidBodyDisplacementPointPatchVectorField::write(Ostream& os) const
     motion_.write(os);
     os.writeKeyword("rhoInf")
         << rhoInf_ << token::END_STATEMENT << nl;
+    os.writeKeyword("rhoName")
+        << rhoName_ << token::END_STATEMENT << nl;
     initialPoints_.writeEntry("initialPoints", os);
     writeEntry("value", os);
 }
diff --git a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.H b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.H
index fa30a7eff2..9c512ab9d3 100644
--- a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.H
+++ b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/sixDoFRigidBodyDisplacement/sixDoFRigidBodyDisplacementPointPatchVectorField.H
@@ -60,9 +60,14 @@ class sixDoFRigidBodyDisplacementPointPatchVectorField
         pointField initialPoints_;
 
         //- Reference density required by the forces object for
-        //  incompressible calculations
+        //  incompressible calculations, required if rhoName == rhoInf
         scalar rhoInf_;
 
+        //- Name of density field, optional unless used for an
+        //  incompressible simulation, when this needs to be specified
+        //  as rhoInf
+        word rhoName_;
+
 
 public:
 
diff --git a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.C b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.C
index f63607c99c..7b7537eec3 100644
--- a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.C
+++ b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.C
@@ -47,8 +47,7 @@ uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField
 :
     fixedValuePointPatchField<vector>(p, iF),
     motion_(),
-    initialPoints_(p.localPoints()),
-    rhoInf_(1.0)
+    initialPoints_(p.localPoints())
 {}
 
 
@@ -61,8 +60,7 @@ uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField
 )
 :
     fixedValuePointPatchField<vector>(p, iF, dict),
-    motion_(dict),
-    rhoInf_(readScalar(dict.lookup("rhoInf")))
+    motion_(dict)
 {
     if (!dict.found("value"))
     {
@@ -91,8 +89,7 @@ uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField
 :
     fixedValuePointPatchField<vector>(ptf, p, iF, mapper),
     motion_(ptf.motion_),
-    initialPoints_(ptf.initialPoints_, mapper),
-    rhoInf_(ptf.rhoInf_)
+    initialPoints_(ptf.initialPoints_, mapper)
 {}
 
 
@@ -105,8 +102,7 @@ uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField
 :
     fixedValuePointPatchField<vector>(ptf, iF),
     motion_(ptf.motion_),
-    initialPoints_(ptf.initialPoints_),
-    rhoInf_(ptf.rhoInf_)
+    initialPoints_(ptf.initialPoints_)
 {}
 
 
@@ -182,8 +178,6 @@ void uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField::write
 {
     pointPatchField<vector>::write(os);
     motion_.write(os);
-    os.writeKeyword("rhoInf")
-        << rhoInf_ << token::END_STATEMENT << nl;
     initialPoints_.writeEntry("initialPoints", os);
     writeEntry("value", os);
 }
diff --git a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.H b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.H
index 631c732a93..d5a17c09c7 100644
--- a/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.H
+++ b/src/postProcessing/functionObjects/forces/pointPatchFields/derived/uncoupledSixDoFRigidBodyDisplacement/uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField.H
@@ -59,11 +59,6 @@ class uncoupledSixDoFRigidBodyDisplacementPointPatchVectorField
         //- Initial positions of points on the patch
         pointField initialPoints_;
 
-        //- Reference density required by the forces object for
-        //  incompressible calculations.  Retained here to give
-        //  dictionary compatibility with other sixDoF patches.
-        scalar rhoInf_;
-
 
 public: