diff --git a/ontology/saref4mari.ttl b/ontology/saref4mari.ttl
index d67ae3d935f4256e64915ca8da78cfd51a22ef34..14207adf9cece1545173581c33c84a7e49c8b58d 100644
--- a/ontology/saref4mari.ttl
+++ b/ontology/saref4mari.ttl
@@ -21,7 +21,8 @@
 
 <https://saref.etsi.org/saref4mari/> rdf:type owl:Ontology ;
                                       owl:versionIRI <https://saref.etsi.org/saref4mari/v1.1.1/> ;
-                                      owl:imports <https://saref.etsi.org/core/v3.2.1/> ,
+                                      owl:imports <http://qudt.org/2.1/vocab/unit> ,
+                                                  <https://saref.etsi.org/core/v3.2.1/> ,
                                                   s4watr: ;
                                       dcterms:contributor <https://it.linkedin.com/in/alexandr-tardo-5b5ba896> ,
                                                           <https://www.linkedin.com/in/ivan-spaji%C4%87-75535413a/> ;
@@ -627,15 +628,6 @@ s4mari:hasUVI rdf:type owl:DatatypeProperty ;
               rdfs:seeAlso "https://emsa.europa.eu/cise-documentation/cise-data-model-1.5.3/model/info/Vessel_UVI.html" .
 
 
-###  https://saref.etsi.org/saref4mari/hasUnitOfMeasurement
-s4mari:hasUnitOfMeasurement rdf:type owl:DatatypeProperty ;
-                            rdfs:subPropertyOf owl:topDataProperty ;
-                            rdfs:range xsd:string ;
-                            rdfs:comment "The unit of measurement of a property's value."@en ;
-                            rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/hasUnitOfMeasurement"@en ;
-                            rdfs:label "hasUnitOfMeasurement"@en .
-
-
 ###  https://saref.etsi.org/saref4mari/hasVersion
 s4mari:hasVersion rdf:type owl:DatatypeProperty ;
                   rdfs:domain s4mari:Document ;
@@ -654,6 +646,10 @@ s4mari:hasVoyageNumber rdf:type owl:DatatypeProperty ;
 #    Classes
 #################################################################
 
+###  http://qudt.org/schema/qudt/Unit
+<http://qudt.org/schema/qudt/Unit> rdfs:subClassOf saref:UnitOfMeasure .
+
+
 ###  http://www.opengis.net/ont/geosparql#Feature
 geo:Feature rdf:type owl:Class .
 
@@ -781,7 +777,11 @@ s4mari:CatchProperty rdf:type owl:Class ;
 
 ###  https://saref.etsi.org/saref4mari/ConductivitySensor
 s4mari:ConductivitySensor rdf:type owl:Class ;
-                          rdfs:subClassOf saref:Sensor ;
+                          rdfs:subClassOf saref:Sensor ,
+                                          [ rdf:type owl:Restriction ;
+                                            owl:onProperty saref:observes ;
+                                            owl:someValuesFrom s4watr:WaterElectricalProperty
+                                          ] ;
                           rdfs:comment "A sensor for measuring water conductivity."@en ;
                           rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/ConductivitySensor"@en ;
                           rdfs:label "ConductivitySensor"@en .
@@ -968,7 +968,7 @@ s4mari:OxygenConcentrationSensor rdf:type owl:Class ;
                                  rdfs:subClassOf saref:Sensor ,
                                                  [ rdf:type owl:Restriction ;
                                                    owl:onProperty saref:observes ;
-                                                   owl:hasValue s4mari:DissolvedOxygen
+                                                   owl:hasValue <https://saref.etsi.org/saref4watr/DissolvedOxygen>
                                                  ] ;
                                  rdfs:comment "A sensor for measuring underwater oxygen concentration."@en ;
                                  rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/OxygenConcentrationSensor"@en ;
@@ -1143,7 +1143,11 @@ s4watr:ChemicalProperty rdf:type owl:Class .
 
 
 ###  https://saref.etsi.org/saref4watr/v1.1.1/WaterElectricalProperty
-s4watr:WaterElectricalProperty rdf:type owl:Class .
+s4watr:WaterElectricalProperty rdf:type owl:Class ;
+                               rdfs:subClassOf <https://saref.etsi.org/saref4watr/WaterProperty> ;
+                               rdfs:comment "The electrical property of water."@en ;
+                               rdfs:isDefinedBy "https://saref.etsi.org/saref4watr/v1.1.1/WaterElectricalProperty"@en ;
+                               rdfs:label "WaterElectricalProperty"@en .
 
 
 ###  https://saref.etsi.org/saref4watr/v1.1.1/WaterProperty
@@ -1323,40 +1327,21 @@ s4mari:Destroyer rdf:type owl:NamedIndividual ,
                           s4mari:OperationalAssetKind .
 
 
-###  https://saref.etsi.org/saref4mari/DetecionOfChangesInAISParameters
-s4mari:DetecionOfChangesInAISParameters rdf:type owl:NamedIndividual ,
-                                                 s4mari:AnomalyKind .
-
-
 ###  https://saref.etsi.org/saref4mari/Detection
 s4mari:Detection rdf:type owl:NamedIndividual ,
                           s4mari:ActionKind .
 
 
+###  https://saref.etsi.org/saref4mari/DetectionOfChangesInAISParameters
+s4mari:DetectionOfChangesInAISParameters rdf:type owl:NamedIndividual ,
+                                                  s4mari:AnomalyKind .
+
+
 ###  https://saref.etsi.org/saref4mari/Deterrence
 s4mari:Deterrence rdf:type owl:NamedIndividual ,
                            s4mari:ActionKind .
 
 
-###  https://saref.etsi.org/saref4mari/DissolvedOxygen
-s4mari:DissolvedOxygen rdf:type owl:NamedIndividual ,
-                                s4watr:ChemicalProperty ,
-                                [ rdf:type owl:Restriction ;
-                                  owl:onProperty saref:hasValue ;
-                                  owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
-                                  owl:onDataRange [ rdf:type rdfs:Datatype ;
-                                                    owl:onDatatype xsd:float ;
-                                                    owl:withRestrictions ( [ xsd:minInclusive "0.0"^^xsd:float
-                                                                           ]
-                                                                         )
-                                                  ]
-                                ] ;
-                       s4mari:hasUnitOfMeasurement "mg/L"@en ;
-                       rdfs:comment "The amount of dissolved oxygen in water."@en ;
-                       rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/DissolvedOxygen" ;
-                       rdfs:label "DissolvedOxygen"@en .
-
-
 ###  https://saref.etsi.org/saref4mari/DoNotAnswerOnVHFCh16
 s4mari:DoNotAnswerOnVHFCh16 rdf:type owl:NamedIndividual ,
                                      s4mari:AnomalyKind .
@@ -1486,6 +1471,10 @@ s4mari:HasSickAnimalOnBoard rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/Heading
 s4mari:Heading rdf:type owl:NamedIndividual ,
                         s4mari:OrientationProperty ,
+                        [ rdf:type owl:Restriction ;
+                          owl:onProperty saref:isMeasuredIn ;
+                          owl:hasValue <http://qudt.org/vocab/unit/DEG>
+                        ] ,
                         [ rdf:type owl:Restriction ;
                           owl:onProperty saref:hasValue ;
                           owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -1498,7 +1487,6 @@ s4mari:Heading rdf:type owl:NamedIndividual ,
                                                                  )
                                           ]
                         ] ;
-               s4mari:hasUnitOfMeasurement "°" ;
                rdfs:comment "The heading orientation of an object."@en ;
                rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/Heading" ;
                rdfs:label "Heading"@en .
@@ -1805,6 +1793,10 @@ s4mari:PerformingAISSpoofing rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/Pitch
 s4mari:Pitch rdf:type owl:NamedIndividual ,
                       s4mari:OrientationProperty ,
+                      [ rdf:type owl:Restriction ;
+                        owl:onProperty saref:isMeasuredIn ;
+                        owl:hasValue <http://qudt.org/vocab/unit/DEG>
+                      ] ,
                       [ rdf:type owl:Restriction ;
                         owl:onProperty saref:hasValue ;
                         owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -1817,7 +1809,6 @@ s4mari:Pitch rdf:type owl:NamedIndividual ,
                                                                )
                                         ]
                       ] ;
-             s4mari:hasUnitOfMeasurement "°"@en ;
              rdfs:comment "The pitch orientation of an object."@en ;
              rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/Pitch" ;
              rdfs:label "Pitch"@en .
@@ -1869,6 +1860,10 @@ s4mari:Rescue rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/Roll
 s4mari:Roll rdf:type owl:NamedIndividual ,
                      s4mari:OrientationProperty ,
+                     [ rdf:type owl:Restriction ;
+                       owl:onProperty saref:isMeasuredIn ;
+                       owl:hasValue <http://qudt.org/vocab/unit/DEG>
+                     ] ,
                      [ rdf:type owl:Restriction ;
                        owl:onProperty saref:hasValue ;
                        owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -1881,7 +1876,6 @@ s4mari:Roll rdf:type owl:NamedIndividual ,
                                                               )
                                        ]
                      ] ;
-            s4mari:hasUnitOfMeasurement "°"@en ;
             rdfs:comment "The roll orientation of an object."@en ;
             rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/Roll" ;
             rdfs:label "Roll"@en .
@@ -1986,12 +1980,15 @@ s4mari:TidalCurrentSpeed rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/TideLevel
 s4mari:TideLevel rdf:type owl:NamedIndividual ,
                           s4mari:TideProperty ,
+                          [ rdf:type owl:Restriction ;
+                            owl:onProperty saref:isMeasuredIn ;
+                            owl:hasValue <http://www.ontology-of-units-of-measure.org/resource/om-2/metre>
+                          ] ,
                           [ rdf:type owl:Restriction ;
                             owl:onProperty saref:hasValue ;
                             owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
                             owl:onDataRange xsd:float
                           ] ;
-                 s4mari:hasUnitOfMeasurement "m"@en ;
                  rdfs:comment "The level of tide."@en ;
                  rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/TideLevel" ;
                  rdfs:label "TideLevel"@en .
@@ -2000,17 +1997,20 @@ s4mari:TideLevel rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/TidePressure
 s4mari:TidePressure rdf:type owl:NamedIndividual ,
                              s4mari:TideProperty ,
+                             [ rdf:type owl:Restriction ;
+                               owl:onProperty saref:isMeasuredIn ;
+                               owl:hasValue <http://qudt.org/vocab/unit/KiloPA>
+                             ] ,
                              [ rdf:type owl:Restriction ;
                                owl:onProperty saref:hasValue ;
                                owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
                                owl:onDataRange [ rdf:type rdfs:Datatype ;
                                                  owl:onDatatype xsd:float ;
-                                                 owl:withRestrictions ( [ xsd:minExclusive "0.0"^^xsd:float
+                                                 owl:withRestrictions ( [ xsd:minInclusive "0.0"^^xsd:float
                                                                         ]
                                                                       )
                                                ]
                              ] ;
-                    s4mari:hasUnitOfMeasurement "kPa"@en ;
                     rdfs:comment "The pressure caused by the tide."@en ;
                     rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/TidePressure" ;
                     rdfs:label "TidePressure"@en .
@@ -2072,6 +2072,10 @@ s4mari:UUV rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/UnderwaterPressure
 s4mari:UnderwaterPressure rdf:type owl:NamedIndividual ,
                                    s4watr:WaterProperty ,
+                                   [ rdf:type owl:Restriction ;
+                                     owl:onProperty saref:isMeasuredIn ;
+                                     owl:hasValue <http://qudt.org/vocab/unit/KiloPA>
+                                   ] ,
                                    [ rdf:type owl:Restriction ;
                                      owl:onProperty saref:hasValue ;
                                      owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -2082,7 +2086,6 @@ s4mari:UnderwaterPressure rdf:type owl:NamedIndividual ,
                                                                             )
                                                      ]
                                    ] ;
-                          s4mari:hasUnitOfMeasurement "dbar"@en ;
                           rdfs:comment "Pressure under the water."@en ;
                           rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/UnderwaterPressure" ;
                           rdfs:label "UnderwaterPressure"@en .
@@ -2091,6 +2094,10 @@ s4mari:UnderwaterPressure rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/UnderwaterSoundVelocity
 s4mari:UnderwaterSoundVelocity rdf:type owl:NamedIndividual ,
                                         s4watr:WaterProperty ,
+                                        [ rdf:type owl:Restriction ;
+                                          owl:onProperty saref:isMeasuredIn ;
+                                          owl:hasValue <http://qudt.org/vocab/unit/M-PER-SEC>
+                                        ] ,
                                         [ rdf:type owl:Restriction ;
                                           owl:onProperty saref:hasValue ;
                                           owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -2101,7 +2108,6 @@ s4mari:UnderwaterSoundVelocity rdf:type owl:NamedIndividual ,
                                                                                  )
                                                           ]
                                         ] ;
-                               s4mari:hasUnitOfMeasurement "m/s"@en ;
                                rdfs:comment "The velocity of underwater sound."@en ;
                                rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/UnderwaterSoundVelocity" ;
                                rdfs:label "UnderwaterSoundVelocity"@en .
@@ -2146,6 +2152,10 @@ s4mari:VoyageLeg rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/WaterConductance
 s4mari:WaterConductance rdf:type owl:NamedIndividual ,
                                  s4watr:WaterElectricalProperty ,
+                                 [ rdf:type owl:Restriction ;
+                                   owl:onProperty saref:isMeasuredIn ;
+                                   owl:hasValue <http://qudt.org/vocab/unit/MilliS>
+                                 ] ,
                                  [ rdf:type owl:Restriction ;
                                    owl:onProperty saref:hasValue ;
                                    owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -2156,7 +2166,6 @@ s4mari:WaterConductance rdf:type owl:NamedIndividual ,
                                                                           )
                                                    ]
                                  ] ;
-                        s4mari:hasUnitOfMeasurement "mS"@en ;
                         rdfs:comment "The conductance of water."@en ;
                         rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/WaterConductance" ;
                         rdfs:label "WaterConductance"@en .
@@ -2165,6 +2174,10 @@ s4mari:WaterConductance rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/WaterConductivity
 s4mari:WaterConductivity rdf:type owl:NamedIndividual ,
                                   s4watr:WaterElectricalProperty ,
+                                  [ rdf:type owl:Restriction ;
+                                    owl:onProperty saref:isMeasuredIn ;
+                                    owl:hasValue <http://qudt.org/vocab/unit/S-PER-M>
+                                  ] ,
                                   [ rdf:type owl:Restriction ;
                                     owl:onProperty saref:hasValue ;
                                     owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -2175,7 +2188,6 @@ s4mari:WaterConductivity rdf:type owl:NamedIndividual ,
                                                                            )
                                                     ]
                                   ] ;
-                         s4mari:hasUnitOfMeasurement "S/m"@en ;
                          rdfs:comment "The conductivity of water."@en ;
                          rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/WaterConductivity" ;
                          rdfs:label "WaterConductivity"@en .
@@ -2184,12 +2196,26 @@ s4mari:WaterConductivity rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/WaterTemperature
 s4mari:WaterTemperature rdf:type owl:NamedIndividual ,
                                  s4mari:MeteoOceanoConditionProperty ,
+                                 [ rdf:type owl:Class ;
+                                   owl:unionOf ( [ rdf:type owl:Restriction ;
+                                                   owl:onProperty saref:isMeasuredIn ;
+                                                   owl:hasValue <http://qudt.org/vocab/quantitykind/CelsiusTemperature>
+                                                 ]
+                                                 [ rdf:type owl:Restriction ;
+                                                   owl:onProperty saref:isMeasuredIn ;
+                                                   owl:hasValue <http://qudt.org/vocab/quantitykind/FahrenheitTemperature>
+                                                 ]
+                                                 [ rdf:type owl:Restriction ;
+                                                   owl:onProperty saref:isMeasuredIn ;
+                                                   owl:hasValue <http://qudt.org/vocab/unit/K>
+                                                 ]
+                                               )
+                                 ] ,
                                  [ rdf:type owl:Restriction ;
                                    owl:onProperty saref:hasValue ;
                                    owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
                                    owl:onDataRange xsd:float
                                  ] ;
-                        s4mari:hasUnitOfMeasurement "°C"@en ;
                         rdfs:comment "The temperature of water."@en ;
                         rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/WaterTemperature" ;
                         rdfs:label "WaterTemperature"@en ;
@@ -2199,6 +2225,10 @@ s4mari:WaterTemperature rdf:type owl:NamedIndividual ,
 ###  https://saref.etsi.org/saref4mari/WaterTurbidity
 s4mari:WaterTurbidity rdf:type owl:NamedIndividual ,
                                s4watr:WaterProperty ,
+                               [ rdf:type owl:Restriction ;
+                                 owl:onProperty saref:isMeasuredIn ;
+                                 owl:hasValue <http://qudt.org/vocab/quantitykind/Turbidity>
+                               ] ,
                                [ rdf:type owl:Restriction ;
                                  owl:onProperty saref:hasValue ;
                                  owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
@@ -2209,7 +2239,6 @@ s4mari:WaterTurbidity rdf:type owl:NamedIndividual ,
                                                                         )
                                                  ]
                                ] ;
-                      s4mari:hasUnitOfMeasurement "FTU"@en ;
                       rdfs:comment "The turbidity of water."@en ;
                       rdfs:isDefinedBy "https://saref.etsi.org/saref4mari/WaterTurbidity" ;
                       rdfs:label "WaterTurbidity"@en .
@@ -2260,6 +2289,28 @@ s4mari:YearBuilt rdf:type owl:NamedIndividual ,
                  rdfs:seeAlso "https://emsa.europa.eu/cise-documentation/cise-data-model-1.5.3/model/info/Vessel_YearBuilt.html" .
 
 
+###  https://saref.etsi.org/saref4watr/DissolvedOxygen
+<https://saref.etsi.org/saref4watr/DissolvedOxygen> rdf:type owl:NamedIndividual ,
+                                                             s4watr:ChemicalProperty ,
+                                                             [ rdf:type owl:Restriction ;
+                                                               owl:onProperty saref:isMeasuredIn ;
+                                                               owl:hasValue <http://qudt.org/vocab/unit/MilliGM-PER-L>
+                                                             ] ,
+                                                             [ rdf:type owl:Restriction ;
+                                                               owl:onProperty saref:hasValue ;
+                                                               owl:qualifiedCardinality "1"^^xsd:nonNegativeInteger ;
+                                                               owl:onDataRange [ rdf:type rdfs:Datatype ;
+                                                                                 owl:onDatatype xsd:float ;
+                                                                                 owl:withRestrictions ( [ xsd:minInclusive "0.0"^^xsd:float
+                                                                                                        ]
+                                                                                                      )
+                                                                               ]
+                                                             ] ;
+                                                    rdfs:comment "The amount of dissolved oxygen in water."@en ;
+                                                    rdfs:isDefinedBy "https://saref.etsi.org/saref4watr/DissolvedOxygen" ;
+                                                    rdfs:label "DissolvedOxygen"@en .
+
+
 #################################################################
 #    Annotations
 #################################################################