diff --git a/fastsim-core/src/macros.rs b/fastsim-core/src/macros.rs
index b5d97773..fd5da1fd 100644
--- a/fastsim-core/src/macros.rs
+++ b/fastsim-core/src/macros.rs
@@ -72,7 +72,7 @@ macro_rules! impl_get_set_eff_range {
                 ];
                 let eff_interp_fwd = self.eff_interp_fwd.0;
                 eff_interp_fwd.set_f_x(f_x)?;
-                self.eff_interp_fwd = InterpolatorWrapper(eff_interp_fwd);
+                self.eff_interp_fwd = eff_interp_fwd;
                 Ok(())
             } else if (0.0..=1.0).contains(&eff_range) {
                 let old_min = self.get_eff_min();
diff --git a/fastsim-core/src/vehicle/powertrain/electric_machine.rs b/fastsim-core/src/vehicle/powertrain/electric_machine.rs
index 93f2f209..dd48cec8 100644
--- a/fastsim-core/src/vehicle/powertrain/electric_machine.rs
+++ b/fastsim-core/src/vehicle/powertrain/electric_machine.rs
@@ -1,7 +1,5 @@
 //! Module for electric machine (i.e. bidirectional electromechanical device), generator, or motor
 
-use utils::interp::InterpolatorWrapper;
-
 use super::*;
 
 #[allow(unused_imports)]
@@ -68,12 +66,12 @@ pub struct ElectricMachine {
     #[api(skip_set)]
     /// Efficiency array corresponding to [Self::pwr_out_frac_interp] and [Self::pwr_in_frac_interp]
     /// eff_interp_fwd and eff_interp_bwd have the same f_x but different x
-    pub eff_interp_fwd: utils::interp::InterpolatorWrapper,
+    pub eff_interp_fwd: utils::interp::Interpolator,
     #[serde(skip)]
     #[api(skip_set)]
     // if it is not provided, needs to be set during init, can figure out what to do
     // for that by looking at how pwr_in_frac_interp is initialized
-    pub eff_interp_bwd: Option<utils::interp::InterpolatorWrapper>,
+    pub eff_interp_bwd: Option<utils::interp::Interpolator>,
     /// Electrical input power fraction array at which efficiencies are evaluated.
     /// Calculated during runtime if not provided.
     #[serde(skip)]
@@ -152,7 +150,7 @@ impl ElectricMachine {
                     .map(|(x, y)| x / y)
                     .collect(),
             );
-            self.eff_interp_bwd = Some(InterpolatorWrapper(eff_interp_bwd));
+            self.eff_interp_bwd = Some(eff_interp_bwd);
             // self.set_pwr_in_frac_interp()
             //     .with_context(|| format_dbg!())?;
         }
@@ -342,7 +340,7 @@ impl Init for ElectricMachine {
                     .map(|(x, y)| x / y)
                     .collect(),
             );
-            self.eff_interp_bwd = Some(InterpolatorWrapper(eff_interp_bwd));
+            self.eff_interp_bwd = Some(eff_interp_bwd);
             // self.set_pwr_in_frac_interp()
             //     .with_context(|| format_dbg!())?;
         }
diff --git a/fastsim-core/src/vehicle/powertrain/fuel_converter.rs b/fastsim-core/src/vehicle/powertrain/fuel_converter.rs
index cae0da18..a1b0f96c 100644
--- a/fastsim-core/src/vehicle/powertrain/fuel_converter.rs
+++ b/fastsim-core/src/vehicle/powertrain/fuel_converter.rs
@@ -68,7 +68,7 @@ pub struct FuelConverter {
     pub pwr_ramp_lag: si::Time,
     /// interpolator for calculating [Self] efficiency as a function of output power
     #[api(skip_get, skip_set)]
-    pub eff_interp_from_pwr_out: utils::interp::InterpolatorWrapper,
+    pub eff_interp_from_pwr_out: utils::interp::Interpolator,
     /// idle fuel power to overcome internal friction (not including aux load) \[W\]
     #[serde(rename = "pwr_idle_fuel_watts")]
     pub pwr_idle_fuel: si::Power,
diff --git a/fastsim-core/src/vehicle/vehicle_model.rs b/fastsim-core/src/vehicle/vehicle_model.rs
index 71ca423d..811c2714 100644
--- a/fastsim-core/src/vehicle/vehicle_model.rs
+++ b/fastsim-core/src/vehicle/vehicle_model.rs
@@ -375,7 +375,7 @@ impl TryFrom<&fastsim_2::vehicle::RustVehicle> for PowertrainType {
                 },
                 em: ElectricMachine {
                     state: Default::default(),
-                    eff_interp_fwd: InterpolatorWrapper(Interpolator::Interp1D(
+                    eff_interp_fwd: (Interpolator::Interp1D(
                         Interp1D::new(
                             f2veh.mc_pwr_out_perc.to_vec(),
                             f2veh.mc_eff_array.to_vec(),
@@ -385,7 +385,7 @@ impl TryFrom<&fastsim_2::vehicle::RustVehicle> for PowertrainType {
                         )
                         .unwrap(),
                     )),
-                    eff_interp_bwd: Some(InterpolatorWrapper(Interpolator::Interp1D(
+                    eff_interp_bwd: Some(Interpolator::Interp1D(
                         Interp1D::new(
                             // before adding the interpolator, pwr_in_frac_interp was set as Default::default(), can this
                             // be transferred over as done here, or does a new defualt need to be defined?
@@ -396,7 +396,7 @@ impl TryFrom<&fastsim_2::vehicle::RustVehicle> for PowertrainType {
                             Extrapolate::Error,
                         )
                         .unwrap(),
-                    ))),
+                    )),
                     // pwr_in_frac_interp: Default::default(),
                     pwr_out_max: f2veh.mc_max_kw * uc::KW,
                     specific_pwr: None,