diff --git a/OpenLocoTool/DatFileParsing/LocoObject.cs b/OpenLocoTool/DatFileParsing/LocoObject.cs
index e3f32e85..a6512167 100644
--- a/OpenLocoTool/DatFileParsing/LocoObject.cs
+++ b/OpenLocoTool/DatFileParsing/LocoObject.cs
@@ -1,5 +1,6 @@
 using System.ComponentModel;
 using OpenLocoTool.Headers;
+using OpenLocoTool.Objects;
 
 namespace OpenLocoTool.DatFileParsing
 {
@@ -103,12 +104,85 @@ public G1Dat(G1Header g1Header, List<G1Element32> g1Elements)
 	//{
 	//	public byte[] S5Header { get; }
 	//	public byte[] ObjectHeader { get; set; }
-	//	public byte[] Object { get; set; }
+	//	public byte[] FixedData { get; set; }
+	//  public byte[] VariableData { get; set; }
 	//	public byte[] StringTable { get; set; }
 	//	public byte[] G1Header { get; set; }
 	//	public byte[] G1Elements { get; set; }
 	//}
 
+	public static class ObjectTypeFixedSize
+	{
+		public static int GetSize(ObjectType objectType)
+			=> objectType switch
+			{
+				ObjectType.Airport => AirportObject.StructSize,
+				ObjectType.Bridge => BridgeObject.StructSize,
+				ObjectType.Building => BuildingObject.StructSize,
+				ObjectType.Cargo => CargoObject.StructSize,
+				ObjectType.CliffEdge => CliffEdgeObject.StructSize,
+				ObjectType.Climate => ClimateObject.StructSize,
+				ObjectType.Competitor => CompetitorObject.StructSize,
+				ObjectType.Currency => CurrencyObject.StructSize,
+				ObjectType.Dock => DockObject.StructSize,
+				ObjectType.HillShapes => HillShapesObject.StructSize,
+				ObjectType.Industry => IndustryObject.StructSize,
+				ObjectType.InterfaceSkin => InterfaceSkinObject.StructSize,
+				ObjectType.Land => LandObject.StructSize,
+				ObjectType.LevelCrossing => LevelCrossingObject.StructSize,
+				ObjectType.Region => RegionObject.StructSize,
+				ObjectType.RoadExtra => RoadExtraObject.StructSize,
+				ObjectType.Road => RoadObject.StructSize,
+				ObjectType.RoadStation => RoadStationObject.StructSize,
+				ObjectType.Scaffolding => ScaffoldingObject.StructSize,
+				ObjectType.ScenarioText => ScenarioTextObject.StructSize,
+				ObjectType.Snow => SnowObject.StructSize,
+				ObjectType.Sound => SoundObject.StructSize,
+				ObjectType.Steam => SteamObject.StructSize,
+				ObjectType.StreetLight => StreetLightObject.StructSize,
+				ObjectType.TownNames => TownNamesObject.StructSize,
+				ObjectType.TrackExtra => TrackExtraObject.StructSize,
+				ObjectType.Track => TrackObject.StructSize,
+				ObjectType.TrainSignal => TrainSignalObject.StructSize,
+				ObjectType.TrainStation => TrainStationObject.StructSize,
+				ObjectType.Tree => TreeObject.StructSize,
+				ObjectType.Tunnel => TunnelObject.StructSize,
+				ObjectType.Vehicle => VehicleObject.StructSize,
+				ObjectType.Wall => WallObject.StructSize,
+				ObjectType.Water => WaterObject.StructSize,
+				_ => throw new ArgumentOutOfRangeException(nameof(objectType), $"unknown object type {objectType}")
+			};
+	}
+
+	public class LocoMemoryObject
+	{
+		byte[] full; // the full bytes of the object, decoded
+
+		public S5Header SHeader
+		{
+			get => S5Header.Read(full.AsSpan()[0..S5Header.StructLength]);
+			set => value.Write().CopyTo(full.AsSpan()[0..S5Header.StructLength]);
+		}
+
+		public ObjectHeader OHeader
+		{
+			get => ObjectHeader.Read(full.AsSpan()[0..ObjectHeader.StructLength]);
+			set => value.Write().CopyTo(full.AsSpan()[S5Header.StructLength..ObjectHeader.StructLength]);
+		}
+
+		int FixedDataOffset => S5Header.StructLength + ObjectHeader.StructLength;
+		int FixedDataLength => ObjectTypeFixedSize.GetSize(SHeader.ObjectType);
+		public ILocoStruct FixedData
+		{
+			get => SawyerStreamReader.GetLocoStruct(SHeader.ObjectType, full.AsSpan()[FixedDataOffset..FixedDataLength]);
+			set => ByteWriter.WriteLocoStruct(value).CopyTo(full.AsSpan()[FixedDataOffset..FixedDataLength]);
+		}
+
+		// variable data
+		// string table
+		// graphics data
+	}
+
 	[TypeConverter(typeof(ExpandableObjectConverter))]
 	public class LocoObject : ILocoObject
 	{
diff --git a/OpenLocoTool/DatFileParsing/SawyerStreamReader.cs b/OpenLocoTool/DatFileParsing/SawyerStreamReader.cs
index ed86ade6..42044881 100644
--- a/OpenLocoTool/DatFileParsing/SawyerStreamReader.cs
+++ b/OpenLocoTool/DatFileParsing/SawyerStreamReader.cs
@@ -87,12 +87,13 @@ public ILocoObject LoadFull(string filename, bool loadExtra = true)
 				locoStructString.LoadPostStringTable(stringTable);
 			}
 
-			// special handling per object type
+			// some objects have variable-sized data
 			if (loadExtra && locoStruct is ILocoStructVariableData locoStructExtra)
 			{
 				remainingData = locoStructExtra.Load(remainingData);
 			}
 
+			// some objects have graphics data
 			var (g1Header, imageTable, imageTableBytesRead) = LoadImageTable(remainingData);
 			Logger.Log(LogLevel.Info, $"FileLength={new FileInfo(filename).Length} HeaderLength={S5Header.StructLength} DataLength={objectHeader.DataLength} StringTableLength={stringTableBytesRead} ImageTableLength={imageTableBytesRead}");