Converting struct so it can be sent from watch to phone

I want to send struct data from my watchOS-app to my iOS-app using WatchConnectivity. As I have understood, you can only send property list objects, hence I must convert my struct somehow. I tried converting it into a NSDictionary, and also make it a Codable struct, but it doesn't work since I have properties that does not conform to the Codable prototocols. Any suggestions on how this can be solved in a good way?

I'm using XCode Version 10.1 and Swift 4.2.

Here is my struct:

struct Storage {
    
    var acc: Acc
    struct Acc  {
        var x: [Double] = []
        var y: [Double] = []
        var z: [Double] = []
    }
    
    
    var gyro: Gyro
    struct Gyro {
        var x: [Double] = []
        var y: [Double] = []
        var z: [Double] = []
    }
    
    var mag: Mag
    struct Mag {
        var x: [Double] = []
        var y: [Double] = []
        var z: [Double] = []
    }
    
    var pulse: [Double] = []
    
    var quaternion: Quaternion
    struct Quaternion {
        var w: [Double] = []
        var x: [Double] = []
        var y: [Double] = []
        var z: [Double] = []
    }
}