Is this transducer compatabile with a 898? Seems like It would be but all I can find is it says used for a 997. Or the 7 series units. Thanks.
Yes it is.
The XHS-9-HDSi-180-T (or just HDSi) transducer is the same one that is shipped with most of the larger Si model units from Humminbird. The 899ci HD Si was shipped with the XNT-9-Si-180-T Compact Side imaging (or CSi) transducer to keep the cost of the overall product down, but many opt to exchange the CSi transducer with the HDSi transducer in order to get better detail in the 455kHz Si sonar and so they can use the 800kHz Si sonar.