The B164 (bronze) comes in 12 & 20 deg offset to suit your deadrise. The zero degree offset units are not in production yet. Nor is the SS164 which is stainless. I am waiting for the SS 164 in zero degree offset but am using a 600W for now. Picking up bottom perfectly up to around 24 knots with trace echoes & depth up to 33 knots.
Check the Airmar site for more info.