The shim is a simple attachment between the Wakesurf Sharper and a boat’s hull. Every hull shape is different – some are mostly flat and don’t require a shim. Others have a step hull and require a 1″ shim – other boats have a more pronounced step and need a 2″ shim, while in some cases you might need both shims to make a 3″ gap between the hull and your Wakesurf Sharper. For installation – Eight.3 recommend the Wakesurf Sharper is 80% subgmerged when boat is properly weighted and as close to the stern as you hull will allow.