Those are the "old style" rudder castings. Those castings were notorious for not kicking up properly when hitting the bottom. You have to make sure that the roller pin & hook are well lubricated with grease and that you don't put too much preload on the cam spring. There is a fair amount of discussion about those castings on the Hobie 18 forum at the Hobie website. If the rudders don't kick up, you will either crack out the lower casting, rip the gudgeons out of the transom, or break the rudder pin.

Also, those look like old lexan rudder blades. They may not be up to the task of handling the load of a 21 foot cruising cat, especially if they've sat out in the sun for many years. Those blades have been known to snap off just below the casting. A composite rudder may be a better choice (it will certainly provide better performance).

Just a couple things to consider.

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