How to lock Mercury outboard steering in straight position for sailboat

I am planning to acquire a Mercury Prokicker 15hp with remote control for a sailboat. I will control shift, throttle and ignition from the remote control handle. However, since a sailboat has a rudder to control direction, I don't need to install any steering cable on the outboard. My issue is that the outboard with no steering cable will just be free to turn in any direction. Is there a Mercury product or way to lock the steering of an outboard into the straight position?

Thanks for your help.

On some smaller outboards, years ago, the transom bracket to engine midsection swivel connection had a tensioner screw, usually on the Port side of the engine centered between the top and bottom of the transom bracket, on the mid section casting.

If you have such, then you may be successful in accomplishing your goal with it. The purpose was such that the "Tiller Operator" could turn loose of the tiller handle and the prop thrust wouldn't turn the (rear of the) engine all the way to the starboard side of it's allowable movement. Tightening the screw meant that hand operation of the tiller had more resistance to the "feel", but stayed where it ws put when one's hand was removed.