Welcome yflyer!
A good tip when entering the pen, is that when trying to reach a complete stop, you can right click on your CE 3d image to man his station, and handle the engines telegraph by yourself, hence being able to change the RPM's a lot faster.
And of course, as said before, getting into the pen at anything = or below 3 knots with your engines dead would be fine.
I don't know if you're dockin astern or head-on but if going backwards, be specially careful when giving out rudder orders!
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