The first step in any kind of design is to clearly define the problem. Some questions would be: How fast does it need to move up and down? How rigidly does it need to be supported when up (against rocking of the boat, pushing buttons on the device, etc.)? Do you need a fail-safe to get it up or down if the mechanism fails? What about water intrusion and its effect on the components? Corrosion is likely to be a problem, especially if you're on salt water. Is there room for mechanism below, or on the sides, or both? Is there a magnetic compass nearby (could be affected by electromagnetic fields of the motors, or steel components)? Have other people done this before? If so, how? If not, why not? Next, break down the mechanism into separate functions: Linear guiding Driving up and down End stops Once you have clearly defined the problem, the solution often becomes obvious. The suggestion of a car window actuator and gas springs (gas spring to lift it slowly, perhaps a small motor winch to pull it down) are good ones. A scissors mechanism is good when you need it to be very compact when collapsed, but linear bearings alongside or below, while less compact, are much more rigid and smoother operating.