They added one to my NT because the guy who built it new rafted up a lot and hung out in the water alot. They put it right above the water line, it works great you would have to try to get into the props, it adds protection to the boat, but the best thing is since it's right on the water you don't need a ladder to get in. NT has done it many times since at first I tought adding a platform to a boat with a built in one already would look funny but as long as it's done right they look good.
Since you don't have any I would build a nice rounded one that is about 3 feet out in the middle and 2.5 on the ends, that way as wide as your boat is people could swim up to the middle without danger of the props. and still be able to see them when getting into the water and you will be able to see the props when you dont want to get in the water. I have seen people jump onto sharpe clever props with nice soft wet skin it aint pretty.