As I am going onto a plane I adjust the trim tabs until I am running as level as possible once at cruising speed. Some boats don't require actual trim tab usage unless you are adjusting for excessive wind/current/waves or everyone sitting on one side of the boat, for example. However, I find that our R-25 requires trim tab adjustment on every run. If you don't use enough trim tab you are not able to get on a proper plane. If you use too much then you become a plow. In either case you use a lot more fuel and your engine works a lot harder. I have found you need to use more trim tab if the boat is fully loaded, going into the wind, or in shallow water (I don't know if the shallow water issue is unique to the set up of the Ranger but running in less the 4 feet it makes a big difference). When you are going slow they really make no difference so I bring them all the way up by just holding the buttons for a minute or so. If it is quiet you can hear the change in the whine of the trim tab pump when it reaches the extremities. All the way down is rare. Usually I find myself only putting them all the way down when we have a full load of passengers. If you have a fuel flow gauge you can usually tell when your trim tabs are adjusted properly because fuel usage will be the lowest. Also RPMs will be the highest because, when properly trimmed, the boat can move through the water more easily.
