Re: Does 2inches above bottom make difference for Trim Tabs?
MyDogMax;
Moving the Plate end of the actuator from hole 5 to 3 or 1 or 2 or 4 will not (normal installation assumed) change the deployed angle of the tab plate. What will change the angle is the Top Transom bracket where the actuator mounts to the transom. Moving this up or down will move the plate up or down. At the plate end of the actuator (holes 1 through 5) is an adjustment for pressure (resistance). The more pressure required to bring the plate up to horizontal, the more stern lift. This is not as critical at slow speeds as it is at cruising speeds and above. Keep in mind that the Smart Tabs (unlike hydraulic or electric) are always under pressure like a compressed spring. The right amount of pressure (downward force) helps control the ride and handling of the boat, and eliminates porpoising. Too much pressure will lift the stern too much when cruising (or at high speeds) and drive the bow down. This causes bow steering (sensitivity to left and right steering), reduced speed at the top end, and of course a loss of fuel economy. In fact this is very common when hydrofoils are used because the stern lift constantly increases as the speed of the boat increases since the foil is rigid and not adjustable.
Moving the actuator from one hole (exp. # 3) to another (exp. #1) allow you to fine tune the system to your specific boat. Once you are getting the results you want, your done.
What you want to achieve is proper controlled balance.
Example 1: If the boat porpoises when cruising (with the motored trimmed to vertical/out) then move from hole #3 to Hole #4 fro example.
Example 2: If the top speed of the boat is less than it was before the tabs were installed, then move from hole #3 to Hole #2.
In the first case (example 1) hole #3 was not resistant enough to eliminate the porpoising so we increased the resistance / stern lift to hold the bow down a bit more.
In the second example (#2) the resistance (stern lift) was too much and even with the motor trimmed out, the bow was forced down too much and cause a loss of top speed (sometimes refereed to as drag).
Remember the most efficient position for the prop is vertical or perpendicular to the water surface. When cruising, tilting the prop one way or the other only makes the prop slip. Therefore the best economy, and performance is when the trim tabs take care of the boat attitude, and the prop simply propels.
The single best advantage for using trim tabs is that you are adjusting the hull design to suite the sea conditions as they occur. The hull dictates the ride, handling, stability, and efficiency of the boat, not the motor.
The adjsutments that you made should put you very close to what you are looking for. Just go try it now!
