We ( boastser and myself) are in fact talking about the "automatic" ones made by Nauticus in the states( www.nauticusinc.com)-
i fitted them becasue I could never get a decent trim on the boat- and its simple to see why. I have 29' of boat with 420 kgs sitting on the back and a cabin in the middle. the total weight of the boat is 2300 kgs- there is no way that you can trim that out to give you a decent ride- with the engines alone. The engine trim area is miniscule
Fitting automatic trim tabs -they adjust themselves whilst moving ,serves two purposes
- it lifts the stern up
- at a certain speed they cease to act as lift and become stablizers. Drag does not seem to come into it
Its like a Boeing - these are the identical to the horizontal stablizer and act in exactly the same way - but havnt seen a Boeing on the water yet???????