As we have seen in previous articles, the application of trim tabs is particularly useful to any boat. They improve hole shot, boat’s attitude and handling, making the ride more stable and comfortable in choppy seas.
However, in order to get the maximum from their use we should choose the appropriate size for our boat and install it in the right way.
The choice of trim tabs
The choice of undersized trim tabs will have insufficient results and they should be trimmed down more to achieve sufficient lift of the stern. We must bear in mind that the larger the trim tabs, the greater lift they will produce with their smallest exposure in the water, creating the least drag. Therefore, the larger the trim tabs, the greater their performance gets.
A quite useful guide could be: for every 1 meter of boat length about 4 cm length of trim tabs is required.
In cases the length of trim tabs in the market is less than the one our boat needs we can choose the wider available.
Installing trim tabs
The proper placement of trim tabs will provide the maximum performance. So we need to be as accurate as possible in our measurements:
- Regarding their mounting height on the transom, their leading edge should be 1 cm higher from its bottom. Their trailing edge must be even higher as the water that flows out from the bottom of the transom is rising up and it should not hit the back part of trim tabs when they are in their highest position (unless for some particular reason we prefer them to be fully parallel with the hull so as to participate permanently in the ride even when they are not trimmed down).
- The farther they will be mounted from the centreline of the transom the more effectively they will operate, they will correct more the boat listing to the port or starboard while they will not disturb the water flow to our propeller. The distance of the inner edge of trim tabs from the centreline of the transom should be greater than 20 centimetres.
- The outer edge of trim tabs should be in a distance of about 8-10cm from the chine of the hull.
The matter of how much higher the trailing edge of trim tabs will be it depends of course on their length. On trim tabs with a length of 20cm, 30cm or 40cm their trailing edge should be higher by 1cm, 2cm or 3cm respectively, related to their leading edge.
And of course, they should be installed symmetrically otherwise they would affect the weighing of the ride when they operate together.
After having installed the trim tabs it would be necessary to operate them for a few minutes. We trim down the tabs to their maximum down angle and after 20 seconds we raise them to the maximum up angle. We repeat that quite many times. Thus, apart from the control of their correct operation, we also ensure the removal of air from the interior of the entire hydraulic system.