How Trim Tabs Change the Game

Trim tabs can radically change the way your boat runs – if you use them properly.

You want your boat to run on an even keel? You want to get the bow down or the stern up? You want your boat to run more efficiently or to stay on plane at a slower speed? These are all things that trim tabs can help with. And while that’s been the case for as long as there have been trim tabs, today’s modern versions can do a whole lot more.

All About Angles

Most seasoned boaters already know what trim tabs are, so we’ll keep this brief. But just so we’re all on the same page: Trim tabs are adjustable appendages used to control both longitudinal and lateral trim, or running angle, of a vehicle. We say vehicle instead of boat because submarines, helicopters, and airplanes have trim tabs, too.

Historically, trim tabs on boats are flat plates of metal attached to the transom or mounted in pockets where they’re even with the hull bottom. At the flip of a switch, the skipper can lower both (to control longitudinal trim) or one (to control lateral trim). But as happens so often in the tech age, this way of looking at trim tabs isn’t merely historic – it’s fast becoming ancient history. The latest trim-taming systems use sensors, computers, and vertical blades or rotary paddles to accomplish the same task in a vastly superior manner. More on these later, but for the moment, let’s stick with traditional trim tabs because these are the ones most commonly found on boats today.

How To Use Trim Tabs

To affect longitudinal trim, both tabs should be activated at once. Lowering them will force the stern up and bring the bow down on a modern powerboat that’s on plane (at preplaning speeds, tabs have little to no effect). But the operator should be careful not to lower the bow too much, or the boat might bow-steer and potentially stuff a wave. Generally speaking, lowering the tabs until the boat is running level or with a slight bow-up attitude produces the best ride. Boaters who have a relatively modern power plant with fuel consumption data at the helm can maximize efficiency by watching the gauges and tweaking the tabs’ positions slightly until they find the best mpg for the rpm setting. Remember, the ideal setting can and will change depending on load, sea state, and speed.

When a boat is heavily loaded or underpowered and has trouble getting on plane, lowering the tabs all the way can help push the bow down and “get over the hump.” On most boats keeping the tabs down will also allow you to continue planing at slightly lower speeds than usual. A boat that falls off of plane at 16 mph, for example, might be able to stay on plane at 14 mph with the tabs deployed, which can come in handy when pounding waves make an uncomfortable ride. But note that tabs can’t be used to raise the bow, only to lower it. On boats with trimmable drives, you may be able to raise the drive unit to push the stern down and get the bow higher. But once the tabs are raised above the hull’s lowest point they don’t have any effect.

To adjust lateral trim, before even touching the tabs you’ll want to make sure the boat’s load is reasonably level and the boat isn’t listing unusually due to an abnormal situation. If it is, slow down and adjust the load first. Assuming it isn’t, once on plane you’ll want to lower the tab on the side of the boat that’s higher until that side starts coming down and the boat evens out. But it’s very easy to apply too much tab if you hold down that switch; it’s best to use small incremental adjustments and give the boat a second or two to settle between each adjustment.

When running with the wind on the beam, you can also use lateral trim to reduce the spray sent back into the cockpit by lowering the downwind side of the boat a bit and raising the upwind side. Naturally, you won’t want to do this too much, especially if there are significant waves. But in a slight chop it can make the difference between taking a pleasant cruise and getting soaked to the skin.

There’s one overriding imperative to keep in mind as you run any boat equipped with trim tabs: If you don’t play around with them, you’ll never even know just how comfortable or efficient your boat can be. Many people ignore those tabs and simply accept that their boats are pounding because it’s rough out, when a slight adjustment might reduce the intensity of those bumps by 5%, 10%, or even more. They assume their boats will never get better than 3.5 mpg even though a click or two on those tabs might gain another tenth of a mpg. A good operator will try different settings and, when conditions change, start trying new ones to maintain the ideal trim.

Trim Tech Triumph

All that stuff we just talked about might make trim tabs seem awesome. And they are. But today the traditional type is vastly overshadowed by systems that have come onto the market in recent years. These are often called “Dynamic Trim Control” or “Vessel Attitude Control” systems, but at their core they work on the same basic principles as trim tabs.

While the tech among different systems does vary a bit, the concept behind these systems is the same: Arm the boat with sensors, software, and a digital brain, and hand trim control over to an automaton. It constantly senses the motion of the boat and adjusts far more rapidly than a human could ever hope, not only keeping the boat on a level plane but even accounting for and reacting to the sudden changes in pitch and roll caused by hitting waves.

The net result? While there’s variation from hull to hull and condition to condition, the latest of these systems, the Seakeeper Ride, reduces pitch and roll when underway by a shocking 45% to 70%, according to the manufacturer. We’ve experienced it and were left slack-jawed by the immense difference you feel at the helm. Cruising through 2- to 3-foot seas up to 30 mph when the system was activated allowed us to relax our grip on the grab rails and stop using our legs as shock-absorbers. When it was deactivated, we suddenly felt like we were on a smaller boat going twice as fast through larger seas. Our internal comfort-o-meter felt like it made the ride at least 50% smoother.

The trick here is in the speed of the system. Some sensors can take up to 1,000 measurements per second, and the computer brain can “think” fast enough to make up to 100 physical adjustments per second. In the case of the Ride system, those physical adjustments can include movement of their rotary actuators of almost a foot in a single second. Some other systems depend on Interceptors (blades that travel vertically up and down from housings on the transom) to make the physical adjustments, and these can deploy in a fraction of a second, according to the manufacturer.

With these systems the ride is smoother and the seas feel calmer. The boat no longer leans over when someone moves from port to starboard. It can put itself at the most efficient cruising angle. Hole shot is improved and bow rise coming onto plane is reduced. Maybe the best – and worst – part: It takes zero skill to operate these systems. Essentially all you do is press a button. (Operator attention and skill are still important and necessary.)

A more significant potential downside is system failure, which is possible with anything reliant on software. Of course, failure is also possible with anything reliant on hardware – it isn’t unheard of for an old-school trim tab to get stuck in the down position and make the cruise home a little lopsided. In any case where a trim system gets wonky with a tab or blade deployed, remember, in most cases you can unscrew and remove an actuator arm or a housing as a get-home measure. That’s one skill everyone should have, because whether you’re pressing the buttons or a computer is doing the job for you, sometimes being able to eliminate trim tabs from the equation is just as important as knowing how to use them.