Boat Accessories

Interceptors – What Are They & Do I Need Them?

Is it worth replacing those traditional trim tabs with interceptors?

Trim tabs are a much-appreciated piece of gear on just about any boat. But, has their time come to an end? In recent years some boaters have instead been opting for interceptors—and most people who have them sing their praises to no end. So, exactly what are interceptors, and do they really do a better job of leveling out the ride?

trim tabs
Trim tabs do a great job of leveling out a boat’s ride and have long been considered critical equipment on powerboats.

Trim Tab Basics

Anyone reading this right now probably has a grasp of how trim tabs work already, but just to be sure everyone’s on the same page: these metal plates extend behind or are recessed under the transom, and they can be manipulated to swing up and down via a switch at the helm. When deployed they create an upward force on the stern as the boat moves through the water. One can be lowered more or less on either side of the boat to laterally even out the boat’s attitude, or both can be deployed to push the stern of the boat up and the bow down to control longitudinal attitude.

Trim tabs work great, but they don’t come without a cost. First off, there’s, well, cost to consider. Aftermarket trim tabs aren’t cheap, and when a boat is built with recessed trim tabs the manufacturer has incurred a cost to design them in and create a more complex mold. Then, there’s maintenance and mechanical failure to consider. Trim tabs do fail from time to time, and when one gets stuck in the down position it can make for an incredibly long and difficult ride home with a constant list, a spray-throwing running attitude, or some other undesirable running characteristic you suddenly can’t fix. Trim tabs also increase a boat’s drag through the water, reducing efficiency a bit.

Zipwake interceptors
Interceptors replace tabs with a blade that slides up and down behind the transom.

The Scoop on Interceptors

Interceptors replace trim tabs completely. Rather than having plates oriented to swing down, they have thin housings attached to the back of the transom with blades inside. The blades come down out of the housing to deploy vertically just below the bottom of the boat. It seems counter-intuitive at first that these blades would be any more efficient than trim tabs, but since they deploy vertically a much smaller surface area can create much more lift. And the difference is major: there’s about one inch of travel for interceptors, versus six inches for trim tabs.

This simple graphic created by Zipwake, an interceptor manufacturer, makes it easy to visualize the difference between interceptors and trim tabs.

Their smaller size gives interceptors one more big advantage over trim tabs: they can do their thing much more quickly. In fact, while it takes the average trim tab five or six seconds to move throughout their range, interceptors can fully deploy in about 1.5 seconds. And this speed gives interceptors a critical advantage: the ability to adjust up and down individually from side to side, counteracting the effects of pitch and roll.

Of course, you and I wouldn’t have the brainpower nor the attention span to constantly work a control pad and counter the effect of each and every wave a boat hits while traveling at 30 or 40 mph. Fortunately, a computerized brain does. Interceptors can harness a dynamic trim control system integrating the blades themselves with gyroscopic and accelerometer sensors, GPS, a control head, and a distribution unit that controls the blade’s action. Voila: you press a button to activate the system, and as the boat moves through the water the blades shoot down and pop up on the port and starboard sides to reduce lateral roll underway, to the tune of over 30-percent. And that’s not based on any interceptor manufacturer’s marketing materials – we took out a boat with a Zipwakes Dynamic Trim Control system installed and measured pitch and roll with the system on and off at varying speeds, in varying conditions, for ourselves.

Surprisingly, the reduction in motion does extend all the way down to trolling speeds (moving at six knots, for our test). Added bonus: since interceptors don’t have sharp metal edges sticking out behind the boat as trim tabs do, they also eliminate a common chaff-point that can result in lost fish.

zipwake performance
Deployed at trolling speeds, interceptors still have a surprisingly significant impact on a boat’s side-to-side motion.

Tabs Versus Interceptors

Of course, everything on a boat requires making some trade-offs and this is true for interceptors, too. One of their biggest weaknesses is that boats which travel at speeds in excess of 60 mph simply can’t take advantage of them, because the force of the water against the blades at speeds like this can cause damage. Very large boats (over 60-feet or so) will also have issues with many of the mass-produced systems, which simply aren’t built in large enough sizes (a handful of custom options do exist). And then there’s the cost to consider. While rigging with interceptors doesn’t cost anything like equipping a boat with other types of dynamic stabilizers (read: gyroscopic stabilization), they do commonly cost more than regular trim tabs and may cost twice as much or even a bit more than that in some cases.

Zipwake diagram
As one would expect the added complexity of a dynamic trim system does increase cost over that of standard trim tabs. Graphic courtesy of Zipwake.

On the flip side of the cost equation, running with interceptors can also help save you money in the long run by boosting efficiency and lowering fuel costs. Just how much of a difference they’ll make will vary from boat to boat and sea condition to sea condition, but five- to 10-percent increases in fuel efficiency have been reported after interceptor systems have been added on to boats in the 30- to 40-foot range.

So back to the original question: do you need interceptors on your boat? Of course not. Nor do you “need” trim tabs. But they certainly do help make for a more comfortable, fuel-efficient ride. And if you do put interceptors on your transom, they’ll out-comfort and out-efficient those trim tabs by a wide margin.

More about Zipwakes on BD Outdoors.

Lenny Rudow
Lenny Rudow …has been a writer and editor in the marine field for over two decades, and has authored seven books. He is currently the Angler in Chie...