Seakeeper Sizing and Performance

It’s easy to watch videos and see the difference between a boat’s side-to-side roll when the Seakeeper is unlocked (on or stabilizing) and locked (off or not stabilizing). But is that real? How do we determine 80% roll reduction vs. 95% roll reduction? Is there more that goes into it?


Let’s go way back to Seakeeper’s beginnings. We had all these same questions. We had to find a way to measure performance that was consistent and accurate while also making predictions about future installations. Of course, that didn’t exist – so we built it. Our proprietary sizing program is how we’re able to provide accurate performance predictions. It’s how we know which unit, or a combination of units, will achieve the highest stabilization. And it’s how you can be sure your days of rolling on the water are long gone.

This is where our Applications Engineers come in. They’re the experts in Seakeeper sizing, and we bring them in when there’s a new or more complicated installation. Using our sizing program, they consider the length at waterline (LWL), beam at waterline (BWL), vessel displacement, and transverse metacentric height (GMt) to select different Seakeeper units or a combination of units to compare. The program estimates the roll reduction performance of the Seakeeper(s) as a function of uncontrolled roll amplitude at the vessel’s resonant, or natural, roll period in zero-speed beam seas. This represents a worst-case scenario for roll motion. We use roll amplitude because different combinations of wave height and wave period can produce similar roll responses in a given vessel, so by looking at the uncontrolled roll motion, we can provide the most accurate results in any sea condition and make the best recommendation for proper stabilization.

If your boat is less than 37 ft. though, those same engineers have an easier solution that you can do yourself! Using years of Performance Predictions, Sea Trial results and sizing data, they built the Small Boat Sizing Guide which allows you to enter your boat’s length overall and beam overall and receive sizing recommendations. You can compare the performance of our DC models (Seakeeper 1, Seakeeper 2, and Seakeeper 3) and get a better understanding of how each will perform in different sea conditions. Try it out!


The proper Seakeeper sizing above is what can guarantee high performance. An undersized Seakeeper configuration won’t come close to achieving the 95% roll reduction numbers we like to see, so we only recommend installations that are going to “wow” you when you step onboard, and we’ve got the results to prove it! Using our Sea Trial Mobile App, performance is recorded for 10 minutes with the Seakeeper off and 10 minutes with it on. It then calculates the roll reduction percentage based on the reduction at the boat’s natural roll period. Depending on the sea conditions, roll reduction percentages can vary, but will always impress you. Generally, the roll reduction percentage for any given boat will decrease as wave height increases.

If you want to see some of those results, check out our Sea Trial page. From there, you can narrow your results down by boat brand, boat size, Seakeeper model, wave height, and performance. If your particular brand/model isn’t listed, there are other comparable installations for which you can find reports. 

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