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Sink or swim: Precise patent language scuttles infringement lawsuit

Generally, using precise and careful language in a patent application is wise. But providing a precise numerical value can work against a patentee when it comes time to bring an infringement claim. A boat manufacturer learned this lesson the hard way when it sued a rival for infringement.

Boat maker makes waves

Cobalt Boats, LLC, owns a patent on a swim step — a small platform attached to the stern of a boat, with a retractable step that makes it easier to get in and out of the water. Brunswick Corporation sells boats with an optional swim step. Cobalt sued Brunswick, alleging patent infringement.

A jury found that Brunswick had indeed infringed the patent and awarded a per-unit royalty of $2,500, equaling $2.69 million. The district court enhanced the jury’s award and awarded damages for postverdict sales, resulting in total damages of almost $5.4 million. It also granted a permanent injunction against Brunswick. Not surprisingly, Brunswick appealed to the U.S. Court of Appeals for the Federal Circuit, which hears all patent-related appeals.

Patent language springs a leak

The patent included a claim limitation (which defines the breadth of the claimed invention) that the court referred to as “the 180-degree limitation.” It specified that the swim step was capable of being rotated 180 degrees from its stored position to its deployed position.

Brunswick argued that the claim limitation required that the step be capable of rotating at least 180 degrees. In other words, a swim step that can rotate at most 179 degrees couldn’t infringe the patent, but one that can rotate 181 degrees could. Cobalt contended the limitation meant “about 180 degrees.”

The appellate court landed on Brunswick’s side regarding the proper interpretation of the limitation. It emphasized that the patent claim said “180 degrees,” not “about 180 degrees.” “Where a precise value is included in the claim without a term such as ‘about,’” the court explained, “we interpret the claim language as imposing a strict numerical boundary,” absent evidence to the contrary.

The court noted that the limitation was added during prosecution of the patent application to distinguish existing patented swim steps that rotated less than 180 degrees. (See “Doctrine of equivalents can’t save the patent.”) Cobalt claimed the limitation was added simply to require flipping of the swim step, which could include rotation by less than 180 degrees. The court pointed out, though, that other added claim terms already required flipping.

The Federal Circuit dismissed the testimony of Cobalt’s expert that the limitation shouldn’t be interpreted as a precise numerical boundary because manufacturing variances would make it impossible to achieve such precision. It found that its interpretation of the limitation didn’t require the swim step to rotate exactly 180 degrees; the interpretation required only that the step be capable of rotating at least 180 degrees, allowing for variance above that threshold.

Court casts off infringement claim

Having determined how to interpret the limitation, the appellate court reviewed the jury’s finding of literal infringement. It was undisputed that Brunswick’s swim step wasn’t capable of rotating 180 degrees. The maximum rotation was between 172 and 179 degrees; the hinges on the step had a “very rigid stop” that prevented any rotation beyond that. Cobalt’s own expert testified that the Brunswick step’s rotation was within a couple tenths of a degree of 177.

The court concluded that there was no evidence supporting the jury’s finding of literal infringement. It ultimately reversed the trial court’s judgment, concluding that Brunswick was entitled to judgment as a matter of law of no infringement.

Chart your course carefully

The court’s ruling in this case provides another clear example of the importance of the language you use when drafting a patent application. Patentees that include a precise number in a claim limitation should understand that courts will interpret it as imposing a stringent boundary — beyond which infringement is impossible.

Cobalt Boats, LLC v. Brunswick Corp., No. 18-1376, May 31, 2019, Fed. Cir.

The patentee in Cobalt Boats, LLC v. Brunswick Corp. (see main article) also argued that the doctrine of equivalents supported a finding of infringement. The doctrine allows a patentee to claim insubstantial alterations that weren’t captured when drafting the original patent claim but which could be created through trivial changes.

But a patentee can’t use litigation to regain patent protection it relinquished during the prosecution of the patent application. The 180-degree limitation at issue here was added during prosecution to distinguish the invention from an existing patent for a 90-degree step.

Cobalt claimed it had only surrendered what was necessary to distinguish the earlier patent, but the U.S. Court of Appeals for the Federal Circuit found that it had disclaimed all steps that can’t rotate at least 180 degrees. It explained that the scope of disclaimer is the difference between the original and amended claims — not between the amended claims and the distinguished prior art. In particular, the court said, when claims are amended to include a specific numerical boundary, the patentee can’t later recapture what’s beyond that boundary through the doctrine of equivalents.


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