Mercury working on three-speed, twin-prop outboard engines

The US inboard and outboard engine maker stunned the world earlier this year when it revealed its all-new 600hp Verado V12 would feature a two-speed gearbox, allowing its users to get the best performance from the engine at low and high speeds.

However, filings submitted to the US Patents and Trademarks office shows Mercury Marine hasn’t stopped there, looking at how it can get more performance out of other members of its high-powered engine range as well.

The solution? Add up to three forward gears to the engine, and by-pass neutral in between the changes to keep the flow of torque constant.

However, rather than locating the gears in the lower gearbox, Mercury plans to use a smaller gearbox located just under the engine.

“In certain configurations, particularly within the space of outboard motors and also those having steerable gearcases, is further advantageous for the input and output of the transmission to be coaxial, further lending itself to reduced space and a denser general architecture,” Mercury’s filing to the USPTO reads.

“Additionally, the present inventors have identified that it would further be beneficial to have an architecture providing easy access to change the overall reduction of the drive system for various vessels and/or engine combinations, as well as speed ranges (for example racing versus standard production, single propeller versus dual propeller, fast boats versus slow boats, and/or the like).”

Mercury’s idea for the gearbox is to use three separate one-way clutches linked to torque-transferring helical gearsets. The first is used for reverse and forward, while the other two are dedicated to the progressively higher gears.

The first gear can be set up specifically for low-speed trolling, leaving the second and third gears for low- and high-rev (overrun) applications.

Mercury has designed the helical gears so that there is no interruption to the flow of torque through to the propeller when they are engaged.

Significantly, with Mercury’s patent filing showing the outline of a 400hp inline six-cylinder Verado engine – but wearing a twin-propeller system. This hints that the technology developed initially for the big V12 is likely to soon flow down into other high-performance members of the outboard engine range.

The engine is also shown using a conventional tilt and trim mount, quite different from the rigid mount used for the high-power V12.

The reason behind adding more gears appears to be an attempt to fill the torque holes that normally aspirated engines tend to have low down in the engine’s performance range.

Adding a three-speed gearbox will help engines gain more performance at low speeds, help with holeshot performance – one of the most fuel-hungry phases of an outboard engine’s performance demands – and also allow the boat to cruise more efficiently.

It also looks as though the Mercury V12’s innovative lower gearbox steering system is making its way lower down the outboard engine performance range, with Mercury saying the lower gearcase is “steerable” in this design.

Mercury's 600hp Verado V12 has a wider steering arc than a conventional outboard engine, meaning any other outboard engine to adopt the technology will have a similar boost to manoeuvrability.

Mercury’s patent was filed early last month. The company has been asked for comment.