Amaroq 40: The British Diesel Two-Stroke Going to Coniston

A 697cc British diesel outboard will run the measured kilometre on Coniston Water this week, on the back of an inflatable race catamaran rather than the patrol boats and tenders it was built for.

The engine is the Amaroq 40, made by Amaroq Ltd in West Sussex. It goes to the 54th Coniston Powerboat Record Week, Monday 2 to Friday 6 November, with Team Endeavour Racing UK, the community interest company that puts wounded, injured and sick service personnel and veterans into powerboat racing.

Driver Aaron Hilton and co-pilot Lisa Johnston, both Army veterans, will share the boat. It is an Aquarius ProCat, and the engine goes on through one of the team’s own modified racing gearboxes.

Almost every diesel outboard on sale solves the weight problem by spending money on it. The Amaroq solves it by changing the cycle.

It is a three-cylinder two-stroke running compression ignition, 697cc from a 68mm bore and 64mm stroke, rated at 40hp (30kW) at 5,500rpm with 65Nm at 4,000rpm.

A diesel that behaves like a petrol two-stroke

Induction is crankcase scavenged through reed valves and lubrication is oil injection on TC-W3, exactly as a petrol two-stroke does it. Fuelling is common rail direct injection, and heater plugs handle cold starting and low load, after which compression alone does the work. Compression is around 15:1, low for a diesel. Dry weight is 80kg on the manual trim and tilt model.

The 5,500rpm ceiling is the part that matters most to the engineering. A conventional four-stroke diesel outboard makes its power low down and loads the gearcase accordingly, which is why diesel outboards usually need a drive leg designed for them. Amaroq’s engine spins close to petrol outboard speeds, so it could take an off-the-shelf leg, from the Tohatsu 50hp two-stroke.

The catalogue gearing is 1.85:1 or 2.08:1 through a mechanical dog clutch, with a three-blade propeller of 7in to 15in pitch and the exhaust through the hub. For a measured kilometre that is not what anyone wants, which is where Team Endeavour’s own gearbox comes in, and with it propeller choice, weight distribution and whether the whole package holds together for a run.

It runs on BS EN590 diesel and meets the NATO single fuel and SOLAS directives, which is the whole commercial case: no petrol on a ship or a forward operating base, and one fuel for the vessel and its tender. Amaroq has built the engine for government, defence and commercial operators, not for racing.

What a record would and would not be

Record Week is not racing. Competitors book individual runs down a measured kilometre on Coniston Water, organised by Windermere Motor Boat Racing Club under British Power Boat Association and Circuit Powerboat Association rules, with world records governed by the UIM. A standing record has to be beaten by at least 0.3 per cent to fall.

Diesel outboards have been down that kilometre before. Cox Marine took the fastest diesel outboard world and British records there with a 300hp CXO300, 62.84 mph in 2022 and 67.95 mph in 2023, Adam Brown driving on both. So the first diesel outboard record is long gone. What has not been done, on the team’s account, is a diesel on an Aquarius, in a corner of the sport where petrol two-strokes have never had a reason to look over their shoulder.

The Crew

Aaron Hilton drives. He spent ten years in the British Army, including tours of Iraq and Afghanistan, before a medical discharge.

He now works in the fire safety team at Hampshire and Isle of Wight Healthcare NHS Foundation Trust.

He joined Team Endeavour Racing in 2018 and is part of its management team.

Lisa Johnston is co-pilot. She joined the Royal Army Medical Corps in 2001 and served 17 years as a combat medical technician, in Germany, the Falkland Islands, Egypt, Iraq and Kuwait.

A training injury in 2014 led to complex regional pain syndrome.

In June 2016 her left leg was amputated above the knee.

Eligibility of the configuration

There is a paperwork problem in front of the engineering one. Team Endeavour says its ambition at Coniston is to establish the eligibility of the configuration and then pursue a recognised record, subject to technical approval and classification. In other words the class has to exist, or be agreed, before the clock means anything. Plenty of record weeks have turned on less.

Writing about the attempt, Hilton said:

There will be no guarantees, no shortcuts and no easy route to success. Only preparation, teamwork and belief.

Amaroq lists the 40 as available to order, with the engine still in test on the water and in its own test cells. A 225hp outboard and a 30hp have both been talked about. It is a small company in Southwick going up against Yanmar, Cox and Caudwell Marine, and a week on Coniston in November will say more about the 40 than another trade stand.