An outboard motor with 350 hp: this was once unthinkable, because such power was only achieved by large-volume inboards. Today, you can easily hang such an engine on your transom, and what's more, you are spoilt for choice.
The 350 hp class is the highest in which there is more than one manufacturer. What's more, Mercury has only recently overhauled its engine. For us, this was the perfect opportunity to pit the revamped Verado 350 against Yamaha's largest outboard, the F350.
Motors in this performance class are attached to RIBs and sports boats in the 8 to 10 metre category. In our case, we were able to secure two identically equipped Axopar 28 AC, a Finnish plastic boat (overall length: 9.01 m, width: 2.85 m, weight: 1790 kg without engine) with a licence for up to 8 people and an extra-long outboard engine up to a maximum of 350 hp. The Axopar 28 AC can be used on waters with a significant wave height of up to 2 metres (CE category C).
The hull has a 22° canting angle and a two-stage design (Airsteps) so that everything can be driven comfortably. A 260-litre built-in fuel tank is installed at the shipyard. We completed the test drives on the Moselle near Traben-Trarbach, the company headquarters including harbour and boat filling station of Boote Polch. Owner Patric Polch provided us with the boats and installed the engines with his workshop team.
Motor concepts
Both the Mercury Verado 350 and the Yamaha F350 are four-stroke engines. However, the former is an in-line six-cylinder engine with a displacement of 2.6 litres and supercharging. The Japanese, on the other hand, generates its power with eight cylinders arranged in a V-shape as a naturally aspirated engine. In order to convert the same amount of fuel-air mixture, it has more than double the displacement (5.3 litres).
In order to fill this well, the engineers gave the engine two cylinder heads with four-valve technology and two overhead camshafts per bank. In addition, an intake camshaft adjustment ensures smooth engine running at low revs and better gas exchange in the cylinders at high revs.
At Mercury, the revised, now water-cooled compressor optimises the forced ventilation of the six cylinders. As a result, the Verado manages with significantly less displacement. To further cool the pre-compressed air, it also has a water charge air cooler, which, like the rest of the engine, works via single-circuit cooling. To prevent salt and corrosion deposits in the cooling system, the inside of the Verado's engine is coated. Yamaha continues to use sacrificial anodes in the exhaust manifolds as corrosion protection for the aluminium engine.
Steering and gearstick
A special feature of the Verado is the electro-hydraulic power steering. It consists of an electronic steering wheel unit, a servo pump and a hydraulic steering cylinder integrated in the bracket. The advantage of this system (drive by wire 2.0): Only cables need to be laid during installation between the helm station and the stern; in addition, a joystick system can be retrofitted relatively easily in the case of dual motorisation using the components installed ex-shipyard.
The Yamaha F350 is not supplied with steering as standard; it is best to use a servo-assisted hydraulic steering system from the accessories catalogue. The advantage here is that the existing steering system can be used if the engine is changed due to a defect or an increase in power (except for the system on the Verado models). An electronic gearstick including engine display is standard on both Mercury and Yamaha. Both are ergonomic and easy to operate. All relevant engine data is shown on the monitors; the display can also be configured.
Service friendliness
The engine oil level should be checked most frequently on a four-stroke engine. Accordingly, it should be easy to remove the bonnet from the stern or the bathing platform while on the water in order to access the dipstick and, if necessary, the oil filler cap. The Mercury's two-part canopy is easy to remove thanks to the central locking system. The dipstick is also quite easy to reach. However, the position of the oil filler cap on the Yamaha F350 is more skipper-friendly. On the other hand, the triple locking mechanism of the canopy makes it quite awkward to remove.
Assembly and propeller selection
So that the engine manufacturers can ensure that their engine is matched as closely as possible to the test boat, we invite the manufacturers' technicians to every test. They determine the mounting height and decide which propellers should be used. Both Mercury and Yamaha have opted for the lowest position.
The propeller chosen for the F350 was a four-blade stainless steel model from the Saltwater XL series (dimensions: 15 3/8" x 22"). This placed the full-load speed at the upper end of the factory-recommended range (5000 to 6000 rpm). The Mercury technician fitted a Revolution 4 stainless steel propeller, also with four blades (14 5/8" x 21"). We reached the lower end of the recommended range (5800 to 6400 rpm) at full load with the test load of two people plus 260 litres of fuel.
Measurement data
The results of our outboard motor test show how economical and quiet the two engines really are. The Mercury can capitalise on the advantage of its small displacement in terms of fuel consumption, especially at low speeds (10 km/h and 20 km/h). The Yamaha with its eight cylinders and 5.3 litre displacement is at a disadvantage here. Expressed in figures: with the F350, you can travel 464 km at 10 km/h on a full tank of petrol, and 201 km at 20 km/h. With the Mercury, you can cover 541 km and 210 km respectively at the same speeds until the tank is empty. From 30 km/h up to top speed, the Yamaha is consistently more economical - by 2 to 11% depending on the speed.
In terms of noise development, the Mercury Verado performs better. It is either quieter or at most as loud as the competitor from Japan across almost all measurement ranges. In contrast, the V8 from Yamaha secured more points in terms of top speed and liveliness. With a measured top speed of 94.3 km/h, it was a full 3.2 km/h faster, and when accelerating from a standstill to 40 km/h, 50 km/h and 70 km/h, it clearly won both the first and third rankings. In the sprint from 0 to 50 km/h, both engines were almost on a par.
Conclusion
In our outboard comparison, the Mercury Verado 350 proves to be the quieter and more favourable representative of the two engines tested. The bonnet and steering system make it user-friendly, and it is also more economical at lower speeds. In the medium and high speed range, on the other hand, the Yamaha F350 is consistently better in terms of fuel consumption, but you have to accept a slightly higher noise level. Another point in the Japanese motorbike's favour is its faster acceleration from a standstill to 40 km/h and 70 km/h.
