Released locally five years ago, the F25 has a counterbalancing piston ahead of the crankshaft, which is designed to cancel out harmonic vibration from the big twin-cylinder powerhead. It also has a single carburettor with accelerator pump that eliminates the need for careful balancing of multiple units using vacuum gauges.

And like its direct Tohatsu MFS 25A competition it has a PTC (Positive Temperature Control) heater system that acts like an automatic choke and eliminates the guesswork in knowing how much choke to use on a cold motor.

The usual four-stroke engine protection features such as rev limiter and automatic rev reduction, should the engine overheat or suffer low oil pressure/level, are fitted.

The manual start F25 is fitted with automatic decompression that raises the exhaust valves slightly during initial cranking and tiller steer models have an upfront gearshift.

Unusually for a four-stroke 25, the F25 is available only with a 'Bigfoot' lower unit, whereas the MFS 25A and Honda BF25 are available in just standard ratio versions.

Testing I've conducted on 'Bigfoot' lower unit four-strokes has shown that on smaller tinnies the increased gearcase size and prop diameter can seriously affect the top end performance on tinnies due to the lower unit drag. For example, a Merc F15 Bigfoot had disappointing upper-rev range performance on a 3.8m tinnie and knocked 6-7kmh off the top speed, although it did have very good hole-shot acceleration for a four-stroke 15.

But despite having the same gear ratio, the demo F25 was particularly throttle-responsive across its entire rev range and averaged a much higher Wide Open Throttle (WOT) speed than anticipated.

Early F25 models had a choke sensor inadequately shielded from powerhead heatsink, so that the choke sensor cooled faster than the powerhead when the engine was switched off. When the engine was re-started after 10-15 minutes the choke valve closed and flooded the still-hot engine. This created difficult hot starting for many customers.

But the manual start model I tested a while back on a Quintrex 385 Explorer Eclipse appeared to have none of these problems. With just a firm two-hand tug on the overhead recoil starter, it started easily hot or cold and warmed quickly from cold. Providing the antiventilation plate was kept immersed, power astern was good and no cooling water starvation occurred. No oil smoke appeared at any time.

Unfortunately, there was insufficient time to connect a tacho to record revs, but like the Tohatsu MFS 25A, the trolling revs seemed too high for serious freshwater anglers. Pushing a total of 480kg, including two adults, the minimum trolling speed was 3.9kmh consuming 0.5lt/hr. And although relatively smooth for a big twin, both noise and vibration levels were higher than the three-cylinder Honda and Tohatsu competition.

The Merc planed us cleanly at 20.6kmh with my passenger sitting on the forward casting platform to help trim this stern-heavy rig. At WOT the F25 averaged 43.2kmh using 9.5lt/h, and through tight figures of eight at WOT there was no prop ventilation. But perhaps the throttle friction had not been tightened sufficiently because the Merc proved very difficult to keep at steady revs for any length of time.

At WOT noise and vibration levels were higher than the Honda and Tohatsu 25s but still pleasantly low for a big twin.

Undercowl access is good and the oil dipstick, filler and spin-on oil filter are easily reached. Mercury Marine recommends servicing the F25 every 50 hours or six months after the first 20 hours, and the waterpump impeller should be replaced every 100 hours or once a year. However, I recommend changing the oil and filter every 50 hours or six months regardless of how few hours are clocked up during this period. The servicing charges below include a six-monthly service, but the oil and filter may be changed by owners, saving about $90 a year.

Torquey, throttle-responsive and fuel efficient, the F25 is a great motor for anglers who fish saltwater more frequently than fresh.