REVIEW: YAMAHA 15F

By: Andrew Norton

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  • Trade-A-Boat

No peers for performance and fuel efficiency...

REVIEW: YAMAHA 15F
Yamaha 15F

When Yamaha Motor Australia lent me a 15F back in 1996, it was the beginning of a beautiful friendship. The combination of a well-balanced power head, excellent fuel efficiency and relatively low pollution on its 100:1 fuel/oil mix won me over from the start.

Released to the Oz market in 1995, the 15F replaced the 15D that was immensely popular among commercial net fishermen on Lake Macquarie, NSW, from the time it was introduced in 1983. The 100:1 fuel/oil mix reduced operating costs, as did the loop-charged power head that used up to 20 per cent less fuel than the US-made competition. When idling the 15D would tick over with scarcely any vibration yet had plenty of grunt to push the 5.5m round bilge semi-planing Asquith LFB that was popular at the time.

I owned an Asquith for three years and the loan 15D had Yamaha’s clever dual-thrust prop that not only effectively transformed engine torque to thrust at the prop but also gave incredible stopping power compared to standard through-hub exhaust props. On the easily-driven Asquith the 15D would cruise all day at 10-11kts with the engine using 3lt/h while pushing a total of 600kg.

Yamaha took that wonderful power head and fitted it in an outboard that was specifically designed to compete with the US competition. Features such as the unique cold-start system and upfront gear shift also made the 15F much nicer to use on a daily basis than the 15D. And a fold-up carry handle simplified lugging the engine around when taking it to a dealer for servicing. The rounded cowl and engine pan actually made the 15F look smaller than the angular 15D even though overall dimensions were similar.

THE NITTY GRITTY

Along with its de-rated 9.9 counterpart, the 15F is Yamaha’s smallest displacement twin-cylinder loop-charged power head and features an easily replaced thermostat plus the ability to fit oversize pistons and rings after reboring the cylinders.

A dry exhaust relief effectively baffles noise making the 15F the quietest two-stroke 15 available.

Mechanical ignition timing advance linkages connect directly with the cold-start system and a multi-position choke knob. Pull the knob one stop and the choke butterfly valve flap is partially closed. Stop two advances the ignition slightly, while stop three also opens the throttle. The result is positive cold starting without the complication of a fuel primer that can be prone to blockages.

A bowl-type fuel filter makes filter cleaning easy, while spark plug access is excellent. However the four-position trim adjustment is a little archaic, but at least there are two shallow-water drive settings. A strut support system is used for the full tilt lock and steering, and throttle friction adjusters are fitted. A 12V 80W alternator is fitted with provision for connecting to a rectifier for battery charging, though as the output is unregulated a battery of at least 40amp/h should be used to prevent "frying" on long runs to and from a favourite fishing spot.

The break-in period is 10 hours on 25:1 before switching to the normal 100:1.

Servicing intervals are every 100 hours or annually after the first 20 hours or three months. Regular maintenance is easy with one example being the handpump for the gear oil that attaches to a Yamalube oil container. Simply screw in the pump nozzle to the oil drain hole, pump until fresh lube dribbles from the oil vent hole, screw in the vent plug, remove the fill nozzle and screw in the drain plug. Quick and easy.

A relatively large-capacity zinc anode is flush-fitted under the anti-ventilation plate and doesn’t interfere with water flow around the lower unit. The recreational-warranty is three years.

ON THE WATER

The loan 15F was used on only one hull over the eight years I tested it and was a perfect match for my 1988 3.6m Sea Al Super Skua tinny. Swinging the standard 10.5in pitch alloy prop it provided as much power as I ever needed with excellent cruising speeds and fuel efficiency. As expected of a loop-charged twin, vibration levels trolling were fairly high but not too much to remove a lot of arm flab, while noise levels were reasonable up to  5000rpm.

Carefully run-in according to Yamaha’s recommendations using standard (91 RON) unleaded and Yamalube 2 oil, the loan 15F never let my partner of 12 years Susan or me down on the many explorations we took on Lake Macquarie. Even during driving rain and spray (how she ever tolerated me for so long is a mystery) the snug-fitting cowl with aft-facing air intake never let water reach the power head.

The cold-start system worked flawlessly summer or winter and the engine always warmed quickly from cold. Starting hot or cold required just a firm one-hand pull. Oddly, after 15 minutes or more of trolling the engine emitted oil smoke, even on 100:1, but throughout testing the plugs remained clean.

Over eight years of testing, three new waterpump impellers and one thermostat were fitted, I know not in accordance with Yamaha’s recommendations but this amount of maintenance seemed to do the job. However, I learned the hard way from one cooling passage blockage due to excess oil in the flushing water never to use a drum with a two-stroke 15 but only muffs or rabbit ears to ensure clean water is always circulated through the passages. No more blockages after that mistake.

Reluctantly, because my back was causing more pain from lifting the 15F from storage trolley to transom, I sold the engine, which was bought by the first person who saw it for the price asked. No doubt about Yamahas, they have excellent resale value.

THE WRAP

Selling the 15F was hard and of all the fifteens I’ve tested over the years the 15F is still my favourite!

SEA TRIALS

Single 15F on 1988 3.6m Sea Al Super Skua, swinging 10.5in prop and pushing a total of 295kg. Average of two-way runs on Lake Macquarie. Range is in nautical miles with a 10 per cent reserve from the 24lt plastic tote tank, rounded to the nearest whole number.

THROTTLE OPERNING/RPM SPEED (KTS) FUEL BURN (LT/H) RANGE (NM)
Trolling/850 2.5 0.6 90
Plane/half/3500 12.5 3.2 84
Cruise/two thirds/4000 14.9 3.6 89
Fast cruise/three-quarters/5000 19.7 4.9 87
WOT/6100 24.9 7.2 75

*"Loop" of cruising with 10 per cent WOT operation and averaging 8kts returned a fuel burn of 2.7lt/h and a range of 64nm.

SPECIFICATIONS

TYPE Loop-charged twin-cylinder two-stroke outboard

RATED BHP/MHP* 14.7/15 at 5000rpm

WOT RPM RANGE 4500 to 5500

DISPLACEMENT 246cc

BORE X STROKE 56 x 50mm

GEAR RATIO 2.08:1

WEIGHT 36kg dry, short shaft

RRP $2500

OEDA STARS 1

*Brake horsepower/metric horsepower or PS

Check out the full review in issue #502 of Trade-a-Boat magazine. Subscribe today for all the latest boat news, reviews and travel inspiration.

 


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