Trade-A-Boat – April 2018

seatrials

Single M9.8B and F9.9 on 3.6m 1988 Sea Al Super Skua tinny, swinging 9.5-inch and 8.5-

inch props and pushing 285kg and 300kg respectively. Average of two-way runs on

Lake Macquarie, NSW, in calm water. Range is in nautical miles from 12lt plastic remote

fuel tanks with a 10% reserve.

ENGINE M9.8B F9.9

TROLLING 940rpm 900rpm

KTS 2 1.9

LT/H 0.7 0.3

RANGE 30 68

PLANE RPM 4400 4500

KTS 13.4 12.8

LT/H 3.5 2.9

RANGE 41 47

CRUISE RPM 4700 5000

KTS 14.4 15

LT/H 3.6 3.1

RANGE 43 52

WOT RPM 5700 6100

KTS 19.2 19.5

LT/H 5.3 4.2

RANGE 39 50

“Loop” of cruising with 10% WOT and 40% trolling operation averaging 8kts

LT/H 2.5 1.8

RANGE 34 48

Tohatsu M9.8B

versus Yamaha F9.9S MHB

THE BEST PERFORMING IN THEIR CLASS...

R

eleased on the

Aussie market

in 1997 and

uprated from its

M8B counterpart

introduced a decade earlier,

the M9.8B is one of Tohatsu’s

most popular outboards.

It’s light for output but has

tonnes of grunt with top-end

performance that leaves

the M8B for dead. It still

operates on a 50:1 premix

after the first 10 hours on

25:1.

The power head has

thermostatically-controlled

water cooling and

mechanical ignition timing

advance. The transom

brackets are virtually

identical to the M5B, but

the much larger leg design

for efficient exhaust gas

scavenging meant it could

only be steered 130 degrees

instead of 360. Also the

cooling water intakes were

relocated above the gear case

torpedo for easy attachment

of flushing muffs, while the

zinc anode doubled as a trim

tab to reduce steering load.

Power head access is

excellent and servicing

intervals are every 50 hours

or annually after the first

10 hours. The recreational

usage warranty is three

years.

The F9.9 is a “stroked”

version of its F8C

counterpart (now both

engines use the same power

head) and leaves its four-

stroke competition for dead.

The counterflow engine

has so much grunt that it

actually outperforms the

M9.8B despite weighing a

whopping 54 per cent more.

Though having a belt-driven

camshaft, the four-valve

engine is a non-interference

type where the valves won’t

contact the piston crowns i

the belt breaks. Electronic

ignition timing advance

is fitted and the ignition

module includes a rev limit

set at 6200. Across its entire

rpm range the F9.9 vibrates

less than the M9.8B and is

way quieter at or near WOT

And the upfront gear shift

makes operating the F9.9 so

much easier than the M9.8B

However, the transom

bracket from the two-

stroke Yamaha F15 is a bit

archaic with only four trim

positions and two shallow-

water drive settings. But

at least the intakes for the

thermostatically-controlled

water cooling are above the

gear case torpedo so flushin

muffs can be quickly

connected.

Power head access is

excellent and servicing

intervals are every 100 hour

or annually after the first 20

hours. The camshaft belt ha

a designed lifespan of 800 t

1000 running hours.

The recreational usage

warranty is four years.

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34 tradeaboat.com.au