Cruising Helmsman – June 2017

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Legend

enlarged

Cruising Helmsman June 2017

SAME FOOTPRINT,

MORE TORQUE. YANMAR’S OLD FAVOURITE

SCORES IN SO MANY WAYS.

PRACTICAL

ENGINES

THE most amount of time I have

spent with Yanmars in yachts was

when I helped a mate deliver his Lagoon 38

catamaran.

Theo had taken delivery of the 38 from

the French factory and sailed it across the

Atlantic and Pacific Oceans via the Panama

Canal. Already the twin 3YM30 sail drives

had clocked up around 1000 hours each

with the only fault being a leaking exhaust

manifold on one of the engines.

A couple of things really impressed me,

one was how quiet and smooth running

the engines were and the other the ability

of the Gori folding overdrive props to keep

the engines running in the maximum

efficiency zone and preventing cylinder

bore glazing from insufficient load.

For example, driving through 2.64:1

reduction ratios and swinging 16.5 inch by

12 inch three-bladed props which, with the

overdrive setting on increased pitch to 14

inches, pushed the 8.5 tonne displacement

38 into 15 to 25 knot head winds with a 1.5

metre swell. Our GPS showed speed over

the ground of six knots at 2500rpm using

2.1 litres per hour each.

Increasing the revs to 2700 returned

6.5kts SOG using 2.9lph, which seemed to

be the best offshore cruising revs.

In calm water with the overdrive on at

3000 revs., the SOG was 7.2kts using 4.0lph.

But to reach wide open throttle (WOT)

we set the overdrive off and at 3700 revs.

averaged 8.3kts using 7.2lph.

As with any cruising yacht it is always

better to slightly under prop diesels so,

under normal loading, it can slightly

exceed the designed WOT revs, in this case

3600. My belly f lab was in no fear of being
      reduced with these engines.
      Cleverly, Yanmar has taken the
      3YM30 concept and morphed it into the
      3YM30AE. Still an industrial tractor base
      engine that has the same footprint, so
      existing engine bearers can be used.
      Even though the new engine has a 14 per
      cent larger piston and develops the same
      amount of power at 3200 revs., it weighs
      only three per cent more. Torque is up 14%
      on the old engine too and at lower revs.

JUST THE FACTS

Yanmar has mated the new engine with a

new sail drive the SD25, though it still has

a dog clutch so rapid shifting is out.

However the new leg does have cooling

water intakes at the aft end where they are

less likely to be clogged by weed.

If you are repowering a cat like the

Lagoon 38, coarser pitch props may be

needed to absorb the increased torque and,

of course power, because the maximum

output is being developed at 400 fewer

revs. Fuel consumption at WOT is slightly

higher but that is to be expected because it

is a more powerful engine.

This engine would also be a good shaft

drive repower choice for the Sparkman

and Stephens 34 and similarly sized fin

keel yachts. Or more than ample power,

say, for a Nicholson 32 in high tidal areas.

The KM2P-1 mechanical gearbox for

shaft drive remains and that is good. The

KM2P-1 has a choice of 2.21:1 or 2.62:1

ratios ahead and a 3.06:1 ratio astern.

What this means is, when going astern

where engine loads are greater than going

ahead as the prop bites into cleaner, less

aerated water at an angle that tries to drag

the stern down, the deeper reduction ratio

allows the engine to reach its torque band

faster for quicker stopping. This deeper astern

reduction eases engine stress when stopping

heavy displacement cruising yachts too.

With the standard 2.21:1 ahead ratio

translating to an efficient 1450 prop revs,

engaging astern brings the revs down

to only 1050 for real stopping power.

ANDREW NORTON