Onan Gensets

Unquestionably, Onan is the most respected name in marine gensets.

It has more than 60 years' manufacturing experience, gained by supplying units to organisations such as the US Coast Guard and Navy.

Onan is backed by Cummins and the Cummins/Onan network is the largest worldwide certified distributor/dealer network in the marine industry.

The range comprises eight 240V models for the Australian market - from 5.5-22.5kW at 50Hz and 6.5-27.5kW at 60Hz.

If more power is needed to run non-frequency sensitive appliances such as lights, it's just a matter of flicking the switch and the revs leap 20% and 60Hz frequency is produced.

All models are powered by indirect-injection diesels, with glowplug pre-heat and Positive Crankcase Ventilation to eliminate engineroom contamination.  The heat exchanger cooling systems have coolant overflow tanks to reduce the need for frequent top-ups.

Most of the engines used are Kubota-based, a plus for owners as reasonably-priced spares are readily available throughout the world.

The two smallest diesels (Kubotas) are rated at 3000-3600rpm, while the others develop their rated outputs at 1500-1800rpm.

The higher-speed 5.5-6.5kW MDKUB and 8-10kW MDKWB gensets come standard with Onan's 'Sound Shield' noise reduction system which is protected against saltwater corrosion by electro-deposition paint.

At 1m, the sound level for both is 69 dB(A) at 50Hz and 71 at 60Hz respectively.
Even the smallest model in the Onan range - the MDKUB - has an impressive range of standard features.  It has a maximum frequency variation of 5% (from no load to full load) and voltage regulation of only +/- 1.5% so that frequency-sensitive items such as TVs, VCRs and microwave ovens can be used without damage.

There are AC and DC (12V for battery charging) circuit-breakers and an automatic engine shutdown facility for high engine coolant and exhaust temperatures and low oil pressure.

The alternator is cooled by a blower on the armature shaft.

The twin-cylinder 479cc engine can develop 11.7hp (8.7kW) at 3000rpm and 12.5hp (9.3kW) at 3600rpm, so in this genset it's completely understressed.

There's a running-time meter for accurate recording of operating time between service intervals, a fuel/water separator, electric fuel pump for lifting fuel up to 1.22m from the main boat tank, spin-on type oil filter and gear-driven seawater cooling pump.

The large oil capacity of 3.8lt effectively reduces sludging between oil/filter changes, and the engine and alternator are designed to operate continuously in ambient (air) temperatures up to 80°C and seawater temperatures up to 37.8°C.  This allows them to function in tropical climates without performance drop-off.

The engine can also operate without lubricating oil starvation at 20° of heel continuously and 30° intermittently.

Options include oil level access from the sound shield roof panel, remote start/stop switch, full engine instrumentation panel, ship-to-shore selector switch and a full cruise kit.
This includes maintenance components such as oil and fuel filters, seawater pump impellers, zinc anode pencils for the heat exchanger and an alternator belt, all in a neat plastic container.

At 50Hz the MDKUB consumes 1.4lt/hr on half load and 2.1 on full load, while at 60Hz the consumptions are 1.7 and 2.7lt/hr (still very reasonable compared to an equivalent petrol genset).  It measures 710mm long, 553mm wide and 596mm high.  The dry weight is 173kg.

The MDKWB is powered by a three-cylinder 719cc engine that has a 4.8lt sump (larger than the 1.6lt Honda Accord car engine!).  It consumes 0.5-0.8lt/hr at 50Hz and 0.7-1 at 60Hz, measures 817mm long, 553mm wide and 596mm high.
The dry weight is 204kg.

The lower-revving gensets are generally quieter and can handle being operated at half load or less without detriment.

From my experience of owning a Dunlite industrial genset for almost 19 years and professionally testing units for the past 14, running an engine at 3000rpm on less than half load for extended periods doesn't do it much good.

But at 1500rpm, it can be operated for these same periods on as little as one-quarter load without harm.  And in auto-startup installations, there's less engine wear as the engine has to reach what are only 'fast idle' revs for many small marine diesels.

The 1500-1800rpm Onans don't come standard with a sound shield but when fitted with one, the smallest of these - the 7-9kW MDKAL ? has a noise level of 66 dB(A) at 50Hz and 69 at 60Hz.

It has the same features as the MDKUB/MDKWB, but is also available with a three-phase alternator instead of the standard single phase unit which has four poles instead of two and has a 300% short circuit current capability.

The brushless design eliminates the need to check and/or replace brushes about every 500 operating hours as in the case of the MDKUB/MDKWB.  And at +/- 1%, the voltage regulation is also better.

The three-cylinder 1124cc engine can develop 13.8hp (10.3kW) at 1500rpm and 17.2hp (12.8kW) at 1800rpm and won't overload in this application.

It can also operate continuously at the same ambient and seawater temperatures and heeling angles as the MDKUB/MDKWB.  At half load on 50Hz, the MDKAL consumes the same amount of fuel as the MDKUB.  At full load, the consumption is 2.7lt/hr and at 60Hz 1.8 and 3.2lt/hr respectively.  With the optional sound shield, the MDKAL measures 915mm long, 568mm wide and 596mm high.  The dry weight is 277kg.

Top-of-the-line is the MDKAF, powered by an understressed five-cylinder 2746cc Kubota diesel, which in turbocharged Nannidiesel form, develops 85hp (63kW) and locally powers the planing-hulled Arvor 20 cruiser.

In naturally aspirated form, it develops a maximum of 38.3hp (28.6kW) at 1500rpm and 46hp (34.3kW) at 1800rpm.

The diesel has a massive 12.3lt sump (about twice the capacity of automotive diesels this size) to reduce sludging between oil/filter changes.

Though a 12V starting system is standard, a 24V system may be fitted which would give better cold-start performance through a lower percentage of voltage drop.  The engine is also available with a front PTO and 12-24V electric clutch for running auxiliary equipment.

The MDKAF has the same alternator and standard-equipment features as the MDKAL and can operate continuously under the same ambient and seawater temperature and heeling conditions.

The optional sound shield reduces noise levels at 1m to 69 dB(A) at 50Hz and 72 dB(A) at 60Hz.

At 50Hz, the MDKAF consumes 3.4lt/hr on one-quarter load, 4.9 on half, 6.4 on three-quarters and 8 on full load, while at 60Hz the consumptions are 3.8, 5.7, 7.6 and 9.5lt/hr respectively.  With sound shield it measures 1355mm long, 602mm wide and 796mm high.  The dry weight is 533kg.

All Onan gensets comply with CARB (California Air Resources Board) and US EPA exhaust emission regulations and come with a five-year limited warranty. 

For more information on the range, contact Mike Jones at Cummins/Dunlite, tel +61 8 8346 3832.