Talking Torque: Affordable Re-Power

Westerbeke's 12D makes good economic sense.

One of the best known Aus cruising yachts of the seventies is the Compass 28, of which 400 were built from 1970 to 1981. This full keel yacht displaced 3.25 tonnes and normally had a 331cc Yanmar 8 diesel auxiliary as standard with the option of a 510cc Yanmar 12.

Although both were wonderfully reliable engines, they were heavy for their outputs and their single cylinders really took the edge off relaxed motoring!

Trouble is, spending well over $10K for a new diesel auxiliary alone means that new owners over-capitalise on their investments. Add new stern gear and controls and the total comes close to $30K, a lot for a 40 plus year old yacht of this size. Owners would have to use their boats constantly and for years into the future to re-coup the investment.

This is where Westerbeke's 12D comes in. Not only is it very well priced, but it is substantially lighter than both Yanmars. Having twin cylinders, vibration levels are well down on the old singles, while maximum torque is normally produced lower in the rpm range, better for boat handling in tight marinas.

IN THE DETAILS

As with its more powerful counterparts in the yacht auxiliary range from 12–38hp, the 12D has indirect injection with swirl pre-combustion chambers, cold start glow plugs and a 23:1 compression ratio. Unusually though the engine is over square, with a bigger cylinder bore dimension than piston stroke. This reduces piston speeds and piston ring wear.

The Mitsubishi-based engine has an overhead valve design with gear-driven camshaft and push rods actuating the rockers to the four valves is a time-proven design. Unusually for a small diesel the valves rotate slightly during operation which cleans the valve seats and ensures even wear for a long service life.

The biggest difference between the 12D and the Yanmar engines is the standard heat exchanger cooling, which enables the engine to run hotter and at more constant temperatures. Running an engine at 80–90 degrees ensures less condensation in the oil sump than when an engine runs at around 60 degrees, virtually the limit for raw (sea) water cooled engines to prevent rapid accumulation of salt crystals in the cooling passages. The condensation, a result of the combustion process and the temperature difference between the hot cylinders and relatively cold cooling water passages, finds its way past the piston rings and down into the sump, diluting lubricating oil.

Also the 12D has a cast aluminium exhaust manifold that's fresh water cooled. Aluminium exhaust manifolds cool faster than cast iron and help scavenge exhaust gases from the combustion chambers. Not only is the manifold lighter than a cast iron unit but should the cooling system leak then only fresh water can enter the combustion chambers, which also applies to the cylinder head gasket. If this fails in raw water engines, salt water can directly enter the combustion chambers, rapidly etching the cylinder walls and piston rings. 

Really the only issue of heat exchanger cooling is the added complication of having a fresh water circulating pump and an expansion tank for the hot water. But the pump and 50A voltage regulated alternator are run from a v-belt driven by the crankshaft while the raw water pump is gear driven from the camshaft as it would be in a raw water cooled engine, so heat exchanger cooling is really no more complex than an automotive engine having a radiator and fan. The alternator is mounted just below the top of the expansion tank and even the starter motor is located well up the cylinder block, away from any possible bilge water. 

Westerbeke recommends using a starting battery of at least 125cca capacity, well within the capability of a normal 40Ah automotive battery. A marine battery would be better but automotive batteries of this capacity retail for around $110 and with regular charging last at least three years, so in my opinion are better value in the long run.

The cooling system capacity of 2.7L is good for an engine of the 12D's displacement and should easily handle operation in tropical climates.

Similarly the oil sump capacity of 2.4L is comparable to some automotive engines displacing 900cc. The deep sump allows for static installation angles of up to 14 degrees and heeling angles to 25 degrees so the engine can be run when the yacht is heeled over while motor sailing. Westerbeke doesn't mention its preferred sump oil viscosity in its tech specs but I suggest using a diesel-specific SAE 15W40 oil in temperate climates and SAE 10W30 in cold conditions (such as when cruising the Southern Ocean) and changing the engine oil and filter every 100 running hours or annually. The canister oil filter is mounted horizontally and won't dribble oil down the cylinder block when being replaced.

Complete with a mechanical gearbox having a 2.05:1 reduction ratio, the 12D is 638mm long (including the forward engine mounting feet), 483mm wide and 518mm high. The old Yanmar 8, which developed 7.9bhp at 3200rpm, measured 637 x 498 x 607mm, while the 11.8bhp (at 3000rpm) 12 was 620 x 570 x 678mm, so the 12D is way more compact. The smaller dimensions allow for better servicing access around the engine, particularly atop it, while the dry weight of 102kg is way less than the 114kg for the 8 and 137kg for the 12.

The 8 produced a maximum torque output of 20 Newton Metres at 2500rpm, while the 12's output was 30NM at similar rpm.

Westerbeke doesn't supply an instrument panel as standard with the 12D but offers two optional units, the latter of which I'd opt for if funds allowed. The ‘Captain’ panel includes an analogue tachometer with digital hour meter inset, plus warning lights and alarms for low oil pressure, engine overheat, battery charging failure and water in fuel, whereas the ‘Admiral’ panel has gauges for these functions. Also optional is a fuel/water separator, which is a must.

THE WRAP

Now for the really good part. Complete with gearbox the 12D retails for AUD$7,800, which is excellent value for a 12hp twin cylinder diesel. Even with an instrument panel and new stern gear there'll be plenty of change left over for a Compass 28 from $30K to set up a seaworthy yacht for coastal cruising. And flab retention from having less vibration is so useful for providing ballast to windward under sail!

Alternatively, the 12D would make a great re-power engine for the old 4.9 metre Savage Dolphin hull or any displacement-hulled launch to six metres.

For more on the 12D, call Marine Energy Systems on (07) 5502 7771 or visit sales@marineenergy.com.au 

QUICK SPECS

Engine type Twin cylinder indirect injection diesel

Rated output 12.1bhp/12.2mhp at 3000rpm*

Maximum torque 31N, 2200–2400rpm

Piston displacement 630cc

Bore x stroke 76 x 70mm

Dry weight w/box 102kg

*Brake horsepower/metric horsepower or PS