Higher power for faster steaming
MAN’s 6-cylinder 860mm bore engine on trials at Augsburg
The Motor Ship, March 1963, as in previous months, continued to focus on large-bore high-power diesel engines.
50 years ago, ‘large bore’ was mostly in the 840mm to 900mm range, so not a lot smaller than today’s large engines. However, power outputs still lagged some way behind. A new size of MAN engine, the KZ86/160C was a step up from its predecessor in a whole 20mm of bore size, retaining the 1600mm stroke (and many of the major basic components), but specific output had risen from 1,800bhp to 1,900bhp/cylinder. The company, at the same time, announced that shop trials of a 900mm bore x 1,700mm stroke engine had proved satisfactory so it was now prepared to accept orders for a 930mm bore version of that unit, which would offer outputs up to 2,500bhp/cylinder.
Engines, and power outputs, were certainly growing. This was to a large extent being driven by the quest for speed. Cargo liners, in particular, were entering a form of race, and The Motor Ship announced that several European shipyards had been invited to tender for two 30,000bhp, 10,000dwt twin-screw vessels for Union Castle, which would operate on the regular mail service between the UK and South Africa, at a service speed of 22.5 knots.
It is interesting to note this trend, particularly in the light of today’s move to slower steaming and smaller engines. Our editorial predecessors noted how speeds of ships on liner service had risen sharply to that level from a norm of around 17 knots. No mention of extra fuel consumption was made then, but the opinion column compared the 18,000bhp needed to push an 11,000gt ship at 20 knots with the 30,000bhp which was specified for the 12,000gt 22.5 knot Union Castle newbuilds, and noted the vast increase in building costs needed to gain that extra 2.5 knots. The column pointed out that in many of these cases it was prestige rather than just quicker voyage times that was at stake, with many of the orders for ‘super-fast’ ships attracting generous government subsidies.
With such scant regard apparently being paid to fuel costs, it was interesting to note that several owners had been experimenting with running smaller auxiliary diesels on the same heavy fuel oil (referred to in those days as ‘boiler oil’) as the main engines. The result of one such programme, by Elder Dempster Lines, was the subject of a lengthy article. Although distillate fuel was used for starting and stopping, so the changeover was not a complete fuel switch, the results had proved encouraging. The first attempts resulted in excessive deposits in the combustion chamber, particularly on the valves, this being alleviated by modifications to the injectors and the timing. Another problem was that lube oil filters rapidly became clogged – this was eventually solved by adopting centrifugal cleaning rather than paper filters.
Once the engines were running satisfactorily on HFO the trial was extended, and after 8,300h running on heavy fuel an internal examination on one of the engines showed it to be in good condition. Some scale was found on the liners, which was easily removed, and there was a small amount of carbon on the piston crowns, otherwise the moving parts had survived well. The only problem was fouling in the exhaust valve cages, put down to over-lubrication.
A fuel cost saving of nearly £500 per year was said to be possible by using HFO – this is partly offset by the need to use a higher grade crankcase lube oil and the cost of modifying the engine to burn the heavier fuel, but these costs should easily be covered by the savings, said the article.