locked Engine Room Exhaust Fan / Blower - lessons learnt #lessons

David Vogel

One thing to keep an eye on, is the 220VAC engine room exhaust fan.

This unit sits in series with a 24VDC exhaust fan, which runs when the service (12V) alternator for the main engine is creating output.

The 220VAC exhaust fan runs when the ONAN GenSet is outputting 220V AC.

I recently discovered a failing capacitor on the 220V exhaust fan, revealed by intermittent running – the worst kind of fault, as it is not always obvious you have a problem. Sometimes the fan would run, sometimes not. I only recognised that I first had an issue when I walked past the deck-level exhaust outlet one day while the genset was running, and I didn’t have the usual plume of warm air blowing past my leg. With the genset running and the fan not, the fan could usually be encouraged to spin up if hand-started – useful to know, as I wasn’t anywhere near any kind of shop at the time, didn’t have a spare capacitor on-board, and with no other cruisers either within an island to two to check whether they had a spare on board.

Back in civilisation, capacitor quickly sourced at less than USD15- equivalent, and 10 minutes to wire it in. Problem solved.

But now I wonder about a few other failures I have experienced over recent years. And whether they might be related to the intermittent exhaust fan, which may have been failing for some time longer than I suspected. For example, the prolonged heat-soak of elevated temperatures in the engine room (measured up to and occasionally exceeding 50ºC whilst in the tropics), may have been a contributory factor to …

+ failure of the nitrile seals on the fuel-tank inspection hatches – portably due for replacement anyway, in light of other’s experiences with these at ~ 15 years of age, but is there something more going on here than simple chemical or age-related deterioration;

+ failure of some of the adhesive for the engine room foam sound insulation (top only, not sides);

+ premature failure (3 yrs) of ceramic water-maker membranes – one was cracked; these membranes are rated to 40ºC, but what happens if they are hot-hot-hot, and colder sea-water is pushed through them, perhaps resulting in thermal-shock-cooling;

+ early failure of the water-maker membrane pressure-vessel end-caps: this was due to erosion of the black delrin material around the stainless-steel bobbin (inter-connector). I wonder if differential heating/cooling of the delrin end-caps versus stainless steel, allowed a seeping of the HP-water past the O-rings, which then compromised the seal, creating leakage, leading to corrosion/erosion. Thinking along the lines of the space-shuttle Solid-Rocket-Boosters here, less violent, and over a greater time-frame, but the result is kind of the same. Perhaps not usually a problem when the engine-room temperature is held within normal range, but excessive temperature differentials creates a problem. Anyway, no–one wants HP salt-water spraying over the inverter, battery-chargers, switch-boxes, or other electronic or electrical components situated nearby. (Note: Dessalator is no longer issuing INOX interconnectors; replacements are now plastic.)

+ premature failure of water-maker HP hoses, running near-by to the genset, and showing signs of early degradation at the highest point they run in the engine room (external sheath falling apart, weeping) - after only 18-months installed;

+ early failure in the manual bulge-pump diaphragm – I could never could understand why this should fail after only 18-months, but maybe this too now makes sense;

+ failing seals on the salt-water supply pumps for the heads – portably age-relater, but … ;

+ failure of the ONAN Genset Main Control Board, a component known to fail, but was elevated engine-room temperature over a prolonged period a contributory factor?

There is no confirmed cause-and-effect relationship for any of these, but there does appear to be a pattern here, so food for thought.

In any event, I now mindfully check that there is warm air blowing out of the engine-room fresh-air exhaust outlet. Not every start, but whenever I happen to be on-deck when the genset (or engine) is running. I now also routinely check that the engine room blower is providing a healthy quantity of fresh air.

I am also considering:

+ installing an engine room temperature sensor & alarm (relatively easy to put onto the N2K bus, I hope); and

+ installing a timer circuit for the DC exhaust fan, to maintain air movement through the engine room immediately after machinery shut-down, in order to reduce residual temperatures and consequent heat-soak.

SM#396, Perigee
Savusavu, Fiji

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