bilbobaggins
N/A
I'll tell this tale against me, as I learned quite a lot from it
Bumbling along, motorsailing, some 15 miles off the North Cornish coast recently, after a night of humungous electric storms which took out all the Coastguard VHF antennae, apparently, I was writing up some logbook stuff when I became aware simultaneously of a stench of burning rubber/plastic and grey-white smoke squirting out of the engine-space box. ‘Engine fire’ came to mind, the lump was shut down PDQ, and I assembled in the cockpit equally PDQ, while calling on my companion to bring some lifejackets and the handheld VHF as he joined me.
We failed to make contact with Falmouth MRCC by VHF/GMDSS. The signs and symptoms of engine fire faded away slowly, and we determined to wait an hour for ‘cooling’, as neither of us was in a hurry to open the engine box. Eventually we had a chat to MRCC Falmouth via mobile phone ( ! ), opened the lid gingerly, and discovered the melted plastic Vetus exhaust gas/water mixer bottle had burned through and melted, damaging an adjacent rubber exhaust pipe. This had happened several times – plastic bag over the water inlet, seaweed ditto – and indicated an waterpump impeller failure. That was confirmed by re-starting the engine briefly and noting ‘no water flow’ through the clear lid of the raw water strainer…. So far, textbook stuff.
The next bit of textbook stuff involved removing the waterpump impeller coverplate. While the pump body was fairly visible through a maze of piping mounted on the side of the engine, the coverplate faced away – of course – and getting a screwdriver in would be ‘challenging’. So would retaining the 6 slot-head screws when they came loose.
Managed that. Managed also to waggle a small mirror such that I could get a view into the chamber, and a small torch gave just enough light to see that the impeller fins all looked intact when poked awkwardly with the point of a slot-head screwdriver. Equally so when the axial driveshaft was rotated by hand, using the pulley. Curious…..
So I reassembled the thing, and tried again. Still no water. We primed the pipes with water poured in; still nothing. Puzzled and beaten for the moment, we settled down to sailing the old Rival down past the Longships, around Lanzen and the Runnel Stone, and in the dying light breeze along into Newlyn. Next morning, we tried again, with a new Vetus bottle and replacement exhaust pipe fitted.
This time, I removed the old impeller; the fins were intact, but the metal core had ‘debonded’ from the outer rubber annulus with the fins. I’d heard of that, so prepared to fit an new impeller. In so doing, I checked for loose bits of rubber debris, both with a finger and by peering into the oily little mirror again. I could see the axial driveshaft and the eccentric ‘key’ that the impeller’s core fitted over, so I bound up the new impeller, temporarily, with a cable tie, greased it, and offered it up – blind, of course, for it was on the far side of a maze of pipes and tubes. That went home after a while, the cover went back on, the screws were refitted without loss ( again ), and we started up the engine…..
No water was pumped.
That had me beat, so we walked along the quay to the port’s busy engineering workshop, and sought some help. ‘Clive’ turned up with his tools and a broad grin. He debriefed us of all that had happened and all that we’d done, thought for a moment, then his grin broadened again. “Let’s have the cover off again”, he asked, “and have a look inside.” He whipped out the new impeller and laid it alongside the old, damaged one. “It’s the right type and size”, he agreed, “but even if the fins had been compressed the wrong way, it should still have worked to pump water.”
It was then I mentioned that the axial shaft with its belt-driven pulley seemed oddly loose, in that it could be pulled out/partially withdrawn from its location running through the body of the waterpump. “Aha!” said Clive. “I think we have an answer,” pointing to the new impeller. Stuck between two of the rubber fins, held by a blob of the grease we’d applied liberally when we first fitted it, was a short steel strip. “That’s the LOOSE key,” explained Clive. “You mentioned you’d seen it in place when you examined the chamber through your mirror....” “...I assumed it was FIXED to the driveshaft. It didn’t occur that it was a loose fit…..”, I interrupted . “Yes, and when you first fitted the new impeller, “ Clive went on, “the 'loose key' must have dislodged from its slot in the driveshaft and got wedged somehow between the fins. That’s why the driveshaft could be partially withdrawn, until the belt tension stopped it moving further.”
Re-assembly took but a couple of minutes. This time, water was pumped as advertised. Sorted.
And we also learned that the rubber specification of impellers differs for differing uses – pumping oils, toilet-waste water, sea water, other stuff – and that certain rubbers used for seawater impellers goes soft and weak when they get contaminated by fuel oils – like ours.
"That can easily happen", he said, "if one motors through a surface patch of diesel or fuel oil, and week/months later the impeller fails without apparent reason….."
Certainly, I’ll encourage the fitting of a SpeedSeal coverplate, for the likelihood of those infernal SLOTTED screws dropping irretrievably into the sludgy bilge under the engine was high. Similarly, the RNLI practice of fitting a pair of coarse fuel filters , in parallel and switched, is a good one. The ruptured impeller /burnt-through Vetus bottle is at the root of several engine failures I’ve experienced; fuel starvation due to a blocked filter is the other main cause, on that boat.
But that’s another story……
Bumbling along, motorsailing, some 15 miles off the North Cornish coast recently, after a night of humungous electric storms which took out all the Coastguard VHF antennae, apparently, I was writing up some logbook stuff when I became aware simultaneously of a stench of burning rubber/plastic and grey-white smoke squirting out of the engine-space box. ‘Engine fire’ came to mind, the lump was shut down PDQ, and I assembled in the cockpit equally PDQ, while calling on my companion to bring some lifejackets and the handheld VHF as he joined me.
We failed to make contact with Falmouth MRCC by VHF/GMDSS. The signs and symptoms of engine fire faded away slowly, and we determined to wait an hour for ‘cooling’, as neither of us was in a hurry to open the engine box. Eventually we had a chat to MRCC Falmouth via mobile phone ( ! ), opened the lid gingerly, and discovered the melted plastic Vetus exhaust gas/water mixer bottle had burned through and melted, damaging an adjacent rubber exhaust pipe. This had happened several times – plastic bag over the water inlet, seaweed ditto – and indicated an waterpump impeller failure. That was confirmed by re-starting the engine briefly and noting ‘no water flow’ through the clear lid of the raw water strainer…. So far, textbook stuff.
The next bit of textbook stuff involved removing the waterpump impeller coverplate. While the pump body was fairly visible through a maze of piping mounted on the side of the engine, the coverplate faced away – of course – and getting a screwdriver in would be ‘challenging’. So would retaining the 6 slot-head screws when they came loose.
Managed that. Managed also to waggle a small mirror such that I could get a view into the chamber, and a small torch gave just enough light to see that the impeller fins all looked intact when poked awkwardly with the point of a slot-head screwdriver. Equally so when the axial driveshaft was rotated by hand, using the pulley. Curious…..
So I reassembled the thing, and tried again. Still no water. We primed the pipes with water poured in; still nothing. Puzzled and beaten for the moment, we settled down to sailing the old Rival down past the Longships, around Lanzen and the Runnel Stone, and in the dying light breeze along into Newlyn. Next morning, we tried again, with a new Vetus bottle and replacement exhaust pipe fitted.
This time, I removed the old impeller; the fins were intact, but the metal core had ‘debonded’ from the outer rubber annulus with the fins. I’d heard of that, so prepared to fit an new impeller. In so doing, I checked for loose bits of rubber debris, both with a finger and by peering into the oily little mirror again. I could see the axial driveshaft and the eccentric ‘key’ that the impeller’s core fitted over, so I bound up the new impeller, temporarily, with a cable tie, greased it, and offered it up – blind, of course, for it was on the far side of a maze of pipes and tubes. That went home after a while, the cover went back on, the screws were refitted without loss ( again ), and we started up the engine…..
No water was pumped.
That had me beat, so we walked along the quay to the port’s busy engineering workshop, and sought some help. ‘Clive’ turned up with his tools and a broad grin. He debriefed us of all that had happened and all that we’d done, thought for a moment, then his grin broadened again. “Let’s have the cover off again”, he asked, “and have a look inside.” He whipped out the new impeller and laid it alongside the old, damaged one. “It’s the right type and size”, he agreed, “but even if the fins had been compressed the wrong way, it should still have worked to pump water.”
It was then I mentioned that the axial shaft with its belt-driven pulley seemed oddly loose, in that it could be pulled out/partially withdrawn from its location running through the body of the waterpump. “Aha!” said Clive. “I think we have an answer,” pointing to the new impeller. Stuck between two of the rubber fins, held by a blob of the grease we’d applied liberally when we first fitted it, was a short steel strip. “That’s the LOOSE key,” explained Clive. “You mentioned you’d seen it in place when you examined the chamber through your mirror....” “...I assumed it was FIXED to the driveshaft. It didn’t occur that it was a loose fit…..”, I interrupted . “Yes, and when you first fitted the new impeller, “ Clive went on, “the 'loose key' must have dislodged from its slot in the driveshaft and got wedged somehow between the fins. That’s why the driveshaft could be partially withdrawn, until the belt tension stopped it moving further.”
Re-assembly took but a couple of minutes. This time, water was pumped as advertised. Sorted.
And we also learned that the rubber specification of impellers differs for differing uses – pumping oils, toilet-waste water, sea water, other stuff – and that certain rubbers used for seawater impellers goes soft and weak when they get contaminated by fuel oils – like ours.
"That can easily happen", he said, "if one motors through a surface patch of diesel or fuel oil, and week/months later the impeller fails without apparent reason….."
Certainly, I’ll encourage the fitting of a SpeedSeal coverplate, for the likelihood of those infernal SLOTTED screws dropping irretrievably into the sludgy bilge under the engine was high. Similarly, the RNLI practice of fitting a pair of coarse fuel filters , in parallel and switched, is a good one. The ruptured impeller /burnt-through Vetus bottle is at the root of several engine failures I’ve experienced; fuel starvation due to a blocked filter is the other main cause, on that boat.
But that’s another story……
