Jellyfish, Steam and the Impeller

As we left Royal Prince Alfred yacht club’s visitor wharf, Vega’s clean decks were gleaming in the early morning sunlight. I pushed the throttle forward to 2500 RPM, engaged the auto helm and headed towards the aft deck for a seat.

I was looking over the transom, mindlessly watching the jellyfish being chopped up by our prop when my eye got drawn to white wisps of smoke coming out of the exhaust. I looked back at the mutilated jellyfish.

Wait..white smoke? That shouldn’t be there. I looked again. There was more. You can tell a lot from the exhaust smoke of a marine diesel engine. In short, there should be very little of it coming out of a healthy diesel. If you have some then it can indicate various issues. For example, blue smoke can mean burnt oil, black smoke is caused by excess, unburned or partially combusted fuel, or conversely by inadequate air supply to your engine. White smoke can be caused by either excess fuel or an internal coolant leak in your engine….there are also a range of other more sinister symptoms that can be induced from the above but you get the point, you’re exhaust emissions guide you as to your engine condition.

I looked at the engine temp gauge and it was climbing through 180 degrees F and still going up. Getting hot. I backed off the Revs, went back to the transom. Less white smoke, but it wasn’t smoke – it was stream. You could see it dissipating. Smoke tends to lie on the water surface, this was rising and dissipating. It was definitely steam. Something was a miss with our cooling system.

With the Revs back at 1800-2000RPM all was well, engine temp stable, no more steam, so we carried on our way..we had friends to meet. Although i was monitoring closely and   mentally thinking through all the issues – it must be the raw water cooling circuit.

Once at anchor, Heather slipped over for a swim and checked the inlet, all clear. I shut off the raw water intake and checked the strainer. All ok here too. Next came the was knackered. I had last replaced it 2 years ago and visually inspected it 12 months ago when it seemed tip top. It was now missing 4 fins…! According to my marine diesel handbook, the missing pieces of rubber needed to be located as they find their way through the raw water system and into the heat exchanger where they can block the tubes. So we dismantled the rest of the raw water system and retrieved all the missing pieces, inserted a new impeller and she was good as new.

Lessons Reinforced:

  • Things on boats break!
  • Notice changes in your engine; temperature, noise and exhaust emissions are all very revealing.
  • If something isn’t right, act immediately and monitor.
  • Systematically chase the suspect system from start to finish.
  • Carry spares and know how to fit them.

To be honest, we were pretty pleased that we managed to identify the issue, locate the cause and managed to fix it. We are slowly growing as sailors…and marine diesel mechanics!!



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Website Powered by

Up ↑

%d bloggers like this: