Bird Of Prey

Something fascinating happened to me on Tuesday…

I went outside in coffee break to get some daily vitamin d, when a huge bird swooped just by me. I thought to myself 'I could have sworn that was an owl'.

It turns out, it was. It flew majestically round the ship for about half an hour, and at one point landed on the rail in front of me. We were staring at each others’ eyes less than ten feet away. 

I was keeping still (as I seem to remember that they see by movement?) and we looked at each other for about ten to fifteen seconds before I moved a tiny bit and he/she flew off again. I was a bit cautious while it was flying around as didn't know if it might swoop down to take a swipe at me, especially as it was very close to me quite a few times. 

It totally made my day, although that is one moment that I felt neutered by not having the DSlr in my hands.  After about ten minutes of watching it gliding around I ran and got the point and shoot camera to see what results I could get. The photos aren’t great quality (have cropped them), but you can identify it as an owl.  Maybe somebody reading this can shed some light on why it was so far from land (about 14 nautical miles) and what it was doing in daylight, as I thought owls were nocturnal.  That's the first time I've seen an owl in the wild - and so close!

Here's a puzzle one: Where's the bird? Send your answers in...

Generally, this week has been busy as usual.  We did some interesting tasks though. 

On Thursday, the Chief and I used “Doctor Diesel” – a kit to determine the indicated power of the main engine.  I say ‘indicated power’, as this is different to the power produced at the flywheel/shaft, which is named ‘shaft power’ (or that’s how I recall from memory).  If you were to measure the power at the shaft then you would do this using some form of brake (thus brake horsepower…I think that’s where it originates from).  Indicated power doesn’t account for the losses in the system such as friction etc.  So, the shaft power would be less than the indicated power. 

The mention of brake horsepower reminds me to inform you of this useless fact:  one average (Joe) horse working all day will produce about three quarters of a horse power.  This probably sounds nuts to you, but I think if you look this up online, you will find it to be true.  In a short burst it can get up to about fourteen or fifteen horsepower, but over sustained periods (like a day) it is likely to be less than one.  A human can produce about one horsepower, but not for long!

Indicated power is calculated by reading the gas pressure in each cylinder, plotting it against the position of the piston during the stroke, working out the area underneath each curve, and adding them all together.  To do this, you attach a sensor to the indicator cock on each cylinder one by one, and open the cock for about ten or fifteen seconds.  This allows Dr Diesel to take pressure readings.  He is, all the while, receiving input from the crankshaft position sensor and recording the positions.  He will take hundreds or thousands of readings, within seconds, of gas pressure and crankshaft position (this number is guessed - I don’t know how many readings are taken per second or in total).  As a result, every gas pressure taken has a position of the piston on its stroke to plot against it.  It then plots a total set of these readings as a graph and can deduce the total power of the engine (produced in the cylinders), by working out the area underneath the graph.  Individual cylinder powers can be compared against each other, to establish whether the power is equally distributed among them, and thus adjustment can be made to the amount of fuel inputted to even them up.

For anybody who is still awake after reading that, you can either look at the photos below of me attaching the pressure sensor and the chief working Dr Diesel (gloves for this one, as the sensor gets very hot receiving engine exhaust gases), or you can read about the opening of the scavenge spaces (choices are limited).

Chief, with the doctor

On Friday, the engine had gone another one thousand hours since the scavenge spaces had last been inspected and cleaned.  So, they were opened up first thing in the morning.  These have to be kept clean to reduce the risk of a fire occurring within the scavenge spaces.  They get dirty quickly on this ship as we are do so much manoeuvring (as in and out of port so frequently), and whenever the engine is on low load, the cylinder lubrication is too much.  See the photos of before and after.  I’ve gone closer in some photos to show the stuffing box sealing rings arrangement.  You can also see the scavenge ports on the cylinder liner which direct the air into the cylinder.  Our MAN B&W main engine uses uniflow scavenging (as opposed to cross-flow or loop scavenging).  Incidentally, ‘scavenging’, is the process of removing exhaust gases from the cylinder by blowing in fresh air.  This is a process that four stroke engines don’t do of course, as they have the exhaust stroke, during which the piston physically pushes out the exhaust gases.

I’m going to stop there, as I seem to have gone into explaining these things, when a photo with a few hastily scribbled words would probably do it justice.

Before cleaning 

After Cleaning

Scavenge Ports

Stuffing Box Sealing Arrangement (only the top is visible, where you can see the small springs)

Sunday 

Since writing those last parts, we have travelled to La Coruna and arrived early this morning.  It looked like we’d hit very bad weather (and it’s still forecast), but we seem to have been ok.  I took a photo showing the nicer weather further away, while a big black cloud was hovering over us.  I do remember waking up in the middle of the night with the ship rolling a lot, but seemed to be able to get back to sleep ok, so it can’t have been too bad.