My Day Job - Tuesday

by Sarah Lake Upton in


I had a lovely idea of writing a serious of posts about a whole week in my day job, and all of the silliness therein, but clearly I write too slowly to carry that off, and anyway I’m home now (I arrived home on the evening of January 25th, just in time for the blizzard) but I managed to write most of the next post before I left the boat, and so I am going to post it anyway.  And even better, now that I am back in the land of reasonable internet, I can include photos. 

Tuesday. 

Still cranky about the previous day, and finding myself with a free few hours in the evening (I usually make repairs to guest cabins during guest mealtimes, but this evening there were no repairs to be made) I decided to rebuild a spare generator raw water pump, at least in part because the “stupid naturalist jerk can’t rebuild a raw water pump” (to put into words the amorphous annoyance that I was still in the grips of). Which is not the most grown-up reaction I will admit, but it was also work that needed to happen, and work that I really enjoy, so I told the deckhands that I’d be down in the engine room in case anyone needed me (deckhands, officers, and engineers all carry hand-held radios with us when we’re working, but I can never hear mine when I’m in the engine room) and set to it. 

 This is a raw water pump for one of our generators

This is a raw water pump for one of our generators

So, what on earth is a raw water pump? (Feel free to scroll past this bit)

Your car’s engine is cooled by via the circulation of coolant.  The coolant must in turn be cooled, otherwise it would get hotter and hotter until it was no longer able to cool your engine and your engine would then overheat.  In your car this is done by sending coolant to the radiator, basically a big flat plane that exposes as much coolant at a time to as much air as possible.  For reasons of stability and propulsion, engines rooms on boats are generally as low in the boat as possible and fairly contained.  There is no way to get enough air circulation in most engine rooms to cool the coolant from one engine, let alone the four that we have (two main propulsion engines and two generators).  So instead most marine systems use sea water to cool their coolant.  There are two general ways to do this.  The first involves piping sea water to the marine version of a radiator, referred to as the “heat exchanger”, which is basically a big tank filled with little tubes.  The coolant flows through the little tubes, which are immersed in sea water that is constantly being pumped through before being pumped overboard again, a few degrees warmer than when in started.  The second involves putting a network of little tubes into a protective housing on the outside of the hull, through which the coolant can then be circulated, and cooled as the boat moves through the water.  Both systems have their advantages and disadvantages, and I’m sure there are whole forums devoted to arguing over which system is better for which circumstance, but that is a much longer post.   We have heat exchangers, which means that we also have a pump that pumps sea water past the coolant. When sea water is used for cooling it is often referred to as “raw water”, hence the “raw water pump”.  In our particular situation, the drive shaft of the raw water pump slots into a set of teeth on the coolant pump, and from time to time the teeth on the coolant pump wear down a bit and grind the shaft of the raw water pump smooth, and eventually the raw water pump stops turning, and then the generator engine overheats and shuts down (and then an alarm goes off, the emergency generator kicks on, and the nearest engineer dashes down to the engine room to very quickly start whichever generator was offline at the moment). 

tldr: the drive shaft on our raw water pumps wears down and sometimes needs to be replaced. 

 

 Raw water pump drive shafts, bad and new.  Note how worn the teeth are on the one on the left.  This is not good. 

Raw water pump drive shafts, bad and new.  Note how worn the teeth are on the one on the left.  This is not good. 

Rebuilding a raw water pump for a generator is one of those rare utterly satisfying engineering projects, being right in the sweet spot of complicated-but-not-too-complicated, and a-little-messy-but-not-too-messy, and heavy-but-not-too-heavy.  The pump housing is about the size of a cantaloupe, and bronze.  The whole thing weighs about twenty pounds, which is heavy enough to feel like a real project, but not so heavy as to be really annoying.  Replacing the shaft requires also removing the impeller, shaft seal, slinger, lip seal, and the bearing, which in turn is held in place by two snap rings.  Strange tools are required, like snap ring pliers, and a large impeller puller.  And to remove or replace the bearing one must employ a mallet.  

 

 The grabby claw looking thing is an impeller puller.  As I tighten it, I am slowly forcing the shaft to slide out of the bearing. 

The grabby claw looking thing is an impeller puller.  As I tighten it, I am slowly forcing the shaft to slide out of the bearing. 

In short, rebuilding the raw water pump is as pleasing a craft project as anything I get up to at home.  On a boat it is made even better by the fact that the work bench is on the other side of the water-tight door, in a section of the boat that only engineers, and once an hour during their engine rounds the deckhands, ever enter.  True privacy is almost impossible to find on the boat and the spot by the workbench is the closest to real privacy that I have found on board.  Which meant that while I worked away with my obscure tools, listening to music that I chose, I also danced like a loon.  And sang along.  Loudly (because engines were running, and who was going to hear?).  

And at the end of the evening I had a rebuilt raw water pump, one more item completed on my ever growing ‘to-do’ list, and a restored sense of humor.  I feel incredibly lucky for my day job.