by Aiona Hartley


Isn’t it pretty? It’s a bilge pump. Or rather the inner windings of one. Its literal guts, if you will. 

This is what heats up if the bilge pump undergoes “rotor lock.” Given enough heat, a bilge pump in “rotor lock” can catch on fire. 

“What is rotor lock?” Well, it’s what happens when that piece of Classic Potato Chips bag blocks the opening to the bilge pump or gets snagged in its impeller and causes this pretty spinning bundle of red wires to stop. However, current is still running through it, and therefore heat will build up in a chain reaction of increased resistance (since heat makes wires even more resistant to electron movement), thereby turning your potato chips into “Hot Fries.” 

That is, unless one has OCP. 

No, OCP isn’t the latest entry in the DSM-V. 

It stands for “overcurrent protection.” Simply speaking, it is a fuse or even a breaker that “breaks” when it discovers that your snack wrapper attempted to assassinate your bilge pump. 

That’s why it’s oh-so-important to check your bilge pump every now and then, but not while tearing open a bag of potato chips. It is also important to make sure that the fuse to your bilge pump is correctly sized for the pump. Most pumps will tell you their ampacity rating, just as most people will tell you their dietary restrictions.

Here’s a bilge pump that’s rated for 2.5 amps
Here is one that’s rated for 15 amps

But rotor lock isn’t just for bilge pumps. Anything with a rotor that could potentially become blocked can overheat with rotor lock — like, for example, a bow thruster that has decided to eat a dangling dockline.  

Again, that’s the reason for OCP with bow thrusters. I mean, blowing a fuse serves two purposes here: 

1. It blows, so you don’t have to.

2. It also potentially saves your bow thrusters “guts” from further damage when it’s bit off more than it can chew.

The OCP to your rotor is like my husband stopping me from getting thirds at Golden Corral.

Here’s the ampacity rating for a macerator pump.
Here’s the ampacity rating for a blower.

Some of the older bilge pumps, like the one whose windings are pictured above, have the ampacity rating engraved on the plastic case instead of printed on it. I would have taken a picture, but someone threw away the case while I was writing this article. So you’ll just have to take my word for it. 

Here is a bag of Tim’s brand potato chips which are made in the Pacific Northwest and are tastier than other chips, but whose wrappers can also stop up a bilge pump.

Biography: Aiona Hartley is attending the Marine Systems Program at the Northwest School of Wooden Boat Building where instructor Kevin Ritz teaches future marine electrical technicians how to contain “the magic smoke.” She had to add the words “ampacity,” “macerator,” “thrusters,” and “windings” to her spell-check dictionary while writing this article.