Since we are talking about seals...



Great write up and perfect timing as I am in the midst of my first Bowthruster service and I will start my first C-Drive service soon thereafter! 

I think that you may have left a paragraph out of the "C-Drive Underwater Shaft Seals" section. You start a paragraph with "Let’s trace the three seals…"  but then you only talk about the outermost seal before going on to extol the many virtues of Molykote 111. ;)  I was hoping you could expound upon the two inner seals as well if you can.

Mark McGovern
SM #440 Cara
Deale, MD USA


Thanks Mark,

The basic job of the two inner seals is to keep a solid "plug" of grease between the oil and the water.  I'll make that clearer.

The primary reason I like silicone greases for that is they wash out in neither water, nor oil.  So they stay in place well.  When mine comes apart for service, the grease between these seals is almost as clear and white as the day it goes in.

Ironically, the wear on the "wear out bearing" is always the worst on the innermost seal, lubricated primarily by the gearcase oil.  It's counter intuitive to me at least, but grease is the more effective lubricant for seals.  

Bill Kinney
SM160, Harmonie
Spanish Wells, Bahamas