Dripless Shaft Seals

I have mentioned previously that the newest version of Nobletec allows you to run copies on multiple computers, without the hardware key (dongle). This is so that you can have one copy of the software on the boat for navigation, but also have a copy on your laptop for trip planning (and backup) purposes.

Jeff Sanson, of Pacific Yacht Management, will be going with us across the Aleutians next summer. Roberta and I will run the boat alone up to Alaska, but then for the run to Japan we’ll bring on Jeff and perhaps one or more of his guys, to help. So that Jeff could start doing trip planning I put Nobeltec onto his laptop. It felt a little funny installing the software on his computer; like we were school kids pirating, but this was completely legal as far as I know…

While we were killing time waiting for the software to install, we started talking about dripless shaft seals. On power boats, the shafts, which connect the engine to the prop, must pass through the hull at some point. Historically, this point where the shaft passes through the hull has been called “the stuffing box”. In the old days, cloth was literally stuffed into the gap between the shaft and the hull to stop water coming in. This is still done today, except that now most boats use a stuffing material composed of cloth dipped in wax.

 

If the cloth is packed in too tightly then it creates friction and heat. If it isn’t packed tight enough, then water can come streaming through into the boat. There are adjustment screws which allow you to tighten or loosen the stuffing, and it can become a never-ending struggle to get it “just right”.

 

Different captains have different opinions about stuffing boxes. The general rule of thumb is that you should see some dripping every few seconds. If it is a constant flow, you need to tighten the stuffing. If you aren’t seeing drips, then you are going to have heat and burn up the stuffing. I personally always err on the side of letting in too much water. It keeps the stuffing box cool, and the bilge pumps quickly throw the water overboard. Other captains believe in a dry bilge and really don’t like the idea of any water getting in.

 

Dripless shaft seals are a fairly new innovation, although not that new. They are currently installed on hundreds of thousands of boats. Jeff has been lobbying me to make the change to dripless shaft seals. These work by forming a water tight seal, that is cooled using the same raw water intake that is used to cool the boats main engine(s).

 

Jeff likes the idea of zero water in the bilge, and it always bugs him to see the bilge pumps run. I certainly agree with him that it would be better to maintain a clean bilge, and to not have to constantly need to be monitoring the shaft seals.

 

That said, few subjects in boating are more controversial. If something interrupts the flow of cooling water to a dripless shaft seal, they can seize up quickly, with disastrous consequences. It doesn’t take much googling to find stories of boats sunk by their dripless shaft seals.

 

Here’s just a few links. You can google for hours on this topic:

http://www.tidesmarine.com/
 

http://www.irbs.com/lists/worldcruising/0801/0011.html

 

http://www.cruisersforum.com/forums/f114/shaft-seal-s-7594.html

 

http://www.cruisersforum.com/forums/f114/pss-bellows-replacement-12559.html

 

http://www.thehulltruth.com/forums/thread-view.asp?tid=109124&start=1&posts=19

 

I am leaning towards going dripless .. but it isn’t an easy decision.

 

Once we had Nobeltec installed on Jeff’s computer we started by making a quick route from Seattle to Japan: 4,100 nautical miles! It’s actually not that bad. That’s only 12 days of running, which we’ll spread out over several months. Roberta and I will take our time in May and June cruising the boat to, and around, Alaska. Jeff and crew will then meet us somewhere around Glacier Bay, and we’ll start the run.

 

Jeff asked “What happens when the boat gets to Japan?” I said I really hadn’t thought that far ahead, and think it is bad luck, not to mention a waste of time, to plan too far ahead. My gut reaction is that we’ll spend a month exploring Japan, then tuck the boat away until the following year when we’ll head towards Taiwan and Indonesia – but, who knows?

 

Now, if only my boat wasn’t stuck in Costa Rica!

 

-Ken W

  

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