Home . Articles . How-to . Boat Doctor . Maintain shaft seals to stay high and dry

Maintain shaft seals to stay high and dry

2013 November 1

Dear Boat Doctor,

I had a PSS Shaft Seal installed on my Sea Sprite 30 a few years back. The seal has worked very well and I love having a dry bilge. However, I recently had a leak situation with the seal that allowed a significant amount of water to enter the boat. I was quickly able to get things under control, but it highlighted that the seals need to be properly installed and maintained. I think it would be a great idea for you to supply the highlights to your readers so that they could avoid the adventure that I recently endured.

Richard Charette

Wadsworth, Illinois

Dear Richard,

The PSS Shaft Seal is a great product, but like every other piece of equipment on your boat they required proper installation
and maintenance.

The PSS is a dripless shaft seal. It consists of a stainless steel ring that mounts to the prop shaft and nitrile rubber bellows that connects to the stern tube. The actual interface between the two is via a carbon flange mounted on the bellows. The stainless rotor and carbon flange interface via a thin film of water, keeping the friction and wear very low. The two faces are held tightly together by sliding the rotor against the bellows compressing the bellows, to both provide a seal and to allow for the thrust of the propeller.

There are a couple critical points to the installation. The stainless steel rotor is held in place with two set screws. These screws come from the factory with thread locker applied and you'll notice they actually give you five screws. The idea here is that you firmly attach the rotor with two screws and then back each of those with another to act as a "lock screw," for lack of a better term. The fifth screw is a spare in case you drop one in the bilge. Also, these screws are designed to be used just once, the tip is designed to bite into the prop shaft and it can only do that once. If these screws are not properly installed the rotor will move and the seal will leak dramatically. It is not a bad idea to check the screws once in a while.

You should inspect the rubber bellows every year or so, looking for any cracks or stiffening. The manufacturer recommends that they be replaced every six or seven years.

PYI, the seal manufacturer, introduced the Shaft
Retention Collar, a few years back. This is a two-piece stainless steel collar designed to mount behind the rotor, providing a very positive lock. It is surprisingly inexpensive; a collar for a 3/4-inch shaft is $20. You can get them on the web at www.pyiinc.com.

Just a little attention will allow the PSS to perform as advertised.