Catch leaky seal problem before it gets too big

Mar 1, 2015 by Rich Merhige

As part of a mechanical engineering services company, we get a lot of common service calls. One of the most popular has to do with leaking seals.

Water coming into the engine room can put even the most seasoned captain or chief on edge, but the reality is, many times, leaking seals are less of a catastrophe and more of something that can be “self-medicated” by properly trained crew.

There are three basic types of shaft seals:

  1. Packing glands, or stuffing boxes, are the basic, old-school-type of seal that uses a waxy cord (flax packing) around the shaft that is then “packed” into the seal housing, causing it to compress around the shaft.

In general, it’s accepted that these seals should drip water no more than two times per minute. Anything more than that and you should tighten the packing nut to reduce the seepage. The tightening of the nut, in essence, “re-squashes” the packing around the shaft.

Eventually, the tightening will no longer reduce the leak, which means the packing will need to be replaced.

With some basic knowledge under your belt — or access to the manual — the packing nut can be tightened, but the threads must be kept lubricated with Teflon or Boeshield T-9. If that’s not doing the trick, it’s time to get some new ones.

  1. Lip seals are common (the ones made by Tides are a perfect example) and tend to be easy to maintain. Additionally, they are self-aligning, flexible and dripless, which keeps the bilge dry.

The “lips” are rubber rings that sit in the housing. When the lip part of the seal gets worn or damaged, water will begin to leak in. Nicks, grooves or growth on the shaft where the seal makes contact can expedite wearing and make a leak even worse.

In most cases, an emergency spare is already in place, and the crew only needs to cut out the old one and slide the new one in. If there is no emergency seal in place, you should call in a

professional company with technicians who can uncouple the shaft from the drive, remove the coupling, and install a new seal.

  1. Mechanical seals, or face seals, are popular with workboats and naval vessels, but are becoming more prevalent with pleasure craft. Wartsila manufactures these seals, and AME is an authorized distributor for their seals and bearings. Wartsila makes fully split, partially split, and non-split seals, all of which have their own specific benefits.

Another example of a mechanical seal is the PSS seal, made by PYI. Mechanical seals are popular with workboats and naval vessels, but are becoming more prevalent with pleasure craft. They usually use a carbon face-type seal, one mounted to the stern tube, the other to the shaft, which rotates. The two faces are pushed together by a retainer ring on the shaft.

When this type of seal experiences a leak, it is either from damage to the seal itself or a burn out. The Wartsila seal has an emergency air bladder that can be inflated around the shaft while repairs are being made. When leaks are present with seals of these kind, a trained technician should be called in because there are procedures that must be followed if the seal is to be set and function properly.

Most of the time, if it isn’t a clamp that needs to be tightened, the cause of a leaking seal is lack of lubrication, which would cause the seal to overheat. Water injection lines are usually in place to feed the seal coming from the engine’s raw water cooling system.

Most yachts aren’t equipped with an alarm or other notification system to signify when there isn’t proper water (or oil) flow to the seal, so it’s crucial that this is monitored on a regular basis. This burnout is caused by lack of a cool water flow, which could also allow for sand or silt to gather and cause damage.

Even if only one engine is running and the other shaft is locked, it is crucial that the seal on the locked side remain properly cooled. This is the most common cause of seal failure that can easily be prevented, and adequate water flow cannot be stressed enough.

Overall, the easiest way to prevent big problems is to catch and fix little problems. Captains and engineers would help themselves to keep accurate records of the seals onboard, their installation dates, and records of any service they have undergone, including parts replaced, and their serial numbers. Knowing this information is half the battle.

If the basic troubleshooting performed by crew doesn’t work, and the seals or their parts aren’t due for servicing or nearing the end of their life, the seals may be victim of premature wear, which is often a sign of a bent shaft or some sort of major misalignment.

Another culprit could be a tear or other fracture to the seal or, even worse, the housing. In some cases, where an improperly trained company performed the installation, this may be the problem, and the best call is to call in a service company to assist you.

Rich Merhige is owner of Advanced Mechanical Enterprises and Advanced Maintenance Engineering in Ft. Lauderdale, which specializes in rotating and reciprocating machinery. This column is co-written by Teresa Drugatz, marketing manager at AME. Contact them through or +1 954-764-2678. Comments on this column are welcome at