I work with the latest and best world class yachts where money is*barely an issue when it comes to the machinery installation.*None of these boats use a seal that cannot be closed off, either by an inflateable bladder or by clamping down on some other type of emergency seal.
Show me another*item below the waterline on a boat where the only thing between the sea and thee is a very thin and very flexible rubber bellows with no way to stop flooding when it fails.
"My PSS dripless systems are working fine and get inspected for temp and leaks every hour I'm cruising. I'd guess far moreso than any standard system gets checked in*most vessels."
That's because other systems can be trusted to behave themselves and don't require that much labor.
As the owner of two dripless seals, I followed this thread with interest.* When I read the following USCG document, I thought others might also find it interesting.* ...........Arctic Traveller
Improper Assembly of Shaft Seals
This document presents lessons learned during a casualty investigation. It
provides useful information for marine inspection and investigation
personnel in addition to owners and operators of Towing Vessels and other
vessels having similar characteristics.
Recently a towing vessel nearly sank while conducting vessel assist
operations in San Juan harbor. A large volume of water flooded the engine
room when the vessel applied astern propulsion. Within a few minutes,
severe flooding filled the engine room with twelve feet of water.
Fortunately the Master was able to intentionally ground the vessel to avoid
An investigation revealed that the water had entered through a gap between
the vessel's shaft seal and its mounting flange. When the vessel applied
astern propulsion, the force of water was directed down the shaft towards
its seal thus dislodging it from the flanged mounting / mating surface. The
vessel had recently installed a Kobelco brand dry shaft seal during a yard
period. Installation required a new flanged mounting welded to the vessel
The mounting flange had been tapped for the use with M20 metric bolts.
During installation the seal was secured to its mounting flange with eight ¾
inch diameter (nominal size) bolts. The differences in the diameters of the
tapped hole for a ¾ inch bolt and a M20 bolt is quite small and the pitch of
the threads are very similar. Because of these similarities the use of a ¾
inch bolt into a 20M metric tapped hole may go unnoticed.
In this instance, the improperly fitting bolts eventually loosened and
allowed the seal assembly to separate substantially from the flange mounting
surface when astern propulsion was applied. Post casualty, the owner /
operator reinstalled the proper bolts and enhanced the installation with the
use of a locking device to prevent future loosening.
"Human error" likely resulted in the selection and installation of improper
bolts. Inadequate "situational awareness" may have contributed and failed to
provide the proper "defenses" to prevent the casualty. Careful and routine
machinery space rounds by competent persons and attention to critical areas
like shaft sealing arrangements may have detected the initial loosening of
the bolts and leakage occurring at the seal.
The Coast Guard strongly recommends that owner operators of vessels
utilizing Kobelco shaft seals or similar devices ensure that the proper
fasteners are used. Further, critical inspection of machinery should take
place anytime modifications are made and regular inspection of important
areas such as shaft seals, skin valves, sea chests and other hull
appurtenances should be part of a daily machinery space rounds onboard any
This document is provided for informational purposes only and does not
relieve any domestic or international safety, operational or material
requirement. Developed by the Headquarters Office of Investigations and
Analysis and the Investigations Division, USCG Sector San Juan. Shaft seal
questions can be addressed to LT Sarah Geoffrion, Chief of Investigations at
. Other questions can be addressed to Mr. Ken
Olsen at Kenneth.W.Olsen@uscg.mil
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