PSS dripless vs packed shaft seal comparison

Two shaft seal designs dominate marine inboards. (1) TRADITIONAL PACKED STUFFING BOX: graphite-impregnated flax packing rings squeezed around the shaft by a packing nut. Requires 2-3 drops per minute of water lubrication while running (zero drips at rest indicates over-tightening, will burn the shaft). Repack every 3-5 years or on failure. Simple, cheap ($20 of packing), forgiving of shaft misalignment, easy to service without haul-out. Downside: constant slow leak into the bilge, must monitor bilge pump activity. (2) DRIPLESS FACE SEAL (PSS by PYI, Tides Marine, Volvo Sealine): a rotating stainless collar clamped to the shaft presses against a stationary carbon ring. Requires no drip in normal operation. Water cools the interface via a small hose from the engine raw water discharge, this hose is critical, if it kinks or fouls the seal overheats and fails. Bellows life: 6 years or 500 hours, replace on schedule regardless of appearance. Requires proper commissioning: after launch, burp air out of the bellows by pushing forward on the collar to open the face and let air escape. Bellows failure = catastrophic leak; carry a spare aboard. Rule: match seal to boat use, packed stuffing box for older/simpler builds, PSS for modern refit or sound-sensitive owners.