Hello again Thomas,
Let's dispell some more myths...and agree with some truths. We
already know thae all boats do NOT have struts, particularly full-keel
sailboats as opposed to fin-keeled....Many boats of higher -end
construction(Nordhaven comes to mind,for instance) have bearings at the
inner and outer end of the shaft log to reduce load on the TAILSHAFT
bearing of the gearbox or reduction gear and to prevent "whipping of
the shaft" ( a jump-rope-like effect) often caused by a long
unsupported length
of shaft and some misalignment-it doesn't take much-...Most commercial
craft DO have strut and cutlass bearings; I have replaced many more
than I care to count, having been in the marine service industry for
the last 27+ years... The ceramic "face seal" that Steve refers to is a
PSS "dripless shaft seal, and I see them far more often in pleasure
boats than in Commercial applications. More commercial boats who have
oil cooled upper bearings or standard logs use a TIDES type dripless
seal, a lipseal very similar to a grease seal, this must be cooled by
oil (the minority)or raw water which is engine supplied if available or
supplied by a static siphon vent in keel- cooled apps, and typically
with lower shaft RPM's (under 2000) The oil cooled stuffing boxes are
becoming increasingly scarce on all but ships, they are environmentally
detrimental as they leak oil to seawater intentionally, the approved
versions are completely lubricant-captive and are quite expensive.The
stand alone bearing and support Steve speaks of(Aqua-Drive) and similar
has a twofold purpose: it allows major shaft misalignment to facilitate
a variety of engine installations and it transfers thust directly to
the stringers as Steve said...However, the vast-almost all-majority of
propulsion engines are mounted on flexible,vibration dampening mounts,
with or without an intermediate bearing and supports...in virtually all
pleasurecraft and most small to medium commercial apps.
........But this is far more information than I think you were
seeking...lol
Good luck in whatever venture you decide to take on...Screw the
NYYC types....
Best Regards,
markvictor