The Navies of the world, seem to spare no money in complicated propulsion
systems in their ships.

My primary experience was with the patrol gun boats (PCs and PCGs) of the
Saudi Navy which had two MTU diesels and a LM-2500 gas turbine into a single
gear box. Each was clutched in or out and could drive the twin shafts.
Diesels for normal cruising and the gas turbine for high speed.

The neat thing about this system (single gear box) with controllable pitch
on each shaft, was to maneuver just like a the shafts had independent prime
movers. While in fact the gas turbine or the diesels could be dividing power
to each shaft or sending all the power to one shaft. (I should note that the
gas turbine was never operated with the diesels (or vise/versa).

Another old school twin scew system I always thought was great, coming from
WWII technology was the PCs we gave to the Cambodian Navy in the '60-'70s.
These were independent reduction gears on each shaft, however there were
four V-8-71 engines on each reduction gear. Each engine was clutched in or
out and at low speed they could run on one engine per shaft. (The
configuration was 2 engines facing forward and 2 facing aft, each coupled to
their independent pinion gear.)

Normally the 8 twin disc clutches were pneumatically controlled but the one
ship I was onboard, while the Cambodian Navy was turning them back over to
the US Navy, had no air compressor working and the engineman was setting on
the reduction gear and "answering bells" manually. When this particular ship
arrived in Subic Bay, loaded with refuges, they only had one engine running
on one shaft and 2 running on the other. Main generator was down and they
were power the steering and navigation gear with a 25 KW aux. gen set.

Just some memories from the (good) Ole Days.

Steve
s/v Good Intentions
wrote in message
ps.com...
Hi

Steve this was the exact system with 99 pct. of the old Semi diesels in
commersial and fishing vessels --- it is great when manuvering as both
reverse and forwerds turn the aft end of the ship in same direction ;
going forwerds and reverse a number of times, simply turn the boat on a
coin , when you back out a harbour you can plan your manuver way ahead
and kindof feel how perfect you navigate 36 ton just with a turnable
pitch propellor a clutch a rudder that make just the final touch man
you can almost make it fly )
Anyway there was no hydrolics to turn a maby one meter diameter two
blade with a flywheel with one ton deadweight and just two cylinders
the sice each of a bucked .
Now these engines are still used but not many are still manufactored
,and that even they are such engines that will run to the ends of day's
at 400 rev.

Sabb copied the best of it all with their small engine with fast
reverse ; 3/4 rounds from fore to aft, without clutch and is proberly
the best thing to look for ; emagine 2 each side the boat, then you can
make it go sideverds ( I could with just one )