On Jun 9, 3:46*pm, "Steve W." wrote:
wrote:
On Jun 8, 7:06 am, Randy wrote:
This is just too neat to not pass on.

http://www.shipsnostalgia.com/guides...d_Sons#The_Man....

no CNC here.

Thank You,
Randy

Remove 333 from email address to reply.

Thanks for the link!

Under the section titled “Later Engines”:” …This system had inherent
advantages over the standard four-stroke engine, as the two-stroke
running enabled a low operating speed (115 rpm), thus eliminating the
requirement for a reduction gearbox between the engine and propeller,
and as the engine was reversible, no reverse gear was required. …”

I found it unusual that a 2-cycle engine would allow them to have a
lower rpm than a 4-cycle one, since most common small 2-cycle engines
are used at higher rpm. *But maybe it makes sense in that the power
stroke is spread out more evenly through its cycles.

Take a look at locomotive engines. Many of those are two strokes and
they turn reasonably slow.



I wonder how they started or reversed those big ship engines. *Did
they use auxiliary engines for this?

Depends on the engine design. Most were set up so that you brought the
engine to a stop by shutting down the fuel, then as it was slowing you
activated the change gears to shift the exhaust and intake systems. Once
they were changed you just used the air start to kick the engine over in
reverse. If you timed it right you went from forward to reverse as fast
as a standard reversing gear set would allow.

Many "modern" 2 strokes can still run in reverse, BUT the results can be
interesting. One of our members found that out with one of our Detroit
equipped engines! He pulled into a parking spot, managed to let the
truck roll forward a bit with the trans in reverse. OOPS. He hit the
emergency shut down after a couple seconds but not until a HUGE cloud of
smoke came out the intakes and showed off the mistake.

--
Steve W.- Hide quoted text -

- Show quoted text -

Thanks for the explanation. I subsequently found something about “air-
starting” from an old Audel’s book for marine engineers:
http://tinyurl.com/kqtr5n. Given the size of the diesel and the
pressures mentioned, I imagine that the compressed air system must be
impressive by itself.