On Mon, 31 Oct 2011 09:15:13 -0700, bill wrote:
On 10/31/2011 5:43 AM, John B. wrote:
On Sun, 30 Oct 2011 23:16:58 -0700, "Steve
wrote:
The reason
that it comes up is that I read about a new class of ULCCs
(UltraLargeCrudeCarriers -- Way big mutha oil tankers) that have 2
cycle diesel engines with NO transmission, clutch or reduction gears of
any sort. The drive shaft comes out the back of the engine and goes out
the back of the hull and the propeller is bolted directly to the end of
it No gears, no clutch, no nothing. The way that they reverse it is by
shutting of the engine and then restarting it BACKWARDS!!?! It is
designed to do this, I'm wondering if all 2 cycle engines will run
backwards or not? Inquiring minds want to know.
Bill
I am amazed that the engines are designed to be stopped, then restarted
backwards. This, I believe, would take at least some time on the larger
engines, but perhaps not. I have been on a lot of motor vessels in the open
sea, but none as large as I believe you are talking about. Starting and
stopping the engines would take too much time to do some of the delicate
maneuvering required using multiple props to get the vessel to do the
intended maneuver. I do not doubt that this may be the case on longer ships
that take a very long time to stop or turn or even slow down. I just can't
imagine that would be the safest and best way to maintain control over the
vessel, and to get it to respond in a timely and safe manner when
maneuvering. There is a lot of jockeying the throttles and gearing by the
captain during maneuvering a boat for docking, or negotiating tight spaces.
I'm wondering if the response times are adequate for the intended result.
I've spent probably more than 1,000 days on various boats in the open sea,
in the 150 - 250 foot class.
Steve
I think that you'll find that most of the larger ships (VLCC, the big
box boats, etc) are all direct drive reversing engines. I believe that
a combination of the giant size of pistons, rods, etc. means that they
can't be designed to run at very high revs, say 100 RPM perhaps, and
the size of any reversing gear and the power they would have to absorb
make the direct drive setup cheaper and less complicated to build.
Yout 150 - 250 ft. boats were something different and likely far more
maneuverable then the "big boats".
An interesting aside I read, was that using a box carrier like the
Emma Maersk it is cheaper to ship a container from China to a West
Coast port then the cost of freight for the box from the port to its
final distention inside the U.S. Obviously internal freight varies
with the distance delivered it does give a good picture of why these
big boats. (and incidentally, part of the reason for moving your
industry off shore)
--
John B.
I spent 3 years maintaining engines on a 92 foot ship, These engines had
a camshaft that could shifted so that a second set of cams could operate
the valves. And they had a distributor for the air starts. They were
made by Winton (sp).
And maneuvering the ship required some planning. Full speed on the
engines was 1200 to 1500 RPM. maneuvering speed was 500 to 600 RPM.
That was 1948 time frame so my memory on the RPMs my be not correct
on the details.
Bill K7NOM
Try
http://www.tugboatenthusiastsociety....ancient-01.htm
1200 - 1500 was really high speed for that type of engine :-) I worked
on a Gardener 6 cyl. that was supposed to have a max continuous rpm of
1500 but was set to run at 1,000 with about 500 RPM idle. I offered
to reset the governor but the Chinese guy that owned it said the boat
did 7 K so leave it alone :-)
--
John B.