Bruce in Bangkok wrote in
:

It seems to be more a matter of size as the BIG engines are all low
RPM engines that at lower RPM while lower power engines are usually
higher speed engines. for example, the Emma Mursk uses a 108,920 H.P.
@ 102 RPM engine and probably doesn't require a reduction gear, while
a smaller ship might use a 5,800 Hp @ 600 RPM engine with reduction
gear.

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)



I've stood atop the 7-cylinder, 2-stroke beast that powers SeaLand
"Performance". It's 38,800hp at 102 RPM and burns 75 tons of heavy oil
boiled in the exhaust stack before injection to thin it at about 76 RPM,
her econocruise speed give or take the load, of course. The massive
flange aft of the engine is directly coupled with huge bolts to the
screwshaft going out to her single screw. If you were standing on a
platform at the base of a blade, you could extend your hand about
halfway up that blade towards the hub. I can't remember how many blades
were in the picture, sorry.

The engine is computer controlled so noone has to sit and baby sit it in
the air conditioned control room where the massive power panel is also
located for the large array of 3-phase 408?V diesel gensets power that
are located in a compartment under the main shaft under the rudder gear.
The day I was there they were about half loaded for sea and the panel
said they were generating a little more than half a megawatt to keep the
fruit cool and the frozen food frozen in the freezer containers. They
got plenty of AC power!

If the computer sees something it doesn't like on an array of engine
sensors in each cylinder, it pages the duty engineer wherever he may be
to come look. If something really bad were to happen, the computer
would shut her down to prevent further damage and all hell would break
loose.

Captain Larry, a ham friend of mine, is one of her two masters and he
says he never gets tired of playing with her...(c; Forward or reverse
she will run either way, being two stroke with no valves. Big blowers
ventilate her when the ports are open at BDC before the next 5 foot trip
up the cylinder, injection and explosion drives her down again. Oh how
I wanted to go to sea with them to see it run and hear that thumping for
myself.

Captain Larry claims he can do an emergency stop from econocruise speed
in NEARLY 2.5 MILES!....which is also about her "turning circle" in flat
water. Not bad considering she's 980' long. Standing on the bridge, I
commented, "Well, at least you won't get hurt in a front end collision.
Hell, you're half a mile back from the accident!" A color TV system
let's you watch for those damned crab pots over the bow, but I doubt
they worry over them like we do....(c;

Air start....either way. Very exciting.

On Wed, 1 Oct 2008 11:31:27 +0200, "Edgar"
wrote:

Have you ever looked at an engine that will turn a big ships propeller at
80-100 rpm with direct drive?
They do not come cheap.

It is a universal, applying to all sizes, that the transmission costs
a much as an engine. All the biggest engines have long been direct
drive. As for price, the big marine engines are cheaper per horse than
the smaller ones. By the way, gears suck up power. So does electric
drive. The family runabout, a jet boat, has no transmission. In fifty
years, I never missed it even once.

Casady

On Wed, 1 Oct 2008 11:31:27 +0200, "Edgar"
wrote:

Have you ever looked at an engine that will turn a big ships propeller at
80-100 rpm with direct drive?
They do not come cheap.

It is a universal, applying to all sizes, that the transmission costs
a much as an engine. All the biggest engines have long been direct
drive. As for price, the big marine engines are cheaper per horse than
the smaller ones. By the way, gears suck up power. So does electric
drive. The family runabout, a jet boat, has no transmission. In fifty
years, I never missed it even once.

Casady

On Wed, 01 Oct 2008 10:27:40 +0000, Larry wrote:

Now disconnected from the drive shaft and its constant alignment
problems,

Family runabout has a tubular driveshaft with a U-joint. Never had any
problems with alignment. A 59 Turbocraft, the tenth jet boat ever sold
in the US.

Casady

On Wed, 01 Oct 2008 10:27:40 +0000, Larry wrote:

A lot of the propulsion noise you hear in a boat is transmitted by rigid
engine mounts to keep it aligned which are marginal dampers and through
the shaft to hull bearings, themselves. Diesel-electric eliminates

You haven't been around inboard runabouts with straight pipes that can
be heard for miles.

Casady