The Steamboating Forum

Quote: "The article being quoted as pointed out later by Greg is a training publication written 130 years after the event so I actually think that the Navy developed the engines to the point of using Stephenson's link in the way that it was designed to be used, as Naval engineers would have understood the concept, and then perhaps the later a training manual was assembled from a scattering of data some of which was already outdated. "

I'll say one thing, you got a sticktuitiveness a man just has to admire

-Ron

I'm curious where the optimal suspension point is for the double bar link style seen on most big ships. I know on the liberty ship Jeremiah O'Brien it is located on the pivot point for the ahead eccentric rod. While running there is an obvious disparity between ahead and astern at low speeds which can bee seen while the reversing engine is running round and round. When in astern the engine is quick to react from a stop, whilst in ahead it is more sluggish from a stop, giving several revolutions in astern to one or maybe one and a half in ahead with the reversing engine running at constant speed and the throttle at a constant.

The difference that you notice there may be caused by the propeller having considerably more slip in reverse than in forward due to the cupping of the propeller blades. This difference is very noticeable on 2 stoke outboard engines when changing from neutral to forward and reverse at idle, the propeller pulls the engine RPM much lower in forward compared to reverse.

That's a very good point which I hadn't taken into consideration. Thank you for that

This is the reversing link for the ST Portland's port cylinder. Note that the "Stephenson" link has a suspension link that is attached at the center, but fixed so that it can only sway back and forth as the link moves. Reversing is done by shifting the 11' long rod to the valves up and down, and thus the backward looking curve in the Stephenson link. To provide scale, the eccentric connection pins are 16" apart. This system is never linked "in or up" since the variable cutoff is controlled by a separate valve and eccentric that only changes cutoff while not affecting release. I will start a new post in the future once I figure out how to explain the system in a way that is enlightening over bewildering.

Maybe a picture from further away might help. If possible.

And the labels are almost impossible for a red/green blind person to read. Maybe white or blue or yellow?

Mike,
This should be easier to see I hope. I'll try to get some wide shots, but from the eccentrics to the engine cylinder is around 25ft so it's hard to get an all in one.

Just for fun I tossed in a shot of the crosshead with drip oilers. There are 19 per side not counting the pressure oilers. This thread did start with a question about lubrication. FYI: the piston rod is 5in in diameter.

The Chautauqua Belle's Engines have something similar to that "sideways" suspended Stephenson linkage.


http://www.youtube.com/watch?v=YL4FhOKG_lE



-CB

Interesting. Is this really Stevenson gear or something close to it?

Somewhere around here I have a book entitled, "101 valve gears." I read through it forty years ago and my headache lasted a week. Haven't cracked it since!