If the screw was free wheeling-windmilling as she sank stern first, would the trialling edge them become the leading edge?
I consulted the "Old Salt", my business partner, Mike and he agrees with you, Double D. He also said that the ship probably would not have been 'backing' very slightly, as I thought, in order to keep the tow line tight, but that even if the propeller was not rotating as she struck the sea-bed, the trailing edge would have struck first if she plunged stern first and upside down as we have read. I would venture that, considering the weight of this armored ship and the large amount of energy expended at impact, the bit of propeller housing aft of the propeller, would have been crushed in an instant, upon stern contact with the sea-bed. Thanks, DD.
In answer to Mike & Tracy, You are correct in your guess, it is a “plate compressor” intended to counter recoil. Its principle was described in a paper in 1866 by the Royal Navy as:
“Frictional iron plates, suspended from bed of carriage between parallel balks of timber placed lengthway on bed of slide, pinched together by two levers, one on each side, which are acted on by screws worked by handwheels on the outside of each bracket.”
The idea had been around for many years previously, in competition with the common compressor carriages that gripped the side members of the undercarriage of great guns.
All before hydraulics were introduced, of course.
Starr
Many thanks, Starr, we were fairly certain of the plate set's purpose, but had nothing on which to base that assumption. That information is very, very interesting to us, because we are keenly aware of the powerful effects of recoil based on our extensive test firing of the reduced scale seacoast guns which we make. Once, while testing 'Counterhurter' compression on our 100 Pdr. Parrot Rifle, we screwed both of them down tight to positively stop recoil of the tube and Upper Carriage. THAT was a mistake!! The whole 80 pounds of gun and 65 pounds of bench lifted up and back, tilting an alarming 35 degrees! We have much admiration for the genius of John Ericsson who had to design his Dahlgren gun carriage so that it would stop in a very short distance within the confines of the 20 foot diameter turret, but not so quickly as to destroy itself.
"The idea had been around for many years previously, in competition with the common compressor carriages that gripped the side members of the undercarriage of great guns."
A most perfect and easily understood example of this lies in the way that the 150 Pdr. Armstrong Rifle of 1864 works. It resides at the USMA at West Point, New York. Large bronze hand wheels on each cheek turn a single-lead screw which has both right hand and left hand threads. Wrought iron brake shoes, on each side of the Chassis rails, hinged near the bottom of each cheek are pushed outward above this hinge pivot and this subsequently causes the lower portion of the shoes to move inward to grip the Chassis (Undercarriage), rails. We could not see much of this mechanism when we studied this gun and carriage at West point and again when it was on loan to Fort Fisher, North Carolina, but we believe that the Jack Coggins book entitled
Arms and Equipment of the Civil War has an excellent depiction of this common compressor braking system.
It's good to remember that however crusty, cantankerous and irascible he may have been, that Captain John Ericsson was a brilliant naval architect, engineer and ship propulsion expert who created a fine revolving turret and an excellent gun carriage as well.
Tracy and Mike
