AN IMPROVED COMPENSATING CHAIN BARREL OR SHEAVE FOR STEAM OR HAND STEERING APPARATUS
Year: 1881

page_text: LETTERS PATENT to John Lynn, of Sunderland, in the County of Durham,
Engineer, for an Invention of "AN IMPROVED COMPENSATING CHAIN BARREL
OR SHEAVE FOR STEAM OR HAND STEERING APPARATUS."
(Void by reason of the Patentee having neglected to file a Specification in
pursuance of the conditions of the Letters Patent.).
PROVISIONAL SPECIFICATION left by the said John Lynn at the Office of
the Commissioners of Patents on the 26th August 1881.
"AN
JOHN 'LYNN, of Sunderland, in the County of Durham, Engineer.
IMPROVED COMPENSATING CHAIN BARREL OR SHEAVE FOR STEAM OR HAND
STEERING APPARATUS."
My Invention relates to an improved chain barrel or sheave specially adapted
for steering apparatus worked either by steam or hand or combined (and applicable
also to other purposes), and has for its object the equalising of the power necessary
in operating the rudder from its middle (or fore and aft position) to "hard over'
either to port or starboard.
"
In order to accomplish this I fix upon the main shaft of any steering gear either
hand or steam (or both combined), instead of the ordinary chain barrel or sheave,
a chain barrel or sheave having its centre eccentric to that of the main shaft in
such a position that when the rudder is in its middle (or fore and aft) position, the
chain barrel or sheave shall be standing in a neutral position, such that any
movement in either direction will cause its eccentricity to take effect. The chains
attached to the "tiller" on rudder head and leading to port and starboard sides of
ship respectively, are carried along the deck in the usual manner and secured to
shackles fixed in the excentric chain barrel or sheaves, each chain working in its
own groove, or as may be in some cases, each chain having its own sheave fixed
excentrically on the main shaft.

page_text: The effect of the excentricity of the chain barrel or sheaves is to give a quick
motion to the "tiller" (through the chains) when the rudder is being moved from
its middle position (when its resistance is least) to "port" or "starboard," and to
gradually reduce the speed with a corresponding increase of power when the rudder
approaches the "hard over" position to "port" or "starboard" where its resistance
is greatest.
In hand steering, this compensating effect of the excentric chain barrel or sheaves,
makes the manual power required in steering more uniform, and in steam steering
where (as is now generally the case) automatic valve gear is used to cut off the
steam, the effect of the excentricity is to give additional leverage upon the rudder
just when it is offering its greatest resistance, namely, when approaching the hard
over position on either side, and when the steam is acting with diminished power
owing to the supply being cut off by automatic action of the valves.
The increased power due to the leverage of the excentric chain barrel or sheaves,
dispenses with the necessity for the expensive and cumbrous quadrant fitting on
the "tiller" end, as the chains may be attached direct to the "tiller."
The diameter. of the excentric chain barrel or sheaves is so proportioned as to
give the required movement of the rudder from "hard over port" to "hard over
starboard "by one revolution of the barrel or sheaves, and the chains leading to
tiller are at all times stretched "taut."
In some cases in lieu of an eccentric chain barrel or sheave, I use a chain barrel
or sheave forming a spiral having its centres of convolution eccentric to that of the
main shaft.