The yacht steering gear in Hiscox item 880f uses right- and left-hand threads on one shaft to move two nuts in opposite directions. Links connect the nuts to the rudder-post cap. Explore an illustrative symmetric linkage and calculate its rudder angle from screw travel.
Declared Opposed-Screw Rudder-Linkage Geometry
Enter declared neutral nut half-spacing, screw lead per nut, signed shaft turns and rudder-cap arm radius. The worksheet solves one symmetric ideal linkage closure; it does not predict steering torque, hydrodynamic load, strength, backlash or safe vessel design.
Equation Used
- Both nuts move equal distances in opposite directions on ideal right- and left-hand threads with the same declared lead.
- At the neutral station the rudder-cap angle is zero and equal link length is derived from the declared half-spacing and cap radius.
- The animation moves between neutral and the declared signed shaft-turn endpoint while preserving both link lengths exactly.
- Thread form, gears, steering wheel, friction, backlash, compliance, buffers, stops, rudder hydrodynamics, torque, strength, materials, structure, redundancy, vessel handling and safety are excluded.
Opposed nut travel rotates the linked rudder-post cap in this symmetric model. The animation moves between neutral and the entered endpoint while the results report the endpoint geometry.
Opposed screw threads move two linked nuts
Hiscox item 880f shows a single horizontal shaft carrying right- and left-hand screw threads. Rotation sends the two nuts in opposite directions, and links between those nuts and the rudder-post cap turn the rudder.
Buffer rings at both shaft ends are identified as taking up jar. The schematic shows those components using an illustrative symmetric arrangement of equal-length links.
A historical yacht steering gear
Hiscox identifies this mechanism specifically with Emperor William's yacht Meteor. The opposed screws provide coordinated movement of the two linked nuts to turn the rudder-post cap.
Declared symmetric linkage closure
The identities preserve equal link length while the opposed screw nuts move symmetrically. The entered dimensions do not represent measured vessel dimensions, and steering loads are not calculated.
Declared geometry example
For x0=240 mm, travel per nut per turn p=8 mm/rev, n=1.5 turns and r=100 mm, each nut travels +12.0 mm, nut separation becomes 456.0 mm, the ideal rudder-cap angle is -7.07°, and each link remains 260.0 mm long.
Geometry and steering loads
Screw lead and shaft turns set the nut travel, while link length and cap radius constrain the resulting angle. Calculating steering torque also requires rudder loads and transmission efficiency. The model does not establish strength, backlash, travel stops or suitability for a vessel.
Novel steering-gear questions
Is this an Ackermann road-wheel linkage?
No. Hiscox item 880f is a yacht rudder-post mechanism.
Are the entered dimensions from Meteor?
No. They are declared illustrative geometry.
Does the calculator determine steering torque or safe scantlings?
No.
Novel steering-gear reference
- Hiscox, Mechanical Movements, page 227, item 880f: primary public-domain plate and caption identifying the Meteor right/left screw shaft, travelling nuts, links, rudder-post cap and buffer rings.
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