This historical mechanism is a boat-detaching hook. Brown’s index labels movement 492 “beat-detaching,” but the drawing and its description explicitly identify a boat-release device. The former clockwork interpretation of this page was incorrect. The mechanism uses a hinged tongue retained by the eye of a release lever mounted on the boat.
Boat-detaching Hook Lever Calculator
Explore the release sequence and compare lever arms, ideal contact force and attachment-point travel. The entered eye force is not the boat weight, and the result does not rate a lifting appliance.
Equation Used
- Latch force is entered independently; it is not derived from a suspended boat load.
- Both lever arms rotate together about one fixed pivot.
- Tongue swing is an illustrative sequence setting.
- No friction, loaded-release dynamics, interlock, strength or lifting-appliance certification is calculated.
Source correction: Brown, 507 Mechanical Movements, movement 492; Hiscox, Mechanical Movements, item 810. The existing URL is retained so links continue working.
How the Boat-detaching Hook Works
An upright standard is attached to the boat. A tongue is hinged at its upper end and passes through the tackle hook. The upper eye of a separate lever holds the tongue in its closed position. The lever pivots near the middle of the standard.
Pulling a lanyard attached to the lever’s lower end rotates the lever and withdraws the retaining eye. The tongue can then turn out of the tackle hook. Brown describes a device at each end of the boat, with both release lanyards operated together.
Historical Use
The reference illustrates detaching a boat from its lifting tackles. This interactive diagram explains the historical arrangement; it is not a modern lifeboat release specification or an operating instruction for an installed appliance.
Ideal Lever Ratio and Arc Travel
For forces perpendicular to the two lever arms, moment balance gives Flanyard × Llong = Feye × Lshort. Each attachment point follows an arc of length Lθ for a rotation θ in radians.
The force at the retaining eye depends on the actual tongue, hook, contact angles and loading. Entering that force independently avoids pretending the boat’s weight can be substituted directly. The animation illustrates disengagement; it does not calculate contact clearance under load.
Worked Lever Example
With a 300 mm lanyard arm, 60 mm eye arm and assumed perpendicular eye force of 100 N, the ideal lanyard pull is 20 N. A 25° lever rotation moves the lanyard attachment through a 130.9 mm arc and the eye through a 26.2 mm arc. These are geometric comparisons, not a release-load rating.
What the Animation Shows
The key features are the boat-mounted standard, hinged tongue, retaining eye, lever pivot and lanyard. Release occurs in sequence: the eye withdraws, then the tongue turns and the tackle separates. The reverse animation is an illustrative reassembly.
Actual operation depends on the complete lifting and release system, including contact geometry and interlocks. Those are outside this lever comparison.
Questions
Why did this page previously discuss a clock?
The index entry says “beat-detaching,” but movement 492 itself says “boat-detaching” and illustrates a boat-release hook. The previous interpretation has been corrected.
Can boat weight be entered as the eye force?
No. The contact force at the retaining eye depends on the tongue and hook geometry; it is not generally equal to the suspended weight.
Does the calculator establish a safe release load?
No. It compares an ideal lever and geometric travel only.
Primary References
Henry T. Brown, 507 Mechanical Movements, movement 492, Boat-detaching hook (Brown & Level’s). Compare the index spelling with the movement’s own description.
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, item 810.
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