This historical boat-detaching hook has a hinged tongue held by the eye of a separate release lever. A lanyard withdraws the eye so the tongue can turn out of the tackle hook. The animation shows the arrangement described by Brown and Hiscox; the calculator compares release-lever proportions.
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.
Historical geometry after Brown492 and Hiscox810. Ideal lever comparison only; no proof-load or release-certification calculation.
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.
Hook and lever questions
Does the long arm carry the boat?
No. It operates the retaining eye. The supporting load path passes through the tackle hook, tongue and standard.
Can boat weight be entered as eye force?
No. The eye force depends on tongue and contact geometry. This calculator treats it as a separate assumed force.
Is this a modern on-load release rating?
No. The model explains a historical mechanism and ideal lever moments, not certification or release under a suspended load.
Primary references
Henry T. Brown, 507 Mechanical Movements, movement492, Brown & Level’s boat-detaching hook. Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, figure810, printed page212, shows the same tongue, retaining-eye lever and lanyard arrangement.
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