NPT35HKC

Common issues

• Hook and pawl wear from repeated drills, reducing the margin before the mechanism fails to hold reliably
• Corrosion or paint build-up on moving parts of the release mechanism, especially after long periods without exercise
• Incorrect resetting after a drill or previous release, leaving the hook only partially engaged
• Hydrostatic interlock (on-load release inhibitor) fouled or seized, preventing correct operation of the safety interlock
• Fall wire or block misalignment putting uneven load on the two hooks of a twin-fall system
• Grease or lubricant of the wrong type used, attracting dirt and stiffening the mechanism instead of freeing it
• Control wire/handle linkage stretched, corroded or misadjusted, changing the force needed to operate the release

Inspection checklist

• Confirm the mechanism has had its 5-yearly overhaul (including load test) per SOLAS/LSA Code requirements and the record is current
• Carry out the required operational test/drill and confirm both hooks release simultaneously under the correct load condition
• Check the hydrostatic interlock (on-load release inhibitor) resets and functions correctly, preventing on-load release until the boat is waterborne
• Inspect hooks, pawls and keepers for wear, deformation or corrosion
• Verify correct resetting procedure was followed after the last drill or use, with hooks fully engaged
• Check control wire/rod runs freely, is correctly tensioned and free of corrosion
• Inspect fall wires, blocks and davit alignment for even loading between the two falls
• Confirm placards/instructions at the release station are legible and match the current procedure
• Check lubrication matches the manufacturer's specified type and interval - not a generic substitute

Service intervals

Typical wear limits

Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.

Critical spares

• Hook and pawl assembly, matching the certified type
• Hydrostatic interlock unit
• Control wire/rod and end fittings
• Return springs
• Manufacturer-specified lubricant (not a generic substitute)
• Fall wire, sized to the original specification

Safety

• This is a life-critical on-load release mechanism - never carry out load-bearing checks with personnel in the boat unless the drill procedure explicitly requires and permits it
• Incorrect resetting or a fouled hydrostatic interlock can cause an inadvertent release under load or, conversely, a failure to release when needed - both are fatal-incident hazards documented in industry casualty records
• Follow the manufacturer's and SOLAS drill safety procedures exactly; do not improvise a test method
• Only use spares and lubricants matching the type-approved specification - substitutions can defeat the release tolerance the mechanism was tested to

Class survey

Class and flag administration surveys check that the annual thorough examination and 5-yearly overhaul (with load test) records are current per MSC.1/Circ.1206, that the hydrostatic interlock functions correctly, and that drill records show successful launching within the required interval. This is consistently one of the most heavily scrutinised LSA items at survey given its incident history industry-wide.