Fatigue, residual life & crack assessment — SMENG-FF

SMENG-FF service

Fatigue, residual life & crack assessment

Practical evaluation of cracked and uncracked rigging parts. One decision for the owner: keep sailing, repair, or replace — with the numbers behind it.

Can this part stay on the boat?

We model the intact part, put the crack found by NDT (or a conservative assumed crack) onto that stress field, and compare it with a new part under the same sailing loads.

Operate

Safe today, and remaining life covers the next season or survey. Keep sailing to the load and inspection date in the report.

Repair

Usable for a short window, or a defined repair restores margin and life. Sail only inside that window.

Replace

Margin too low, life shorter than the next season, or the crack cannot be inspected or repaired with confidence.

The three numbers on the cover

1. Safety margin today A load factor, not millimetres and not a stiffness ratio. “1.7 × peak sailing load” means the cracked section is assessed as still safe up to 1.7 times today’s expected peak load. Below 1.0 ×: do not rely on the part.
2. Remaining life Seasons or hours until the crack reaches the agreed limit. Best when we have sensor data. If we do not, we use an agreed sailing programme and label it as an assumption.
3. Life versus new Remaining cracked life ÷ life of a new part, same design, same sailing programme. That “new” definition is written once in the report and not changed later.
Worked example — how to read the cover line

Operate this season — forestay fitting, crack depth 2.1 mm (from NDT).

1.7 × peak sailing load = safety factor on load, not 1.7 mm. If the highest expected load in that section is 80 kN, the cracked part is still assessed as safe up to about 136 kN. If that factor were 0.9 ×, the part would not be safe at today’s sailing load.

~4 seasons at last year’s spectrum = crack-growth life using last year’s measured loads from a sensor or similar. No sensor file: we agree a typical year with you and state that it is assumed.

~35% of a new fitting = 4 seasons left on the cracked part ÷ about 11 seasons estimated for a new part under the same programme. Same programme both sides; the formula does not change mid-job.

Illustrative example only. A real report uses your NDT and your working load or sensor file. Re-inspect by the date on the report.

Repeated sailing loads and sensor spectra are in scope. Hard slams, grounding or shock studies are a separate job. This is a decision aid for the owner and technical manager; it is not class certification unless the contract says so.