A catamaran survey concentrates on load paths a monohull never sees: bridge-deck to hull attachment, forward and aft crossbeams, nacelle underside slamming damage, bulkhead tabbing, and core saturation in the bridgedeck and dagger-board cases. Rig loads on sailing cats can be asymmetric and show as hull distortion.
Structure: where multihulls differ
| Area | Why it matters | What we look for |
|---|---|---|
| Bridge-deck to hull junction | Carries all cyclic loading between the hulls | Tabbing condition, laminate cracking, print-through, movement evidence |
| Forward crossbeam / dolphin striker | Takes forestay and wave loads | Cracking at the beam ends, corrosion in metal beams, bonding integrity |
| Nacelle underside | Wave slamming, repeatedly, for the vessel’s whole life | Delamination, star cracking, core saturation, previous repair |
| Bulkheads and their tabbing | Primary structural connection in a composite hull | Tabbing lifting, resin-starved joints, cracking at hard corners |
| Dagger-board or keel cases | High local load and a water path into the structure | Case integrity, core saturation around the case, bearing wear |
| Rudders and steering linkage | Two of everything, often unequally worn | Bearing clearance both sides, linkage synchronisation, stock condition |
| Engine installations | Two, in confined spaces, often poorly ventilated | Bed condition, alignment, exhaust routing, ventilation adequacy |
Composite condition work
- Percussion sounding across the bridgedeck, nacelle, hull sides and deck, listening for tonal change.
- Moisture mapping with the instrument type and scale stated, after an adequate drying period.
- Core saturation checks around every deck penetration — stanchions, cleats, hardware, hatches.
- Gelcoat crazing patterns at hard points, which indicate load rather than cosmetics.
- Agreed core samples where percussion and moisture disagree and the answer matters.
- Previous repair areas mapped and treated as areas of interest, not as resolved.
Rig and asymmetry on sailing catamarans
A catamaran rig loads both hulls through the crossbeams. Where one hull has taken more load — from a grounding, a hard landing off a wave, or a rig tune that has been wrong for years — it shows as distortion: doors that no longer fit, tabbing cracks on one side only, or a measurable difference in the geometry between hulls. We check both hulls against each other as well as against the drawing.
Systems on a cat
Two of most things doubles the survey time and the failure surface: two engines, two saildrive or shaft installations, two rudder systems, often two battery banks and two heads. The most common finding is asymmetric maintenance — the accessible engine serviced, the awkward one not.
Frequently asked questions
Do catamarans cost more to survey than monohulls?
Slightly, because there is more structure and more systems to inspect. Expect the upper end of the band for the length.
Do you check saildrives?
Yes — diaphragm condition and date, leg corrosion, anode condition, oil condition and seawater ingress evidence. Saildrive diaphragms have a service life and are frequently overdue.
Is osmosis a problem on catamarans?
Same as any GRP hull, but the higher-consequence moisture issue on a cat is core saturation in the bridgedeck and around deck penetrations, not hull blistering.