Today’s Survey — Understanding Catamaran Hull Construction in Practice
- Feb 5
- 2 min read
Today’s assignment involved a focused hull structure inspection of a cruising catamaran ashore in Aktio. This was not a pre-purchase survey, but a targeted assessment requested by the owner following historic repair work and with the intention of gaining clarity on overall structural condition before marketing the vessel.
These types of surveys are often some of the most interesting, as they allow a deeper look into construction methods and how different inspection techniques interact with modern composite builds.
One of the key observations during the external inspection was a widespread dull response when percussion sounding the hull, particularly in way of compound curvature and the transitions between the hulls and the underside of the bridgedeck. For those unfamiliar with survey practice, percussion sounding is a standard non-destructive technique used to identify laminate inconsistencies or delamination. However, interpretation must always be considered in context.
On multihulls, especially those designed for offshore cruising, laminate schedules commonly vary across the structure. Areas may incorporate a mix of solid GRP laminate and localised cored sections to achieve stiffness without unnecessary weight. These transitions can naturally produce acoustic responses that differ from flat solid panels and are not inherently indicative of defect.
Internal inspection confirmed this was exactly the case. By examining accessible bilges, areas beneath sole boards, and under berth spaces — and even using controlled lighting to observe laminate zoning — the hull construction showed consistent and well-defined boundaries between laminate types. Moisture meter readings were taken throughout and did not indicate abnormal ingress patterns.
This illustrates an important point for owners and buyers alike: no single inspection technique provides a complete picture. Professional surveying relies on correlation — visual inspection, acoustic response, moisture assessment, construction knowledge, and experience — all combined before drawing conclusions.
The historic repair area that prompted the inspection was also assessed. Structurally, the work appeared sound and comparable to original construction below the waterline. Some cosmetic finish variation was visible above the waterline where surface refinishing had been undertaken, but this did not affect laminate integrity.
The inspection also noted ageing of the epoxy Coppercoat antifouling system, with localised detachment and deterioration around the waterline. This is typical of coatings reaching the latter part of their service life and falls within routine maintenance considerations rather than structural concern.
Days like today reinforce why marine surveying remains as much an applied craft as a technical discipline. Composite yacht construction is sophisticated, and understanding how materials behave — acoustically, visually, and structurally — is critical to providing balanced, reliable advice.
Every vessel tells its own story. The key is knowing how to read it properly.
Steven Truss MIIMS
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