Non-destructive evaluation of the 18th century ship wreck Vrouw Maria

We analyze the current condition of pine and oak samples recovered from a sunken, 240 years old Dutch merchant ship wreck, the Vrouw Maria, with ultrasound and other non-destructive methods. To evaluate its physical condition - mechanical properties- ultrasonic through-transmission sound velocity measurements at 0,3-4 MHz were performed along the radial and longitudinal wood fiber directions. Presence of large discontinuities (e.g. holes created by ship worms) within the samples were probed using 2 MHz ultrasonic pulse-echo measurements. DNA-based methods (community DNA extraction, amplification (PCR) of SSU rDNA, cloning, restriction fraction length polymorphism (RFLP), sequencing) probed presence of microbes, particularly fungi, in the samples. X-ray diffraction and X-ray fluorescence measurements were performed with a synchrotron to determine the extent of degradation at the nanometer-level in the wood cell walls and changes in the elemental composition of the samples. The ultrasonic measurements detected a layered structure in the pine sample featuring a thin (1-4 mm) mechanically degraded layer on top of almost intact wood (60 % decay in the stiffness modulus compared to the intact part). For the oak sample, a 49% stiffness modulus reduction was detected compared to a freshly felled reference sample. DNA-analysis detected the presence of soft-rot fungi in the degraded layer and in the underlying compact wood (to 2 cm depth). Fungal DNA was more abundant below the heavily degraded layer indicating that fungal degradation had moved deeper towards the non-degraded parts. X-ray diffraction and fluorescence indicated presence of Fe throughout the sample and heavy degradation of the crystalline cellulose in the degraded layer. The results offer insight into the condition of the entire ship wreck, and therefore support decision making regarding possible lifting of the ship.