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Treatment behaviour of fresh and inservice catamaran logs
2001 - IRG/WP 01-30255
Catamaran is a conventional fishing craft fabricated by lashing 4 - 6 shaped logs of soft timber together. Over 73,000 of these craft fabricated out of 165,000 m3 of wood are in use along the vast east coast of India. Each craft lasts for 5-7 years. Over 15,000 m3 of timber is required annually for repairs and replacements of the craft. Such huge demand exerts enormous pressure on the resources. It is apt, therefore, to extend the practice of wood preservation to the catamaran sector and conserve the precious raw material. In order to achieve this objective, our Institute took up technology demonstrations way back in 1968. However, because of illiteracy and socio-economic constraints of the traditional fishermen, the efforts did not catch up well. Under these circumstances, as a renewed measure of propagation, treatment of 3 each of fresh as well as inservice catamarans was taken up some time ago. The results of pressure impregnation of these six catamarans made of Albizia falcataria timber with copper-chrome- arsenic (CCA) preservative were analyzed to understand the preservative absorption of the constituent logs. The study revealed that there was no significant variation in the total quantity of chemical absorbed among the fresh as well as inservice catamarans that served for three different periods prior to treatment . However, significant difference was noticed between all the fresh catamarans clubbed as one group and the inservice craft as another group. The CCA absorption ranged from 13.52 to 15.30 kg.m-3 averaging at 14.60 kg.m-3 in the fresh craft and 18.65 to 22.10 kg.m-3 averaging at 20.42 kg.m-3 in the inservice catamarans. Also, each constituent log of the six catamarans differed in its chemical content from the other. The analysis proved that it is possible to treat the inservice catamarans and achieve good preservative retentions.
V Kuppusamy, M V Rao, M Balaji, K S Rao

Preservative absorption response of planks of Anogeissus acuminata for plank-built catamarans
2002 - IRG/WP 02-40245
Due to shortage of timber coupled with other compelling factors, traditional fishermen along the east coast of India, especially of Andhra Pradesh, of late, are departing from conventional log type wooden catamarans. Instead, they are fabricating catamarans out of timber planks of hard woods and utilizing thermocol for buoyancy. Mostly, locally available timber of a Combretaceae species, Anogeissus acuminata (Yon) is used to fabricate these plank-built catamarans. Since these catamarans are also built with untreated timber, there is every need to extend wood preservation technology to these craft also so as to achieve enhanced service life and conserve the resources. Therefore, the Institute of Wood Science and Technology took up treatment of timber meant for five such craft with copper-chrome-arsenic (CCA). Thirteen different logs were procured and converted into planks and batons of suitable sizes, debarked, cleaned and air dried under shade. While the length of the planks ranged from 0.81 to 6.53 m, the width varied from 16 to 44 cm. After sufficient seasoning, the material was pressure treated with 6% CCA by full cell method as per IS: 401 (1982). Chemical retentions were computed from the weight gained by the individual planks and sets of 20 batons immediately after treatment. The preservative absorption in the planks ranged from 13.05 to 69.80 kg/m3 averaging at 25.90 kg/m3 and that in the batons averaged at 32 kg/m3. The quantity of CCA absorbed by the planks was analyzed with reference to their length, width, thickness and volume. Planks when categorized to different length and volume groups exhibited clear difference in the intake of chemical by them but when categorized into different width and thickness classes showed not much variation. All the treated planks and batons after air drying in shade for 15 days were fabricated into five catamarans. Thus, though the planks of A. acuminata are either very long or very wide, they showed a positive response to CCA treatment by absorbing reasonably good quantities of preservative. Similarly, on fabrication of the catamarans, an average retention of 21.79 to 25.43 kg/m3 of CCA per craft could be achieved. These values fall into the recommended preservative absorption range of 16 to 32 kg/m3 (IS: 401, 1982) for marine structures.
V Kuppusamy, M V Rao, M Balaji, K Rao