Damage to Opunake Jetty.

Opunake Times, 3 July 1894, Page 4

Damage to Opunake Jetty.

■ Mr J. 'H. Stewart’s Report. I'.have the honor to submit the following report as result of survey of damage done to the Opunake wharf. be two seaward spans of 80 feet (60 feet in all), together with the lauding or T platform have been carried bodily away, and the pier which now remains in position at the outer end of the remaining portion of the wharf is unsafe. The marine borers ( Teredo nacalis) having- so thoroughly perforated sections ox the main piles of this pier that it is in imminent danger of collapsing, and dragging with it the superstructure of the attached SO feet span. [Which has since occurred. — Ed.] * . 'iuo wharf gave way sometime in the early morning of the 25th of April last during a south-westerly gale with a heavy sea breaking over the shelter reef (bearing south-wes-terly aud about 80 from wharf), but a careful examination of tho wreckage and of the condition of the position of the wharf now standing leaves no shadow of doubt that the piles of the wrecked pier had been so thoroughly honeycombed by the marine borers that their collapse within a few weeks, even in ordinary weather, would have been an inevitable result. The bolts, shafts, and joints of the remaining piers aud superstructure are not strained or started ; nor is the timber damaged, except by the ravages of the teredo. The pile worm is secreted in large numbers in the present seaward pier (or 7th from shore). Tire adjoining pier coming backward is also very badly damaged, but the strength of the succeeding piers is not impaired, though the presence of the teredo may he detected in all but the first from the shore. The ravages of tho worm are apparently confined to sections of the timber which are submerged for the greater portion of the day, and I attribute the attack made on the inshore pier of these infested by the worm to the formation of small pools of seawater round tho piles, where a slight scour has taken place in the sand. From personal knowledge of Opunake, I can confidently say that the wharf bad previously weathered gales and seas quite as severe as those of the 2-fib and 25th April unharmed ; and taking into consideration that the piles and superstructure still remaining in position give no evidence'of damage from strain or any other natural effects of a heavy gale, and that the pile end which I had an opportunity of examining on the 25th April, fresh sawn from the wreck, then exhibited a proportion of tear or fracture not more than one tenth of the end area of the pile (the remaining nine-tenlhs of the cross section of the pile having literally crumbled away). I have no hesitation in fixing the teredo as tho s >le cause of disaster. Pelyention of i urther Damage from , the “ Teredo.” * ~ X Vvi-h to preface what little has lb he place dander the above heading by expressing surprise that, his precautions have hai to be taken to prevent the destruction of piles driven, fat New Plymouth from of the kr pi'owoim; it had not Sbcurred tsshc enginoer in-chatg.3 that svnilar preventives would be necessary at Opunake, I have it on go»d aufeqrity that twelve years ago timber tumi!afly J employed in New Plymouth harbor was being coppered as a protection. There appears to be only the one reasonable hope of success in dealing with those posts. The piles or any other pier timber, which, from its position is in danger of attack, should be well coated in boiling tar and cop-* pered. In those piers which have escaped almost unscathed I feci assured that the coppering will chock and eventually cxicnaSuato the* worm, but thetwo remaining - enter piers are so far. damage;! that the piles shall have to be immediately replaced by now ones, or at least strengthened by additional piling. Totava unsheathed lias, I understand, been used with success in northern par ts cf Now Zealand •in harbor Works, but after inspection of the old timber (ironbark) I cannot recommend unprotected timber of any kind to be used. (JoriO'ivc sublimate, creosote and other preparations and remedies have been suggested, but in nearly every case the expense is prohibitory, and’ in all cases the results are doubtful. Repairs. If undertaken at cnee the repairs necessary to render the present wharf useful for surf boats discharging will .not bo costly beyond the price of the ’ P il ° timber. It has been suggested to use the sound lengths of the wrecked piles by driving these beside the present damaged piles of the outer • phrs and bolting together. In following ;h‘s recommendation it must be borne in mind that as nothing can lxp, d no to save tlio original piles. in a short time be harfPSg a dead weight bolted onto # the now and healthy timber. In all ■ structures such superfluous loading must 1)3 injurious, more especially, where the force of heavy seas has to be resisted. ' I would advise that heart cf iotara be Use I in preference. vV : Tho attached extract from Chambers’ M icyelopoedia referring to the rapid operation of tho teredo shows tho nr rent n ce-siky of immediate action on tho part of tha ccunpa -y. Also attached yon will find memoranda of tho proposed rod. la conclusion, I would urge the iito;nodixv.‘.u. of a’l fho remaining pica, winch miy ho suiiicion’lv hrfal to warrant thru \?-itiir (kmc. . ’ Hf '