HARDWOOD POLES.

Manawatu Standard, Volume XLIII, Issue 521, 6 October 1922, Page 5

HARDWOOD POLES.

WHAT THE DISTRICT NEEDS. SILVER PINK FOR LOW VOLTAGE LINES. Sonic intoresiing information bearing on the matter of hardwood poles for electric transmission lines in (hia district whs given to a “Standard” reporter by Mr W. A. Witters, engineer to the Manawatn-Oroua Electric Power Hoard. The selection of suitable poles lias become a matter of vital interest in recent times and was, it will be remembered, provocative of a discussion at the last meeting of tho Manawatu. County Council. Anent the points there raised, Mr Waters made to the pressman some very interesting statements concerning his observations and investigations in this unmeet-ion, especially regarding some of the South Island lines. Conversing on the subject, bo ndirtnod that, lor lho past fifteen years, iron bark poles of the natural round type had been imported into this country by tho thousand. This was, he said, the cheapest typo of Australian pole imported and was generally classed as ironbark, or “mixed hardwoods.” It was pointed out that there were over 120 varieties of the eucalyptus family, die source of the Australian pole supply, but it had not been generally realised until lately that thousands of those imported polos contained only a small proportion of heart timber —in many in. stances the proportion of sap wood varied up to as high as 80 per cent, of the total wood in the pole. This sapwood had now been proved to rot away completely in a period varying from twelve months to seven years, leaving only the heart of the pole, but ns the heart m many eases was such a small proportion the durability of the remaining part was a negligible factor, as the strength of the polo minus the sap was below the safety limit. At tho Power Board’s ofllce there is a striking collection of photographs taken by tho engineer during a recent trip in the South Island showing natural round Australian polos in an advanced stage of decay after a period of service of only eight years. Poles that were Sj inches in diameter at the butt had rotted away, the reporter was informed, so that only five inches of lu-art wore left. In some of the photos the heart was only inches, An interesting experiment was carried out By Mr Waters on similar poles 10 years ago. The poles were tarred at “wind and water” lino before erection, tarred again six months after erection, and again three years later, but the experiment was u failure as the poles rotted just the same. The Manawatn-Oroua Power Board, he said, was calling tenders for 12,000 ironbark polos at the present time, tho specifications calling for dimensions of the poles to be clear of sap and the timber must be all heart.

The board Lad also joined with the Manawatu County Council in taking over an area, of silver pine forest at Pokako, to cut poles and sleepers, etc,, the Manawatu council requiring the sleepers for its tramway. Silver pine is not, commented Mr Waters, generally known in this part of the island, as the timber only grows on the slopes of Mount Ruapehu and on the west coast of the South Island, It is a close-grained timber similar in colour to the familiar white pine, but the grain _is more akin to toturn. Its lasting qualities are undisputed, but its strength is considerably below that of ironbark, hence the latter timber will be used in the lines at angles and terminal poles. Another shortcoming of the silver pine is that it is difficult to get in lengths over 28 feet of the requisite size for poles, hence the board will use silver pine generally on the low voltage transmission Tines in tho country, for which it is eminentlv suitable.