SCHOONER HOKIANGA.

New Zealand Herald, Volume LXVI, Issue 20162, 24 January 1929, Page 12

SCHOONER HOKIANGA.

ADJUSTING THE COMPASS

READY FOR TRIALS TO-DAY

SHIP'S TWIN DIESEL ENGINES

The new auxiliary schooner Hokianga, which will take the place of the lost Isabella de Fraine in the Hokianga trade, is now equipped with her twin Diesel engines. and to-day will go for her trials. Yesterday afternoon she made her fust trip under her own power, going down to the dolphin below the eastern breakwater to have her compass adjusted—in othet words to have compensation mado for the contra-attraction of iron in the ship. To tho average person, doubtless, a mariner's compass is just an instrument which one buys in a shop to enable one to steer in the exact direction required. 'l'o begin with, however, its needle usually does not point to the geographical north, but diverges to one side or the other, this being called the magnetic variation declination Whet, fitted in a ship, the distribution of iion makes for further variation, and after being launched the first essential is for such deviations to be counteracted. And once every year a vessel miist have her compass 'ested for errors brought about by such influences. For this purpose the dolphin has been erected It is a massive concrete structure, and round it they " swing ship," a job that is not always froo from difficulty. The Tell-tale Pelorus. On board is the adjuster—Captain Clifie officiated yesterday —and he places alongside the compass his pelorus, or dumb-card, on a iirm tripod. From bearings ashore he checks the instrument, and by magnets corrects it. Captain Cliffo has no fewer than 32 bearings which he uses. They are fioin three to seven miles distant. He takes such points as a mast of the radio station, the cone of Rangitoto. a point ou Brown's Island, and odd trees down toward Mount Wellington. So aided, he checks every point as the vessel, tied fore and aft to the dolphin is swung round it. Horizontal and vertical magnets are used to compensate the influences of metal in the ship, and arc fixed and sealed in position under the eye of the expert, whose work is subsequently checked by official officers. It is interesting to note that in some parts of the world disturbance is caused to a ship's compass by the presence of magnetic rocks at the bottom of the sea It is obvious, therefore, that " plain sailing " can often be just a figure of speech. A Stout Craft. The Hokianga is a stout craft. She is 97ft. long, 25ft. in beam, and has a beam draught of Bft. She has been specially designed for working the Hokianga Bar, and experts are pleased with her.

Although she has two masts, her trisails will be more auxiliary than her engines, which will drive her at 10 knots. Each of the four cylinder lairbnnks-Morsc full Diesel direct-reversing engines has a nominal rating of 100 h.p., but their axle power is 156 h.p. The Hokianga is the first coastal vessel, other than a launch, to be so powered at launching. The engines burn residual oil. the initial pressure of compressed air being raised by the heat of the flame from the fuel valve. They will start instantly from cold, and are so sensitive that a half-turn of a wheel will reverse them in three seconds. Their use obviates the employment of firemen, and two engineers will comprise the mechanical staff. It is computed that the vessel can be run at 10 knots for a cost of five shillings an hour m fuel and lubricating oil-. She has a high poop to withstand following seas, and a bridge amidships will enable the master to con her over a bar without having to take the customary course of going into the fore rigging.