COMPASS ADJUSTMENT

Evening Post, Volume CVII, Issue 21, 25 January 1929, Page 11

COMPASS ADJUSTMENT

PROCEDURE DESCRIBED *

On Wednesday afternoon tho new auxiliary schooner Hokianga, recently launched at Auckland, made her first trip under her own power. She went down to the dolphin below the eastern breakwater (writes the "New Zealand Herald") to have her compass adjusted —in other words, to have compensation made for the effects of the iron in the ship. To the 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. To begin with, its needle usually does not point to the geographical north, but diverges to one side or tho other, this being called the magnetic variation. When fitted in a ship, the distribution of iron causes further variation, and after being launched the first essential is for such deviations to be counteracted. And once every year a vessel must have her compass tested for errors brought about by such influences. -For this purpose the dolphin has been erected. It is a massive concrete structure, and round i? they "swing ship," a job that is not always free from difficulty. On board is the adjuster—Captain Cliife officiated on the Hokianga—and he places alongside the compass his pelorus, or dumb-card, on a firm tripod. From bearings ashore he checks the instrument, and by magnets corrects it. Captain Clifl'e has no fewer than 32 bearings which he uses. They arc from three to seven miles distant. He takes such points as a mast of the radio station, the cone of Bangitoto, a point on 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 are 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 spa. It is obvious, therefore, that "plain sailing" can often bo just a figure of speech.