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E I R MA ‘ ‘ ‘ 4 3 < \ % ; 4 : ; TS FORTY CEN Tu il il HN WOW WAKER cell voltage rather than charge time and stop the charge when the open circuit voltage has risen to 2.1 volts. If high charging rates are used for any particular reason it is best to arrange to start the charge at a high rate and then progressively reduce the charging current as the on-charge voltage of the cell rises. This will keep the temperature of the cell within bounds and reduce the risk of damage to the elecrodes. This occurs naturally, incidentally, using a lead-acid battery to charge a silver-zinc cell, the normal maximum load-voltage of the lead-acid cell corresponding almost exactly to the terminal voltage of the silver-zinc cell fully -charged. Normally, however, silver-zinc cells would be charged at constant current equal to the 10-hour or 20-hour rate and any conventional charger with a terminal voltage greater than 2.1 times the number of cells being charged (in series) should be suitable for the job. All that is then necessary is a variable resistance of ballast resistors to limit the current to the required value, and an ammeter to check the current and a voltmeter to check the cell terminal voltage from time to time. It cannot be emphasised too strongly that the only satisfactory check on the state of charge is the terminal voltage of the cell. Until this rises to 2.1 volts the cell can be anything between one third and (nearly) fully charged; and to continue charging after the cell has reached 2.1 volts per cell can result in damage, or at least reduced working life. The ampere-hour efficiency of a silver-zinc cell, incidentally, is higher than that of a lead-acid cell (90-95 per cent), hence it is easy to over-charge on a ‘time’ basis by allowing a similar extra period of 20 per cent, as is commonly used with lead-acid cells. In the main, however, silver-zine cells are extremely robust and can take a lot of abuse which would quickly ruin a lead-acid battery, certainly in the matter of discharge rates. Maintenance, too, is reduced to an absolute minimum with just an occasional topping up with distilled water. As a guide to discharge rates, most silver-zinc cells are readily capable of repeated continuous operation at the 1hour rate (although the makers usually specify a 2hour rate as a maximum discharge). M.V.A. International M. Class Open Championships 1 gree the early date (April 27th and 28th) the 1963 event, held at Princes Park Lake, Eastbourne, attracted 26 entries including three from from Hamburg. On the first day, Saturday, conditions proved very calm and because of this and the comparatively large entry it was decided to sail the championship in two divisions, taking the top three boats of each to make a six boat final. .By Saturday evening nine heats and all outstanding resails had been completed and Sunday’s weather was awaited with apprehension. As it turned out, a light, south-westerly breeze had sprung up overnight and all divisional sailing was com- pleted before lunch. After lunch, the wind having dropped again, the final was sailed and out came spin- nakers which failed to fill. The fact that the westward end of the lake was almost completely blanketed by a row of houses and a line of trees made crews’ tasks even more difficult, still leaving the outcome of many boards more dependent upon luck than on skill. ; Despite all this, Ken Roberts built up a lead with Fandango which he sealed in the last board. The prizes were presented by the Mayor of Eastbourne, the German visitors receiving a small memento of the visit and they, in turn, presented Eastbourne with a china plate bearing the crest of Hamburg in way of a trophy for M class Championships at Eastbourne. The winning boat, Fandango, was a modified Foxtrot from C, Adams, Throughout the contest she carried a 70 in. rig and at the slightest hint of a breeze she would start to plane. fied Witchcraft Final Positions Fandango Tinpot Yvonne II Araba Doreen . Spindrift TJinpot, who came second, was a modi(Priest). ; K. Roberts C. Dicks D. Hardwicke D. Reed G. Porter A.J. Taylor Birkenhead Clapham Bournville Brighton and Hove Clapham Southend pts. pos. 20 1 1612 15 11 8 5 3 4 5 6 Far left: D. Hardwicke prepares “‘Yyonne II” for the start of qualifying board, Next: The second boat at readiness — C. Dicks’ **Tinpot’’, Above : The winning boat and crew. 356
