Tests et comparatifs d'ancres 2eme partie
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Practical Cruising Will my anchor hold - Part 2 annhnr hnlri Prof John H Knox continues his series of tests. Having identified anchors which roll out, he now turns his attention Tpfopw THERE are many reasons why some anchors tend to roll but this month I show how the holding of a roll-stable anchor depends upon scope, anchor weight and the rate it's dragged For those who missed last month's article, I'd simply say that my experiments were conducted in a shallow tidal pool at Longniddry beach on the shores of the Firth of Forth, where the bottom was medium-hard sand. Anchors were dragged through the sand by a 5 or 10-part pulley system that enabled forces of up to 700 kg to be applied at the anchor. The cable was either nylon multiplait or, for the heavier anchors, wire plus K-inch chain. It passed over a pulley held one metre above the sand by means of a pyramidal frame. The scope, S/D (S=cable length from pulley to anchor, D=the height of the pulley above the sand), was therefore equal to the length of the pulling cable from the anchor to the pulley, The tension on the anchor cable was measured using ANCHORWATCH, a device invented by Kevin Scott and myself which uses a load cell to measure forces up to a ton. The CQR type, HiBlade, Delta, Brittany, Danforth, Danforth copy, Bruce, claw and SPADE anchors tested ranged in weight lifelong interest in boats and in in kayaking while on sabatical leave in Utah. He took to first in a Graduale and later an bought Myfanwy, a Hustler 35, the west coast of Scotland. Practical Boat Owner 428 August 2002

Practical Cruising Will my anchor hold? - Part 2 IN CASE YOU MISSED PART 1 The SPADE gave the best results in last month's test I looked at the roll stability I of some commonly used yacht anchors. The results kg) rolled out when dragged some five shank lengths and when veered. The plough (10 lb) also behaved in the same rolled out consistently when concluded that, under stress, these anchors could drag - with serious consequences HiBlade, Delta, claw and SPADE anchors, on the other hand, were stable to rolling, both when dragged straight and when veered, with the SPADE giving the best...

Basically, what this all comes down to is scope and angle. As the scope gets less and the angle becomes bigger, the less likely your anchor is to hold well. In Prot Knox's experiment, the SPADE gave the flattest dependence on scope, while the claw and HiBlade gave the steepest. angle at the anchor increased, and the scope lowered. The decrease in hold was more or less linear with the angle but wasn't the same for all anchors. Those which showed the least decrease as the angle steepened were the SPADE and Danforth. The Delta came next. The steepest decline of hold with angle was found on the...

Practical cruising Will my anchor hold? - Part 2 precise, that under the peak loading it'll drag or plough at three centimetres per second, which could be regarded as a maximum for safety. For this situation, we can then replace 'Peak Cable Tension' from Formula 3 with 'Maximum Anchor Holding': Maximum Anchor Holding = (1/500) x (L0A); x What this implies is that if we want to keep below the Maximum Anchor Holding, the wind speed can't be above some critical value which can be found from Formula 4. So, we should now re-label 'Wind Speed' as 'Maximum Safe Wind Speed'. We can also incorporate...