Choosing an anchor (longish)
This article was recently published in the UK.* Interesting reading.
Choosing An Anchor
by Alain Hylas (Inventor of the 'Spade' anchor)
To select an anchor, I will base my choice on three points:
Your anchor is your best insurance and, like your insurance, it seems expensive only before the accident occurs. When the weather deteriorates and your boat drags towards the rocks, it is too late to regret the tens of pounds saved on the purchase price. If your boat is tossed on the shore, then the cost may well be thousands of pounds. Security and quiet nights at anchor don't have a price.
The weight of your anchor has almost no relation to the holding. Holding is related to :
The stability of your anchor
Its surface area
The shape of the holding surface
All recent tests have proved that aluminum anchors have the same holding as steel anchors of the same size (Practical Sailor, Bateaux, Voiles magazine.)
However, weight is very important for the PENETRATION of the anchor. If you choose a light (i.e. aluminum) anchor, then favour stable models, those with a penetrating angle like a chisel and those with a heavily weighted tip. (More on this later.)
Efficiency of an anchor is a function of both penetration and holding.
To ensure good holding, an anchor must first penetrate regardless of the sea bottom type, as quickly and deeply as possible. Once set, the anchor must not break free regardless of weather conditions. This is a function of anchor stability and the shape and size of the holding surface
Penetration is related to two factors:
1 - Penetrating angle : I will define the working angle of four classical tools:
Spreader: - a tool forming an angle with the material in front of it of less than 70 degres.
Scraper: - a tool forming an angle with the material close to 90 degres
Chisel: - a tool forming an angle with the material in front of it of about 120 degres
Razor: - a tool forming an angle with the material in front of it of more than 150°
- Out of these four tools, only the "chisel" has been concieved for penetration.. ask the Carpenter.!!..
- The penetrating edge has to be as sharp as possible...
2 - Pressure on the tool: More the pressure, easier will be the penetration... Obvious...
Look at the percentage weight on the tip of some classical anchors:
(from Practical Boat Owner, page 80 n° 391 - July 1999)
The anchor having both the right penetrating 'chisel like' angle and the heaviest tip will have the maximum chance of penetrating, even in difficult sea bottoms such as hard sand, coral and weed
Holding is related to three factors:
Holding surface area
1 - Stability:
In this regard, the conclusion of John Knox (P. 81 - PBO n° 427 July 2002) confirms completely my own observations as well as the results of the tests done by the French "Voiles Magazine":
- Generaly speaking , ALL HINGED ANCHORS are unstable (Plow anchors, fluke anchors) Under strong pulls, they corkscrew and break free.. (and I can explain why..)
-Stable anchors of the new generation could slightly drag under strong wind gusts, but they keep a constant high holding and they will not break free suddenly... (Very SAFE behaviour)
2- Holding surface:
Try to pull one square meter of steel on the bottom, this is quite easy.. Now bury this plate of steel in the bottom an try again.. Holding has nearly no relation with the weight, but is related to:
- The surface area perpendicular with the direction of the pull..
3-* The shape of this surface -
a "wing" shape has an "holding" coeficient of 0.1
a "chevron" shape has an "holding" coeficient of 0.5
a "flat" shape has an "holding" coeficient of 1.1
a "concave" shape has an "holding" coeficient of 1.7
Or in other words, a surface with a "Chevron" shape must be more than three times the area of a surface with a concave shape to have the same holding.
This may seem simple, but in addition:
A good anchor must hold regardless of wind and /or current change of direction.
lt sould not have the possibility to become tangled with the anchoring rode.
lt should not require any specific anchoring technic.
lt should fit snugly on a the bow roller
Used with an electric windlass, it should be self launching and retrieving .
lt should be very strong
As you will have noticed, I haven't mentioned any brand names . . . this will be YOUR responsibility..
If you assess all models, and can find one that has all the characteristics mentioned in the article, then you can be sure you have made a good choice.