More food for thought!
"Anchor Rodes
by Alain Hylas (Inventor of the 'Spade' anchor)
NB - these are Alain's opinions, and as with all advice you must eventually make up your own mind. He does do a lot of anchoring though!
CHAIN OR ROPE?
The main and ONLY advantage of the chain is that it is the only and perfect mean to avoid chafing of the anchoring rode on agressive sea beds...
Except for this point, chain has all the disadvantages..:
Stored in the bow chain locker, it adds a heavy weight in the last place you want one. When deployed, chain is actually working in the the opposite way to the way it should work:
with light wind, it gives a perfect horizontal pull to the anchor and the best holding.
with moderate wind, its weight and catenary effect give a perfect shock absorbing effect.
As the wind builds up, the chain will become straighter (and this with as little as 25/30 knots of wind). The pulling angle will increase and as a consequence, the holding of the anchor will decrease.
When the shock absorbing effect is most necessary, the "bar tight" chain will not allow this to happen.
If there are waves entering the anchorage, the resulting shocks will be then directly transfered to the anchor, which then has more chance to break free .. . and more seriously, the chain is subject to high "peaks" of pulling force and has a consequently higher risk of breaking..
WHAT LENGTH OF CHAIN?
During the last seven and half months, I spent 129 days anchored (out of 228) in 61 different anchorages. The mean water depth was 6.50 metres and the scope 5/1. The total lenght of the mooring line was about 30 meters, of which 23.5 metres was lying on the bottom (30 - 6.50 m) Therefor, I believe a lengtht of about 25 meters is perfect. If the water height is less, then you will be anchoring with an all chain line .. . if the wind build up, you can pay out more scope but the wind will push the boat and the rope line will not chafe on the bottom.
WHAT LENGTH OF ANCHORING RODE?
Holding is in direct relation to the pulling length of the rode .. . (or more accurately, the pulling angle). Generally speaking, with a scope of 4/1 you will have about 55 % of the maximum holding of the anchor, with a scope of 6/1 about 70 % with a scope of 8/1: 80 % and with 10/1 about 85 % the maximum. - 100 % holding will be achieved with a horizontal rode or a "Infinite/1 scope.
Increasing the scope will be efficient up to 10/1 - With more than 10/1, a large increase in the scope will give only a negligable increase in holding. Therefore, the total length of the rode has to be adapted in relation with the conditions you are expecting to meet, and should be about ten times the maximum d epth you expect have to anchor in. (I suggest 100 meters).
WHAT ROPE TO USE WITH THE CHAIN?
Natural fibers are no longer used .Of the artificial fibers, the one which has the best elasticity (shock absorbing effect) is polyamide (Nylon, Perlon, Enkalon). As the breaking strenght of 10 mm chain is 5 tons, a 16 mm polyamide line will be well suited. (Breaking strain 5.6 tons). Don't oversize the rope. Yes, you will increase the strength, but at the same time you will decrease the elasticity . . . and "elasticity" is the secret.
You have the choice of three strand rope or eight strand rope (also called "square line"). Eight strands rope is better.
CONNECTING ROPE TO CHAIN
Remember: A CHAIN HAS THE RESISTANCE OF ITS WEAKEST LINK...
a) With an "eye" splice over a thimble and then a shackle on the chain.
ALWAYS use a shackle one size biger than the chain.. and secure the pin with a monel wire. This is a perfectly safe solution but the eye splice will have difficulties to go throuh the bow roller.. will no pass the windlass gipsy and will never go through the deck pipe...
b) with a rope to chain splice.. There are two ways to do this: the wrong one and the right one.
Wrong: NEVER splice the rope over the rope after a "U" turn into the last chain link . . . you will lose about half of the strength of the rope.
Right: Make a direct rope to chain splice. This is quite easy to do.. when you know how!!! (We hope to publish Alain's detailed description of this in the future - ed)
FINAL OBSERVATIONS:
Last point, I'm currently in the LAS PALMAS (Canaria) harbor covering the A.R.C. event. (Nov 2002). Curiosity prompted me to check the rodes of these boats, which will cross the ocean and spend plenty of time anchored in the Caribbean. I was alarmed to realise than more than half the boats are relying on what is in my opinion a dangerous rode. (Note - I am not talking about inadequate anchors here).
Main points are:
A too small, rusted and not secured shackle
The use of beautifull stainless steel anchor connectors. The most common one has an axe drilled to put a "security " screw on the opposite side.. although this is a wonderfull idea to avoid unscrewing of the axe. the hole in the middle of the axe decreases the strenght. For a 5 tons chain resistance, this connector has only three tons of resistance ... check yours!!!.
Swivels . . . the theory is perfect, but under load, swivels don't work. More importantly, check their breaking strength, not only with a straight pull but also with a sideways pull..
Connecting links - these have a breaking strength of only few hundred kg . . . NEVER use them on a mooring line.
CONNECTING THE ANCHOR AND CHAIN
A shackle is perfect. As before, always use one size bigger than the chain . . .and secure the pin! The simplest and perfect way is to use a toggle, the same you use for your rigging. Again, use one size bigger than the chain (12 mm for 10 mm chain). "
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