The challenges of anchoring

Phil May and Andrea Twigg
Fri 20 Jan 2012 16:16
There is a certain amount of skill required to anchor a boat.  First you have to pick a spot to drop the anchor.  A rule of thumb is you drop chain to around 5 times the depth of water.  So for 10 meters of water you would drop 50m of chain, ideally in a place where you could draw a circle of about 35m radius (the chain hangs in a curve) around the boat, and that circle would not contain any shoreline or other boats.  You usually don't have that much space and you have to have a couple of boats inside your anchor circle.  What you try and do then is arrange that if the boats all generally point into the wind then they will not swing into each other regardless of the wind direction. 
Then you have to stick the anchor in the ground.  Often you can't see the bottom where you drop the anchor.  Reviews of anchorages generally talk about the "holding" which is a measure of how well the ground will grab on to your anchor.  There are different anchors for different types of ground, but what you need for most cruising anchors is fine, close packed sand.  Too coarse (loose sand/gravel) and the anchor will plough through it.  Too fine (mud) and the anchor will slide through it.  If you are lucky then even if your anchor slips it will just slide a bit and grab again.
It seems that some patches of ground in Portobello harbour are mud.  Last night we were unlucky because there was a clunk at 3am as Anastasia bumped into something.  My first thought was a wind shift causing us to swing into another boat, but running onto the deck it was obvious that we had dragged back about 40 meters to hit another boat, and its bow was now wedged between one of our hulls and the tender.
To cut a long story short we separated the boats and re-anchored well away from any other boats, with a lot of anchor chain.  In the morning I went over to see Bruno, the guy on the boat we hit, and he was very nice about it.  Apparently just a bit of anti-fouling scraped off and not worth bothering about.  We chatted in French for a while (well he chatted and I tried to work out what he was saying).  The holding is really bad in that area and he has 70 meters of chain out for just 10 meters depth.  Bruno is also sailing round the world, but his batteries have failed and he has no working electrics at all.  He has to take the batteries in to Panama City for testing/replacement.  He had three massive batteries in his tender and we later saw him heading over to the dinghy dock with them.