Suzie Too's Anchoring Tips
Suzie Too - Western Caribbean
David & Suzanne Chappell
Tue 12 Jul 2011 18:59
Girls skip to the next chapter, and read about nice fluffy things, relationships, feelings and missing people (no, no one is lost you know what I mean – girlie stuff).
Wherever we travel in the world all the Brits seem to be following the RYA Mantra regarding the amount of chain to be used when anchoring, often I hear 3 x depth for chain and 4 x depth for rope (who on earth sleeps with their boat tied to the seabed with a bit of string!).
I have just checked on the RYA and its seems below may be the current calculation, but it’s still not enough in many instances and as a result we have had several of our English cruising friends come to grief using this ratio. For a lunchtime stop in a crowded anchorage, obviously all scope should be similar and if you are not leaving the boat it may well be OK. I would say anchor away from everyone else, put out plenty of chain and enjoy your lunchtime power nap and if you decide to stay the night, you have already been anchored for 8 hours and can be relatively assured all should be well.
From the RYA Website
How much rope and chain needs to be put out?
Scope of Chain
The Yachtmaster Instructors I sailed from the Iles de Glenan Sailing School with on the RIDS use a better ratio – never less than 2 x your boat length plus 1 1/2 x the depth.
Yes, I know the French don’t always follow this, but often they use a Brake anchor which does just that, guaranteed to break out in the middle of the night.
So if I were to anchor in 5m of water under the RYA I would put out 20m – NEVER and Elsie wouldn’t sleep – there will be no scope on the seabed and every chance in such shallow water that on the turn of the tide we could catch our keel. We have swum over our anchor, a 40kg Delta, in the Caribbean in 10m water with 50m of chain in 15kts of wind and you would be horrified at how little scope there is left on the seabed.
Under the French Guideline in 5m I would put out 2 x boat @ 18m plus 1.5 x depth 7.5m = about 45m – Yes, plus extra is now going out on the snubbing line.
But to be honest we would never anchor in such shallow water. We usually look for a 6-10m depth because if the sea cuts up rough with a 2m wave and swell combination in 5m you have a 40% change in the water height. Suzie Too, in 10m well we only get a 20% change in water height.
PS If you do get your chain around your keel – walk a rope back down both sides of the boat (get a friend to take the other end) giving it time to sink and pull gently backwards when you get to the stern quarters. If you have a torpedo shaped fin on the bottom of your keel then I suggest you enrol your wife on a PADI dive course as she probably can’t hold her breath long enough to snorkel down and unhook it.
A snubbing line is meant to do just what is says, most Brits and others seem to have about 2-3m of line which only stops the anchor chain graunching on the stemhead, it gives your chain, anchor holding and deck fittings no protection.
Again my French friends say they should be not less than 8m – this gives 1-2m to the stemhead, 2m to the water and allows 4-5m for current and wind – look at the photo below – if you anchor in wind against tide you will have the chain all the way down the side of your hull. Here we are in Nantucket Harbor (local spelling) in a 3kt Spring Ebb and a 30kt wind (but still in shorts!)
We secure our snubbing line on the deck by taking a full turn around the anchor capstan and then taking the eye splice back to a bow cleat. This keeps the load straight through the stemhead, shares the load between the 2 fittings and means we can pull the turns off the capstan, quickly loose the splice and throw the whole thing overboard while retrieving our anchor if we have to move in a hurry, cos someone's dragging theirs and heading for you.
Most times though with 50m of scope you have enough room to drive around the anchor to miss them and that we have had to do on several occasions. Another good reason to anchor away from the crowd and have lots of scope, you just have a longer dinghy ride.
Once you have the snubbing line in place let out at least another 3m otherwise in this photo the chain would be against our hull, as it is it is just the force of the current pushing the scope towards the boat. Our snubbing line is 25mm octoplait with a 2m length of clear plastic pipe to prevent chaffing in the stemhead.
The other thing we always do is set our anchor alarm. We have a separate Furuno GP-33 that uses very little power and set it as soon as we drop the anchor so that it is at the centre of our anchor circle. As we mostly seem to anchor with 45m of chain and about 7m of snubbing line we set the anchor alarm on 0.06NM.
OK Here is the calculation a Nautical Mile is 1,850 metres, so then 0.01 is 18,5m, as my scope is 50 metres the total distance from one side of the circle to the other is 100m – therefore 6 x 18,5m is about 100 metres and allows us to swing on the tide without alarming.
Finally it is located in our AFT CABIN right next to the bed, it is very reassuring when you turn over at night to look at the track it has plotted, often a doughnut shape and if you hear the wind get up you can see the display says 0.04Nm and go back to sleep. Yes it costs about £300, but if you spend 10 night less in a marina this year – its FREE, after that you are squids in – well more beer money anyway.
From the Bridge of the Exceptionally Good Ship “Suzie Too”