How Much Anchor Rode Should You Use?
Whenever I am doing a Courtesy Vessel Safety Check, I always ask how long their anchor rode (line) is and how deep they could safely anchor in with that amount of rode. The most common amount of rode is 150 fset, and I am invariably told that that is sufficient in up to 50 feet of depth or a 3-to-1 ratio. Initially that is incorrect, but it is more complicated than just depth.
The most important thing to understand is how an anchor works. Almost all anchors work best when being pulled horizontally, in other words along the bottom, NOT when being pulled vertically (upwards). This is the main reason why there is often a length of chain attaching some kind of rope to the anchor. The chain helps to keep the rode lying on the bottom to keep the “pull” horizontal. But no amount of chain will salvage an anchoring with insufficient rode. The safest ratios are between 7-to-1 and 11-to-1, though a 7-to-1 to a 9-to-1 range is fairly safe except in unusual circumstances.
That being said, you have to consider where you are and the weather. If you are on a lake on a calm day and you are just anchoring to have a quiet lunch, you might get away with a 3-to-1 ratio if you are paying attention and watching for drag. If you are in a coastal location, even without any wind there might be swells, so even that short lunch would demand at least a 5-to-1 ratio with that watchful eye kept on your position, but a 7-to-1 ratio would be a far better choice. If you are anchoring overnight, then a 7-to-1 ratio would be a minimum, and you would use more if the weather or seas demanded it. Even on that calm lake, an overnight anchoring demands a minimum 7-to-1 ratio if everyone is going to be asleep.
As I said earlier, there are other complications too. If you are looking at your depth gauge at low tide, your calculation of the amount of rode will not be correct at high tide. If you are in 20’ of water at low tide, and have 140’ of rode out, but the high tide is 10’ higher, you are going to be at less than 5-to-1 at high tide (140 divided by 30 is 4.6-to-1). Another thing to consider is the amount of freeboard your boat has – how high is your boat’s deck above the waterline? If you are in 8’ of water and you out 56’ of rode to give you a 7-to-1 ratio, but you have 3’ of freeboard, you have to add the extra 3’ to equal 11’ of depth, so your 56’ of rode just went down to 5-to-1. You would need 77’ of rode in that situation. Bear in mind also whether your depth gauge has an offset – my sailboat has a 4′ offset, so when it says I am in x feet of water, I am actually in x+4 feet of water. When you think you are anchored properly, put some strain on the anchor by backing down a little to see that it is holding.
I am reminded of our first trip to the Virgin Islands. I would take our time to ensure that we had enough rode out and would test the set before deciding we were OK. My wife chided me that everyone else just dropped their anchor and did not fuss so much. The chiding stopped the night we were in the anchorage in the Bight at Norman Island with something like 75 other boats. That night the wind kicked up and only two boats did not drag their anchors and we were one. Of course we were bumped into that night but only because we were bumped Into by two boats that dragged their anchors. That was the night the chiding stopped!
It is often said that anchoring properly is one of boating’s most difficult skills to master, and that is likely correct. Take the time to do it correctly a few times and you will be among the few that learn to be an “expert” at it.
————————————————————————————————