Anchoring in swift tide chnges

[liveaboardL]

I'm seeking experienced advice on anchoring in a river with fast-moving tide changes.
I'll also share what I've learned.
I've helped save a few boats who's anchors were dragging...
One boat just drifted into the shore and was hanging onto the mud by 2 chains. When the chains were lifted, a few feet of the last segments of chain had badly eroded chain links. They were much skinnier than the good links at the top of the chain. One of the chains had a big, rusted, bent nail at the end. Well no wonder the anchor came loose! That just sounds unreal that someone would trust a bent nail! You gotta be really desperate! Now I'm wondering why only the last segment was corroded. Did he use a different metal for his anchor/swivel, than the chain's metal? If he did, then the chain may have became an anode. This makes me wonder if perhaps it's better to not use one of those super shiny, expensive anchors.

Another boat had a CQR sized appropriately. The links on it's chain had alot of twists & kinks. The owner never bothered to unravel it. The kinks raised the anchor & the boat dragged & needed a rescue.

Another boat had a nylon roap rode. Need I say more? It looked like perhaps an oyster may have cut right through it. Bye bye anchor.

Now I've been reading about which anchors are best for fast, changing tides & most people say Rockna, CQR & Bruce cause they reset themselves quickly. They're pricey!

They say the Fortress isn't good for tide changes. One guy said his Fortress lasted for 6 tides & then got clogged up & wouldn't reset. That would suck, to be dragging an ultra-light-weight anchor. The Fortress inventor says that you can power down with a lot of horsepower & bury the Fortress deep into the mud & it will hold during tidal changes, BUT, how much horsepower is needed? 25 hp? Your typical sailboat's horsepower? What about using a sentinal?

Sentinals can stop drag, but if it's a big heavy chain, it can also foul the anchor. The line used to hold the sentinal away from the anchor is very susceptable to chafe.

As far as backing down on an anchor to help set it, that's not an option for my boat. It's all prop-walk! Backing down with this boat would take quite a bit of skill.

Why do so many people distrust the Bruce-type anchors? Even those who like them say it's good "Most of the time". When is it not good in a changing tide?

[markpierce]

Use an anchor like this if you're semi-permanently anchored. Works for lightships.

[JPA Cate]

LiveaboardL,

We are liveaboard cruisers, so my input may not be helpful, but I'll try. We have a 60 lb. Manson Supreme, the boat has relatively high freeboard, so fairly high windage, and she displaces about 12 tonnes. In a river with tidal changes, we would lay out 3:1 scope, and more, if the holding was mediocre. We would usually re-set the hook after 3 days, to avoid the possibility of wrapping the chain around the anchor. This latter deal does not seem to happen till after some time has passed, and how frequently you would do it, say if you're anchored and working from your boat, your conservatism or risk comfort will determine. If we were going to be in such a situation for 6 months or more, we'd consider the old fashioned Bahamian mooring technique, for peace of mind. However, it can be a pain in the neck to undo it, so you have to weigh the security against the inconvenience.

The Fortress style anchor is not suitable for this application because it can jam up and be unable to re-set itself. But IMO, even with an anchor that is likely to re-set itself, you need to take up the chain and then pay it out again to be sure you won't drag. You choose your schedule.

[Kenomac]

I think much has to do with the bottom material. Two years ago, I anchored for two weeks in the bay outside St. Peterport, Guernsey successfully using a 35kg CQR and 50 meters of chain. It was like anchoring in a giant toilet bowl with the 30ft tidal changes and walls on three sides, but the anchor held nicely because the bottom composition was sand. Another CF member, Dockhead had difficulty the same day using a 45kg Spade anchor... Go figure? Had the bottom been mud, my guess is our results would have been the opposite, or maybe... I was just lucky and he was unlucky that day.

[noelex 77]

It sounds like you are after a permanent, or semi permanent set up. In this case cheap very oversized anchors can usually be found at low cost if you ask around.
You can even make a full mooring using concrete or railway wheels.

If you want a conventional anchor system the emphasis is on the performance in soft substrates which are common in river systems and on an anchor that copes with different directions of pull.
The large surface area of the concave roll bar anchors (Manson Supreme, Mantus and Rocna) is hard to beat in these conditions and they are also great general purpose anchors if you venture further afield in the future.

[Scott Berg]

After years aboard with many spent on rivers with changing currents I came up with what always worked. Takes a bit of effort but worth it.

Two Fortress or Danforth HD anchors, each large enough for the boat; set one up stream and one downstream, each on it's own chain rode; for 20' of water you'd want a couple of 60' shots. Shackle the roads together after each is set and run a (in this case about a 40') chain up from the joint to the bow and set it on a good snubber. Then you'll lie to a properly set large fluke anchor in each direction. It takes me an hour or to set it and half that to pick it up. While it can't be instantly picked up it isn't a 'lee shore' set up but one for the Hudson or upper Potomac river or such and works very well in that situation.