Backing Down? Why Bother When Tide Changes

[zeehag]

in some anchorages in which i anchor,. backing down the anchor causes dragging as it loosens anchor from the silt into which it was set with boat motion and wind.
i donot use full reverse to set my anchor in those locales--i usually use the wind and current.
my only drag queen misadventures in my own boats was one time in mazatlan old harbor in a 25-30 kt gale when my chain slipped into a channel cut for a research vessel--then the chain pulled anchor into that cut and i was almost into rocks when a friend i called brought friends via panga to reanchor my boat--i would havebeen fine if not for the research boats channel. backing down there is a practice that does not lift anchor out of the muck.
btw--i do a 24 hour anchor watch post anchoring.

[Dockhead]

Originally Posted by zeehag

in some anchorages in which i anchor,. backing down the anchor causes dragging as it loosens anchor from the silt into which it was set with boat motion and wind.
i donot use full reverse to set my anchor in those locales--i usually use the wind and current.
my only drag queen misadventures in my own boats was one time in mazatlan old harbor in a 25-30 kt gale when my chain slipped into a channel cut for a research vessel--then the chain pulled anchor into that cut and i was almost into rocks when a friend i called brought friends via panga to reanchor my boat--i would havebeen fine if not for the research boats channel. backing down there is a practice that does not lift anchor out of the muck.
btw--i do a 24 hour anchor watch post anchoring.

This is true, and complements what I wrote earlier.

There are some bottoms -- generally thin mud or silt -- where it is impossible to set the anchor well enough to take a full power pull.

In such cases you have to decide whether you've achieved enough holding to stay there, or not. In calm weather and in the absence of really dangerous obstacles, I sometimes take the risk on such holding.

Using 2000 RPM as Kenomac does might be enough of a test, to cover the amount of holding you really need in most conditions. But if the bottom is reasonable, and you REALLY want to know how well the anchor is set as well as it can be, only a full power pull will do. On my boat, for example, 2000 RPM does not pull the chain tight.

[a64pilot]

Originally Posted by Dockhead

On my boat, for example, 2000 RPM does not pull the chain tight.

Even with an Autoprop? Mine pulls hard at 2000, but that is my normal cruise speed too, so maybe that is the difference?

[Dockhead]

Originally Posted by a64pilot

Even with an Autoprop? Mine pulls hard at 2000, but that is my normal cruise speed too, so maybe that is the difference?

I'll bet the difference is 1/2" chain which weighs 3.3kg/meter or 750 pounds for the whole rode.


Yes, 2000RPM is more or less normal cruise speed for me too. I get about 7 knots with a clean bottom and flat water at that RPM.

[a64pilot]

Originally Posted by Dockhead

I'll bet the difference is 1/2" chain which weighs 3.3kg/meter or 750 pounds for the whole rode.


Yes, 2000RPM is more or less normal cruise speed for me too. I get about 7 knots with a clean bottom and flat water at that RPM.

Likely deeper water too, I normally anchor is 10' or so and let out 30' to 50' of chain.
First thing I noticed about the Autoprop is how hard it pulls in reverse, and I think maybe I don't have as much gear reduction in reverse and if that is true then mine will pull harder in reverse than forward?

Never mind, I looked it up, I have more reduction in reverse than fwd

[rognvald]

D,
I assume you are laying on one hook. So, if the holding is generally good and you are not expecting big winds and sloppy water, you will "probably" be fine. However, "probably" is a dangerous term in cruising since conditions change quickly and a clean bed can become dirty/foul in less than a foot of dragging in some anchorages. So two options:
1. set your alarm and re-set the hook with your engine on tidal shifts or
2. set two hooks and generally anchor/sleep with confidence
We experienced this while anchored in the Marquesas Keys en route to Fort Jefferson. Florida. We anchored with two hooks in clean sand protected from the prevailing winds but were exposed to a very strong tidal shift from the GOM to the Atlantic Ocean. On our first tide shift around 1 a.m., the boat swung hard on the aft hook, dragged slightly and then reset. The next morning, there was a previously unpredicted strong Northerly closing in on us and we decided to pull the hooks and head back to Boca Grande Key for better protection. We were laying on the hook that dragged the night before and the tide was ripping. When we had the hook perpendicular to the bow, we couldn't budge it. As we moved forward of the hook's position, we saw it was lodged in a previously unseen coral ledge about 15 feet from its original position. Only luck allowed us to retrieve it without cutting the line. When we initially anchored, we set both hooks. The moral of the story: "probably" is a dangerous word in cruising. Good luck and safe sailing. P.S. I have always believed that a good dose of anchor paranoia is a healthy thing.

[Delancey]

Okay, here's a little more of what I am getting at, and in the back of my head are Panope's excellent videos of anchors setting where he sets the anchor and then reverses the pull.

I qualified my OP saying everyday anchoring, not preparing for a storm. I also said good holding and new gen anchor.

When I say I haven't been doing any backing down after setting I mean to say that however I set the anchor, backing down, under sail, using wind or current, or whatever, the anchor is generally considered to have set when the boat usually and often very abruptly jerks to a stop.

So far whenever I dive on it I can confirm it has fully engaged in the bottom with the fluke completely buried and the shank and the top of the roll bar visable.

Seems like any further backing down after the anchor is "set" is basically an attempt to and may result in either "burying" the anchor including the shank if possible or to confirm, what I know from the violent jerk to a stop I just experienced, that the anchor is in fact set. I question the benefit of this in reversing current situation that may include wind against tide situations where things go all sideways.

I wonder if "burying" the shank could be bad in that situation for making it harder for the whole anchor to turn while remaining engaged in the bottom and that you couldn't have situation involving side loading at the shackle attachment or even a 180 degree reversal in the load causing the anchor to pull out?

Things perhaps less likely to happen if the shank isn't buried and the fluke can more easily rotate while remaining in the bottom? Isn't the boat jerking to a stop confirming I am set?

[zeehag]

clearing things up a tad--in the shallow bad holding lagoon i mentioned with silt and dont back down, i use 150 ft chain-there is never a time during which the anchor is stressed, unless we get a 30-40 kt breeze with stronger gusting.
all folks laying down under 100 ft have been drag queens..- delta does not do well in the lagoon. without the gentle 30 kt breezes daily, 120 ft seems adequate, and 150 for good nights sleeping. i choose to sleep well. the depth of lagoon is 8-14 ft. it is a summertime runoff riverbed.

[rwidman]

Since there are hundreds of varieties of boats out there, I don't think a given RPM has the same effect on all boats.

It's a judgment call on what RPM is suitable for your boat.

[rognvald]

"I wonder if "burying" the shank could be bad in that situation for making it harder for the whole anchor to turn while in the bottom and that you couldn't have situation involving side loading at the shackle attachment or even a 180 degree reversal in the load causing the anchor to pull out?

Things perhaps less likely to happen if the shank isn't buried and the fluke can more easily rotate while remaining in the bottom?" Delancey

D,
To bury or not to bury, that is the question? This becomes a moot point in most anchoring situations(benign) since the bottom characteristics(soft, hard, gravel, sand, sand/shell, mud/sand, etc.)are many times out of your control since factors such as tide, current(as you have mentioned) and bottom topography make a controlled environment unlikely. In living aboard for ten years, we learned early on: always set the hook with your engine in progressive stages: 1000 rpm's, 12,000 rpm's, 1500 rpm's works on our boat. We sleep better and have only dragged twice in 18k miles of cruising--both in 50-70 knot winds. I don't think it is possible to control shank/fluke positions in most practical scenarios. Good luck and safe sailing.

[four winds]

Delancy,

When my Manson stops the boat suddenly after the slack in the rode takes up and the bow veers laterally I consider that to be set well. However, I still take a range on shore objects if possible and backdown slowly to verify. Then slowly increase throttle and see if I can get the boat to move back a foot or two, usually noting no apparent movement.

If the set seems a little soft, I'll take my time and let the wind work on it for a bit. Then range and slowly back down until the boat stops moving, increase throttle to verify. Then sometimes I'll throttle back and let the chain settle the boat forward some. Then throttle up a bit to get the boat moving back again with momentum and give the set a little snatch. That sudden stop feeling seems reassuring to me.

Can't imagine not backing down on a set.

[Cheechako]

Backing down gives you an indication of what the holding ground is as well as if you are holding. I don't over do it, maybe 1400 rpm for less than a minute. I just want to see the chain tight with no movement. If there is movement of the chain, then you are dragging some. This at least gives you an indication of your odds when the tide reverses.
You are right about tide reversals though, most often I have seen the anchor hold in it's original position without it turning around, probably because it's buried. However strong winds or waves and that wont happen. When it turns around it often isn't going to hold/reset very often. The CQR, Delta, Danforth are not good at resetting after a 180 shift at all.
With no wave action at all, I have snorkeled the anchor in 35 mph of wind, there was still catenary in the anchor chain. We were maybe 100 ft off the beach and protected from any water waves by the beach.

[Tessellate]

Delancey (OP), it would help if you listed your location. The question is very dependent on location and types of anchorages you're going to. You list your location as "nondum cognita" - not sure what that is, but according to Google it is a hypothetical continent?

[Dockhead]

Originally Posted by a64pilot

Likely deeper water too, I normally anchor is 10' or so and let out 30' to 50' of chain.
First thing I noticed about the Autoprop is how hard it pulls in reverse, and I think maybe I don't have as much gear reduction in reverse and if that is true then mine will pull harder in reverse than forward?

Never mind, I looked it up, I have more reduction in reverse than fwd

10'? We have tides up to 45' here in the Channel, so I am sometimes anchoring in 60 feet or more of water if I'm anchoring at high tide; 100 feet is not unheard of. That's why I need 750 pounds of chain.

[Dockhead]

Originally Posted by rwidman

Since there are hundreds of varieties of boats out there, I don't think a given RPM has the same effect on all boats.

It's a judgment call on what RPM is suitable for your boat.

Certainly. It is not, however, a judgement call, whether redline exerts a greater force on the ground tackle, than half of redline.

I'm not really sure, why people would be so easily satisfied, by pulling daintily on the chain. That midnight thunderstorm might be less dainty, and where will you be then, if you didn't use all available power to check the quality of the set earlier?