Active Anchoring

[wdkester]

Somebody probably already mentioned this:

Given squally conditions in a crowed anchorage, according to the peanut butter principal, the boat most likely to drag is the one in front of you. To prepare for this, start your engine and leave it idle. When the boat drags simply motor to one side and let him pass, perhaps with a word of encouragement like "been there done that". There is some chance that his anchor will snag your rode. If so cursing becomes the most effective remedy.

I've had this happen 3 times and never got snagged. One guy asked me if I was dragging (upwind?)

On one occasion I tried motoring upwind to release some load on the anchor. It didn't work well for me as I caused more strain on the anchor due to veering. If you have 2 engines and computer control (like cruise ships) this might work.

[noelex 77]

Originally Posted by tomfl

If forced to deal with adverse weather of this level conventional advice is the first thing you need to do is select a good location.

Good advice. Location is probably the most important.

However there are a few things to consider.
1. Forecasts are not always accurate.
The worst weather I have experienced at anchor only a force 6 was forecast.

2. In out of the way places anchorages sometimes bear no resemblance to the crusing guides.

3. Everyone heads to the same most sheltered places when really bad weather is forcast. If you have good anchoring gear the biggest danger is other boats dragging. Often the safest place is not the optimum location if there were no other boats.

4. In some conditions it is impossible to find an ideal anchorage because the wind direction is changing during the storm.

5. In some areas it is long way between good anchorages.

The bottom line is that if planning to cruise and spend most of your time at anchor sooner or later you will end in in a poorish anchorage (bad holding, poor protection etc) in bad conditions. Plan your ground tackle and practice techniques with this in mind.

[belizesailor]

Originally Posted by noelex 77

Good advice. Location is probably the most important.

However there are a few things to consider.
1. Forecasts are not always accurate.
The worst weather I have experienced at anchor only a force 6 was forecast.

2. In out of the way places anchorages sometimes bear no resemblance to the crusing guides.

3. Everyone heads to the same most sheltered places when really bad weather is forcast. If you have good anchoring gear the biggest danger is other boats dragging. Often the safest place is not the optimum location if there were no other boats.

4. In some conditions it is impossible to find an ideal anchorage because the wind direction is changing during the storm.

5. In some areas it is long way between good anchorages.

The bottom line is that if planning to cruise and spend most of your time at anchor sooner or later you will end in in a poorish anchorage (bad holding, poor protection etc) in bad conditions. Plan your ground tackle and practice techniques with this in mind.

Re 3. Big consideration in popular places. I used to watch anchor lights head down wind in strong squalls from my favorite snug little mangrove hole near the often crowded main anchorage in Placencia. Local knowledge and shoal draft required to enter. A little local knowledge can go a long way toward finding an appropriate anchorage that is not full of other boats. Often the ones in the guides are crowded. Also at risk from boats with different swinging characteristics. For example, I was anchored in a popular spot last year, with plenty of room, when a couple of smallish monohulls came in late and anchored close, wind picked up just as the tide changed setting up an opposing current (it was well after dark by then and not a good time to move...eyeball nav all around). We all spun like minarets in the oppossing forces and of course all spun differently. Lot of active anchoring going on that night to avoid going bump in the night. Fortunately at least the nearby boat's skipper was attentive and in the cockpit at the helm ready with a quick shot of thrust when needed. Finally it settled down and we could get some sleep.

.... and you forgot one...

6. Hubris. Judging from some posts here, it greatly increases holding power. :-P

[Andrew Troup]

The long-heralded final part of the explanation of my claim

<<It's not exceeding their load limit that breaks anchor chains, it's exceeding their Energy capacity>>

is finally under way, on the "Bigger is Better - part 2" thread

[Andrew Troup]

Originally Posted by tomfl

Not sure I am understanding this post.

.... the first thing you need to do is select a good location....

My point is this: there are lots of worthwhile places, wonderful, enchanting places, particularly islands, but also in the very high latitudes, where there are NO truly good locations,

no locations where you can be sure of not dragging provided you have the right gear and skills.


As in, no good locations within several days sailing, or more.

Not many boats go to these places, but to me that's all the more reason to go.

Not just to escape crowds, but to discover people and wildlife living the way they lived in those places before tourism and cruising changed the nature of everything everywhere (well, nearly)

[belizesailor]

Originally Posted by weavis

Just a little bit too much information here...........

"Threadless Drift"...dragging at anchor sans underwear. :-P

[DavefromNZ]

Anchoring in 60kts, I think the link will work:

http://m.youtube.com/watch?v=d2sw2Hjku2E

Our Lagoon 450 which has serious windage. We had a Sea Blade (spade) anchor with 80m of 12mm chain at a ratio of 1:16. The cat dodged hard left and right until the bridle was on then pointed dead into the wind for the 18 hour blow. I always set a GPS for drag and it was odd as we had about 1m per hour drag. I suppose because of liquefaction in the gusts.

If interested there are 2 more videos of the wind and one shows the tension on the chain/bridle.

Dave

[noelex 77]

Originally Posted by DavefromNZ

Anchoring in 60kts, I think the link will work:

Thanks for the videos

For those that don't know the Seablade is a bit of cross between a Rocna and a Spade, made by the Spade people.

[Andrew Troup]

Thanks for those, Dave. Good old Wairarapa coast in a NW, eh. Thank dog there's no lee shore...

How heavy is the Seablade?
And how deeply dug was it, when it came time to leave?

(I remember as a young'un, goggle-eyed at Peter Smith's account of a delivery trip on the first Cav 32 he built, getting smacked about in full-on survival conditions, just a bit further south of you, maybe forty miles offshore? in about half as much wind again, from the same quarter.
That's almost the worst place to be: enough fetch for very steep, high seas, not enough offing to escape the accelerated windflow from the ranges.

I read about it at the time, but I checked his story more recently: the main hatch got levitated so hard, by the sudden ear-popping drop in air pressure each time they fell into a trough - that the keepers (or their fasteners?) eventually bust, and it flew away.

The later ones had stronger arrangements, and were notoriously tough little suckers all round, great heavy weather boats to this day.

They managed to nail a spare sail over the opening (pretty small hatch, with a garage ahead) and jogged inshore under storm jib and motor, and eventually (a day later?) conditions had moderated (probably to about 60 knots) and they managed to struggle into the Castle Point lagoon, just a mile or two behind you in the video, and make proper repairs.

And then there was Captain John Mansell, a well regarded Cook Strait ferry commander, who went on to become a solo sailor and racer and got hammered in that same area - he got knocked down in the same Nova 28 he had sailed in the OSTAR (transatlantic). IIRC, when it righted, it happened so violently he got flung straight up into the air until his tether snatched tight, jerking him back down across the boom, on which he very nearly broke his back - I think he cracked a vertebra or two....

Not exactly what you want to happen on a solo trip ...)

In those conditions when travelling up or down that notorious stretch of coast I reckon it's best to either hug the land, for a lee, (and put up with the gusts) or stand off seventy miles or more to get outside the worst of the land-affected (often foehn-assisted) zone mentioned above.

The inshore option is not attractive if there's also a big SE swell coming up from the Southern Ocean, because as you will know there are some wickedly steep undersea cliff close inshore in places, and the resulting upwellings are what Mansell reckoned caused his knockdown.

I'm sure I'm telling you stuff you already knew, and it's not rocket science in any case, but someone else reading this might glean something useful...

[DavefromNZ]

Hi Andrew,

Our Seablade is 25kg. I have not had it drag yet. I was obviously pleased it held in 60kts but we had 80m chain in about 3m depth. It was soft sand so not sure how deep it buried but it was odd to watch it move on GPS about 0.5m per hour.

We were fortunate to be maybe 5nm off shore when the winds rapidly hit, even then the swells were close to 2m and steep. We could see the gust front coming as a wall of spray. The forecast was for 30kts.

Cheers
Dave

[Andrew Troup]

Hmmm -- you did well, I reckon, it's damn tricky getting a good hold in that strength of wind in such shallow water (contrary to intuition), and your heavy chain is not much help in that specific situation.

(Although in the general case I'm a big fan of heavy chain ... and I applaud you for carrying it, on a cat)

I guess the relatively short fetch was a help. If you snatch an anchor in such shallow water, you can drag a really big anchor in anything but great holding, I've found.

If there had been a prospect of it blowing another 20 or 30 knots, and you had a bit or warning, I reckon (in the specific case of an offshore foehn wind, which is not going to shift direction without a major reduction in strength) a Fortress on another rode, set in a V, would be the way to go. In shallow water, it wouldn't need much chain: the more rope, the better the snubbing absorption.

Two anchors in a V is not popular these days on sailing forums because of perceived problems with crossing rodes, but in our part of the world where it regularly blows a hoolie from a single direction, I reckon it still has a place, especially for shallow water or bad holding. (Pray you don't have to anchor in both!)

People say the load won't be shared, but in soft sand, the anchor under the most load will simply creep downwind until it's no longer under that much load.

I have a theory which I have not dared to promote; I'm not in any way confident about it. But here goes:

The mere fact of 'taking turns' may help each anchor to set deeper than it would as a single in the same wind strength.

I have a suspicion many anchors dive slightly, early in each drag sequence, effectively they're simply digging in further ... until the resistance to burying of the shank, and the inability of the soil to provide enough resistance, causes them to start to 'porpoise' upwards.

So if there's another anchor which will progressively take the strain as the first anchor digs (because at the same time it's moving towards the vessel, de-stretching the rode) I can see how both anchors would help the other to dig deeper.

It does rely on the wind strength staying remarkably true, though, (which in this part of the world does happen, with foehn and katabatic winds particularly)

[DavefromNZ]

We actually set the anchor twice at Castle Point. The first time we battled our way into the bay closer to the houses. After a breather we decided that we were not well placed if the anchor popped out or chain broke with the rocks only 500m downwind. So we moved further north and in across the bay so a failure would blow us out to sea. The Seablade held fast each time.

[JPA Cate]

Originally Posted by Andrew Troup

Hmmm -- you did well, I reckon, it's damn tricky getting a good hold in that strength of wind in such shallow water (contrary to intuition), and your heavy chain is not much help in that specific situation.

(Although in the general case I'm a big fan of heavy chain ... and I applaud you for carrying it, on a cat)

I guess the relatively short fetch was a help. If you snatch an anchor in such shallow water, you can drag a really big anchor in anything but great holding, I've found.

If there had been a prospect of it blowing another 20 or 30 knots, and you had a bit or warning, I reckon (in the specific case of an offshore foehn wind, which is not going to shift direction without a major reduction in strength) a Fortress on another rode, set in a V, would be the way to go. In shallow water, it wouldn't need much chain: the more rope, the better the snubbing absorption.

Two anchors in a V is not popular these days on sailing forums because of perceived problems with crossing rodes, but in our part of the world where it regularly blows a hoolie from a single direction, I reckon it still has a place, especially for shallow water or bad holding. (Pray you don't have to anchor in both!)

People say the load won't be shared, but in soft sand, the anchor under the most load will simply creep downwind until it's no longer under that much load.

I have a theory which I have not dared to promote; I'm not in any way confident about it. But here goes:

The mere fact of 'taking turns' may help each anchor to set deeper than it would as a single in the same wind strength.

I have a suspicion many anchors dive slightly, early in each drag sequence, effectively they're simply digging in further ... until the resistance to burying of the shank, and the inability of the soil to provide enough resistance, causes them to start to 'porpoise' upwards.

So if there's another anchor which will progressively take the strain as the first anchor digs (because at the same time it's moving towards the vessel, de-stretching the rode) I can see how both anchors would help the other to dig deeper.

It does rely on the wind strength staying remarkably true, though, (which in this part of the world does happen, with foehn and katabatic winds particularly)

You may be onto something there, Andrew. What you've written kiind of supports our experience in Pt. Davey (TAS), when the addition of our 20 lb. HT Danforth stopped our dragging in Ila Bay in 50k. However when we got the hooks up, the bits of bottom adhereing to the anchors looked different between the two: the Manson was in gooier, softer looking stuff than the wee DAnforth..

Now, for a 46 ft. boat, even if she's only 11 or 12 tonnes, a 20 lb. anchor might be considered ridiculous; however, we have used it this way (in the other arm of the "Y") a few times; and it has so far proven successful. It has maybe about 10 m. of chain, and the rest is rope rode.

FWIW. My $.02.

Ann

[JonJo]

Originally Posted by DavefromNZ

Hi Andrew,

Our Seablade is 25kg. I have not had it drag yet. I was obviously pleased it held in 60kts but we had 80m chain in about 3m depth. It was soft sand so not sure how deep it buried but it was odd to watch it move on GPS about 0.5m per hour.

We were fortunate to be maybe 5nm off shore when the winds rapidly hit, even then the swells were close to 2m and steep. We could see the gust front coming as a wall of spray. The forecast was for 30kts.

Cheers
Dave

This seems in stark contrast to the Bigger is Better concensus. In fact almost contradictory, small anchor, for the size (windage) of yacht; (seriously) larger chain.

80m of 12mm chain deployed is 264kg, that's like an extra 3 reasonably fit crew. That really is a lot of chain.

And Ann and Andrew - again your joint suggestions seems to contradict the consensus - you are suggesting there is real merit in setting 2 anchors in a 'V'.

Jonathan

[Andrew Troup]

Thanks for that, Ann. Interesting

The tradeoff Dave mentions is interesting, too.

With katabatics, it can be well worth trading quite a lot of exposure and windward fetch for a clear escape route to leeward, because even a 90 or 100 knot katabatic will only extend a few miles offshore before it has moderated considerably.

So the increasing fetch, contrary to what you'd expect, does not pick up fast enough to be a problem, even if you get blown completely offshore

It's an inconvenience rather than a major issue; just a matter of stooging around and waiting for the accumulated cold air to drain from the catchment area.

Unless you're off the Antarctic continent, that's likely to be hours, rather than days.