Big anchors

[geem]

Interesting question.

My cruising cat had about 500 pounds thrust in reverse (twin high thrust outboards), enough for a good power set. My trimaran (F-24) has a 4hp, the exhaust comes through the prop, and has only about 50 pounds of reverse thrust. It can't power set an anchor that is even several sizes under. You can increase that by gathering some slack and backing down hard a few times. I don't anchor out with that boat too often. Generally only for the afternoon in a couple of good sand swimming and kayaking locations with firm, fine sand. It can just barely set a 2.5-pound Gaurdian. I mosly use an alloy Excel #1 (8 pounds) or a 13-pound Northill. I know if I had the recomended 15- to 20-pound anchor (high windage trimaran) it would not be set.

Of course, this is rarely the case with a cruising boat. But some boats are seriously underpowered for power setting and rely mostly on the rising wind.

With a windlass and a good engine, the standard size is great. Up a size is OK. There is no sense in having a smaller fair weather anchor. But with little power and no windlass, a smaller anchor has a number of advantages, IF the sailor knows how to take full advantage of what a good anchor can do. I rely on good technique and rigging.

With 86hp engine swinging a 22" prop, I can power set the 30kg spade anchor or rip it out of the seabed.

 

[thinwater]

I dragged!!
Red before, magenta now.

Now that is interesting. No real wind from that direction don't think. LAT/LONG/wind/heading/sog/cog all in a database. Might take a few days with an AI to get the data into some sort of useful format.
If anyone wants an objective chat about digging into the data & see if anything useful can be found it's blatantly oblivious here is not the place. I've a random discord channel, Join the Raspberry Pi boat monitoring Discord Server!
Good a place as any imho, public forums just end up in a conformation bias fueled bun fight.

It looks like you might need tide information as well, since the AW and TW seem quite different. With a strong tide, this could be close to impossible to decipher, and even to decide if you did drag. Maybe not. The location of the original drop would also help.

 

[GHA]

It looks like you might need tide information as well, since the AW and TW seem quite different. With a strong tide, this could be close to impossible to decipher, and even to decide if you did drag. Maybe not. The location of the original drop would also help.

Pretty sure it didn't drag but a silly error instead. To get it to fit the range ring distance seemed to need to be greater than the chain length, but if you remember that the gps isn't at the bow it all seems to fit better. Confidence in the impeccably (so far) behaved oversize spade restored. But a good thing to think it might have dragged really, reminders to keep a very open mind & not have too much confidence in anything are a good thing Opposite of "the forum way"


AW &TW seem OK I think but in the previous image the heading sensor was turned off. I did have a look at tide regarding the range ring but it's less than 3m here & with some simple Pythagoras it doesn't really make enough difference to be bothered about.
Regarding the drop, tried to be very careful logging the position at the bow when the anchor drops so often but it never seems to work. Don't like buoying the anchor but at some point will have a little float on a pulley & weight attached to the hook so it's easy to go out with a mobile phone & measure pretty accurately the position & try to see how accurate the final position is to the drop position. Which is sort of why I really don't rate these extended anchor threads, just reeks of conformation bias with page after page of extremely confident "it's like this, 62% of that & 20% of the other" Not a mention of ", hmm, maybe not.."
Kurt Vonnegut nailed it-

“Tiger got to hunt, bird got to fly;
Man got to sit and wonder 'why, why, why?'
Tiger got to sleep, bird got to land;
Man got to tell himself he understand.”​

And Bertrand Russel substantially more in yer face
"The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt."

Bottom line imho is "IS THIS USEFUL". Derailed anchor threads are not, a keen interest in looking at anything & everything to see if the real world matches how you think the universe should work likely is..

Only so far to go without a logging load cell recording 24/7 along with all the other data to look for patterns but too many projects on the go atm. Like getting wind data out of grib files into a database along with real wind which would be fascinating, who knew grib files don't contain wind speed & direction??
Ever onwards

 

[Tranona]

Interesting question.

My cruising cat had about 500 pounds thrust in reverse (twin high thrust outboards), enough for a good power set. My trimaran (F-24) has a 4hp, the exhaust comes through the prop, and has only about 50 pounds of reverse thrust. It can't power set an anchor that is even several sizes under. You can increase that by gathering some slack and backing down hard a few times. I don't anchor out with that boat too often. Generally only for the afternoon in a couple of good sand swimming and kayaking locations with firm, fine sand. It can just barely set a 2.5-pound Gaurdian. I mosly use an alloy Excel #1 (8 pounds) or a 13-pound Northill. I know if I had the recomended 15- to 20-pound anchor (high windage trimaran) it would not be set.

Of course, this is rarely the case with a cruising boat. But some boats are seriously underpowered for power setting and rely mostly on the rising wind.

With a windlass and a good engine, the standard size is great. Up a size is OK. There is no sense in having a smaller fair weather anchor. But with little power and no windlass, a smaller anchor has a number of advantages, IF the sailor knows how to take full advantage of what a good anchor can do. I rely on good technique and rigging.

This
yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

Is a useful reference for engine/propeller performance and gives a guide to probable reverse thrust available. The engine in the test boat was a 20hp Yanmar and the best props achieved over 175kgs in reverse on bollard pull. I know from the extensive work I carried out in another life that for the same design prop thrust is broadly linear to power so would expect around 270kgs with a 30hp. This is similar to the effect of 25knots of wind on a 34' monohull, just as Vyv Cox has measured with his boat and the tables from ABYC.

In the example that GHA uses there is no reason why boats should drag if they power set with a 5:1 scope even with a Delta. From a load point of view the conditions described are pretty undemanding - the problems are twofold. Poor holding because of the weed and poor setting. Nothing really to do with anchor type nor size of anchor.

 

[srm]

Interesting, all the discussions about power setting. Way back in the 80's I was running a 42 ft classic sloop with oversized 30Kg genuine Bruce as a skippered charter yacht/RYA sailing school. We often anchored under sail, it gave crews a sense of achievement:
Head to wind to take way off, lower anchor, let head fall off under backed jib while paying out chain, check the chain and swing head to wind as anchor set, drop jib and main.
In light winds the anchor and chain would be paid out on a slow run under jib, putting the wheel over before snubbing the chain to keep it clear of the hull.
No memory of an anchor drag following anchoring under sail.

 

[NormanS]

Interesting, all the discussions about power setting. Way back in the 80's I was running a 42 ft classic sloop with oversized 30Kg genuine Bruce as a skippered charter yacht/RYA sailing school. We often anchored under sail, it gave crews a sense of achievement:
Head to wind to take way off, lower anchor, let head fall off under backed jib while paying out chain, check the chain and swing head to wind as anchor set, drop jib and main.
In light winds the anchor and chain would be paid out on a slow run under jib, putting the wheel over before snubbing the chain to keep it clear of the hull.
No memory of an anchor drag following anchoring under sail.

I frequently anchor using either of these two methods. Unlike the super super intelligent anchors preferred by some of the experts here, my anchor doesn't know whether it's being set by engine, wind, or the boat's momentum.

 

[geem]

I frequently anchor using either of these two methods. Unlike the super super intelligent anchors preferred by some of the experts here, my anchor doesn't know whether it's being set by engine, wind, or the boat's momentum.

Neither doesn't my SHHP Spade. Funny that isn't it?

 

[vyv_cox]

I frequently anchor using either of these two methods. Unlike the super super intelligent anchors preferred by some of the experts here, my anchor doesn't know whether it's being set by engine, wind, or the boat's momentum.

I would dispute that. In light winds we would almost certainly enter an anchorage under engine. We stop, drop anchor, motor astern fairly gently and pull until the chain is out to the selected length. Then pull astern, with no shock load.

Under sail or in strong wind we drop anchor, let out chain, boat quickly yaws to one side or the other and moves rapidly sideways. Chain pulls up tight and transmits a shock load to the anchor.

Usually achieves the same result but by two distinctly different means.

 

[thinwater]

... Under sail or in strong wind we drop anchor, let out chain, boat quickly yaws to one side or the other and moves rapidly sideways. Chain pulls up tight and transmits a shock load to the anchor.

Usually achieves the same result but by two distinctly different means.

Interesting point.

If catenary is so good at attenuating gusts and waves, is there a shock load (there is an impulse, but whether I would call it a shock load is not clear)? Over what time or distance? Was there a snubber? How long? What about the case of a mostly rope rode? Obviously, this varies.

Not all boats have the power in reverse to set strongly by engine alone. Can momentum (get some slack and back down) help the process or make it worse? Obviously, this is a central principle when setting under sail. Back in the day, when I had a boatwith no engine, it was common for me to pull up a lot of slack and let the boat drfit back hard with backed sails, to test the anchor and to drive it in deeper.

 

[NormanS]

I would dispute that. In light winds we would almost certainly enter an anchorage under engine. We stop, drop anchor, motor astern fairly gently and pull until the chain is out to the selected length. Then pull astern, with no shock load.

Under sail or in strong wind we drop anchor, let out chain, boat quickly yaws to one side or the other and moves rapidly sideways. Chain pulls up tight and transmits a shock load to the anchor.

Usually achieves the same result but by two distinctly different means.

But how does your anchor know the difference? What is it that you're disputing?

 

[Neeves]

This
yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

Is a useful reference for engine/propeller performance and gives a guide to probable reverse thrust available. The engine in the test boat was a 20hp Yanmar and the best props achieved over 175kgs in reverse on bollard pull. I know from the extensive work I carried out in another life that for the same design prop thrust is broadly linear to power so would expect around 270kgs with a 30hp. This is similar to the effect of 25knots of wind on a 34' monohull, just as Vyv Cox has measured with his boat and the tables from ABYC.

In the example that GHA uses there is no reason why boats should drag if they power set with a 5:1 scope even with a Delta. From a load point of view the conditions described are pretty undemanding - the problems are twofold. Poor holding because of the weed and poor setting. Nothing really to do with anchor type nor size of anchor.

I measured our 2 x 20hp Volvos with a Volvo folding prop and achieved 400kg tension running both engines. This is in line with your and other results. If you yaw and tension the rode from a direction that is not the original set direction it will be possible to side load the anchor and it might trip and might trip at a rode tension less than the tension imposed on the anchor by the engine. Hence managing yawing is important as you can set the anchors for one of the two to take a direct in line tension at each 'side' of the yaw angle.

I'm not in favour of snatch loading the anchor to engender setting - simply because you cannot control the set tension, at the extreme you are unnecessarily tensioning something that may not withstand the tension. I look at bow rollers on some yachts and find them 'puny' and looking suspiciously vulnerable to a snatch side load.

Jonathan

 

[GHA]

I frequently anchor using either of these two methods. Unlike the super super intelligent anchors preferred by some of the experts here, my anchor doesn't know whether it's being set by engine, wind, or the boat's momentum.

Apparently that's all wrong. Guy on the internet said so. At considerable length. Many times. Story goes you can only set the hook with the engine, then if the engine isn`t big enough it won`t get dug in properly & if there's a wind shift you'll all die.
But then another bloke on the internet said "anchor size by engine" never happened. Even though it did. What are us mere sailors meant to do Luckily no one really pays much attention to blokes on the internet..

 

[Tranona]

Apparently that's all wrong. Guy on the internet said so. At considerable length. Many times. Story goes you can only set the hook with the engine, then if the engine isn`t big enough it won`t get dug in properly & if there's a wind shift you'll all die.
But then another bloke on the internet said "anchor size by engine" never happened. Even though it did. What are us mere sailors meant to do Luckily no one really pays much attention to blokes on the internet..

You do seem to have a habit of misreading what people say and write. Give a link to anywhere in this thread (or anywhere else) that says anchor size is related to engine size. Also to where anybody has said that an anchor can only be set by engine.

It is correct that the anchor does not know the difference. it is an inanimate object and just responds to the load placed on it. The point of discussion is what that load is rather than how it is generated and a boat at low wind strengths clearly does not generate high loads, just the same as an engine at low power.

There is a direct linear relationship between load and hold - rather obvious so the greater the load the higher the hold until the anchor reaches its maximum in that particular seabed.

Suggest you read the test data that show what sort of loads can be generated by wind acting on the boat and pull from the use of the engine in reverse and decide for your self which is better for setting your anchor in any particular set of conditions. Just as Vyv described in post#146.

Can't see how anyone could dispute that.

 

[thinwater]

I measured our 2 x 20hp Volvos with a Volvo folding prop and achieved 400kg tension running both engines. This is in line with your and other results. If you yaw and tension the rode from a direction that is not the original set direction it will be possible to side load the anchor and it might trip and might trip at a rode tension less than the tension imposed on the anchor by the engine. Hence managing yawing is important as you can set the anchors for one of the two to take a direct in line tension at each 'side' of the yaw angle.

I'm not in favour of snatch loading the anchor to engender setting - simply because you cannot control the set tension, at the extreme you are unnecessarily tensioning something that may not withstand the tension. I look at bow rollers on some yachts and find them 'puny' and looking suspiciously vulnerable to a snatch side load.

Jonathan

Good points.

I counter that with a very basic engineering understanding, it is not hard to calculate the load, and in fact, I have measured it with a load cell to confirm my calculations. It should be no more than the force applied by a sailor with a larger engine. Practiced as intentional backing down with limited slack (I don't mean a lot of slack, just no load on the anchor and the chain drooping straight down) there should be no side load, if you know how to back straight. Additionally, I had a bridle taking the load, so zero on the rollers. I would not try this without a long bridle; there force will be too great, and very importantly, not applied over a long enough period of time to move the anchor properly. The springyness of the snubber, combined with the catenary coming out, should result in an impulse that lasts 3-5 seconds, not a breif hit. Indeed, if you are not going straight back the keel will probably prevent you from drifting back at a useful speed.

This is a method that requires thought and control.

 

[RunAgroundHard]

Apparently that's all wrong. Guy on the internet said so. At considerable length. Many times. Story goes you can only set the hook with the engine, then if the engine isn`t big enough it won`t get dug in properly & if there's a wind shift you'll all die.
But then another bloke on the internet said "anchor size by engine" never happened. Even though it did. What are us mere sailors meant to do Luckily no one really pays much attention to blokes on the internet..

We are all just a “guy on the internet”. Why should I believe any of the guys on the internet?

 

[GHA]

You do seem to have a habit of misreading what people say and write. Give a link to anywhere in this thread (or anywhere else) that says anchor size is related to engine size. Also to where anybody has said that an anchor can only be set by engine.

How many do you want? Loads to choose from.

A contradiction with bigger anchors

have yet to hear of anyone but Dashew actually anchoring at short scope in strong winds and documenting the experience. I oft hear it quoted but never see it documented, let alone photographed. I am very wary of anecdotal comments without any corroboration (at all). Few mention when quoting that his experience is of a Rocna anchor well over 100kg used on a 40t x 64' yacht with 240hp engine. None of us have the pulling power anywhere near that size nor that pulling power to weight ratio. I am sure he can set that anchor deeply - not so most of us with a maximum of 50hp available - which is why the oversize anchors I mostly see are shallow set with the shank protruding well above the seabed (the engine is too small to set the anchor). And short scope is not a well known technique to use to expect wind to set the anchor for you - I might even suggest its irresponsible suggestion without further evidence of success.

 

[GHA]

We are all just a “guy on the internet”. Why should I believe any of the guys on the internet?

Exactly. Not that many do pay much heed.

 

[GHA]

I know that area pretty well. A few years back, the eastern end of the anchorage had better holding than near the village. This was because it was clear of sea grass. For whatever reason the seagrass is now in the eastern end of the anchorage and there is less seagrass by the village. We were in the Eastern anchorage a couple of years ago because we prefer it there. The wind was blowung about 20kts. We were anchored on our Spade anchor. 3 boats with delta anchors were nearby. The wind started to gust to about 25kts and one of the boats started to drag. 5 mins later the next one started to drag. A local Portuguese guy who also had a delta anchor, went over to tell both boats that they must put out at least 5:1 with there delta anchors before they load them up. They both did this and didnt drag again. Delta a chorus seem to really struggle with seagrass both at Culatra and here in the Caribbean. They are still widely used by charter boats but they really are not suitable for grass seabeds in my experience. They are the number one dragging anchor in the Caribbean based on what we see

There's a well known difficult patch in front of the village.
Just heard back from a very experienced cruiser friend. He had problems when I was there month or so ago. with 40m chain out in 6m water. Scope isn't always the cure all. Note sure what hook he has but been out cruising for decades all over so knows what's what. He went east & held solid. And had the exact opposite opinion to you. Nice big spade I've never had a problem there.

 

[GHA]

In the example that GHA uses there is no reason why boats should drag if they power set with a 5:1 scope even with a Delta.

But drag they do, back out in the real world. Example above, 40m chain in 6m. Shuffle those feet again......

 

[Neeves]

A comment has been made and reiterated that someone recommended anchor size with reference to engine size. I must have missed this.

There is a a rough correlation between engine size and yacht length and equally a rough correlation between length and anchor size - thus a correlation between engine size and anchor. However I'd stick to the rough correlation between yacht length and anchor size.

A 'larger' engine with a 'decent' prop will more deeply set an anchor, than a smaller engine - seems simple and unnecessary to mention.

Unless the anecdotal story of an anchor dragging is supported with data, anchor design, size, rode (size) scope deployed, depth etc - the anecdotal story is simply an anecdotal story - and not worth much. So if an experienced cruiser drags, one might doubt his experience but if we don't know what his anchor is - the story is worthless.

I read anchor posts (but also other posts - I have catholic interests) and despair at the absence of data. People want help or are offering help - and they omit critical detail such that their post is a waste of time, intriguing but not useful. How can anyone expect a sensible recommendation if they don't mention anchor size, type, depth, seabed etc etc.

Jonathan