Another anchor

vyv_cox

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I would agree that 60 knots is a reasonable design figure. I have not seen that much but have seen 50s when I still used a Delta, without dragging. But on a different seabed, relatively soft mud with the same anchor, I dragged three times at around that windspeed.
 

Neeves

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If I missed a forecast of a forthcoming 'strong wind event' I would be inept. There are good long term warnings of gales and storms and even better warnings of cyclonic storms. Short term thunderstorms might 'slip through the net' of long term warning - but if you were in an area where such events were common you would surely be prepared. Our forecasts can be heard anywhere in Australia and far offshore - as long as you have HF.

But returning to forecast strong wind events - ours are well forecast with a decent few days warning and we would move to an anchorage sheltered from wherever the storm comes from. We have sat out 70 knot storms - but only experienced 35 knots. We were caught once (in the last 20 years) and measured 55 knots at the masthead (and we were crossing Bass Strait and found ourselves in a small unforecast storm cell of 55 knots for 8 hours - but that does not count).

So - call us wimps - if we have storms forecast - we anchor where we are sheltered from the storm - we certainly do not seek them out. We do not have insurance cover for the 'cyclone belt' - this is sufficient deterrent (and heat and humidity in such belts are not very pleasant anyway - without A/C). We also do not boast we have sat out 70 knot storms - when the measured wind was only 35 knots (and anyone sitting in the brunt of s genuine Storm - needs their heads examined (and better system of forecasting).

I know our anchoring system will cope with 55 knots - I'm not sure at what point it would prove inadequate. I would suggest 55 knots would be as bad as it gets, outside of a cyclone on mainland's Australia's east Coast and 70 knots I think is fairly extreme for Tasmania (but there is lots of shelter - and in shelter 70 knots is just a lot of noise with lighter winds, wherever you choose to shelter.

Jonathan
 

noelex

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60 knots is decent amount of wind. The anchor tables from Rocna, Mantus etc usually assume only 50 knots. For many companies, even respected names such as Fortress, their sizing tables assume a maximium of only 30 knots, which is setting the bar far too low for crusing boats that plan on anchoring overnight.

However, the real advantage of a larger anchor is the ability to safely anchor in poorer holding ground, or in areas of less protection, or at a lower scope. These advantages are useful in much lower windspeeds.

The latter is frequently disputed even when it just pure common sense. It has been discussed many times before and this was my answer last time:

http://www.ybw.com/forums/showthread.php?495296-Anchor-chain/page7&highlight=%93Anchor+chain%94
I have reproduced the answer given atthat time to save people looking it up.

“Jonathan, you seem to have a bee in your bonnet about this subject.

It is not difficult to understand. A bigger anchor has more holding power than a smaller anchor of the same design. Conversely, an anchor deployed on a shorter scope has less holding power than than the same anchor deployed on a longer scope.

Thus, in general, for the same holding power you can use a shorter scope with a bigger anchor. Simple.

This advantage applies across all scopes not just to so called "short scopes". For example a larger anchor at 5:1 might have the same holding power as an identical design smaller anchor at 7:1.

This is just one advantage of larger anchor, there are many others, but it is not a miracle cure. You cannot use a short scope in very strong wind even with a large anchor. In the same way if using a very small anchor a medium scope may be inadequate in even moderatly strong wind.

Chain left in the locker does little good so generally it is better to deploy a longer scope if you have any doubts. It is difficult to know the nature of substrate and this is generally the largest variable. No one is advocating because you have a larger anchor you must use a shorter scope, but It does open up some options that would not othervise not be prudent especialy compared to those using a small anchor. Long scopes are sadly not always practical.

You have long been an advocate of very small anchors, it seems to work for you but it does have some obvious limitations. By using smaller anchors than most cruisers you are forced to use longer scopes for the same holding power. You have indicated before that you always deploy two anchors if the forecast is above 25 knots and you now indicate that you never anchor at less than 5:1. Both of these limitations are unnecessary with reasonable anchor gear, and personally I would find them restrictive.

Snubbers are a seperate issue. I agree completely that a good snubber is an important component of the anchoring system. I think snubbers have been discussed at length on this forum and doubt any regular reader of anchor threads is unaware of their use.”



It is also worth reading Steve Dashew’s comments. He has fitted a large 110 kg (240 lb) anchor on his FPB 64 power boat and also on his previous Sundeer sailing boat. You can read his comments here:


https://setsail.com/anchoring-systems-refining-a-tried-and-true-approach/#more-46615

http://setsail.com/anchors-and-sizing/

Here are some extracts:

“We are surrounded by a lot of 40- to 50-foot (12- to 15-meter) yachts. The water is 55 feet (17m) deep at half tide. We set our big ROCNA anchor on 2.5-1 scope, and then, with a firm bite established, shortened the chain rode to 100 feet (30m). A scope of 1.6-1. If you calculate the angle off the bottom, combine the chain length with Wind Horse’s length, we need about 150 feet (45m) of swinging room.
Compare this to a 40-foot (12m) yacht anchored with a normal sized anchor. They will need at least 4-1 and probably 5-1 scope. Take their length and add it to 240 feet (74m) of chain, allow for angles, and you have a swinging radius of 220 feet (67m) at a minimum. The smaller boat with its normal (undersized by our standards) anchor takes a lot more room than the bigger boat with an oversized anchor. Is there a lesson here?
Not only does this work in crowded anchorages, but it benefits you in secluded spots which might otherwise be too tight with a normal anchor.
The anchor, regardless of design, will set faster, being bigger. This means it drags less before it digs in. That reduces the risk of it fouling debris. And since you take less swinging room, the chain sweeps a much smaller area of the bottom as the boat changes position, again reducing the risk of fouling.”

Once again, to quote Steve and Linda Dashew:


'When we purchased ground tackle for Sundeer, we went with a 110-pound (50kg) Bruce as the next size available, 240 pounds (110 kg), was simply too much. But when Bruce came out with a 167-pound (80kg) hook, we traded up. You wouldn’t think that 57 pounds (25.9 kg), roughly a 40% increase in weight, would make a big difference. Yet it made a huge difference in all condi- tions. We were surprised at the increase in short scope abilities. In crowded anchorages we found that we could set the anchor at 4-to-1 scope, then shorten down to 2- or 3-to-1 to reduce swinging room. This allowed us to anchor on a single hook in conditions where two might otherwise have
been required. In Alaska we anchored several times in very deep conditions with 2 to 1 scope, and the Bruce held well"
 

RupertW

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Replying to noelex:

I agree with the logic of the post with a couple of caveats - and I’m no anchor expert as we anchor a lot but I haven’t moved off my Delta yet.

Firstly that a lower scope with larger anchor will logically be better but only definitely for the same anchor design with the same angle of shank to tip. Designs with higher angles must dig in more at shorter scopes.

Secondly I do digging in under power to test the seabed as I know my anchor works. There is an advantage there for a smaller anchor as you may be fooled by a heavier anchor holding the boat under power but in a seabed that won’t hold in a squall.
 

noelex

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Replying to noelex:

I agree with the logic of the post with a couple of caveats - and I’m no anchor expert as we anchor a lot but I haven’t moved off my Delta yet.

Firstly that a lower scope with larger anchor will logically be better but only definitely for the same anchor design with the same angle of shank to tip. Designs with higher angles must dig in more at shorter scopes.

Secondly I do digging in under power to test the seabed as I know my anchor works. There is an advantage there for a smaller anchor as you may be fooled by a heavier anchor holding the boat under power but in a seabed that won’t hold in a squall.

Yes, I agree Rupert. “Bigger is better” only works if the the other variables such as anchor design and construction materials are unchanged. I should have made this clearer.

It is also a great point you have made about an oversized anchor not challenging the substrate as well under motor alone. This is one of the drawbacks of a larger anchor. Full reverse from the engine (for yachts) only produces about the same force as 25-30 knots of wind. Setting the anchor provides a test that the substrate and anchor combination will hold to roughly to this wind strength. A very small anchor will only do this in a good substrate (there are exceptions such as rock), the recommended size anchor will do this in a reasonably good substrate, but a large anchor such as I have fitted will do this in virtually all substrates unless it is really poor (such as smooth rock). So the feedback about the quality of the substrate is somewhat diminished.
 

Neeves

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If you look at the Fortress Chesapeake Bay thin mud tests there is no data to support the idea that a larger anchor would provide sufficient security for an over night stay with even winds as little as 30 knots. A bigger Rocna or Spade might hold a bit more but the anchor would need to be 3-4 times as big to offer security.

In marginal seabeds you do not need a bigger anchor but the anchor of the design suited to that substrate.

If you can provide quantitiative data that supports your ideas - I would like to see it.

As a anchor expert - when you have completed the drawings of a Mantus set with the long of its shank horizontal and prove that the fluke angle is not 16 degrees - I might then find your comment credible - in the meantime the jury is out (but the parts of the jury I speak to suggest you are arguing from a position of weakness). You obviously have some reason for not conducting the analysis and publishing the same to support your views. You can then illustrate that, say, Rocna has the same fluke angle. I think you will find it not difficult - but impossible.

Basically everything you suggest cannot be supported numerically - its all gut feel, and wishful thinking and dangerous nonsense.

Your memory does serve you well - if winds are forecast to be 25 knots in an anchorage I would expect gusts to be 35 knots, maybe more. Of course we deploy 2 anchors - its called prudence - especially as once that 25 knots turned out to be 55 knots (a southerly buster) - even though it only lasted at the speed for 30 minutes. When you have a high windage yacht - you would be wise to show prudence - and what else are you doing once you anchor up - a row in the dinghy is good exercise and hardly complex. Its a bit like an insurance policy - you take out the insurance and hope you never need to use it, and year after year you renew the policy. Its the same with anchoring - if gusts are going to be 35 knots you take appropriate action - whether it is necessary you never know. But deploying to anchors in a 'V' reduces yawing and allows the vessel to be more stable and comfortable - strangely a stable yacht engenders relaxation (and whether you need that 'different' hold is not actually relevant. Not every has large stable yachts - most have lighter flight vessels and have different techniques.

Jonathan
 
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thinwater

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When you power set, do you know how much wind that is equivalent to? You should know this figure off the top of your head. How many HP, thrust/HP, and approximate wind load curve.

And, don't for get that when the boat begins to yaw that will increase rode tension and reduce holding. This may be as much as double, combined.

Bottom line, I doubt many boats have enough motor to power set past about 30 knots equivalent. Most only about 20 knots, by the time all factors are included.
 

skipmac

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I can’t help thinking that Professor Taylor and Simpson Lawrence were “onto something” with the drop forged shank of the much derided CQR. Many new generation anchors seem to rely on simple flame cut plate shanks and the others have complex built up section shanks which are bound to corrode from the inside out over time.

The ‘I’ section drop forging gives the best combination of strength, light weight and durability. I don’t think there has been a single case of a CQR ( not a CQR “B” or a clone) failing at the shank.

So why has no new generation anchor got one?

I have often wondered the same thing. Think I'll ask one of the anchor makers but I'm betting it's cost.
 

vyv_cox

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I have often wondered the same thing. Think I'll ask one of the anchor makers but I'm betting it's cost.

I agree. The midlands in UK used to be full of drop forging shops making a huge variety of equipment. Very few of them left now because fabrication has taken over as being far cheaper and cleaner*. A fabricated anchor shank of T or H section would be far stronger but probably double the price of the product. The hollow Ultra shank is a neat solution but horrendously expensive. Easier and cheaper to build a plate shank from strong steel and rely on the likelihood that very few will bend one.

* The atmosphere in foundries and drop forging shops was so smoke filled that it was nearly impossible to see across them. Even the best modern extraction systems would struggle to cope with the amount of smoke generated.
 

noelex

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When you power set, do you know how much wind that is equivalent to? You should know this figure off the top of your head. How many HP, thrust/HP, and approximate wind load curve.

I think doing the calculations as you suggest is a valid approach, although there are differences between the setting force produced by an engine in reverse and the force produced by wind. The duration of force is an obvious difference.
It has been some time since I did the sums, but from memory the results for my boat suggested a similar 25-30 knot windspeed, which is reassuring. I assume you done these calculations, what windspeed did these suggest?

Some anchor manufacturers have tables on their website to enable rough calculations if you do not want to go into great detail.

The other way is to observe anchors underwater. If the anchor is set in light wind with full reverse held for around thirty seconds (my usual technique) the anchor will stay unchanged until the windspeed rises to 25-30 knots. Above this amount of wind the anchor will set deeper. There are limitations with this observational technique, but it suggests that the test of the holding force created by applying reverse on a typical diesel engined yacht is valid up to around 25-30 knots. Above this wind strength the anchor has to bury deeper to increase the available holding force.


Bottom line, I doubt many boats have enough motor to power set past about 30 knots equivalent. Most only about 20 knots, by the time all factors are included.

I think we are in broad agreement. The exact number will depend on factors such as the performance of the propellor in reverse, HP of the engine (relative to boat size), whether the boat develops any momentum (which can apply considerable extra force while setting). But I think it is helpful for owners to have a rough guide.
 

noelex

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Just one note of caution. It sometimes suggested in these threads that when anchoring you can avoid strong wind and the most you are likely to experience is 30-35 knots. That has not been my experience.

If you anchor overnight frequently, sooner or later you will experience winds that are significantly stronger than this.
 

vyv_cox

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The other way is to observe anchors underwater. If the anchor is set in light wind with full reverse held for around thirty seconds (my usual technique) the anchor will stay unchanged until the windspeed rises to 25-30 knots. Above this amount of wind the anchor will set deeper. There are limitations with this observational technique, but it suggests that the test of the holding force created by applying reverse on a typical diesel engined yacht is valid up to around 25-30 knots. Above this wind strength the anchor has to bury deeper to increase the available holding force.

That agrees with my observations. The highest wind speed in which I have swum on the anchor was a full gale, 35 knots or so. It did seem that the anchor was only a little deeper set than when we had pulled it back at our usual 2500 rpm earlier. I don't usually go to our engine maximum of 3500 rpm as this seems to make very little difference over the lower figure.
 

sailaboutvic

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Just one note of caution. It sometimes suggested in these threads that when anchoring you can avoid strong wind and the most you are likely to experience is 30-35 knots. That has not been my experience.

If you anchor overnight frequently, sooner or later you will experience winds that are significantly stronger than this.

I have to say that's not our experience too . We seen wind well above that many times each year .
Personally All these figure throw around are great as a reference, but the prove in the pudding is out there in a stormy day if you have the right gear or not.
This year week after week we seeing report of yachts. Not one out two but seven or eight in the same anchorage being blow ashore , you have to wonder , are every one of thos skipper haven't got anchoring skills or is it their gear not man enough to do the job.?
 
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Neeves

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I've measured the tension in our rode upto 35 knots and have measured the tension developed with our engines, 2 x 20hp Volvo with 3 bladed folding props. The tension developed by the engines is similar to the tension developed at 30 knots - but that's our catamaran and our 2 x 20hp engines with those same props. This is at a 5:1 scope.

However when you set an anchor such that it achieves the tensions measured, from memory (though its not relevant) of 350kg. That's a hold of 350kg, whether its a big anchor or small - its still 350kg - in a straight line.

If you are hit with a gust of 30 knots, that same 350kg of windage pipes up - but if that gust drives the yacht at 90 degrees to the set direction - then bets are off. It does not matter if the anchor is big or small - it is not designed to hold sideways at that 350kg tension - which is why setting 2 anchors in a 'V' such that they cover the extremes of yaw - offer more certainty.

Read the second paragraph of Post 47 carefully and then mull it over.

Don't yaw... does not matter - gusts can come from many directions.

Jonathan
 
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GHA

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Just one note of caution. It sometimes suggested in these threads that when anchoring you can avoid strong wind and the most you are likely to experience is 30-35 knots. That has not been my experience.

If you anchor overnight frequently, sooner or later you will experience winds that are significantly stronger than this.

Another big +1 !

Live on the hook you're going to get hammered sooner or later. Good chance of it not being forecast as well, most years there seems to be a biggun in the Med like Vliho
http://www.ybw.com/forums/showthread.php?287823-vliho-storm

Experienced cruisers like to go up a little in anchor size from recommendations for many reasons, and for most no real downside.
 

Neeves

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Experienced cruisers like to go up a little in anchor size from recommendations for many reasons, and for most no real downside.

Up a little? Does not quite support the adage that your anchor is not big enough until people laugh.


I am very firmly of the belief that anchors do not drag as result of an absence of holding capacity. The chance of anyone exceeding the holding capacity of a 1st gen anchor is unlikely and a 2nd gen anchor almost impossible - and anchors drag in much more benign conditions.

We are blessed that we have access to more forgiving anchors that are easier to set more reliably - but that will not stop them being fouled - which is a reason for power setting (but your anchor will set more deeply if subjected stronger wind and may then become fouled (another reason for 2 anchors as the chance of both being fouled is less likely). But anchors are designed to develop their hold pulled in a straight line (with a steadily increasing load).

We, you and I, subject our anchors to yaws (and if not yawing, bullets) where the tension direction changes, our vessels hobby horse in chop (which if the chain is off the seabed reduces hold). I frankly don't believe a few kgs extra will overcome these issues - either a 20kg anchor and a 25kg anchor is stable when attached to a yawing anchor - or not. 5kg difference in anchor weight is not going to factorially increase the hold from a rode tensioned at 50 degrees to the set direction and then pulled 50 degrees in the other direction.

We need to remember - it does not matter if your anchor weighs 20kg or 40kg the hold when you power set will be, say 400kg, If the wind gets up the windage from the yacht may increase that hold to 500kg - in either anchor. Neither anchor is holding more. if the vessel yaws they will both be subject to a tension in the chain of say 300kg - does anyone know what the holding capacity is of their anchor when the rode is at 30 degrees, 50 degrees (make your own choice) to the set direction. The bigger anchor has a longer shank - I wonder what impact that longer lever arm might have....??? If you yaw and have set your anchors with skill - then the one under tension at the edge of each yaw is being tension, again in its set direction.

If you know differently - I'd like to see the data.

To re-assure you - the data will be produced and will come as a surprise. Just keep watching Practical Sailor where an independent review of this very effect will be provided. Just go and read Post 47 again the author of the post knows what he is saying - and I for one take note..

Jonathan
 
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MM5AHO

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I have recently started using an interesting phone app that using gps position watches the position of the boat recording deviation from the initial set point. I was interested last month when anchoring in winds measure at deck level of 40kn (a howler). We yawed 20m either side of dead downwind, but within the accuracy of such a system, not more than a metre downwind. It was a northerly, and we didn't move to the south.
I'd never measured the distance of yaw previously, so found that really interesting. We were in 5m with 30m rode out.
There are various techniques to keep reduce yaw, but I've not generally used any of them. But severe yaw is a real test on an anchor, both on the shank's ability withstand bend, and on the whole anchors ability to stay set.

It did take a while to retrieve the anchor, felt like it was stuck on something initially, but at still blowing 30 knots in the morning, wasn't able to see it, or figure how deep it buried. But it eventually came to the surface!
 

Neeves

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I sat one day and simple measured yacht angles in relation to the anchor, which I had buoyed. So I checked bearing to buoy and and the variation from that bearing to which way the yacht was actually facing. The rode was varying a total of 60 degrees but the cat was yawing a further 30 degrees at the end of the rode. So the total yaw was 90 degrees - though this will vary with the characteristics of the wind. The results were quite eye opening as at some point the cat would be almost at right angles to the wind.

My experience with our 13kg Knox is that it sets deep (and can be difficult to retrieve) but as, any, deep set anchor is a well set anchor as if the shank is buried it takes considerable tension to get it to move laterally (simply because it presents such a large area) and because you need to move the chain that will also be buried in the sand (or seabed). The chain might move - but some of the energy of the moving yacht is lost in simply freeing up the chain and its friction through the seabed - which is why I like a fully buried anchor.

its not something I had thought of - but the Knox has a shorter shank than some and this may help it in reducing the effects of a lateral tension - as the effective lever arms is less.

Obviously if you have stable wind or a yacht not subject to yawing - none of this matters.

But with an unstable wind a riding sail will not help, maybe better with a hammerlock.

https://www.practical-sailor.com/is...ate/Rest-Easy-with-a-Riding-Sail_12626-1.html

Jonathan
 
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Bouba

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Gentlemen, thank you for your thoughtful answers:encouragement:
Jonathan has said something that might ring true, my Rocna is big! On a Beneteau Swift Trawler 34 motorboat with 425 hp single engine, total weight I’d guess to be 9 or 10 tons, but very high compared to length and lots of windage up front. We have eight millimeters chain and a twenty kilo steel Rocna, no swivel or banana. When setting I try and do as it says on the instructions and just lay the chain on top of the anchor and then let the wind do the work. However in the summer there isn’t room for a lot of scope so I reverse (very slowly with minimal power) to set it. I always look for a sandy patch.
Too late for editing but I meant 10 mm chain (not 8)
 

Neeves

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I don't know if its been said already but:

Boaba, deploy your anchor at about 3:1 - and reverse up gently - this will set the anchor - and if it does not set then there is something wrong, possibly the anchor is fouled - try in a slightly different location.

Once you are confident the anchor is set - deploy 5:1 and use the grunt of your engine. With 425hp you have the potential - if extrapolation is correct - which I doubts - to produce 4,000kg of tension!! (most of us have little engines (40hp would be large!) and our rule of thumb is 'about 100kg per 10hp (nice mix of imperial and metric). But it depends on the prop - so its simply a rule of thumb. I actually measured it, with a load cell, and for us its about right - but our engines a re 2 x 20hp with 2 x 3 bladed folding props. Other people might quote data - but I'm not aware anyone else has actually measured it.

I'd go easy on the revs, maybe 1/3 maximum, but increase the revs gently. - and you should set that Rocna completely.

You are the first person I know who has the engine capacity to set an oversize anchor deeply - so you are breaking new ground.

I don't know of anyone who has tested 'our' anchors beyond the 15kg weight. But a modern second gen 15kg anchor in nice sand will develop a hold of 2,000kg - and then drag. Double the size and maybe the hold will be 3,000kg and triple the size maybe 4,000kg.

In general once our, those 2nd gen, anchors set - if the tension applied, from wind or engines, is in the set direction - the anchor will set more deeply. If the wind direction varies - the anchor might swing round or it might pop out and then need to reset.

Now - when you power set - the tension should not be direct to the windlass. Use a chain lock or short strop attached to a strong point and a chain hook. You will do the windlass no good if you stress - unnecessarily. I assume you are using a decent snubber once the anchor is set and you settle down for that glass of wine and the roast leg of lamb.....?

https://www.sailmagazine.com/diy/how-to-dealing-with-snatch-loads-in-an-anchorage

https://www.sailmagazine.com/cruising/anchor-snubber-tips

Most snubbers and bridles are far too short - to be effective they need to be long.

Jonathan
 
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