If you like to know the anchor load and minimal chain length... here is the tool to do it...

AntarcticPilot said:
Sorry - don't think I can recall all the values I used. They were sensible ones for a Moody 31, anchoring in 5m of water with 1m from stemhead to the water, no snubber, 30 knots wind. The only value that I wasn't sure of was speed through the water - I put 5 knots.
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Ah, yes, that explains it, I guess. 5 kn speed at anchor, that is not normal! This velocity is meant to be the velocity component pointing away from the anchor WHILST AT ANCHOR. It then describes the impact of swell.

Cheers

Mathias
 
Tradewinds said:
Some of the values required were a little obscure to me. One of those little click-on ( i )nfo buttons with an explanation of what's needed would have helped (in my instance).

Some of us (ie me) have simple minds and need guidance.
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Thanks, yes. I might add that. But it is a real nightmare to support all the different browser versions, and so we tried to keep the interface as clean as possible. But I will reconsider! :)

Explanations can be found in the tutorial video, a link to which is explained.

Cheers, Mathias
 
Neeves said:
Mathias - great work - you are getting there, or are there.

I'm a bit time short currently and will look into the link later. I note that in post 16 you mention that the speed refers to speed, when yawing? Yawing speed is inordinately difficult to measure as our mechanical paddle wheel logs are insufficiently sensitive and our GPS are also insensitive.

You can derive speed using an accelerometer - part of every modern phone and tablet - what do you use to measure speed?

Antarctic Pilot - there are a number of Apps, free, available to measure boat speed have a look at VibSensor, Accelerometer and I think the best one SCraMP (these are all free). They work on tablets and phones, though not necessarily the phone you have. These 3 all work on an iPad. I think 5 knots might be a bit high. AP - if you look and then use one of these Apps, or any other you might find, I would be interested in your experiences (and the data) as (I am sure) would Mathias.

My granddaughter, finishing first year engineering, is building me one to affix to the rode itself (the problem being it needs to be fairly robust). The one she is building will measure movement of the rode, vibration, rather than speed and horsing (in chop). I will get the rest of the data from SCraMP. I have only played with SCraMP but when the new device is built I'll sit down and record everything at once.

Many people are still using snubbers that are too short and too beefy and a 1.5m amount of elasticity will be a surprise (and impossible).

If you have a load cell it would be easy to rig up to measure actual tension, for tension on a snubber you could simply use a suitcase 'balance' (cheap as chips) ,would need a bit of faffing about to set it up. Crane 'balances' are also quite cheap now - and adequate for the rode itself. But none of these are waterproof.

Thanks Mathias

Stay safe, take care

Jonathan
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Thanks Jonathan!

And yes, you are right, the speed at anchor is rather difficult to measure precisely. But I think a ball park figure will do, erring a bit on the high side. So, I simply use the chart plotter to get this estimate. If I wanted to improve on this front, I would also have to improve on modelling the snubber in the first place. In this tool the snubber is assumed to work linearly (Hook's law). In the next release of my app for Apple and Android, it will be possible to define non-linear snubbers. But those beasts will not be easy too set up and calibrate in any tool... not at all...

If people find that the snubber stretch the tool states is much higher than what they see with their snubber, then likely, they have overrated their snubber and it is not quite as good / excellent as they had thought. Again, defining a non-linear snubber would make things more realistic on this front, but I would dread to receive all the queries on how to do that, if I were to release such a tool online... ;)

BTW, I am using a simple crane scale for my measurements.

Cheers

Mathias
 
MathiasW said:
Thanks, yes. I might add that. But it is a real nightmare to support all the different browser versions, and so we tried to keep the interface as clean as possible. But I will reconsider! :)

Explanations can be found in the tutorial video, a link to which is explained.

Cheers, Mathias
Click to expand...
I've arrived at my anchorage, I'm cold and tired - last thing I want to do is watch an explanatory video.

Neeves likes it - it's not for me.
 
What's the point, when the actual security of the anchor depends 100% on the substrate? You can play with all sorts of formulae, but if your anchor fouls a tin can, your calculations won't help one little bit. I'll stick to real world anchoring. But if it keeps you happy and gives confidence to those without it - fine.
 
NormanS said:
What's the point, when the actual security of the anchor depends 100% on the substrate? You can play with all sorts of formulae, but if your anchor fouls a tin can, your calculations won't help one little bit. I'll stick to real world anchoring. But if it keeps you happy and gives confidence to those without it - fine.
Click to expand...

Well, not quite 100%. If you use too little chain, it will do you no good. Likewise, if you anchor in shallow water without snubber, it will do you no good at all.

It is the combination of anchor, chain, possibly rope and snubber / bridle, which needs to be right. With this tool you can study the chain and the snubber / bridle. I have left out - on purpose - the maximal anchor holding power that depends on the substrate, and the rope.

Cheers, Mathias
 
Tradewinds said:
I've arrived at my anchorage, I'm cold and tired - last thing I want to do is watch an explanatory video.

Neeves likes it - it's not for me.
Click to expand...

That's why normally I do not like to code and provide a tool for free. People always moan and are unhappy with what they get for free. Want this, want that. Like children. The information buttons you have been asking for are all in the commercial app for Apple and Android. You just need to pay for them. This is a LITE version, and LITE means free, but less functionality.

So, suit yourself - that is fine with me. I hope some folks will find it useful and then I am happy to pay for the server fees for this calculator. Fees that I will need to cough up every year. There is no free lunch! If something is free for you, it only means somebody else is paying for it!

Really, the nerve some folks have - it is unbelievable!

Cheers, Mathias
 
MathiasW said:
Some of you will know already my fascination for the physics and mathematics of anchor chains. Knowing when a chain will work well (deep water), and when it does not (shallow water), and what one can do about it to improve it (good snubbers).

I have now created a free web-based online calculator with which you can calculate the anchor load and minimal chain length for various vessel characteristics (including snubbers), sea and weather conditions. No guarantee it will work well in all browsers - that was quite a nightmare, actually (just fixed Android mobile), but still, you may find it useful:

https://anchorchaincalculator.com

What I like in particular is that it allows you to perform what if scenario plays. Before bad things start to happen. Feedback is always welcome.

Cheers, Mathias
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I don't think this adds very much to knowing that the length of chain and depth of water dictates the angle of the anchor, and that you need some kind snubber if there's any motion?
Since the app doesn't tell us how it's getting the numbers, we don't know if the assumptions are relevant on the day.
We put i n a rough guess for the swell or vessel speed in the chop, it comes back with a snubber stretch to 0.1%.
Guesses in, garbage out.

Most people find chains work well in shallow water?

Do people really want or need an ap to tell them the motion of the boat is bad so they need to either let more rode out, use a better snubber or find somewhere better to park?
 
MathiasW said:
That's why normally I do not like to code and provide a tool for free. People always moan and are unhappy with what they get for free. Want this, want that. Like children. The information buttons you have been asking for are all in the commercial app for Apple and Android. You just need to pay for them. This is a LITE version, and LITE means free, but less functionality.

So, suit yourself - that is fine with me. I hope some folks will find it useful and then I am happy to pay for the server fees for this calculator. Fees that I will need to cough up every year. There is no free lunch! If something is free for you, it only means somebody else is paying for it!

Really, the nerve some folks have - it is unbelievable!

Cheers, Mathias
Click to expand...
Apologies but you have taken my comments the wrong way. As I said - it's just not for me, even if free to use. Neeves likes it and so will many others. It's a forum - we're allowed to comment (on some subjects nowadays :rolleyes:). I pay for a few apps and use a lot of free ones too. Good luck with yours but it's of little interest to me.
 
MathiasW said:
People always moan and are unhappy with what they get for free. Want this, want that. Like children.

Really, the nerve some folks have - it is unbelievable!

Cheers, Mathias
Click to expand...
Was that comment really necessary? You could have ignored it or simply said “thank you for your feedback” and moved on. Your response says more about you than it does about the poster giving feedback.

If you ask for feedback, you must be prepared to accept negative comments, it’s pretty poor form to insult people for giving what you’ve requested.

Purely out of intrigue after reading through the thread, I clicked on the link.

Looking at it, it made me think of target audience. For many years, new sailors have learned (any variation of) 4x or 6x and this usually keeps them safe until their own intuition and experience takes over.

Perhaps it’s targeted at young people, new-coming to sailing and who are obsessively and compulsively addicted to some form of electronic device.

I am reminded of the story from a Sailing School. Our modern day hero was under instruction and was planning to leave a marina berth. In discussing how to leave the instructor asked “what’s the tide doing”, expecting a quick look over the side. The day was cold and wet and the student was fully togged-up with foul weather gear, gloves etc etc. He duly started to remove his life jacket and outer layer jacket. When asked “what are you doing”, he replied “my phone is in my trousers pocket”.
 
Wing Mark said:
Do people really want or need an ap to tell them the motion of the boat is bad so they need to either let more rode out, use a better snubber or find somewhere better to park?
Click to expand...

You are correct - people do not want an App etc etc - because they don't realise what a correctly sized snubber will do for them. Ignorance is bliss.

Next time you are at anchor securely in a crowded anchorage just go round and try and ascertain how many people are using a snubber - one that offers elasticity. Most who use a snubber use a very short length of rope, any old (or new) rope, to keep the tension off the windlass. Most use nothing at all and a few use a proper elastic snubber. Elasticity means you can anchor at short(er) scope and use the elasticity of (a correctly sized snubber) instead of the catenary of chain - and have a comfortable time in a windy anchorage. This means you can snuck into a tight anchorage (tight because it is small or because it is crowded).

Most who have seen the advantage of a snubber have worked out by trial and error what works best- Mathias offers a short cut.

We were quite happy to accept GPS as a short cut to establishing a position. Some of us have been happy to buy a modern anchor for its reliability. A few have downsized their chain, because there are others options - rejecting the idea that a correctly sized snubber might be useful (and having the tools to Size/ fit correctly - seems a little perverse - especially when it is free). There will always be people who have been born and bred to sailing - but some of us (and more and more of us) come to sailing as complete neophytes and we were unable to rely on our parents for that ingrained knowledge - GPS, modern forecast, advances in cordage have made our lives easier and safer - Mathias is simply offering another short cut.

As was said in the last couple of weeks - many couples are buying a 45' yacht as their starter boat.

Don't look a gift horse in the mouth - try and see - then come back with comments.

Mathias cuts out the trial and error - you can still fine tune. You can reject Mathias offering - because what you do has served you well - that does not mean the neophytes can follow that same practice as they don't have hefty chain and a long keel - they have a boisterous plastic fantastic with light(er) chain (because that's what Benny/Jenny and Bav offer - and that's what neophytes sometime buy.

I know a number of forum members now use long snubbers and have found them a success.

It would not do if we were all the same.

I thank Mathias for his work, and offering it for free and I will freely quote his link


Wing Mark said:
I don't think this adds very much to knowing that the length of chain and depth of water dictates the angle of the anchor,
Click to expand...

Actually when your anchor is well 'set' and holding and you have buried the anchor out of sight and also buried some chain then the tension angle is not that of the scope - its the angle of the buried shackle. As your modern anchor sets it buries the shank end, with the shackle - the shackle resists burial (along with the chain) and there thus develops a vertical component (imposed by the shear strength of the seabed) which results in the shackle angle increasing well above that of the scope. Fortunately modern anchors accept this higher angle.

If you use an overly large shackle, a swivel or an overly large chain this effect become more pronounced.

But if you have been following the forum for a few years you will recall some respected members here admitting they have anchored, by mistake, at short scope under arduous conditions without ill effect. Not a practice to be followed - but modern anchors are very forgiving - and more so if you use a, proper, snubber


I think we are all obsessive about electronic devices: MFD, GPS, windspeed, depth and now our mobile phones. Why spend a King's ransom for a device you don't use? :)


Take care, stay safe

Jonathan
 
MathiasW said:
That's why normally I do not like to code and provide a tool for free. People always moan and are unhappy with what they get for free. Want this, want that. Like children. The information buttons you have been asking for are all in the commercial app for Apple and Android. You just need to pay for them. This is a LITE version, and LITE means free, but less functionality.

So, suit yourself - that is fine with me. I hope some folks will find it useful and then I am happy to pay for the server fees for this calculator. Fees that I will need to cough up every year. There is no free lunch! If something is free for you, it only means somebody else is paying for it!

Really, the nerve some folks have - it is unbelievable!

Cheers, Mathias
Click to expand...
Seems to work fine to me. It confirms that my very elastic nylon snubber is indeed very elastic. It predicts 1.4m of stretch why is pretty much what I have witnessed under 50kts at anchor?
Great work
 
I tried some numbers. On the "basic" setting the results were non-sense, about 5-10 times too high. On the "expert" setting they agree reasonably well with what I have measured. However, the swell effect is tricky, and I feel it would be easier for most people to try a cheap scale, as Neeves suggested; that way they will actually believe the number.

The range is huge, depending on the snubber, depth, wave exposure, and other factors, and that is the value of calculators. No one wants to be out there at 50 knots or more (I did that twice in severe thunderstorms and I didn't like it--never again)! I did confirm that with a good snubber, the storm values agreed with force ~ V^2, so I don't need to do it again. With a short snubber or all chain, snatching will begin at some speed, often 30-35 knots, so force may go up considerably more than V^2 in that case, in most tests several times more.
 
NormanS said:
What's the point, when the actual security of the anchor depends 100% on the substrate? You can play with all sorts of formulae, but if your anchor fouls a tin can, your calculations won't help one little bit. I'll stick to real world anchoring. But if it keeps you happy and gives confidence to those without it - fine.
Click to expand...

You're funny. Security depends equally on the substrate AND the force. You know this. Do you use a 5-pound anchor on good bottoms attached to 6mm chain? Didn't think so. So the force apparently does matter.

Your real world anchoring experience takes all oft he same factors into account, whether you consciously recognize it or not. Some you cover over with safety factors, some you use your own rules of thumb, and a few, perhaps you have gotten lucky with. Haven't we all.
 
How do you allow for variations in yawing characteristics? That can increase load 50% or even more. My initial testing used a boat used a boat on a bridle that did not yaw. I then added yawing later. hobby horsing can also be a factor in exposed areas that shelve rapidly. Very dangerous.
 
I may be in a small minority here, but I think that all this technobabble about anchoring actually puts people off. People have been anchoring for generations, using their common sense. Remember that?
When I started cruising under sail, anchoring was the only way, and that was what you did, night after night.
OK, I sail on the West Coast of Scotland, and we are blessed with innumerable anchorages, many perfectly sheltered from the sea, from the wind - less so, and in many cases not at all. Being anchored in 60 knots or even 70 knots of wind is not unheard of. Frankly, I find choice of anchorage, and taking measures to prevent yawing, far more important than fancy calculations. But, if that's your style, go for it, but please don't make anchoring seem more complicated and difficult than it really is.
 
NormanS said:
I may be in a small minority here, but I think that all this technobabble about anchoring actually puts people off. People have been anchoring for generations, using their common sense. Remember that?
When I started cruising under sail, anchoring was the only way, and that was what you did, night after night.
OK, I sail on the West Coast of Scotland, and we are blessed with innumerable anchorages, many perfectly sheltered from the sea, from the wind - less so, and in many cases not at all. Being anchored in 60 knots or even 70 knots of wind is not unheard of. Frankly, I find choice of anchorage, and taking measures to prevent yawing, far more important than fancy calculations. But, if that's your style, go for it, but please don't make anchoring seem more complicated and difficult than it really is.
Click to expand...
You forget that there are a huge number of people with little experience of anchoring. We have witnessed some appalling anchoring practises recently. Some of these people may benefit from understanding a little more about how it works. It's not aimed at the vastly experienced sailor who anchors regularly in conditions that the average marina berth holder who never consider anchoring in
 
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