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Old 06-04-2011, 19:41   #31
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Re: How to Test Anchors?

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Originally Posted by markpierce View Post
You need to know your bottom. Start there when choosing an anchor.
I agree completely.
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Old 08-04-2011, 01:18   #32
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Re: How to Test Anchors?

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It is rather amazing that so much to do with anchoring is based on no, or very little, scientific data at all. I believe the ABYC guidelines for anchoring forces, which are quoted everywhere, are totally theoretical--not based on any actual measurements.
Correct, 99% of what is on the Net is theoretical. Last year we build a couple of machines that are on boats now which datalog all the numbers related to the rode, bow and associated gear every 2 seconds.

Also one has recently been tweaked to show what load is on the anchor to chain connection.

Interesting data so far but they have only been on 4 boats so we need to expand the range more to get better numbers to work with. So far the data is suggesting much of the theoretical stuff is over stating loads generally speaking. We have set up a anchoring system up to a huge lump of concrete, we don't want it moving at all, and are waiting for a big storm. We'll hook a boat onto that with a machine and see what we get, that's going to be very interesting. We have the use of a blunt bowed tug so would like to use that as we think it'll be more 'worst case' than an average boat.

I decided to do it after working out from one popular interweb spot that our rode should have had 450kgs on it. When my wife was pulling it in by hand and with little effort I suspected that I'd either been really lucky in not annoying her too much or the numbers weren't quite right. Soon we will have lots of real life data off real life boats doing real life anchoring.

We test anchors a lot and you can't really get a definitive answer on which is best, there are just to many variables, the biggest of which is the dick on the stick. We get told 'my anchor is crap' a lot only to find the anchor is fine and it's either a poorly matched rode or it's being used wrong.

Most of our testing is to look at a specific aspect, for example setting characteristics or veering and stuff like that. About the best you can do is collect all the results from all the tests you can get and a pattern does appear. We've done that and they mirror pretty much what we have found ourselves. That being there is no one 'best anchor' unless the question is qualified with a fair amount of information.

Most tests only focus on max holding load and most of those tests are flawed to some degree.

You could ask 'What is the best anchor for a coastal cruzer with a XX boat who only anchors in YY type seabeds?' for example. That answer will narrow down the choices a lot but the answer will still have multiple options, or most likely will.

If you ask the question 'What is the best anchor is mud?' you will get a very different answer than if you ask 'What is the best anchor in Clay?'. Even them the 'best anchor' will most likely be answered along the lines of 'a X, a Y, a Z and a ABC, take your pick'.

The best anchor is the one that gives you a good solid 8hrs sleep even if the weather is nasty. If that means you use a brick rather than a million dollar wonder so be it.
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Old 08-04-2011, 06:58   #33
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Re: How to Test Anchors?

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Correct, 99% of what is on the Net is theoretical.
I'm not sure that is true. GMac, you know I think well of you and we have corresponded in the past to good effect. That said, there is a difference between theoretical and analytic. There are shortfalls to empirical data as well and sometimes analysis is the most useful approach to generating understanding.

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Last year we build a couple of machines that are on boats now which datalog all the numbers related to the rode, bow and associated gear every 2 seconds.
That is just cool. Are you collecting data from the NMEA bus on the boat at the same time? It would be great to have time, position, heading, depth, wind speed, and wind direction as well. There are some latency issues to deal with but the total data set would be outstanding to work with.

Can I get one? *grin*

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The best anchor is the one that gives you a good solid 8hrs sleep even if the weather is nasty. If that means you use a brick rather than a million dollar wonder so be it.
Who can argue with such a theory? *grin*
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Old 08-04-2011, 14:55   #34
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Re: How to Test Anchors?

GMac,
How do you intend to take the anchoring conditions into account?
- wind speed & direction, intensity and duration of gusts
- tidal stream speed & direction
- waves (height, period...)
- water depth
...

IMO, this has a big influence on the result.

Alain
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Old 08-04-2011, 14:56   #35
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Re: How to Test Anchors?

Opps, yes theoretical is probably not the best word. Nor is 99% really, there has been a few small studies into various forces at work of boats at anchor.

You don't want one, ugly and a bit baulky. A mate reckens he can make it smaller and tidier. Yes it collects wind data and even what the bow is doing in relation to wave action. Been pretty limp down this way for bad weather this season, actually most of it has suffered no weather only sun, not good if you have a yacht. We need some yuckier weather, I'm sure it'll come.

Oh, one boat was at anchor during the Japanese Tsunamis. Haven't seen that data set yet so I wonder what we will see? The owner didn't feel much so probably not a lot.

Trying to con a fishing boat into fitting one. We recently supplied a couple of very old school anchors to a couple of 70ft commercial fishing boats. They are required by the Surveyor to carry and anchor of 'XXXkg', usually with no holding power classification i.e. HHP or SHHP or whatever, so they fishos go for the cheapest they can get, which in this case was stock-less ex-china, they are as cheap as chips, just a few $$ per kg. In these boats cases those anchors just seem way under spec but the boats say they work and do use them in some nasty don't get it wrong spots. They use a rode which is just 13mm galvanised wire, no chain and no rope. It all seems way under sized for the boats. Chatting to a Skipper he said if the weather packs up the mantra is 'Scope, Scope and more Scope', and it does work. One has sat thru 70kts quite happily and does so often.

Actually that dudes wife brought him a huge Rocna a few years back for a birthday present (what a wife that is, good girl) but one night during one of those big blows the bugger set so deep they couldn't get it back even using the very large hydraulic drum winch they have, he lost the anchor and most of his rode. So he's gone back to 150kg stockless, due to the significant price difference unfortunately. They are very interesting lads to chat to about anchoring. They seem very much of the opinion that as long as the gear is 'OK', rather than super duper or total c**p, it all comes down to scope, use a lot of it and all will be good. They have been doing it for many many years so I suppose have learnt what does and doesn't work for them.
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Old 08-04-2011, 16:01   #36
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Re: How to Test Anchors?

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GMac,
How do you intend to take the anchoring conditions into account?
- wind speed & direction, intensity and duration of gusts
- tidal stream speed & direction
- waves (height, period...)
- water depth
...

IMO, this has a big influence on the result.

Alain
It sure does Alain.

We are recording wind data and the boats movement or at least the bows movement, up/down and sideways, plus a few other things every 2 seconds. It has GPS so we can see how far the bow wonders around. Don't have tidal info nor depth but the book the boat has with it lets the skipper record depth and scope used. They are basic and a bit clunky at the moment but a mate is fine tuning that more at the moment, in that is a connection to the boats instruments, the full suite which will bring in more info like depth. At the moment the wind data is from the unit not the boat. We didn't want wind from the masthead as that is often a lot different than just what it is down on the bow. The new version will collect both wind sets, winch counter info, depths and more.

So while not getting every aspect they are getting a lot. With the 2 sec interval we can see a wind gust or wave hit, what that may make the bow do and what loads that generates.

Graph all that up and it's starting to show a few things we think. Still a tiny set of data hence we need a lot more on a wider range of boats in a wider range of weather to make any calls one way or another.

We have around 50 days worth of data so far from 4 boats, 3 yachts and a 50ft fizzy nasty. Little of it has been in much over 25kts. Also as these dudes aren't, or at least don't have to, anchoring in sloppy waters we have not much wave related data either.

As we want real everyday life data we haven't yet got too jiggy by pushing into stuff 99.9% of boaters will never actually see. Hence of mother of all anchoring systems has been primed for a BIG blow to look more at the extreme end just to see those numbers in relation to the rest, even if next to no boats will actually anchor in that sort of weather.

It's early days and will take time to collect a good set of data. I'd like more units but they aren't a budget item. And contrary to what many think, not many, if any, will retire rich after playing in the anchor game, it is a low margin corner of the industry. Way more money in selling those far more important flat screens onto boats than there is in selling 'Oh I suppose I better chuck on a' anchoring systems
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Old 08-04-2011, 16:27   #37
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Re: How to Test Anchors?

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I would want to test a selection of mainstream anchors that are readily available at retail in major USA stores. I would want to test equal weights amongst anchors of vaguely similar shape and material.
Don't think you can do a test like this. Each manufacturer will specific a weight for a size of yacht and there are some surprising differences. For example a 31 foot yacht could have a 10kg Rocna or a 15 Kg Spade. That's a 50% difference if the manufacturers recommendations are followed. Chose an anchor on weight alone and they would cry foul.

Instead if you ask the manufacturers what they recommend then it is up to them to size the anchor for the boat. This also means an aluminium anchor can play on a level field.

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Old 08-04-2011, 16:28   #38
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Re: How to test anchors?

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Toss your anchor out and takes your chances.
THIS.
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Old 08-04-2011, 19:28   #39
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Re: How to Test Anchors?

I enjoy talk as much as anybody.
When it comes to trusting and understanding how my boat handles weather, the only answer is, data that is real and specific to my boat.

I carry a hand held wind speed indicator and frequently use it to "tune" my internal sensors. It's easy to overestimate wind speed.
The great thing is to have a benchmark and to know when a new experience is coming.

When the wind is up the compass can be used to measure the boats swing. Then when changes are made, the improvement can be measured directly and instantly.

Observing the anchor snubber gives me some idea of load. This gives me an idea. My snubber is a modified elastic mooring element. The amount of stretch can be calculated into actual load, including dynamic load.
Just have to come up with an easy way to do it.

The best thing is the wonderfull seat of the pants feeling when my next gen anchor bites in and sets, untill I decide it's time to go.

No other "old standby" anchor has ever given me that feeling.
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Old 09-04-2011, 10:11   #40
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Re: How to Test Anchors?

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Don't think you can do a test like this. Each manufacturer will specific a weight for a size of yacht and there are some surprising differences. For example a 31 foot yacht could have a 10kg Rocna or a 15 Kg Spade. That's a 50% difference if the manufacturers recommendations are followed. Chose an anchor on weight alone and they would cry foul.
First, thanks to GMac for doing some testing that sounds like it will prove to be very interesting! Please keep us informed. I'll pre-buy your book if you intend to publish one--no kidding.

As to the above quote, I don't care what the anchor manufacturers want us to do or don't want us to do. One of the most important characteristics of an anchor is its holding power relative to its weight. In other words, its efficiency. Weight is the major limiting factor (along with size to a lesser extent) to what anchor can be carried by a boat. Sure, I could be really secure if I wanted to drag around a 100 lb. anchor on the bow of my 38-foot boat, but it would impact sailing performance, offshore safety, load carrying, wetness on deck, etc. Plus, it would be really hard to haul up, creating stress on the windlass, etc. So, I think holding power per pound of weight should be the basic criteria on which an anchor is judged, and then secondarily ease and quickness of setting, and thirdly reliability of resetting when the wind changes. Some people put setting ability ahead of holding ability, but I don't understand this point--if an anchor won't hold you in a blow, I don't care how easy it is to set because I won't be using it.
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Old 09-04-2011, 10:26   #41
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Re: How to Test Anchors?

GMac: I'm sure you're aware of Professor John Knox's Anchorwatch system sold in the UK that measures loads at anchor and can act as an anchor alarm. He's done some interesting testing on loads at anchor onboard ordinary-sized sailing yachts and they have proven to be much lower than the ABYC tables. He wrote some articles for Practical Boat Owner back in 2002 that described some of his findings, and some of his formulas. He also did some interesting testing on things like how much chain you should use and what changes in scope did to holding power. Not sure what he is up to these days, but someone introduced a Knox anchor in 2010, though I'm not sure it has ever made it into retail production.

By the way, I'm not so sure that using a tug as your primary vessel for measurement will translate well to what happens on yachts, though maybe it is more important to you to get information related to larger commercial vessels. I have observed many types of vessels at anchor in many types of weather, and even amongst the cruising sailboat fleet there is a huge differential in the way different boats pull on their anchor rodes. I wonder if some boats generate some lift to windward in high winds as they seem to have slack in their rode while a boat right next to it is pulling the rode bar tight.
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Old 09-04-2011, 10:53   #42
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Re: How to Test Anchors?

how to test an anchor???
USE IT!!!!!! throw it overboard -- make sure bitter end is attached ...
always worked for me......
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Old 09-04-2011, 10:53   #43
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Re: How to Test Anchors?

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test for maximum holding. . . .tests in good East Coast mud, plus in good clean deep sand
As others have commented this is more complex than that.

For me the test you describe seems to be a 'racers test' - eg to answer the question 'what is the lightest anchor that will hold in a good bottom'. Personally I think the answer to that is both obvious (something like an aluminum fortress) and worthless to say a live aboard cruiser.

Most live aboard cruisers carry significant size anchors of one of the major well known designs. All these anchors will set in good bottoms. And once set, given the typical extra large size, all will then hold well in good bottoms.

So, IMHO the more important question for the live aboard cruiser is 'which anchor sets (And resets) most reliably in not perfect bottoms'? We anchor in many different places and we often don't know what the bottom will be like and sometimes (I previously calculated 1 out of 7 times) it's not a perfect bottom. So the anchor challenge is to get setting in these unknown and not perfect conditions.

A secondary important question for live aboard cruisers is related to short scope holding. We often wedge into tight or crowded places (have you looked at English harbour recently!). We gain a lot of extra flexibility if the anchor has good low scope capability. That's one of the reason we carry heavy anchors, but design also does have an influence on short scoping.
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Old 09-04-2011, 11:12   #44
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Re: How to Test Anchors?

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Originally Posted by markpierce View Post
You need to know your bottom. Start there when choosing an anchor.
Quote:
Originally Posted by capn_billl View Post
I agree completely.
works for me ...
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Old 09-04-2011, 11:18   #45
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Re: How to Test Anchors?

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(I previously calculated 1 out of 7 times) it's not a perfect bottom.
OK, but doesn't it make more sense to have a main anchor that performs well 6 out of 7 times than one that performs well in the 1 out of 7 bottoms that are unusual? I would venture to guess that mud and sand would easily account for more like 90% (maybe more) of the anchorages frequented by typical world cruisers. I've seen your test on the shingle beach in Chile, but I don't think that is very common anywhere in the world. Is it common in Chile? Even in your case, I would argue that it might be better using a special anchor in that situation, one that is ideal for those conditions, while using a general purpose anchor that works well in mud and sand for the other 86% of the time you are anchoring.

Shorter me, I would rather use two anchors, or maybe one specialized anchor for the oddball anchoring times, so that I can use a lighter, more efficient, general-purpose anchor 90% of the time.

On the short scope thing, it is far better to use two anchors to limit your swing if it is very tight. You can then fine tune your boat placement so as to avoid everyone else and you will not be dragging when the wind picks up.
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