Anchor Weight Question

saltwater_gypsy

saltwater_gypsy

Well-Known Member
Joined
13 Jan 2008
Messages
1,946
Location
Now back in Scotland . Boat for sale
www.saltwatergypsy.com
Right lads no fannying around , this is a proper question!!!

I had another look at the YM Anchor Test article and noticed that the anchor tests were for anchors in the weight range 10 to 16kg.(ie fairly light) As you know the "Claw"anchor(16.3kg) did badly but my 30kg genuine Bruce performs very well and I see no reason to change it.
My point is that heavier anchors of a particular type probably have a better chance of penetrating the seabed than lighter ones. .
It would be interesting to have information regarding holding power versus weight of anchor of a particular type. I suspect it will not be a simple proportional relationship.
SENSIBLE comments please!!!
 
There's a thunderstorm, the rocks are 40 m away. The gusts are over 50kts. You are side on in the gusts, its hard to stand on deck. My anchor is 20kg heavier than the recommended size of 34kg.
 
I'm not going to talk weight vs design or holding power as in tables - as I regard them as factory theoretical. Even the so-called tests are questionable.

I shall talk in terms of what I've found in use.

Light but good design ie large sharp flukes but in lighter construction would dig into various other than thick weed and rocky strata. But then work them selves out and possibly skip. Having trouble getting a bite again.
Same but heavier and much better, less tendency to break out and better re-set having the weight as well as fluke design.
Didn't seem to matter really what style of anchor in the common forms ...

The surprising one I find is the old Fishermans - which seems to want to dig in no matter what - and is particularly good in dense weed and rocks. In fact I've had great difficulty freeing a Fishermans in strong dense weed or rocks.

I have small anchors such as Fixed Grapnel, Fishermans, CQR, Danforth etc. and all suffer similar due to lack of weight.
I have medium sized CQR, Fishermans, Danforth and these all seem to perform reasonably with the Fishermans being the least able unless again dense weed or rocks.

To large anchors - it's years since handling such but the Adm. Cast pattern seemed to be clear favourite.

IMHO opinion there is no substitute for good fluke design, angle of presentation to sea-bed, and a hefty amount of KG's to keep it there. Remember that despite metal not floating - it still loses effective weight when in water .... pain the a to lift out of water, but less so in !

I despair of many small mobo's that seem to be supplied with daft small but cosmetically acceptable anchors. It doesn't really matter that boat is small, the fact is that small light anchors don't set well ... so need something bigger / heavier. A large stone is better than some diddy anchors you see !!
 
I have often though along the same lines, though a 30kg anchor would probably sink my boat (I use 45lb CQR & 10kg Bruce). It should be very easy to publish a table of measured holding power for different sizes of the same anchor which I would expect to follow something like an exponential curve, with lighter anchors underperforming somewhat.

This would be quite complex of course, and you would need to distinguish "digging-in" performance from mere holding. Lighter anchors have a higher area for their weight and would probably show up well on a static load but fail on digging in. Perhaps.
 
One test article I saw ... the anchors were each set into a sandy beach. A set length of chain + rope rode was made to each and a tractor used to pull against each in turn.
The results were used by an "expert panel" to promote certain designs.

What was wrong ? a) each anchor was dug in by external force applied ie. a great big boot on top !, b) rode was near enough horizontal in its whole length, c) tractor didn't mimic a snatching boat ... it just increased it's pull until break-out and then kept anchor skipping on surface as it towed it up beach supposedly trying to reset it.

IMHO - the test was a waste of a good beach.

The other factor that is seldom mentioned is that certain designs excel in certain bottom conditions. The Fisherman is prime example where it will hold in rocks and dense weed when others will fail.
 
There are many more variables than anchor weight:
Nature of bottom
Weight/length/elasticity of rode
Weight/windage of boat
Shape of boat
Wave height and pattern.
It's not enough to consider the steady state or average force on the anchor, think about the peak force as the bow is lifted by a wave.
You would have to either standardise everything, in which case the tests would be irrelevant to most people, or do an awful lot of tests. Even then it would be hard to make any justifiable conclusions that were applicable to everyone.
I just take the view that a CQR with a good heavy weight on the rode works well in most cases for me.
Riding out storms on a lee shore at anchor is not my preferred modus operandi, but I want something more than a 'lunch hook'. Everyone has to work to his own needs, which for serious 'away from civilisation' cruising may mean carrying more anchors than I would want to be weighed down with in the English Channel.
 
You are quite correct . Weight on the point will help penetration as will the sharpness of the point. So one thing you can do to help your anchor is to sharpen it.

The tests can only be a very rough guide because there is no such thing as a BS sea bottom let alone BS conditions etc. But most tests do say that the claw anchor (I have one) is not particularly good, so I'm thinking of changing

One issue which is never properly covered is the rode. Basic physics suggests that in extreme conditions (and provided there is room) you are better off with mostly nylon than with chain. The tests that have been done show that we traditionally wildly over spec the rode too - the tensile strength of the rode is way more than the anchor can ever withstand or indeed the cleat at the other end..

The saving grace is that most of us never anchor in conditions that test the equipment.
 
Anchoring is, at best, an inexact science. There are too many variables. To give yourself a reasonable chance, have a variety of anchors aboard, all heavier than the recommended size and weight for your boat, use heavy chain. Forget about breaking loads, it's catenary you want. Choose as carefully as you can, the type of bottom. i.e. not rock and weed. Put out plenty scope, and hope for the best.
The annoying thing is that the only real way of telling whether the anchor has a good grip is to try to lift it again, which kind of defeats the whole idea.
 
I am well aware of all the points and items that affect anchoring. I narrowed it down based on OP and his question.

Leaving aside all the anchoring I did as a Ships guy .. I can say that I've anchored in many types of bottom conditions and still haven't arrived at the universal solution. (I'm being a little comical here in reply to others who appear to have solved it !! /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif ).
The river I have my house next to is glacial based and has a deep U form with only thin mud covering hard strata. About only holding you get is with a big rock or concrete bit, as anchors just do not bite at all.
In solent when my boat was there - Priory Bay for example - anchors don't bite there either as it's hard packed sand and stones ....

DSCF0205.jpg


amply illustrated here by the CQR sitting just ahead of my bilge keels. Note that it's hardly dug in. But the weight and chain have been sufficient to hold the boat such that turn of wind / tide has created a 'bight' in the all chain rode and boat still anchored and not dragging.
 
For a given bottom, you might expect the area of the buried anchor would be significant, as it dictates the area of bottom that must be displaced.
In other scenarios, the linear dimension might be proportional, for instance where the peel strength of a layer of clay is what matters.
For an anchor design of fixed proportions these factors will be proportional to l^2 or l, with weight being proportional to l^3.
I can't think how a higher power of l would come into play, maybe some of the 'new design anchor' proponents can illuminate?
 
I think your nice picture shows that in benign conditions, the forces involved are quite small. Had the CQR slid along the surface and not dug in, or just not dug in because it stopped the boat as it is?
Hard sand at low tide is different when the tide's in, just as when walking on the beach below the waterline the sand moves alot more under your feet than above the waterline.
I take your point about a thin layer of mud/sand/whatever over a sheet of rock, in these conditions it's a matter of either finding a flaw in the rock or just weight and friction between the anchor and the bottom.
 
The conditions were favourable and the CQR had just basically dug in the tip. It is as anchored except for the bight in rode that came with turn of wind etc.
I remember it was 'bumpy' in there while settling on bottom - which is not unusual there. Always makes you worry about holding. But as boat dries out for majority of time you are there ... or other way is to nose onto beach for the party period .. it's accepted. Very few people overstay tides there.
 
Third attempt to add some value to this discussion (killed my other two)! Within a given TYPE of anchor it's very likely that increased weight will help penetration, and of course holding power as it's a proxy for projected area.

But...that assumes there is an issue of penetration in the first place. We use smallish high efficiency anchors as the stemhead was never designed to take anything larger and they becomes a real pain to handle and properly stow and secure.

I've had problems setting a 25 lbs CQR copy on hard sea beds (sand & stone for example), and a heavier model would probably be better in this respect (your point) so long as I could dig it in with my puny engine.

However, on the same sea beds a 15 lbs Delta, and especially a Manson Supreme set more-or-less every time...so they are already heavy enough to set it seems. Added weight might theoretically improve their penetration efficiency even further, but I'm probably not going to notice the difference in most cases with these types of anchor.
 
Hi Nigel, how are the plans going for the summer cruise?
Anchors....
For what it's worth, my research before buying meant that I read a bit, looked at anchor tests in mag's, looked at various websites, went to the Cruising Associations Mediterranean day and talked to many livaboards who cruise the World as well as the Med' and I decided to buy a 10kg Rocna.
Its lighter than my original 25lb CQR copy and so far seems to be better.

I have a brand new, unused 35lb CQR copy for sale . £50
cheers
Scotty
 
[ QUOTE ]
<span style="color:blue"> Within a given TYPE of anchor it's very likely that increased weight will help penetration, and of course holding power as it's a proxy for projected area </span> .

[/ QUOTE ]


Well, CQR anchor are not manufactured under 7 kg weight – just because they didn’t work!

Same comment about the small 2 kg Bruce which was no longer manufactured for the same reason...

Big ship anchors, are horrible! but so heavy that they penetrate!

So, as usual, it’s a compromise! /forums/images/graemlins/ooo.gif

A well designed anchor should penetrate, regardless of its weight. It’s a question of design: the best penetration angle and enough weight for the first phase of « static » penetration.

Few anchors have a well designed penetrating angle and few also have a good static weight on the tip, just for example the good old CQR has about 60% of its total weight at the hinge and only about 18% on its tip... a small CQR will work in Mud but will have problems of setting in Med hard sand bottoms.

And the best holding anchor will not work if it hasn’t first penetrated!

Then if the penetration problem has been resolved – Holding as nearly no relation with weight, but is related to the fluke surface area

IMOH both characteristics are important: enough weight to penetrate and then the biggest possible surface area.

João
 
[ QUOTE ]
IMOH both characteristics are important: enough weight to penetrate and then the biggest possible surface area.

[/ QUOTE ] Which is of course the perfect description of the danforth, a much underrated anchor by newbies.
 
Yes, I have had good results with a danforth on my first yacht. It also had the advantage that you could stow a 12kg danforth under the cabin sole where you couldn't get any other hook of similar holding power. We find the small ones (copies I'm sure) work well with racing marks in a lot of tide and often on a short scope.
 
You must log in or register to reply here.

Share this page

Top