Anchors - Bigger is Better ?

[s/v Jedi]

Originally Posted by JonJo

Jedi

Fortress are not aggressive in Oz, from your personal experience what's wrong with them?

Nothing wrong, they are perfect... as long as the pull doesn't change direction much. They also won't reset once broken loose and the boat dragging fast. I have seen them come all the way up to the surface like a hooked fish.

I have used them during hurricanes hiding in mangroves and I use them for the stern line to the palm tree on the beach when there is no palm tree. I put it in knee-deep water so that it doesn't get much attention from passers-by

[Hudson Force]

Location makes a huge difference. We are US East Coast and Bahamas gunkholers and my primary is a 45lb Bruce. I also keep a 45lb CQR and a 35lb grapnel. For more than one hurricane I've set on my Bruce alone in 6' of protected water with a mud substrate an 250' of chain. Excessive rode can trump excessive weight. With a split rig and a shoal draft I have more options for protection and I don't carry anchors heavier than standard for my boat.

[Jim Cate]

G'Day all,

Thanks for the link to the USL codes -- they make interesting reading!

Their application to yachts is not straightforward IMO, primarily in that there is no adequate means of adding ones rigging into the "H" dimension, nor for that matter, ones displacement. Rather it seems to be merely a factor of OAL and a height which they seem to define as the hull freeboard plus some fraction of the height of the superstructure (deck house, bridge, etc) typical of a merchant vessel. Nothing about the very considerable windage of mast, furled sails, rigging wire, solar panels and all the extraneous stuff we garland about on our cruising vessels.

Variations in the assessment of "H" make big differences in teh required masses of anchors.

For our boat, whose length is about 14 metres (also laden weight of about 12 tonnes) if one chooses to say that H is just the hull+house height (about 2 metres) the required anchor for a seagoing vessel is 45 kg, or 31.5 kg for a high holding power hook -- rather similar to the 60 lb Manson Supreme that we carry. But if we try to compensate for the demonstrable additional windage, things escalate rapidly: if we arbitrarily add a metre to the height, the required mass is about 43 kg (HHP anchor). If we look at the actual height of our dodger and solar panel arch which is about 4 m above the WL the requirement goes to 57 kg! And if one tries to add anything like the actual height of the rig, well the numbers become astronomical.

So, JonJo, how do you interpret this information? Maybe I have missed something in the lengthy document, but I'm left with the impression that when you have been quoting USL code numbers the method of calculating them is arbitrary.

Now, as to adding our bit of anecdotal experience: We are full time cruisers, and very seldom use marinas or moorings. We've had this boat for ten years now, and have used in turn a 20 kg genuine Bruce, a 30 kg knockoff Bruce and for the past 5 years a 60 lb Manson. The smaller Bruce dragged once in Iluka harbour, soft mud bottom, 12 feet depth with about 75 feet of chain out. We were off the boat, there was a violent thunderstorm and neighbors reported that a gust of about 60 knots came from a different direction from the prevailing 30+ knot winds and the boat just took off. We arrived back just as she was going on the beach and were thankful to be able to simply motor her off. Dumb luck... The 30 kg knockoff did not drag in the few months that we used it.

The Manson has dragged twice. Once during a major flood on the Clarence River, again soft silty bottom, around 30 feet of depth, 175 feet of chain, around 6 knots of current. We collected a log across the chain, and that in turn collected a huge mass of weed and other debris and we were unable to shed it (0300 hrs, of course). The anchor dragged quite slowly downstream. We veered our remaining chain (~250 feet total) and it slowed down to a crawl. Maintained an anchor watch until dawn and were able eventually to get rid of the mess and find a better spot to ride out the flood. The second time was recently in Sandy Bay, Hobart. 32 feet depth, 125 feet of chain, good mud/sand/shell bottom. Situation was a 25 knot NW wind all morning followed by a brief calm and then 25 knots from the SE when the sea breeze kicked in fairly quickly. The anchor broke loose, the boat moved a cable or so and re-anchored herself. When I raised the anchor to re position the boat I found the remains of a plastic bag fouled on the anchor... perhaps the cause of the failure, perhaps not.

These are the only failures we've experienced in roughly 3000 nights of anchoring. I'm unable to interpret the USL codes to say if our anchor is properly sized, but experience says that it could perhaps stand to be a size larger (80 lb), for that MIGHT have avoided the two incidents. And FWIW, from observation of the chain and anchor when weighing, the anchor appears to bury well in soft bottoms. No evidence for harder bottoms... and it has failed to set in weed over hard sand bottoms.

That's my story and I'm sticking to it!

Cheers,

Jim

[barnakiel]

Originally Posted by foggysail

I could not follow this. Mass = density X volume not related to surface area. And twice the weight does not have twice the holding power.

I can't help. And it is an example to show things CAN be computed, not an answer to what the actual values are.

If you want to say my computation algorithm is wrong, please point to the apparent mistake. There may be one. Till then considered correct.

20 kg anchor will have roughly 60% larger surface area than 10 kg anchor, so it will also have 60% higher holding power.

b.

[barnakiel]

Originally Posted by DumnMad

I follow you Barny and I agree with your ratios but holding power to area only applies to anchors at the same depth.
Shallow sand on hardpan you are right.
However in deep sand, double the depth = 4 times the holding power.
Therefore in sand or mud the diggier the better.

Uhm, I see. The diggier will depend on some factors too: weight aside, I guess flukes' shape and their angle of attack play a major role. Right?

Some Danforth clones have adjustable angle. Fortress does, I think.

b.

[s/v Jedi]

Hmm, so, do we agree that the same anchor a size or two bigger digs in the same way than the smaller one except needs more pull to dig in?

[JonJo]

Originally Posted by s/v Jedi

Hmm, so, do we agree that the same anchor a size or two bigger digs in the same way than the smaller one except needs more pull to dig in?

I'd go with that!

On Fortress: a 'dragging' Fortress contradicts the comments from those that use a Fortress (for whatever reason) in a big blow - namely they are very difficult to retrieve. Consequently might a 'dragging' Fortress be the result of an inadequately set anchor - and have nothing to do with the anchor itself. Sort of like your quote above

And you quote above is the reason I query big is better. Better a well set small anchor or a poorly set big anchor - when the wind or tide changes?

[s/v Jedi]

Originally Posted by JonJo

I'd go with that!

On Fortress: a 'dragging' Fortress contradicts the comments from those that use a Fortress (for whatever reason) in a big blow - namely they are very difficult to retrieve. Consequently might a 'dragging' Fortress be the result of an inadequately set anchor - and have nothing to do with the anchor itself. Sort of like your quote above

And you quote above is the reason I query big is better. Better a well set small anchor or a poorly set big anchor - when the wind or tide changes?

The Fortress doesn't drag when well set. But it breaks out if direction of pull is changed too much.

[JonJo]

Jim Cate,

As far as I am aware the USL Codes were developed for bare boats but if you decide to build a high rise apartment on the stern of your yacht in the form of targa, dinghy, davits, solar panels, bimini, dodgers then the USL codes and recommendation with them, for say a 45' yacht, will be incorrect. If you speak to a number of anchor makers they will all tell you that their recommendations are based on the USL Codes, they would be stupid to ignore them. I assume if there is any flexibility in their interpretation they err on the side of caution (again they would be stupid to do otherwise). But their own charts are based on the USL codes but for a bare yacht - excluding the bimini, targa etc. Interestingly I have never seen one of the 'new gen' anchor makers factor in the CS concept of 30% smaller - anchor makers size their anchors as if they are old gen - which seems to show real caution!

[JonJo]

Originally Posted by s/v Jedi

The Fortress doesn't drag when well set. But it breaks out if direction of pull is changed too much.

Set a Fortress and subject it to strong wind and it does not matter how you try to retrieve it - it takes for ever! My limited experience is that if well set its almost immovable and I have heard of people who have had to abandon their Fortress because they could not get it out.

[Bash]

Originally Posted by JonJo

It is interesting that none of the respondents have any experience of 'recommended' sized smaller anchors.

You seem to have missed post #31.

[JonJo]

Originally Posted by Bash

You seem to have missed post #31. I remember a few others saying essentially the same thing earlier in the thread.

sorry bash,

I had noted your post - but no-one or few have bought the recommended sized new gen and then upgraded to a bigger model of the same type because they found the recommended size inadequate ie it dragged.

[Kettlewell]

Interestingly I have never seen one of the 'new gen' anchor makers factor in the CS concept of 30% smaller - anchor makers size their anchors as if they are old gen - which seems to show real caution!

One reason is that new-gen boats keep gaining windage--some of the cats being advertised for charter look about as aerodynamic as a Winnebago (and not nearly as nice looking).

[Dockhead]

Originally Posted by JonJo

It is interesting that none of the respondents have any experience of 'recommended' sized smaller anchors. It seems as if they got rid of their old gen anchors, CQRs, Deltas, Bruces and immediately bought anchors much bigger, often 2 sizes bigger. No-one seems to have gone the intermediate step.

This might explain why everyone, well nearly, who has posted has no experience of smaller new gen anchors dragging - they have never tried them in anger. Which begs the question, how do they know that correctly sized new gen anchors would not hold?

The second interesting facet is that all the respondents are using concave anchors - obviously because they have no easy access to new gen convex anchors. And as far as I can make out no-one, who has posted, uses Fortress or Danforth either.

Its a pity we did not have some responses from convex (and Fortress) owners - but they are probably worried that if they become vociferous the thread will be closed

I have plenty of experience with convex anchors (CQR, Delta), with Fortress, and with Danforth.

The convex anchors never worked very well; the Fortress, on the other hand, is tremendous -- holding power out of all proportion to its mass, and sets aggressively to boot.

My first concave anchor was the same size as the CQR it replaced. The difference was amazing.

[DumnMad]

The classification societies specify safe working loads for ships fittings, mooring ropes, anchors etc for winds up to 60knots. For a named storm or hurricane the ship is expected to flee before the storm or hurricane gets to them. Yachts at 7 knots can't always do this so those sheltering outside a marina need bigger than than classification size anchor. Furthermore they need an anchor that suits the ground condition at their chosen anchorage. Bigger is usually better but if in sand or silt I figger digger is important too.