Displacement to Anchor Weight Ratio

[estarzinger]

we are recreating the wheel here a bit . . . the "accepted" formula (by those who study this professionally) for anchor look up tables is summarized as: displacement ^(2/3) + windage (see more details and links below)

MCA does have an anchor table for "small vessels, sport, pleasure, work boat and pilot boat)" that simply uses length (for MCA "small" usually means under 24m) link:http://www.dft.gov.uk/mca/mgn_280-2.pdf

Originally Posted by congo

boats under survey have their anchor sizes specked by survey officers, they take in rigging, length, weight, displacement the list goes on,

mmmm . . . Rex, as I presume you well know, it is not actually all that complex . . . . Classed vessels typically have their ground tackle set by their 'Equipment number'. That is you calculate the vessel equipment number and then there is a simple look-up table for the anchor size. And the equipment number is calculated from the following formula (for monohull yachts) . . .

EN = (D)^(2/3) +2 x H x B + A/10

where

D= moulded displacement [t] to design waterline in sea water with a density of 1,025 t/m3
B= greatest moulded breadth [m]
H = effective height (m) to the top of the house
A = area [m2], in profile view of the hull, superstructures and houses, having a breadth greater then B/4, above the design waterline within the length L and up to the height a + Σ hi For sailing yachts the rig has to be appropriately considered when determining area A.

details: http://www.iacs.org.uk/vdunifiedrequ...r_a_pdf148.pdf, and http://www.gl-group.com/infoServices...gl_i-3-2_e.pdf

[congo]

mmmm . . . Rex, as I presume you well know, it is not actually all that complex . . . . Classed vessels typically have their ground tackle set by their 'Equipment number'. That is you calculate the vessel equipment number and then there is a simple look-up table for the anchor size. And the equipment number is calculated from the following formula (for monohull yachts) . . .

EN = (D)^(2/3) +2 x H x B + A/10

where

D= moulded displacement [t] to design waterline in sea water with a density of 1,025 t/m3
B= greatest moulded breadth [m]
H = effective height (m) to the top of the house
A = area [m2], in profile view of the hull, superstructures and houses, having a breadth greater then B/4, above the design waterline within the length L and up to the height a + Σ hi For sailing yachts the rig has to be appropriately considered when determining area A. details:

http://www.iacs.org.uk/vdunifiedrequ...r_a_pdf148.pdf, and http://www.gl-group.com/infoServices...gl_i-3-2_e.pdf
__________________
www.bethandevans.com

Rex Wrote:


Yes well I must confess I have no idea of how they work it out but there seems to be something missing between the information--links you have supplied and what a survey officers method, or methods in comparison when they explain it to me?

Regardless of their outcome on specking we have found longevity over twenty years by sticking close to their recommendations it has served us well, the problem we find with successful anchoring is with the rooky users, more so in trailer boats, they just do not have a clue, (not always their fault) when it comes to setting an anchor, length of Rhode and so on.

I suppose the other thing is if it was all that easy a very big part of anchor discussions would evapourate, and that would not be a good thing, look our method of anchor sizing and how we apply it works well for us,thats really all I can say.

Regards Rex.

[DoubleWhisky]

Originally Posted by estarzinger

We are recreating the wheel here a bit . . . the "accepted" formula (by those who study this professionally) for anchor look up tables is summarized as: displacement ^(2/3) + windage (see more details and links below)

MCA does have an anchor table for "small vessels, sport, pleasure, work boat and pilot boat)" that simply uses length (for MCA "small" usually means under 24m) link:http://www.dft.gov.uk/mca/mgn_280-2.pdf

Classed vessels typically have their ground tackle set by their 'Equipment number'. That is you calculate the vessel equipment number and then there is a simple look-up table for the anchor size. And the equipment number is calculated from the following formula (for monohull yachts) . . .

EN = (D)^(2/3) +2 x H x B + A/10

where

D= moulded displacement [t] to design waterline in sea water with a density of 1,025 t/m3
B= greatest moulded breadth [m]
H = effective height (m) to the top of the house
A = area [m2], in profile view of the hull, superstructures and houses, having a breadth greater then B/4, above the design waterline within the length L and up to the height a + Σ hi For sailing yachts the rig has to be appropriately considered when determining area A.

details: http://www.iacs.org.uk/vdunifiedrequ...r_a_pdf148.pdf, and http://www.gl-group.com/infoServices...gl_i-3-2_e.pdf

Hmmm......
Up to the MGN 280 for my boat the HHP anchor of 27 kg is sufficient.
For Your boat the HHP anchor of 21 kg is envisaged.
Can not see any one of us happy with this...
As far as I remember You do use 50 kg HHP anchors, I'm quite satisfied with my 40 kg SHHP

Classification societes guidance is not for yachts under 24 m. but can be extrapolated for our own use
GL table starts from 120 kg for standard stockless and equivalent SSHP is 60 kg and equivalent HHP is 90 kg. Lowest EN in the table is 50, EN for my boat is somewhere in the area of 45, so probably the proper weight of SSHP could be somewhere near 50 kg. It is in accordance with my feeling that 40 kg is for me slightly undersized, but 55 kg should be really O.K
Anyway, it is only loose extrapolation.

I think that we are in the need to have a simple rule of thumb to assess the proper weight of the anchor for our boats, something to start with.
May be this wheel needs reinventing..?..

[estarzinger]

^^

I have bought anchors for a couple super yachts and the skippers have all wanted bigger than the class society requirement (which is a 'minimum size allowed').

I always willing to learn a better way . . . but I guess I think we need some new or better science (which I don't see) to contribute before this wheel is worth reinventing . . . as it is a reasonably simple process today and in the end it will always be the skipper's judgement that makes the final decision. It in fact depends so much on where and how the skipper anchors.

[DoubleWhisky]

Originally Posted by estarzinger

^^

I have bought anchors for a couple super yachts and the skippers have all wanted bigger than the class society requirement (which is a 'minimum size allowed').

I always willing to learn a better way . . . but I guess I think we need some new or better science (which I don't see) to contribute before this wheel is worth reinventing . . . as it is a reasonably simple process today and in the end it will always be the skipper's judgement that makes the final decision. It in fact depends so much on where and how the skipper anchors.

Surely You are right
What is disturbing for me:

• underspecced anchoring equipement on the new boats, coming even from reputable yards
• inconsistiency of sizing charts published by manufacturers
• all-round cry "we have the anchor better than any other - You can downsize!!!"

When anchored I can sleep well because of MY anchor. But I have problems with sleeping, as I doubt if any boat around has decent hook and decent rode...

When I was speaking about some simple rule of thumb, I was thinking about enlightening somehow all people happy with their poor anchors three or four sizes to small...

[Delfin]

Originally Posted by TacomaSailor

The wide variety and style of anchors is a plot by the beer makers of the world. They keep the controversy stirred to a simmer so that we sailors will have a topic of endless duration to discuss over countless beers.

And... as we all know - the more beer we drink - the more we know about our particular anchor and the more desperate where the circumstances and consequence of our last or most interesting dragging episode.

That is why - I keep a 6-pack of of Anchor Steam on board in case someone questions by choice, technique, location, or otherwise wants some sage advice about staying put!

That is not the connection between beer and anchors, sorry. Beer drinkers are far smarter than most people and know which anchor is best for a simple reason. We all know that alcohol kills brain cells, but what is not well understood is that it is the slower moving, less fit brain cells that are killed, leaving the high performance brain cells used for making anchor buying decisions intact, since they are able to avoid the alcohol molecules. So, drinking beer obviously makes you smarter and a better anchor evaluator. Since I drink a lot of beer, I can see the deficiencies of roll bar anchors; understand that the Fortress is one of the best anchors in the world, and carry an Ultra for my primary bower with the Fortress as a storm/backup.

[estarzinger]

By the way . . . Australia commercial survey does use the equipment number calculation (as the rest of the world).

See page 12:
http://www.amsa.gov.au/forms-and-pub.../NRIP00092.pdf

This specific formula construction might be interesting for those of you with multihulls, as it gives specific coefficients for mono vs cat vs tri.

There is also a formula to relate holding power to equipment number.

I have to say I am a bit surprised Rex was not familiar with equipment numbers. It is the worldwide accepted method for sizing commercial classed/survey anchors.

Note: If I read the following correctly, the basic formula is the same but for some reason the coefficients are slightly changed to give lower numbers in Queensland . . . http://www.msq.qld.gov.au/~/media/ms...le_c_sub7d.pdf

[noelex 77]

The formula are interesting, but the standards are minimum requirements rather than best practice recommendations.

For example the Australian standard also considers chain length and only 3m (9 feet) is required ( if your anchor is less than 50lb). Similar low requirements are are reflected in a lot of these recommendations and I would urge caution in simply implementing these standards.

[congo]

estarzinger wrote:

I have to say I am a bit surprised Rex was not familiar with equipment numbers. It is the worldwide accepted method for sizing commercial classed/survey anchors.

Rex wrote:

Yes we are aware of most of the commercial rules, problem being I find it all too confusing, regardless of what anchor size we would speck for commercial anchors you can be sure the survey officers will differ, they seem to have a pocket book of rules that overrule what appears to be the rule, they change for example , what is the purpose use of the vessel, where in offshore waters will it be deployed, is it for oil or gas, is it only used in inland waters, there is a list that goes on and on, we are not allowed to speck anchors for boats under survey full stop.

The rules used to be different for Queensland, indeed most states used to have a different set of rules, that is no longer the case as the rules are now national throughout Australia.

We are regularly in conversation with survey officers as they attend as a witness to most of our proof testing, as I said being involved, supplying anchors to commercial vessels has a allowed us a broad summary of what is needed to satisfy their needs, this experience has allowed us a very reliable method for specking our anchor sizes, and like I said this has been refined, tuned over twenty years, end result it works well for us.

For customers that want their anchors specked as if they were in survey, we send them to a survey officer as a second choice, most don’t bother and run with what we have specked, regardless I have had feedback from some customers that have spent the dollars for survey standard, they have said it is the only way to go for peace of mind.

Regards Rex.

[estarzinger]

Originally Posted by noelex 77

The formula are interesting, but the standards are minimum requirements rather than best practice recommendations.

You can always add whatever 'safety factor multiplier' you consider to be best practice, which will surely depend on where and how you anchor.

My point in posting this was to suggest the structure of base formula (disp ^2/3 + windage) is what the professionals marine engineers have decided on worldwide for scaling anchors. I doubt we here on this thread are going to do better for a base formula. Coefficient sizing for that formula will depend on your desired environmental/safety factor, and that's where the 'med' vs 'penguin' sort of scenarios (eg where and how you actually sail) have to come in.

The puzzle here regarding Rex . . . he claimed in JoJo's thread that the reason he did not recommended much smaller anchors, despite claiming his have twice the holding of Rocna or Supreme, was because he had to keep to the survey/class tables . . . and yet here we are with him not even knowing about the equipment number basics of survey/class sizing tables (the equipment number is used to pick the proper row when reading those tables).

[JonJo]

Originally Posted by estarzinger

You can always add whatever 'safety factor multiplier' you consider to be best practice, which will surely depend on where and how you anchor.

My point in posting this was to suggest the structure of base formula (disp ^2/3 + windage) is what the professionals marine engineers have decided on worldwide for scaling anchors. I doubt we here on this thread are going to do better for a base formula. Coefficient sizing for that formula will depend on your desired environmental/safety factor, and that's where the 'med' vs 'penguin' sort of scenarios (eg where and how you actually sail) have to come in.

The puzzle here regarding Rex . . . he claimed in JoJo's thread that the reason he did not recommended much smaller anchors, despite claiming his have twice the holding of Rocna or Supreme, was because he had to keep to the survey/class tables . . . and yet here we are with him not even knowing about the equipment number basics of survey/class sizing tables (the equipment number is used to pick the proper row when reading those tables).

Rex will know of the equipment number etc as he sat on the committee that developed the rules. I have a copy of the original draft, from 13 April 2007, and he is one of the 12 committee members. The draft is word for word the same as the link (or it is as far as I can see) and includes all the equipment number vs anchor mass etc. The draft will have been scrutinised page by page by the Committee prior to being released for public consultation, the copy I received.

I think what he said was that he did not quote for vessels in Survey because Survey Officers take into account factors that seem omitted, such as the application of the vessel (say whether anchoring to support gas wells etc).

I think I also noted that if 2 anchors were carried they both had to meet the minimum requirement (ie either be used as a primary anchor).

In any even it is the Survey Officer, not Rex nor anyone else, who determines whether the vessel and equipment on the vessel meets a min requirement. If the system allows the Survey Officer to recommend that item it seems to save someone making a recommendation that is then not subsequently accepted (for whatever reason). Might not work in the US, seems to work fine here.

I'm not sure that Rex has ever claimed his anchors are twice as good as a Supreme, they are rated SHHP which is the same as a 55kg+ Rocna or any Manson Supreme of equivalent weights.


As an side - anchor 'performance' is rated by weight (the Anchor Mass on the various spread sheets) - where/how do alloy anchor fit into this? They are obviously accepted as meeting requirement and are certainly lighter (than the 'Anchor Mass' spreadsheet indicates) so how do they fit into the system?


Jonathan

[congo]

Hi Evan,

The claims I made double the holding power, this claim was made as a result of the Robertson test chart , they are not our claims, further if you take a look double was only achieved in gravel and hard sand, the other sea bed types our anchors were still up, but certainly not double.

I think based on the above here lies the advantages, if a design is producing a stand out performance in these difficult sea bed types, then it would be obvious this performance may offer more reliable anchoring across a wider range of sea beds.

Yes of course I am very well aware of survey tables --requirements, but like I said we will not down speck an anchor size based on our certification, this decision is always best left up a survey officer for the many variables that come into their calculations, further it would not be wise for us to down size simply because we can produce more holding power, proof strength is yet another forgotten element when downsizing an anchor, it may well produce twice the holding power but the build strength required, proof load, may not meet survey for a host of reasons.

Evan previous on this the BIB thread Noelex probed me from every angle on the above, I think some twenty pages prior on the BIB thread, I don’t want to be branded yet again as being rude, nasty, its just that all of what you are asking me has been recycled so many times, if you go back over Noelexs posts questioning our holding power right through to who made the coffey, many of his enquirys just stop short of calling me a liar.

I rest my reputation on twenty years in the Marine industry, from sitting on the N.M.S.C. to supplying tested anchors to all walks and types of water born craft to the marine industry, we have a reputation that has been tried again and again. is their anybody out there that we have wronged,this Longevity in the Marine Industry surley deserves some recognition.

Regards Rex.

[africanmarco]

Originally Posted by Sharki127

When I was considering upgrading to a Rocna from a Delta 70 lb for my 39 ft Amel Sharki (21,300 lbs.) I decided to look at what manufacturers of a few high quality boats provided with various models.
To make some sense of the information I looked at the ratio of the boat's displacement and the anchor's weight. This ratio may be meaningless scientifically. Anyway, here is what I found.

Amel 55 48,000lbs 66lb Brugel 727 to 1
Amel 64 75,000lbs 92.4lb Brugel 812 to 1
Morris 45 22,300lbs 45lb CQR 496 to 1
Morris 48 32,000lbs 45lb CQR 711 to 1
Morris 52 40,300lbs 55lb Delta 733 to 1
Oyster 475 35,273lbs 44lb CQR 802 to 1
Oyster 545 46,893lbs 75lb CQR 625 to 1
Oyster 635 73, 854lbs 75lb CQR 985 to 1
Halberg Rassy 48 40,700lbs 70lb Delta 581 to 1
Halberg Rassy 55 58,000lbs 70lb Delta 829 to 1
S/V Hanoah Amel 39 21,300lbs 73lb Rocna 292 to 1

Hi Sharki 127,

I own the Sharki 68 of 1982, which has a 30 kg Jambo anchor, with 10 mm chain. I would like to add a Mantus M1 30 kg as primary anchor, but I am not sure it fits the Sharki's bow. I see from the photo you posted, that you have a Rocna 33, fairly close to the Mantus. Does the Rocna 33 fit well on the Sharki's bow? Any idea if the Mantus fits? Fair winds, Marco