What is your Bigness Factor?

[Seaworthy Lass]

Originally Posted by Dockhead

Since the displacement of a boat, and the windage of a boat, are not linear functions of length, I think this metric is flawed. Larger boats with average sized anchors will have much greater "Bigness Factors" than smaller boats with average sized anchors.

Dockhead raised this and lots of people (JK n Smitty, Panope, Snowpetrel etc) have chimed in as well - the relationship is not linear. This poll is absolutely useless .

Both displacement and windage need to be factored in, and as these can vary dramatically for each specified length, even comparing boats of the same length will not give exact comparisons. It would be better than bundling every length together though!

[JonJo]

Originally Posted by Seaworthy Lass

Dockhead raised this and lots of people (JK n Smitty, Panope, Snowpetrel etc) have chimed in as well - the relationship is not linear. This poll is absolutely useless .

Both displacement and windage need to be factored in, and as these can vary dramatically for each specified length, even comparing boats of the same length will not give exact comparisons. It would be better than bundling every length together though!

The idea of the poll has sparked much response, in terms of poll numbers. There seems to be much support.

If you think the poll too simple come up with a system that invokes less criticism and offer a new poll.

Jonathan

[sailorboy1]

Originally Posted by JonJo

If you think the poll too simple come up with a system that invokes less criticism and offer a new poll.

Polls always result in some people being more interested in trashing the choices. The best thing about them is that you don't have to read though the comments, just read the poll.

[JonJo]

Interestingly the BIB thread I had analysed as about 75% in favour of BIB - my analysis was on a very subjective basis. But BIB was meant to be restricted to 'new gen' and 'Bigger' being 2 sizes bigger. The poll is more catholic and is open to anyone with an anchor, old or new, though some who contributed to BIB (usefully) had old gen anchors

The poll though indicating support for larger does not come through as being as heavily in favour as I 'felt' and it includes older anchors where 'Bigness' might be less unexpected.

[sailorboy1]

I do a fair number of polls. The poll results never match the comments.

I would have expected the poll to more closely match what one would see if walking the marinia or the mooring field noting anchors on boats. But I don't think it does as the results would be much more on the light side and there might be 5% BIB

[atoll]

Originally Posted by Don L

I do a fair number of polls. The poll results never match the comments.

I would have expected the poll to more closely match what one would see if walking the marinia or the mooring field noting anchors on boats. But I don't think it does as the results would be much more on the light side and there might be 5% BIB

it would be interesting to find out how many out of the posters can actually lift their anchor by hand from 30ft of water in the event of their windlass failing,and what their back up plan is in the event of a failure .

[Ziggy]

Queen Mary 2
Anchor weight: 23 tonnes (50,700 lbs)
LOA: 1,132 ft
BF: 44.8

[seandepagnier]

this is a stupid metric to go by as it doesn't really take many factors.

Length of boat has little to do with anchor weight. I mean this because if you double a boat in all dimensions (now boat is 8x the weight) this does not mean you would use an anchor that is twice the weight considering you have 4x the windage and 8x the bouyancy.

And yes I lift my anchor by hand as I have no windlass, and have done this in more than 30ft of water

[Andrew Troup]

Originally Posted by atoll

it would be interesting to find out how many out of the posters can actually lift their anchor by hand from 30ft of water in the event of their windlass failing,and what their back up plan is in the event of a failure .

With a chain pawl on the bow roller: No sweat for two people with 30kg anchor and 13mm chain. The pawl means you can get into a good hauling posture before progressively taking the load; when you have pulled a hitch, the chain stays put while you get back into the starting posture. Makes a huge diff.

With one person: need to break out a chain hook and take a line to a winch, but again the chain pawl makes it very easy to reposition the line.

Lacking a chain pawl, best to use two lines to two winches.

Both hauling methods are easier if there's a reasonable distance from the bow roller to the navel pipe.

Vertical windlasses which are inoperable generally render the navel pipe unusable, unless you remove the windlass completely.

Horizontal windlasses tend to be a lot more accomodating even if the gearbox jams: usually if the clutch is eased, the chain will gravity feed over the chainwheel/gypsy.

The other thing (in light conditions): if your bow setup doesn't work well for manual retrieval: it may be easier, particularly if it's a 'oncer', to retrieve the anchor from the cockpit, rigging some serious chafe protection where the chain comes in over the toerail.
Or even from the swim platform.
You can skid piles of chain forrard on sacks or carpet squares at leisure, or carry it in buckets (Yay for strong buckets!).

These may be good options for people with dodgy backs to consider, particularly: if hauling upwards, you can keep your back straight and use your thighs for lifting. A notch carved in the piece of wood used for chafe protection might be enough to hold the chain between pulls: slide away from the notch as you take the strain, then back towards it towards the end of each pull.

With a mixed rode, you could consider what maxi racing yachts with no windlass do on the rare occasions when they anchor: haul in the rope by winch or 'tug of war' style, then clip a genoa halyard to the end of the chain and grind it up the mast.
They use same trick in reverse to launch the anchor, but that's only because they don't have a bow roller.

To get a BiB anchor in, in top gear, you can get several people grinding without getting in each others' way by leading the tail from one winch to another (and then maybe a third), only using the self tailer on the last one.

[Snowpetrel]

Originally Posted by JonJo

If you think the poll too simple come up with a system that invokes less criticism and offer a new poll.

Just ran the numbers on the tweaked formula that should remove most of the scaling effects, at least between say 20-60 foot.

LOA(ft)^2
Anchor weight(lbs)

The result should lie roughly between 22-34 with

• 22-25 being OTT
• 25-28 being very conservative
• 28-31 being Conservative
• 31-34 recomended

This breakdown can be argued about, interested in your thoughts

Running a few numbers


Snowpetrel 33.5^2/45=24.9
Snowpetrel 33.5^2/35=32.1

Reiger 26^2/25=27.0
Reiger 26^2/30=22.5

QE2 1132^2/50700 =26.3 Proof it works?
Dinghy 10^2/5 =20.0 further proof?

Kettlewell-------38^2/45.....=32.1
Atoll--------------62.3^2/99..=39.2
ReMetau--------33^2/60.....=18.15!
Cfarrar----------42^2/55......=32
Panope---------34^2/44......=26.3
Paul L-----------44.......77.....=25.1
Painkiller--------41.....66.......=25.4
Oceangirl-------34......45.......=25.7
Jedi-------------- 64.....176.....=23.3
Target------------32.......60....=17.1 !
Boatsail----------27.......35.....=20.8
Don L-------------41.......55.....=30.6
Tim R-------------40........45.....=35.6
Sabray-----------44.......70......=27.6
Cpq--------------47........60......=36.8
Sailmonkey-----32........35.......=29.3
Mike OReily------37.......55.......=24.9
Oh drunk boy---22........16......=30.25
Delfin-------------55 ......176.....=17.18!
Minaret-----------52.......105....=25.7
FS mike-----------40........33.....=48.5
Onestep----------37........45.....=30.4
Lone wolf---------37........66.....=20.7
Pelagic------------65........98......=43.1
BobConnie--------51......100.....=26.0

CATS

Colemj............40......55....=29.1
Cotemar.........36.....500....=2.6
Jonjo..............38.......38.....=38


To run the formula the other way to find out a sensible anchor size select the bigness factor you want, say 25 for a decent BIB anchor

Then the formula is LOA^2/Bigness factor So for snowpetrel it's

33.5^2/25=45lbs

For my new boat it's 40.5^2/25=65lb would be similar to Snowpetrels.

To allow for an aluminium anchor multipy or divide the Bigness factor by 0.5?

ie 40.5^2/(25/0.5)= 33lb fortress or alloy spade

To allow for a next G multiply or divide the Bigness factor by 0.8?

ie 40.5^2/(25/0.8)=52.5lbs (55lb)

Still need to sort out how multi's, light displacement and super heavy displacement boats fit, but at least it seems to me that we have a formula that roughly gives a more standard metric than manufacturers figures.
From here we need to fine tune the factors for different anchor types and boat types.

So final formula looks like

((LOA^2)x vessel factor)
(Anchor weight x anchor factor)

Anchor factor

0.5? for alloy anchor
0.8? for Next Gen anchor and danforth
1.2? for fisherman anchor, dreadnought

Vessel factor

0.8? for uldb
1.5? for square rigger
1.1? multihull

[Kettlewell]

If you look at anchor manufacturer tables of recommended sizes I think the Bigness Factor correlates pretty well until you get above 50 feet in boat length. I must admit that my goal was to keep the math really simple as a first stab at understanding what people mean when say Bigger is Better is the way to go. I will work on trying to come up with something more refined.

Obviously, when choosing your own anchor you need to account for windage first and foremost, but displacement plays some factor too. However, you can imagine that displacement is not of much concern until you start to get wave action. Imagine two hulls of identical proportions above the water, but with one weighing twice as much as the other. That would mean the heavier boat will have a lot more below the water, but it would mean 0 extra pull on the anchor until waves got high enough to start heaving the vessel. However, at long enough scope, with short enough waves, there will be very little extra pressure. In practice, I have found that heavier vessels often ride much more calmly at anchor and create less strain in the anchor system. So, unless you're anchored in six-foot seas, I don't see displacement as a critical component. Wind drag is the biggy.

[Sandero]

Actually... this is another stupid anchor thread which tries to select the proper anchor when there are scores of factors which contribute to its performance.

My experience is 27 years with a SL CQR 35 5/16" chain on Contest 36s 16K displ, fractional rig deep fin keel and includes 3 years of daily anchoring ... no docks... no slips... in Eastern Caribe and Southern NE.

Did I ever drag? You betcha... probably half dozen times, But that pales compared to the thousands I didn't drag.

I did drag a 500# mushroom in Hurricane Sandy 700 feet.

I have no complaints with my tackle.

YMMV

[Kettlewell]

Nobody is trying to tell you what anchor you should select--it is just a poll to learn more about one aspect of anchor design that has been discussed a lot on this forum.

[vamoose]

45 foot boat with a 100 pound Manson supreme. I believe that works out to 2.22 .Nick would probably say its a little light compared to his 2.7

[atoll]

Originally Posted by vamoose

45 foot boat with a 100 pound Manson supreme. I believe that works out to 2.22 .Nick would probably say its a little light compared to his 2.7

ever tried lifting it without the windlass on your own