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View Poll Results: What is your Bigness Factor?
0.5 - 0.9 = Light 18 13.85%
1.0 - 1.2 = Normal 33 25.38%
1.2 - 1.4 = Conservative 37 28.46%
1.5 + = BIB 42 32.31%
Voters: 130. You may not vote on this poll

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Old 28-03-2013, 16:34   #46
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Re: What is your Bigness Factor?

Quote:
heavier boats carry lighter anchor relative to their displacement.
My initial theory on why that might be is that displacement is not the most relevant factor--it is wind drag. So if you take two 45-foot boats and one weighs 5,000 lbs more it doesn't require much more of an anchor, if any larger, than the lighter boat. A lot of that extra weight is below the water surface and doesn't add to drag on the anchor. In fact, I believe anchor studies, including one I have here from Danforth, confirm that wind drag is the most important factor in anchor loading, with displacement barely mentioned. Current drag can be a factor, but that has more to do with shape than anything else, but wetted surface does come into play. However, wind drag is the big component. In my own experience this is true. My previous boat, a 32-foot catamaran, had significantly more pull on its anchor than my current boat which weighs twice as much. The cat had a lot more windage.
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Old 28-03-2013, 16:34   #47
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Re: What is your Bigness Factor?

I'll play. I'm at .73. A 16lb danforth on my 22' sailboat that weighs 2100lbs. The lake I sail on has a clay mud bottom. Once the anchor sets it does not let go. I've had to winch the anchor up after a storm it digs so well.

If anything I am over anchored.

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Old 28-03-2013, 16:52   #48
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Re: What is your Bigness Factor?

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Originally Posted by Kettlewell View Post
Anchor size poll above. Take your main anchor weight in pounds (1 kg=2.2 lbs) and divide by your LOA in feet (1 meter=3.28 feet). The result is your Bigness Factor.

For example, my Finnsailor 38 carries a 45 lb. main anchor, so 45/38=1.18, or on the high side of what I have labeled "Normal."

Let the quibbling begin about the factor ranges!
Not so sure that 1.5 would be BiB. For Delfin, that would be an 80# anchor which would hardly be large for the boat. Currently, my ratio would be 3.2, and I'd like to upsize to 4.0. Is there something wrong with the formula, or am I just a tubby bitch?
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Old 28-03-2013, 19:14   #49
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Re: What is your Bigness Factor?

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Originally Posted by Hydra View Post
A few weeks ago, I processed the data in the anchor poll and obtained 2 graphs, "Bigness factor" and "Weight ratio".

The first just shows a cloud of dots but the second clearly shows a trend: heavier boats carry lighter anchor relative to their displacement. Then, the "Bigness factor" is possibly not the most relevant ratio.

Alain
Great stuff Alain, and also Kettlewell. I am not sure if mathmatically the formula is completely valid due to scaling but I am sure you are both aware of this, and there are ways to post process the results to remove this error. Such as by plotting them on a graph we could run a scaled line to allow for this as you mention.

Double the boat size gives four times the windage but only twice the anchor weight givings only 1.6 times the area. But I think something along these lines of more mathematical methods is the way to go instead of relying on often vague and unspecified anchor charts. I gave it a go with some formulas here But they are too complex and further reading of the Vryhof manual has reveals that the heavier anchors penetrate deeper and so hold much better than the direct surface area comparison would show.

From the bruce website For the FFTS MK 4 ANCHOR I get the following formulas for the Ultimate Holding Capacity HC(chain/sand) = 46.86W^0.94 HC(chain/mud)= 39.95W^0.92 HC(wire/mud) = 49.66W^0.92 which matches very closely with the scaling factor of the results for the Stevpris Mk6 UHC from page 186 vryhof manual.

I guess what I am getting at is that I think anchor weight is a good measure of holding capacity rather than anchor area (as long as the anchor can bury to full depth), but the formula could easily be tweaked to allow for the scaling of windage.

Anyway my results are:
25 lbs/26 foot gives 0.96 it was adequate
45 lbs/33.5 foot gives 1.34 Excellent, probably could have gone lighter.
?lbs / 40 foot = ? maybe 1.34 gives 54 lb)
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Old 28-03-2013, 19:32   #50
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Re: What is your Bigness Factor?

Either of my bowers put me right about 2.0. Boat is 52' on deck, 60' LOA, has a 105 CQR and a 110 Danforth on the rollers. Sheet anchor is a folding bronze Herreschoff in the bilge, unknown weight but its massive. At least 200 lbs, probably way more. I've never dragged it out of there, LOL!
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Old 28-03-2013, 19:47   #51
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Re: What is your Bigness Factor?


Interesting.

Well, I haven't been called stupid for a while so --

My main working anchor on my 40' boat is a 33lb. Rocna. This gives a ratio of .82 Bigness Factor.
If I deploy my storm anchor, a Fortress FX-37 that weighs 21 lbs., my Bigness Factor decreases to .52.
Maybe I should call it my Tiny Factor?

I would like to point out that my 40' boat has a design displacement of 8,500 lbs., and anybody that thinks my boat has more windage than a 40' cruising monohull hasn't seen my boat.

Lastly, anybody who feels the need to vent about Rocna anchors please save your breath.

And now, on with the show.
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Old 28-03-2013, 20:07   #52
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Re: What is your Bigness Factor?

We are a 1.0, comfortable with it and its stood us in good stead for around 5 years now.

Might be good to later make an 'arbitrary' split of anchors into old and new gen (and work out how to include alloys) and then run the poll again. And if boredom has not set in do it by weight of vessel. But each time maybe repeat the existing earlier poll numbers.

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Old 28-03-2013, 20:17   #53
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Tweaked formula? Something like Loa^2/anchor weight. In reality it should be more like Loa^1.95/anchor weight but this is to complex. Or maybe my maths is totally wrong...
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Old 28-03-2013, 20:32   #54
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Re: What is your Bigness Factor?

37' cutter, 45lb manson (best damned anchor i've ever owned!!!). so i'm a 1.21, which puts me just over the normal and into the conservative. actually wouldn't mind being a bit more conservative....
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Old 28-03-2013, 20:41   #55
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Re: What is your Bigness Factor?

66lb, 37': 1.78
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Old 28-03-2013, 20:51   #56
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Re: What is your Bigness Factor?

Judging a boat’s anchoring safety factor by just looking at anchor size is akin to judging a woman by just looking at her feet.
In other words, her feet can be just too big for the rest of her rig!!

Lloyds Survey and other classification societies also include Chain size and SWL as well as Deck fittings so that anchoring system is balanced, so as not to destroy the weakest link (Including deck fittings).
http://www.iacs.org.uk/document/publ...R_A_pdf148.PDF

A1.2 shows how the Classification Societies calculate the Equipment Number

My anchor just makes the 1.5 factor in this CF poll, but I have heavier chain than required.
I have rarely dragged, except in circumstances like doing a short overnight in poor holding when a major squall comes thru the exposed stop in the opposite direction.

Those are the poor anchorage choices where you sleep light anyway
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Old 28-03-2013, 21:16   #57
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Re: What is your Bigness Factor?

AND I'm hung like a 2 year old.
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Old 28-03-2013, 22:06   #58
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Re: What is your Bigness Factor?

We have a 51 ft overall with a 100 lb Danforth, with a 100 lb Luke rock hook as a back up also a 50 lb stern anchor also a Danforth with a manual windless so our primary anchor is a 1.96 right ?? and here I was looking to get a new style anchor!! heck I think I will just stick with my good old Danforth lol
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Old 28-03-2013, 22:55   #59
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Re: What is your Bigness Factor?

If you are looking at breaking down the numbers further I think you would see a very positive correlation between "bigness" and the amount the anchor is used.
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Old 29-03-2013, 01:44   #60
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Re: What is your Bigness Factor?

In view of the posts on this and other threads - I'd like to see a poll on what anchors are actually carried, one biggie and nothing else? Or maybe a poll on the total anchor weight or numbers carried vs length

Basically the view that seems to be coming through is applause for one anchor, BIB and 1 basket, and incredulity for small is adequate, but have maybe an arsenal of 3 (different designs).

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