What is your Bigness Factor?

[The Garbone]

.55 with a Fortress FX23 on a 27ft boat. If it was heavier I would probably put on a bow roller.

[Delfin]

Originally Posted by Snowpetrel

By all means feel free to quibble, the more quibbling the better it will get. I really just plucked those numbers based on a few preliminary calculations. it would be great to compare the results with the manufacturers reccomendations and see how they stack up, or reverse engineer them to find out what factors are being used...

The next challenge I think to to validate this formula more using real life loads like jonjo's and to work out how displacement and effects the loads.

I suspect it would be validated. Like all useful formulaic insights it won't be perfect, but a very good starting point to know where your gear stands relative to other vessels and their experience. For example, from memory I seem to recall that Steve Dashew carried a 225# or thereabouts on a 65 ft boat, yielding a "Snowpetrel Anchor Suitability Factor" of 18.78 if my memory is correct. I believe Evans 47' vessel carries a 105# anchor or thereabouts, yielding a SASF of 21, and he hasn't cast up on the rocks yet. Now, I know that Delfin will have more windage than a Sundeer or Evans' boat, but a whole lot less than a new slab sided Nordhavn. So if I want to be in the ballpark of tackle that worked for them, I'd need to have a lower SASF number, which I do. Yippie Kiyeah.

Positive experiences from others whose tackle puts them outside the BIB envelop are interesting, but then again, everything works just fine until it doesn't, and then usually it is 2 am and pitch dark. And raining. So I would prefer to learn from those who years of experience cover a lot of situations and compare my gear to theirs. Your contribution makes that a whole lot easier, so again, thank you.

[Dennis.G]

Currently 65 lb CQR / 48' = 1.35

Planned 85 lb Mantus /48' = 1.77

Have to agree that this metric has its shortcomings as boat displacement is not linear to LOA. A conservative "bigness factor" would be much higher number for a 50' boat than for a 30' boat.

[vamoose]

Originally Posted by atoll

ever tried lifting it without the windlass on your own

I have big powered cockpit winches and would use a snubber line to bring it up 20 or 30 feet at a time.

[JK n Smitty]

Originally Posted by Kettlewell

Not ignoring science, just pointing out what has worked for me over the course of many years. I would consider that "testing" even if not a double-blind study. My own experience, and yours, is certainly much more scientificly valid than any of the anchor tests I have read, which always seem to have fatal flaws in methodology. Here's a quote from Wikipedia on the Scientific Method. I consider my 35+ years of cruising to be a "field study."

I would be very hesitant to call your cruising experience a "field study" as it likely suffers significantly from confirmation bias.

I have read many anchor tests and I don't find them to be so invalid. Most try as best they can to limit the variables down to the anchor. They try to use similar sea bed conditions, the same boat, the same pull power, same scope, same rode, etc. Designing a scientific test is never easy but is almost impossible when you try to execute it in the real world.

When I selected my anchors (primary and backup), I had different goals and needs for each. For my primary the goals, in order of importance, were 1) holding strength, 2) lowest weight possible (wanted to save room for more rum and beer), 3) build quality and 4) cost. I did not hold any bias as to more weight = more holding strength because it doesn't. I chose a Manson Supreme 1-2 sizes larger than recommended. I honestly don't think I could go bigger because this one barely fits. I could have been convinced to go with a Rocna but when I purchased they were just coming off of the Chinese made quality issues.

For my backup anchor, the ability to store it was the second concern after holding strength. I chose a danforth style. Purchased used after a detailed inspection.

IMHO, your thread has introduced a confusing, inaccurate metric to the tough decision of anchor selection. It fails to account for the design of the boat or the anchor. Countless engineers are employed by the anchor manufacturers to determine proper anchor sizing. Their knowledge, testing and experience can't be replaced with an A/B=C equation.

Engineers put so many levels of conservatism into these types of calculations that I would bet you can't find one instance of a properly sized anchor dragging. Anchors drag due to operator error. Either someone doesn't set their anchor correctly (something that is almost impossible with some of the new generation anchors) or they have chosen an anchor that is not compatible with the bottom type.

[Seaworthy Lass]

Originally Posted by Snowpetrel

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

Looks MUCH better than LOA/Anchor weight

Displacement needs more consideration though I think.
So LOA needs to be a bit more than squared (but well less than cubed)?
And include building material in vessel factor?

Also rather than LOA, use LOA-bow sprit for the length?

[Kettlewell]

IMHO, your thread has introduced a confusing, inaccurate metric to the tough decision of anchor selection. It fails to account for the design of the boat or the anchor.

This thread isn't recommending anything to anyone--it is asking for feedback on what others have done! Where in the original post or the poll does it say anything about how you should select your anchor?

[JK n Smitty]

Originally Posted by Kettlewell

This thread isn't recommending anything to anyone--it is asking for feedback on what others have done! Where in the original post or the poll does it say anything about how you should select your anchor?

Seriously?!

Your poll states that "0.5- 0.9 = Light, 1.0 - 1.2 = Normal, 1.2 - 1.4 = Conservative, 1.5 + = BIB"

That is stating that a "Bigness Factor" of 1.0 for a Fortress FX-55 on a 30 foot sailboat is "Normal" despite the fact that the FX-55 has upto 16,000 lbs of holding power and is sized for a 52-58 foot boat. That holding power is probably 5-7 times greater than the chain holding it!

[noelex 77]

Originally Posted by JK n Smitty

Engineers put so many levels of conservatism into these types of calculations that I would bet you can't find one instance of a properly sized anchor dragging. Anchors drag due to operator error. Either someone doesn't set their anchor correctly (something that is almost impossible with some of the new generation anchors) or they have chosen an anchor that is not compatible with the bottom type.

I see a lot of boats dragging each year.
As a rough guide I would estimate about 50% are operator error. The other 50% drag despite competent use.

[noelex 77]

Originally Posted by JK n Smitty

Seriously?!

Your poll states that "0.5- 0.9 = Light, 1.0 - 1.2 = Normal, 1.2 - 1.4 = Conservative, 1.5 + = BIB"

That is stating that a "Bigness Factor" of 1.0 for a Fortress FX-55 on a 30 foot sailboat is "Normal" despite the fact that the FX-55 has upto 16,000 lbs of holding power and is sized for a 52-58 foot boat. That holding power is probably 5-7 times greater than the chain holding it!

The aluminium Fortress (or Spade) is much lighter than the equivelent steel anchor. It does not fit into the normal anchor classification, or the classification category of this simple poll.
It is not often used as primary anchor, so it should not have much impact on the results.

[JK n Smitty]

Originally Posted by noelex 77

I see a lot of boats dragging each year.
As a rough guide I would estimate about 50% are operator error. The other 50% drag despite competent use.

OK, let me add some empheisis for you.

Originally Posted by JK n Smitty

Engineers put so many levels of conservatism into these types of calculations that I would bet you can't find one instance of a properly sized anchor dragging. Anchors drag due to operator error. Either someone doesn't set their anchor correctly (something that is almost impossible with some of the new generation anchors) or they have chosen an anchor that is not compatible with the bottom type.

There are two possible operator errors that I have identified. I would bet hard currency on either of these accounting for 99% of dragging issues.

Originally Posted by noelex 77

The aluminium Fortress (or Spade) is much lighter than the equivelent steel anchor. It does not fit into the normal anchor classification, or the classification category of this simple poll.
It is not often used as primary anchor, so it should not have much impact on the results.

Where does it state that in either the OP or the poll? It simply states "anchor" with no qualifications.

If the OP said this was a poll for "traditional style anchors" or something like that I wouldn't have commented.

By the way, the OP's own anchor is a new generation and his blog is full of posts about anchors. He has obviously put some time into thinking about anchors. That's what makes this over simplification so strange to me.

Sorry, but the equation and the poll yeilds no useful information.

[s/v Jedi]

Originally Posted by JK n Smitty

I would be very hesitant to call your cruising experience a "field study" as it likely suffers significantly from confirmation bias.

You are getting psychology into this thread? Seriously? Real cruisers having years long of real anchoring experience in every conceivable cruising area is much more worth than anything else.

Originally Posted by JK n Smitty

I have read many anchor tests and I don't find them to be so invalid. Most try as best they can to limit the variables down to the anchor. They try to use similar sea bed conditions, the same boat, the same pull power, same scope, same rode, etc. Designing a scientific test is never easy but is almost impossible when you try to execute it in the real world.

They fooled you. Those tests are about conflicts of interest, advertising etc. and only make it appear so that they are independent and scientifically correct.

Originally Posted by JK n Smitty

Engineers put so many levels of conservatism into these types of calculations that I would bet you can't find one instance of a properly sized anchor dragging.

Now we know you are just joking. Tell us for which anchor manufacturer you work!

[JK n Smitty]

Originally Posted by s/v Jedi

You are getting psychology into this thread? Seriously? Real cruisers having years long of real anchoring experience in every conceivable cruising area is much more worth than anything else.

How many of those years involve using every type or even more than 3-4 types of anchor in the same anchorage with as close to possible of the same pull? Probably none. People tend to pick one or two types of anchors and then stick with those. Then they tend to defend that choice to the end of days while ignoring all contradictory facts. That is why most people don't make good scientists and why scientists are very popular at cocktale parties. Pointing out others' flawed logic is not a popular thing.

They fooled you. Those tests are about conflicts of interest, advertising etc. and only make it appear so that they are independent and scientifically correct.

Sure, I will give you several of the tests are flawed and about advertising. Most of them are easy to see through. But independent people like MaineSail have done tests that have confirmed many of these same findings.

Now we know you are just joking. Tell us for which anchor manufacturer you work!

Nice ad hominem attack. Way to discuss on logic.

[sailorboy1]

How come on anchor threads we can not just talk about anchors without all the BS? Not like we are talking trash about your Mom etc.

[JonJo]

Don L

+1

Its odd, I think most are genuinely trying to share their ideas and experiences. Some are genuinely looking for answers. But some take personal offence at the oddest things. I find answering the query beats being rude or offensive (but people then get upset about repetition).

But why it happens specifically on anchor threads - a really interesting question.