What is your Bigness Factor?

[Kettlewell]

Snowpetrel:

Very interesting, but I'm not sure it is so clear what scaling does.

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.

I think that is too simplistic. I don't think doubling the length gives four times the windage--longer boats get progressively sleeker in proportion with more of the boat below the water--at least traditional monos. Alain Poiraud's anchoring book has a little table that estimates anchor loads based on both length and beam. Ideally, probably should add in freeboard measured somewhere--I would guess the bow might be a start. Or should we measure to the top of fixed cabin structures?

[s/v Jedi]

Originally Posted by atoll

ever tried lifting it without the windlass on your own

Atoll, why would he or why would I try that? There are probably 30 easy ways before it would come to hauling by lifting it.

I actually had to do it once when a hurricane broke my anchor sprit with anchor roller. The windlass was okay but without roller, the chain would lock itself into corners preventing it to haul the anchor up. Even with my heavy gear and without roller, it was an easy process using a jib halyard with halyard winch to lift the chain way up high, then set snubber, let chain drop through windlass back down into chain locker and repeat. In the end we hauled the whole anchor up and over the lifelines into the sail locker and done. It was easy.

Then there's winches in cockpits etc. that can all work when the roller is still available. This is even easier when a chain stopper can be used.

[Andrew Troup]

Hey, awesome, SnowP. I beat Jedi ! (again....)

But not Hawk (21ish) - so nicely in the middle of the Big Bruce Boys...

Is K temporarily off your case BTW, or just asleep? (Just kiddin')

On a slightly more serious note: I guess you're expecting to include a few more gradations for anchor factor, eg say 1.0 for Bruce (and CQR, maybe?)

I have a feeling fishermen should be a bit more than 1.2, and dreadnought a fair bit more (which might leave QM2 looking a bit under-endowed, but I guess the massive chain is partial compensation...), but this is just a crude proportioning hunch.

Do you think there should be any factor for hull and especially rig windage, especially given that there's quite a lot more breeze at the top of a tall rig?
In comparison with a motor sailer with a short stick - although arguably that would tend to have more hull and cabin windage....
( I guess a gaff rigged ketch, say, has a lot more windage than mast height alone would suggest, too)

Hmmmm ....

When Mirabella V dragged in France (246', lying to a 600kg x 2.2= 1320 lbs shiny Bruce knockoff:

246^2/1320= 46 !!!) WHY DIDN'T THEY CONSULT SNOWPETREL???

Afterwards, the classification society rules were criticised for taking heed only of her hull and superstructure windage, taking no account of her rig.

Reworking the calcs to account for the frontal area of the 90m mast and the three furling headsails, (but without factoring in the fact that in the F6-7 blowing when she dragged, it would have been 45 knots at the top of the rig)

it was reckoned her main anchor should have been 1080kg (over one TONNE! for a sloop...)

1080kg x 2.2= 2376 lbs:
246^2/2376= 25.5 .... Bingo!

I think you're onto something here, mate -
"very conservative" takes some heed of the altitude/windspeed problem, and what's more, it seems appropriate for a boat which cannot row out a kedge at the drop of a hat ....)


It's hard to know where to stop, isn't it, once you start...

[s/v Jedi]

Originally Posted by Andrew Troup

Hey, awesome, SnowP. I beat Jedi ! (again....)

Ah, is that what you're trying to do Well done, even though I have no clue what you're talking about

Just to make sure: I'm not here to win or to beat anyone. I won when I sold my company and moved aboard and into paradise Here on CF I'm just trying to help people

[barnakiel]

'Light' now but waiting for arrival of a 'conservative' anchor.

b.

[Kettlewell]

In the end I think rules of thumb are close enough for most of us. Here's a rundown of the Bigness Factor on my last four cruising sailboats that I have done extensive cruising on. Boats owned prior to these were smaller and just used for coastal sailing. (Rounded to nearest tenth.)

30 feet, 35 lbs. = 1.2
37 feet, 45 lbs. = 1.2
32 feet (cat), 35 lbs. = 1.1
38 feet, 45 lbs. = 1.2

I have found through experience a formula that has served me well, so I have no need to experiment further. This has worked with CQR anchors, so if I gain holding power or setting ability by switching to another anchor, I will look at that as a bonus but I probably won't be downsizing or upsizing.

[Kettlewell]

Just to make sure: I'm not here to win or to beat anyone. I won when I sold my company and moved aboard and into paradise Here on CF I'm just trying to help people

Sounds like Win-Win to me!

[Snowpetrel]

Originally Posted by Snowpetrel

Anchor factor

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

screwed these factors up... too late at night.. Duh

Should read
LOA^2 x Anchor factor
Anchor wt (lbs) x Vessel factor

Anchor factors

• 2? for alloy anchor
• 1.25? for next G anchor
• 0.8? for fisherman...

Vessel Factors

• ULDB 0.8?
• Light disp and low windage 0.9?
• Multihulls and heavy disp vessels 1.1?
• Square riggers 1.5?

I am not sure it is worth messing with these factors. this formula just makes a easy way to compare vessels of different sizes. for a crude formula it seems remarkably effective. Possibly this is due to the real scaling errors canceling out, IE as boats get larger windage really scales by about 1.90-1.95? rather than 2.0 but at the same time the anchors UHC also scales by about 1.92-1.94? rather than 2.0.

I checked a few more ships, most seem to be in the range of 25-30 except anchor handlers that seem to have colossal anchors for their size, with values around 13-15 or so. maybe because they are often called on to tow or salvage? any thoughts Nigel1?

[JK n Smitty]

Originally Posted by Kettlewell

In the end I think rules of thumb are close enough for most of us. Here's a rundown of the Bigness Factor on my last four cruising sailboats that I have done extensive cruising on. Boats owned prior to these were smaller and just used for coastal sailing. (Rounded to nearest tenth.)

30 feet, 35 lbs. = 1.2
37 feet, 45 lbs. = 1.2
32 feet (cat), 35 lbs. = 1.1
38 feet, 45 lbs. = 1.2

I have found through experience a formula that has served me well, so I have no need to experiment further. This has worked with CQR anchors, so if I gain holding power or setting ability by switching to another anchor, I will look at that as a bonus but I probably won't be downsizing or upsizing.

Yes, let's just ignore all that "science" stuff that goes into anchor design and only pay attention to weight. Seems like a reasonable plan to me.

[mrohr]

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 .

My anchor 25# manson supreme. 5/16 chain ,approx. 1 llb. per foot ,so 30 pounds in 30 ft of water plus 25 for the manson =55 lbs. no windlass and have old back with damage from motorcycle accident. Am in only ok condition so have a chain pawl when necessary but yes, I can get the anchor up in 30' but I can usually find anchorages with less than 20 feet and by using my legs and keeping my back straight can get under way without mechanical help

My boat is only 24' waterline and 9500 lbs. so I'm a lightweight @ .7 but with nothing on decks and a very low profile to begin with there is little windage to put a strain on the ground tackle in a blow.There is extra chain (10 fathom lengths in bilge) that can be added from the deck to my main anchor and a larger fortress on poly pro line that is easily deployed if things start looking grim.

If dragging ( never with Manson, often with CQR) I can get my 25# anchor up in a hurry with pure adrenaline power much quicker than any windlass so that I am safely under way without fouling other anchored craft or running up on the dreaded lee shore. I don't believe that I could use this system if I were to go up to a larger boat again or to cruise without crew to Terra del Fuego or some such.

And yes, Atoll, in Block Is.I encountered a lovely gold plater with its fuming owner wearing the obligatory blue blazer unable to get back to Newport as a couple of mechanics scratched their heads over a recalcitrant windlass .That yacht was still firmly anchored there when I sailed out of the harbor 2 days later.

[Snowpetrel]

Actually probably easier to just calculate the anchor ratio and then apply a correction, say multiply the size x 0.8 for next G or 1.1 for multihulls rather than combine them into a more complex formula.

Andrew, I think you might be right about the various factors, fishermans should be more like 1.4 or something, we can all argue about what factor "our" anchor should have until the cows come home... or we can treat it for what it is as a simple metric like say S/A to Displacement ratio, rather than any sort of gospel.

Having something like this could help diagnose anchoring issues as well, as you showed with Mirribella V. Good work finding that one.

Something like

LOA(ft)^2
Anchor (LB) x factor= Anchor ratio

Any way well past my bedtime...

[Delfin]

Originally Posted by Snowpetrel

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



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

That's a very useful contribution, SP, thank you. I would quibble with your characterization of what is conservative vs recommended since it seems pretty subjective, but one thing I think you could say is that if anchored downwind from a vessel with a higher number than yours, they are more likely, all things being equal, to drag than you are.

But of course all things are not equal. The formula does take into consideration the scaling effects of the vessel, but not the anchor. A light Bruce type is a far less effective hook than a heavy Bruce type and a Fortress is going to hold much better than an equivalent weight in whatever else ya got.

I think the rule of thumb that you should put on the biggest anchor your vessel can handle without making her look like a Probiscus Monkey still holds. But the information on this thread has made me re-think whether to bother going one size up on Delfin's hook. Starting to seem like breast implants on Dolly Parton, if you know what I mean.

[Group9]

I think that's a pretty good scale.

My boat is 42' and my primary anchor is a Manson Supreme 45 lb. (1.07 with the formula)

It has been fine, even holding in a 65-70 knot blow on one occassion, (Tropical storm Issac) but I always kind of wished I had went ahead and got the Manson Supreme in 55 lbs. instead. I probably will before I go on a long cruise again.

[Kettlewell]

Yes, let's just ignore all that "science" stuff that goes into anchor design and only pay attention to weight.

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."

The scientific method requires observations of nature to formulate and test hypotheses.[1] It consists of these steps:[2][3]
Asking a question about a natural phenomenon
Making observations of the phenomenon
Hypothesizing an explanation for the phenomenon
Predicting a logical consequence of the hypothesis
Testing the hypothesis by an experiment, an observational study, or a field study
Creating a conclusion with data gathered in the experiment, or forming a revised/new hypothesis and repeating the process

[Snowpetrel]

Originally Posted by Delfin

That's a very useful contribution, SP, thank you. I would quibble with your characterization of what is conservative vs recommended since it seems pretty subjective, but one thing I think you could say is that if anchored downwind from a vessel with a higher number than yours, they are more likely, all things being equal, to drag than you are.

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.

But of course all things are not equal. The formula does take into consideration the scaling effects of the vessel, but not the anchor. A light Bruce type is a far less effective hook than a heavy Bruce type and a Fortress is going to hold much better than an equivalent weight in whatever else ya got.

Very true, there is a whole lot of wriggle room for exactly these sorts of factors, preference and prejudice. What I really wanted was a way to take size out of the equation. I think this more or less has, although we could argue for weeks (and probably will) about bowsprits, freeboard, underwater shape, catboats, submarines, heavy, light, narrow, and tall boats. but really you need to factor all them in as well but calculating it with any sort of accuracy is never going to work except in a very crude way.

I think the rule of thumb that you should put on the biggest anchor your vessel can handle without making her look like a Probiscus Monkey still holds. But the information on this thread has made me re-think whether to bother going one size up on Delfin's hook. Starting to seem like breast implants on Dolly Parton, if you know what I mean

I can't remember what your anchor factor was but if I remember rightly it was pretty low under 20, and I recon she would lie pretty quietly with the windage aft, and no tall mast to blow her around.

I once worked on a ship a bit like yours. it was a little icebreaker called Sir hubert wilkens. A very neat ship, as your looks to be. But it looks like she certainly would need a very big bra