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Old 14-12-2011, 12:27   #91
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Re: Just When You Think You're Safe . . . CRASH !

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If it was a completely stable system, I'd agree, but how often does that happen? One or the other will end up taking the full, now multiplied, load from time to time. It's sorta like sailing at anchor with bigger angles. Anyway, do as you wish...
Multiplied load? Sailing at anchor with bigger angles?

You have not explained yourself. Math or pictures or clear text.
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Old 14-12-2011, 12:30   #92
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I understand you skepticism, but just for fun, try this little experiment. Take a fish scale and suspend a weight from it. Now attach another line to the weight, and pull it horizontally to one side, then read the scale.

The weight will seem to increase because it's no longer pulling in exactly the opposite direction. If you tilt the other line down, it gets worse, up it gets better. The weight of the object didn't change. It's a summation of forces, e.g., a "free body diagram" can help describe it.

If both are always up, which you can't count on, and nothing's moving, you have the situation you describe. It's just something to keep in mind when anchoring.
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Old 14-12-2011, 12:35   #93
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Re: Just When You Think You're Safe . . . CRASH !

We have the same cat a Gemini 105Mc and we have a 35 lb CQR and 75 ft of 2 lb per foot 3/8 chain and 250 ft of rode on our Quick 1000 windless and our backup anchors are a 27 lb Lewmar claw that "came on the bow with the boat" and added 75 ft of 3/8 chain and 250 ft of rode ( it came with 30 ft of chain not enough in my book) and and a big Fortress that's unassembled and stowed with 75 ft of 3/8 chain and 200 ft of rode. At one time I thought it was overkill but not now. We've never dragged after our CQR was set good but I don't think we have ever been in simular conditions as Brian, YET. I have put 2 bow anchors out about 20 ft apart on our last boat a 26 ft monohull but smaller anchors were used and we never dragged once we were set. I always get the motor up to half rpm in reverse to set the anchors and haven't dragged afterwards yet.
A big danforth anchor with 15 ft of chain came with our boat but I sold it for $15.00 at a yard sale to a person who wanted to decorate there flower bed I think it will hold the flower bed in place .
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Old 14-12-2011, 12:46   #94
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Quote:
Originally Posted by thinwater

Multiplied load? Sailing at anchor with bigger angles?

You have not explained yourself. Math or pictures or clear text.
Btw, this has been covered in other threads much more eloquently.

Sailing at anchor is when the bow goes back and forth in the wind. It's also called hunting. At each extreme, the forces are greater. My boat hunts a bit, but only to about 30 degrees. I'd assume you'd put anchors out at more than 60 degrees (double 30).

Does that help? I'm anchored out in the boonies, so cell access is a little spotty, but I'll try to answer any questions I can. Sorry if I wasn't clear. I've been up the mast and need a drink. Perhaps I'll be better after a scotch. ;-)
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Old 14-12-2011, 12:55   #95
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Re: Just When You Think You're Safe . . . CRASH !

I think Mr B, as he has stated is on the right track subsequent to his incident for future crusing in Australia's offshore and coastal waters.

A oversized modern design with backup.
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Old 14-12-2011, 12:57   #96
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Re: Just When You Think You're Safe . . . CRASH !

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I just cannot see how one anchor can multiply the load on another anchor that is already taking the full load. (Unless the non-loaded anchor was hanging over Niagara Falls,)

I need to think this one over better, I guess. It sounded to me like he didn't have the inclination to deal with anchoring for a full watch circle type of excursion. I assumed that this was because it would put him out further into the wind that existed when he first anchored. Thats the tough thing about hindsight. you really don't know all the factors that went into a decision.
Load multiplying? Yes, it can. Think of it as a tight rope effect. If the angle between the 2 anchors excedes 120 degrees and the load is from the side, the load on both anchors will excede the wind load. Generally actually setting 2 anchors at greater than 120 degrees requires very focused effort... unless the tide rises. Then the angle can reach near 180 degrees and the wind comes from the side, the forces can be several times greater than on a single hook.

As for the sailing around argument, that's unexplained bunk. I generally use one large anchor, but I've used 2 many dozens of times, and properly done, the boat barely wiggles and certainly does not swing more or in a rough manner. I always set the second 80 -120 degrees apart; that's is generally the trouble-free sweet spot. Out of that range, there are problems.

The primary down sides of using 2 anchors are:
  • Hastle. You need a good drill for placing them.Sail Delmarva: Laying a Second Anchor
  • Tangles. See above. If you spin and both rodes go into chain lockers, it's going to take time to unwind. Very avoidable.
  • Fouling anchor with rode. This requires care. Setting at >60 degrees eliminates the risk.
  • Unequal anchors. Unless each anchor can hold the load, one will fail and the whole thing will become a tangled mess. However, many of us carry 2 anchors that will do; a large primary and a Fortress.
  • Swing. If there are other boats around, you need to consider your swing vs. the group. However, the most commn reason I set a second hook is to keep me off to one side, away from someone or something.
  • Dragging. If you drag with 2 anchors, 1 of 2 things will happen: 1 of the anchors will catch (or both if the angles improve and each is holding 1/2, though I doubt it) and dragging will stop; both will drag and you will havea mess to retrieve as you try to relocate, which is not fun.
  • Difficulty in setting 2 anchors. Setting 1 anchor is too much for some folks, setting 2 anchors 100 degrees apart is not difficult, but it can certainly be done poorly.
Often folks throw out a second hook without thinking about how the parts of the system work together, hoping it will work some majic. No question, setting 2 anchors is many times--not double--more complex than setting 1 anchor. But it is a skill, like splicing, that is handy. Like splicing, it's generally poo-pooed by those that haven't learned it well. Like splicing, it isn't needed most of the time; knots and big modern anchors can usualy get the job done much more simply.
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Old 14-12-2011, 13:04   #97
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Re: Just When You Think You're Safe . . . CRASH !

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Originally Posted by nv5l View Post
Btw, this has been covered in other threads much more eloquently.

Sailing at anchor is when the bow goes back and forth in the wind. It's also called hunting. At each extreme, the forces are greater. My boat hunts a bit, but only to about 30 degrees. I'd assume you'd put anchors out at more than 60 degrees (double 30).

Does that help? I'm anchored out in the boonies, so cell access is a little spotty, but I'll try to answer any questions I can. Sorry if I wasn't clear. I've been up the mast and need a drink. Perhaps I'll be better after a scotch. ;-)
a. I did pleanty of free body diagrams in school. The math is correct.
b. A boat "open hawse" does not "hunt." It can't. Cat sailors know this, which is why we use bridles (no hunting).
c. I suppose if the angle were sufficiently narrow, there are some jerky dynamic situations. I would never set that narrow and I have not witnessed them. Setting narrow has many hazards.


My current boat has a windlass, lots of chain and a big Manson Supreme. I use only one anchor and it is solid and simple. That is best.

My last boat had 3 danforth-style anchors and no windlass, and I cruised some pretty remote waters. I used 2 anchors every night, since one danforth-style hook is never relaxing (Fortress with 10 feet of light chain). Not with thunderstorms and strong tides about. What I have described proved absolutely dependable with very light tackle. More complex, but absolutely dependable in some very tough conditions. A big hook and chain would not have been compatible with that boat (1200-pound 27-foot cat).
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Old 14-12-2011, 13:09   #98
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Quote:
Originally Posted by thinwater

Load multiplying? Yes, it can. Think of it as a tight rope effect. If the angle between the 2 anchors excedes 120 degrees and the load is from the side, the load on both anchors will excede the wind load. Generally actually setting 2 anchors at greater than 120 degrees requires very focused effort... unless the tide rises. Then the angle can reach near 180 degrees and the wind comes from the side, the forces can be several times greater than on a single hook.

As for the sailing around argument, that's unexplained bunk. I generally use one large anchor, but I've used 2 many dozens of times, and properly done, the boat barely wiggles and certainly does not swing more or in a rough manner. I always set the second 80 -120 degrees apart; that's is generally the trouble-free sweet spot. Out of that range, there are problems.

The primary down sides of using 2 anchors are:
[*]Hastle. You need a good drill for placing them.Sail Delmarva: Laying a Second Anchor[*]Tangles. See above. If you spin and both rodes go into chain lockers, it's going to take time to unwind. Very avoidable.[*]Fouling anchor with rode. This requires care. Setting at >60 degrees eliminates the risk.[*]Unequal anchors. Unless each anchor can hold the load, one will fail and the whole thing will become a tangled mess. However, many of us carry 2 anchors that will do; a large primary and a Fortress.[*]Swing. If there are other boats around, you need to consider your swing vs. the group. However, the most commn reason I set a second hook is to keep me off to one side, away from someone or something.[*]Dragging. If you drag with 2 anchors, 1 of 2 things will happen: 1 of the anchors will catch (or both if the angles improve and each is holding 1/2, though I doubt it) and dragging will stop; both will drag and you will havea mess to retrieve as you try to relocate, which is not fun.[*]Difficulty in setting 2 anchors. Setting 1 anchor is too much for some folks, setting 2 anchors 100 degrees apart is not difficult, but it can certainly be done poorly.
Often folks throw out a second hook without thinking about how the parts of the system work together, hoping it will work some majic. No question, setting 2 anchors is many times--not double--more complex than setting 1 anchor. But it is a skill, like splicing, that is handy. Like splicing, it's generally poo-pooed by those that haven't learned it well. Like splicing, it isn't needed most of the time; knots and big modern anchors can usualy get the job done much more simply.
You missed my point. I didn't say you sail with 2 anchors, all unsaid was that as the wind shifts around, or the waves bounce you around, it's more or less the same effect.

I was trying to put it in simple terms that could be understand without drawing a picture. But you actually made my point better with you 120 degree example. That's what I was trying put across -- you're much better at explaining things than I... Cheers...
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Old 14-12-2011, 16:49   #99
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Re: Just When You Think You're Safe . . . CRASH !

I sailed my boat from Fiji to Australia, I encountered some very horrific weather.
The currents running north were like crossing the rapids in a very fast running river.
It threw up chop and waves vertically out of the sea,
Both sides of the current. which were a couple of miles, Had these crappy wave actions.
Coming down the Tasman Sea. Was an experience all its own, I was using the southerly current to make better time,
Each side of the current, Couple of miles, It had these very nasty chops and waves, The waves were by no means small, The waves along the coast where the ocean floor changes, It also has these very nasty chops and waves,

Broughton Island has the lot, Southerly current, ocean floor changes,
A bay that collects the force of the waves from all directions, and concentrates them into a funnel. The Bay, Chuck in a south easterly, You dont want to be there, I was,
But I was sheltering from a North westerly,

The Tasman Sea, is the Pacific Ocean, It comes all the way from South America with nothing to stop it, So when it hits these ledges, Differing ocean floor levels, It does tend to stand up out of the sea. Very nasty chops and very large waves, Throw in the southern current running at 4 knots,

I did prefer Fiji to Australia, full of reefs and volcanic islands that came straight up out of the sea, Even coming through them in the night,

To the trip down the Tasman, Even 40 miles out, Was still a **** of a trip.

The Tasman has a bad name for itself, I now know why.
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Old 14-12-2011, 19:59   #100
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One great option for increasing your anchor holding, provided you are only worried about 1 direction, is two anchors on the same rode. 15 feet of chain between them atttached to the trip ring on the first anchor and the shank eye on the second anchor.
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Old 16-12-2011, 02:40   #101
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Re: Just When You Think You're Safe . . . CRASH !

I will see if I can upload a video on here.

Nope,

How do I upload a video on to here,
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Old 16-12-2011, 02:47   #102
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Re: Just When You Think You're Safe . . . CRASH !

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I will see if I can upload a video on here.

Nope,

How do I upload a video on to here,
I don't think you can - the usual thing is to upload to Youtube, and then link accross.
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Old 16-12-2011, 02:56   #103
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Re: Just When You Think You're Safe . . . CRASH !

Create an account on youtube and upload your video there.

Once it's uploaded it will give you a link that you can post on here.

Follow your nose.

If you can't work it out post again and we'll give you more details.
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Old 16-12-2011, 05:36   #104
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Re: Just When You Think You're Safe . . . CRASH !

It seems people are missing the point. I wasn't talking about what YOU do with YOUR boat. Or what Mr. B. COULD have done IF he had this or that. He had what he had. For those saying he should have put out ONE anchor because that's what YOU do with YOUR boat.....

Are you sure that's your response? He should have just put out ONE anchor in his situation? Which one? Why would that have been better than what he did, with what he had on board? Why would that have been better than my suggestion of using both of his anchors offshore to hold him?

I understand vectors, but think you are missing the definition of "full load". If one anchor already has the "full load", I don't see how anything another, stationary anchor can do would increase what has already been defined as the full load. The full load is the full load. There is no additional load to be added to a load that has been defined as the full load. Which is the boat, correct?

I'm trying to understand your thinking on this. I might be in a similar situation someday, and like to have these things already thought out in advance.
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Old 16-12-2011, 05:52   #105
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Re: Just When You Think You're Safe . . . CRASH !

If I can up load this video. Its the one I took leaving on the Marine Rescue boat,
It will show you what sort of sea I was in,

Further out in the bay, we were riding over 8 to 10 metre waves,

You might have a different opinion about it then,

But it is good getting all the different opinions,
Further knowledge is allways helpfull, Even for people reading this thread and not commenting,
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