[Rhodes22-list] anchoring

[Rik Sandberg]

Bill,

> Plow type anchors work differently -- but the chain works the same -- 
> and it can't pull an anchor in any direction without maintaining an 
> essentially straight line to the vessel. 
>
> Imagine the boat is directly above the anchor, with chain on the 
> bottom.  Does pulling in the rode move the anchor?  Horizontally?
>   
We don't try to set our anchors from directly above them .... unless we 
are completely clueless.

Lets do another little test. You can do this on the way to the tree we 
were talking about earlier. while you are walking out there, let ten 
feet or so of that chain drag along behind you. As you walk along, does 
the chain pull out into a straight line before the free end begins to 
follow you? I'm pretty sure you will find the answer is no. Half, or so, 
of that chain will be flat on the ground following along behind you and 
the rest will curve on up to your hand in an arc. Where the chain leaves 
the ground will be no where near the trailing end, but nearer the 
middle. When trying to begin to move and set an anchor there will be 
somewhat less of a curve in the chain, but it will still begin to move 
the anchor long before it is straight unless the anchor is very heavy 
(not likely with a danforth) or the chain is unrealistically light.

Rik

Ayn Rand was a prophet - - it isn't my fault



Bill Effros wrote:
> John,
>
> If the chain is lying on the bottom where does the horizontal movement 
> of the anchor come from?
>
> Do you think you can pull one end of the chain at a 45 degree angle from 
> the bottom, and move the other end of the chain parallel to the bottom?
>
> I don't think so.
>
> I think you keep pulling that chain off the bottom at a 45 degree angle 
> until it moves the flukes of the anchor into perfect position to dig 
> into the bottom.
>
> The flukes swing on the shank so that the anchor almost always lands in 
> position to dig in.  The shank is angled at 45 degrees when setting.  
> The chain lying on the bottom defeats the ability to set the anchor -- 
> you must pull it off the bottom before the anchor can set. 
>
> This requires you to buy an anchor heavier than your chain, or you can 
> never set your Danforth style anchor properly.
>
> Plow type anchors work differently -- but the chain works the same -- 
> and it can't pull an anchor in any direction without maintaining an 
> essentially straight line to the vessel. 
>
> Imagine the boat is directly above the anchor, with chain on the 
> bottom.  Does pulling in the rode move the anchor?  Horizontally?
>
> Bill Effros
>
>
>
> John Lock wrote:
>   
>> At 11:52 PM 9/16/2008 -0400, Bill Effros wrote:
>>   
>>     
>>> The point is that the anchor most of us use is designed to set by being
>>> pulled at a 45 degree angle from the bottom.  If you pull it parallel to
>>> the bottom it just stubs its flukes along and never sets properly.  And
>>> if you have too much chain, you can never pull it at a 45 degree angle,
>>> so it will never set at all.
>>>     
>>>       
>> Let me jump in and say I have to disagree with Bill here.  As I 
>> understand the physics of the Danforth-style anchors, they actually 
>> depend on a certain amount of horizontal (or parallell) movement to 
>> get the points of the flukes to dig in.  Here's why...
>>
>> With the flukes hinged at the back of the anchor and free to rotate 
>> about that axis, their mass, pulled downward by gravity, will have a 
>> natural tendency to rest directly on the points.  Consequently, an 
>> initial horizontal movement will naturally force the points downward 
>> and into the mud.  Pulling up on the rode at a 45-degree angle will, 
>> in fact, help defeat the design by not allowing the mass of the 
>> flukes to perform their downward deflection.
>>
>> The main reason a few feet of chain helps an anchor set is that the 
>> extra weight helps keep the initial movement of the anchor more 
>> horizontal, because the rode will begin to rise before the chain 
>> does.  This helps the flukes get their initial "traction".  Once the 
>> points dig in and force continues to be applied the rode and chain 
>> can rise and increase to the 45 degree angle that is ideal to finish 
>> and maintain the set.  It's those first few inches of movement that 
>> are critical to the set of the anchor.
>>
>> Cheers!
>>
>> John Lock
>> ~~~~~~~~~~~~~~~~~~
>> s/v Pandion - '79 Rhodes 22
>> Lake Sinclair, GA
>> ~~~~~~~~~~~~~~~~~~
>>
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