[Rhodes22-list] anchoring
Bill Effros
bill at effros.com
Tue Sep 16 15:17:47 EDT 2008
Herb,
Catenary curve is fascinating and real -- extremely important for towing
and holding up suspension bridges. Anything where the object on the end
of the line is subject to movement. But that's not the case with
anchoring, where the object at the end of the line is stationary, and
you are trying to keep yourself from moving as well.
When anchoring, the principle of the catenary curve works against you.
You don't need to create slack in the rode to cushion the load if you
use rope. Simply use rope with stretch and you can forget snubbers and
overly taut line.
The load on the line is truly minuscule, almost all the time. (If the
load were more than a few pounds, you would not be able to pull it in by
hand.)
I remind you of the worlds oldest shoe store joke:
A woman comes into a shoe store and says:
"5 is my size, but 6 feels so good I buy a 7."
I believe the same applies to anchors. Might as well buy more anchor
than you need...just in case. Soon enough you never use the over sized
anchor because it is such a pain, and when you might really need it, you
can't trust it because you never deployed it frequently enough to have
confidence in your ability to do so in an emergency.
Bill Effros
Herb Parsons wrote:
> It was about 3 years ago. Catenary curve affects not only anchoring, but
> towing as well. They touched on both, but interestingly enough, towing
> is where they talked about it the most. Here's an interesting
> perspective on that.
>
> I've towed some big boats (not ships, but 40'+ boats) after taking the
> class, and remembered what I had learned. In a good tow, the hawser
> seldom goes taught, or straight. The weight of the line itself will pull
> it down causing the curve.
>
> Bill Effros wrote:
>
>> Herb,
>>
>> How long ago did you take the class?
>>
>> If you look at older West Marine catalogs they had diagrams of anchor
>> rode showing "catenary curves" in "taut" anchor rode explaining that the
>> weight of the chain pulled the anchor parallel to the bottom. Then, one
>> year, they explained that their own diagrams were nonsense, and that the
>> anchors were designed to be pulled at a 45 degree angle to the bottom,
>> and that the notion of "scope" had no validity if the chain could change
>> the angle of pull.
>>
>> I just looked again. The catenary curve diagrams and explanation are
>> gone. But the chain lying on the bottom diagram is back, along with the
>> straight 45 degree angle of scope.
>>
>> The recommendation has changed from a flat 6 feet of chain, to 1 foot
>> per waterline foot, to the current recommendation of 65 feet of chain
>> tied to 200 feet of rope.
>>
>> The explanation varies from "bottom abrasion" to "Shorter scope."
>>
>> BUBBA MEISAS! (As Stan's Grandmother would say.)
>>
>> There is no bottom abrasion if your rode floats. -- It never hits the
>> bottom. It never gets dirty except for picking up seaweed.
>>
>> Scope is scope. The angle is the same whether it is chain or rope.
>>
>> Dumping 65 feet of chain on a bottom just 8 feet below; never setting
>> your anchor, and then wandering around within a 150 foot circle unable
>> to determine if your anchor is set or dragging, makes no sense at all.
>>
>> If you don't have a windlass you don't use the anchor because it's too
>> difficult to retrieve and never reliably sets.
>>
>> Get a $100 2 1/2 lb. guardian. Try it on an all rope rode. Deploy it;
>> retrieve it; learn to flake the rode; store the whole shooting match
>> under the cockpit seat. Then ask the CG guys to explain to you, again,
>> why they recommend what they recommend.
>>
>> BE
>>
>>
>>
>> Herb Parsons wrote:
>>
>>
>>> Bill will continue to say this is nonsense, and I'm not going to say
>>> he's wrong. I AM going to say I think he's wrong. The coast guard
>>> captain's class I took went over this, and disagrees with him. Sometimes
>>> CG folks continue to do things based on "tradition", but I think in this
>>> case, they knew what they were teaching.
>>>
>>> Bill Effros wrote:
>>>
>>>
>>>
>>>> Rob,
>>>>
>>>> You need chain if your anchor is so heavy you can't pull it up by hand.
>>>> Then you need a windlass. The windlasses destroy rope -- they work best
>>>> on chain. Everybody makes a lot of money by suggesting that you anchor
>>>> better if you have a chain rode, but that is nonsense, and the enormous
>>>> weight of the chain in the bow totally throws off the balance of boats.
>>>>
>>>> In the process, people start drawing diagrams and providing pseudo
>>>> scientific explanations that make absolutely no sense when you start to
>>>> think about them.
>>>>
>>>> Then somebody comes up with the 22 feet of chain on the 22 foot boat
>>>> rode rule. Which also makes absolutely no sense.
>>>>
>>>> A modern anchor is not like a cinderblock or an engine block. It does
>>>> not just sit on the bottom, it digs in like a railroad spike, and is
>>>> designed so it can be easily released by changing the angle of the rode
>>>> from the surface. Adding weight does not help it in any way. Modern
>>>> anchors are designed to be pulled at specific angles -- mostly around
>>>> 45 degrees -- which is what the 7:1 scope accomplishes. Chain sitting
>>>> on the bottom defeats the angle of the scope relative to the anchor. It
>>>> is counter-productive.
>>>>
>>>> If you want more weight on your anchor, get a heavier anchor. But there
>>>> is no need to do so. A 2 1/2 lb guardian anchor, properly set, will
>>>> hold you in place forever. Your rope rode will withstand far more load
>>>> than the fittings on your boat.
>>>>
>>>> Bill Effros
>>>>
>>>>
>>>> Lowe, Rob wrote:
>>>>
>>>>
>>>>
>>>>
>>>>> Bill,
>>>>> So why does everyone (well, most everyone) suggest using chain on the
>>>>> rode? - rob
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: rhodes22-list-bounces at rhodes22.org
>>>>> [mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of Bill Effros
>>>>> Sent: Tuesday, September 16, 2008 10:59 AM
>>>>> To: The Rhodes 22 Email List
>>>>> Subject: Re: [Rhodes22-list] anchoring
>>>>>
>>>>> Ben,
>>>>>
>>>>> In order to set the anchor you must put tension on it. This pulls the
>>>>> rode taut. When there is no wind or current, the rode will lie flat on
>>>>> the bottom, or float to the surface if it is a floating rode. But it is
>>>>>
>>>>> not holding the boat in place.
>>>>>
>>>>> What most people call "dragging the anchor" is usually "dragging the
>>>>> chain". If you fail to set your anchor -- which you will fail to set
>>>>> properly if you never draw the rode taut -- you can drag the chain all
>>>>> over the place, without ever properly setting the anchor. If you draw
>>>>> the rode taut and properly set the anchor it just won't drag.
>>>>>
>>>>> A very small anchor can be used to hold a very large boat in place if
>>>>> the anchor is properly set. It is much easier to set an anchor with an
>>>>> all rope rode. The chain portion of the rode does not change the angle
>>>>> of pull.
>>>>>
>>>>> Bill Effros
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>
>>>>
>>>>
>>>>
>>>>
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